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* [PATCH v2 00/10] virtio-mem: paravirtualized memory
@ 2020-03-11 17:14 David Hildenbrand
  2020-03-11 17:14 ` [PATCH v2 01/10] virtio-mem: Paravirtualized memory hotplug David Hildenbrand
                   ` (11 more replies)
  0 siblings, 12 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Sebastien Boeuf, Samuel Ortiz, Robert Bradford, Luiz Capitulino,
	Pankaj Gupta, teawater, Igor Mammedov, Dr . David Alan Gilbert,
	Alexander Duyck, Alexander Potapenko, Anshuman Khandual,
	Anthony Yznaga, Dan Williams, Dave Young, Jason Wang,
	Johannes Weiner, Juergen Gross, Konrad Rzeszutek Wilk, Len Brown,
	Mel Gorman, Michal Hocko, Mike Rapoport, Oscar Salvador,
	Oscar Salvador, Pavel Tatashin, Pavel Tatashin, Pingfan Liu,
	Qian Cai, Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

This series is based on latest linux-next. The patches are located at:
    https://github.com/davidhildenbrand/linux.git virtio-mem-v2

I now have acks for all !virtio-mem changes. I'll be happy to get review
feedback, testing reports, etc. for the virtio-mem changes. If there are
no further comments, I guess this is good to go as a v1 soon.

The basic idea of virtio-mem is to provide a flexible,
cross-architecture memory hot(un)plug solution that avoids many limitations
imposed by existing technologies, architectures, and interfaces. More
details can be found below and in linked material.

It's currently only enabled for x86-64, however, should theoretically work
on any architecture that supports virtio and implements memory hot(un)plug
under Linux - like s390x, powerpc64, and arm64. On x86-64, it is currently
possible to add/remove memory to the system in >= 4MB granularity.
Memory hotplug works very reliably. For memory unplug, there are no
guarantees how much memory can actually get unplugged, it depends on the
setup (especially: fragmentation of physical memory).

I am currently getting the QEMU side into shape (which will be posted as
RFC soon, see below for a link to the current state). Experimental Kata
support is in the works [4]. Also, a cloud-hypervisor implementation is
under discussion [5].

--------------------------------------------------------------------------
1. virtio-mem
--------------------------------------------------------------------------

The basic idea behind virtio-mem was presented at KVM Forum 2018. The
slides can be found at [1]. The previous RFC can be found at [2]. The
first RFC can be found at [3]. However, the concept evolved over time. The
KVM Forum slides roughly match the current design.

Patch #2 ("virtio-mem: Paravirtualized memory hotplug") contains quite some
information, especially in "include/uapi/linux/virtio_mem.h":

    Each virtio-mem device manages a dedicated region in physical address
    space. Each device can belong to a single NUMA node, multiple devices
    for a single NUMA node are possible. A virtio-mem device is like a
    "resizable DIMM" consisting of small memory blocks that can be plugged
    or unplugged. The device driver is responsible for (un)plugging memory
    blocks on demand.

    Virtio-mem devices can only operate on their assigned memory region in
    order to (un)plug memory. A device cannot (un)plug memory belonging to
    other devices.

    The "region_size" corresponds to the maximum amount of memory that can
    be provided by a device. The "size" corresponds to the amount of memory
    that is currently plugged. "requested_size" corresponds to a request
    from the device to the device driver to (un)plug blocks. The
    device driver should try to (un)plug blocks in order to reach the
    "requested_size". It is impossible to plug more memory than requested.

    The "usable_region_size" represents the memory region that can actually
    be used to (un)plug memory. It is always at least as big as the
    "requested_size" and will grow dynamically. It will only shrink when
    explicitly triggered (VIRTIO_MEM_REQ_UNPLUG).

    There are no guarantees what will happen if unplugged memory is
    read/written. Such memory should, in general, not be touched. E.g.,
    even writing might succeed, but the values will simply be discarded at
    random points in time.

    It can happen that the device cannot process a request, because it is
    busy. The device driver has to retry later.

    Usually, during system resets all memory will get unplugged, so the
    device driver can start with a clean state. However, in specific
    scenarios (if the device is busy) it can happen that the device still
    has memory plugged. The device driver can request to unplug all memory
    (VIRTIO_MEM_REQ_UNPLUG) - which might take a while to succeed if the
    device is busy.

--------------------------------------------------------------------------
2. Linux Implementation
--------------------------------------------------------------------------

Memory blocks (e.g., 128MB) are added/removed on demand. Within these
memory blocks, subblocks (e.g., 4MB) are plugged/unplugged. The sizes
depend on the target architecture, MAX_ORDER, pageblock_order, and
the block size of a virtio-mem device.

add_memory()/try_remove_memory() is used to add/remove memory blocks.
virtio-mem will not online memory blocks itself. This has to be done by
user space, or configured into the kernel
(CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE). virtio-mem will only unplug memory
that was online to the ZONE_NORMAL. Memory is suggested to be onlined to
the ZONE_NORMAL for now.

The memory hotplug notifier is used to properly synchronize against
onlining/offlining of memory blocks and to track the states of memory
blocks (including the zone memory blocks are onlined to).

The set_online_page() callback is used to keep unplugged subblocks
of a memory block fake-offline when onlining the memory block.
generic_online_page() is used to fake-online plugged subblocks. This
handling is similar to the Hyper-V balloon driver.

PG_offline is used to mark unplugged subblocks as offline, so e.g.,
dumping tools (makedumpfile) will skip these pages. This is similar to
other balloon drivers like virtio-balloon and Hyper-V.

Memory offlining code is extended to allow drivers to drop their reference
to PG_offline pages when MEM_GOING_OFFLINE, so these pages can be skipped
when offlining memory blocks. This allows to offline memory blocks that
have partially unplugged (allocated e.g., via alloc_contig_range())
subblocks - or are completely unplugged.

alloc_contig_range()/free_contig_range() [now exposed] is used to
unplug/plug subblocks of memory blocks the are already exposed to Linux.

offline_and_remove_memory() [new] is used to offline a fully unplugged
memory block and remove it from Linux.

--------------------------------------------------------------------------
3. Changes v1 -> v2
--------------------------------------------------------------------------

- "virtio-mem: Paravirtualized memory hotplug"
-- Use "__u64" and friends in uapi header
-- Split out ACPI PXM handling
- "virtio-mem: Allow to specify an ACPI PXM as nid"
-- Squash of the ACPI PXM handling and previous "ACPI: NUMA: export
   pxm_to_node"
- "virtio-mem: Paravirtualized memory hotunplug part 2"
-- Squashed previous "mm: Export alloc_contig_range() /
   free_contig_range()"
- "virtio-mem: Allow to offline partially unplugged memory blocks"
-- WARN and dump_page() in case somebody has a reference to an unplugged
   page
- "virtio-mem: Better retry handling"
-- Use retry interval of 5s -> 5m
- Tweaked some patch descriptions

--------------------------------------------------------------------------
4. Future work
--------------------------------------------------------------------------

One of the next TODO things besides the QEMU part is writing a virtio-mem
spec - however, that might still take some time.

virtio-mem extensions (via new feature flags):
- Indicate the guest status (e.g., initialized, working, all memory is
  busy when unplugging, too many memory blocks are offline when plugging,
  etc.)
- Guest-triggered shrinking of the usable region (e.g., whenever the
  highest memory block is removed).
- Exchange of plugged<->unplugged block for defragmentation.

Memory hotplug:
- Reduce the amount of memory resources if that tunes out to be an
  issue. Or try to speed up relevant code paths to deal with many
  resources.
- Allocate vmemmap from added memory.

Memory hotunplug:
- Performance improvements:
-- Sense (lockless) if it make sense to try alloc_contig_range() at all
   before directly trying to isolate and taking locks.
-- Try to unplug bigger chunks within a memory block first.
- Make unplug more likely to succeed:
-- There are various idea to limit fragmentation on memory block
   granularity. (e.g., ZONE_PREFER_MOVABLE and smart balancing)
-- Allocate vmemmap from added memory.
- OOM handling, e.g., via an OOM handler/shrinker.
- Defragmentation
- Support for < MAX_ORDER - 1 blocks (esp. pageblock_order)

--------------------------------------------------------------------------
5. Example Usage
--------------------------------------------------------------------------

A QEMU implementation (without protection of unplugged memory, but with
resizable memory regions and optimized migration) is available at (kept
updated):
    https://github.com/davidhildenbrand/qemu.git virtio-mem

Start QEMU with two virtio-mem devices (one per NUMA node):
 $ qemu-system-x86_64 -m 4G,maxmem=204G \
  -smp sockets=2,cores=2 \
  -numa node,nodeid=0,cpus=0-1 -numa node,nodeid=1,cpus=2-3 \
  [...]
  -object memory-backend-ram,id=mem0,size=100G,managed-size=on \
  -device virtio-mem-pci,id=vm0,memdev=mem0,node=0,requested-size=0M \
  -object memory-backend-ram,id=mem1,size=100G,managed-size=on \
  -device virtio-mem-pci,id=vm1,memdev=mem1,node=1,requested-size=1G

Query the configuration:
 QEMU 4.2.50 monitor - type 'help' for more information
 (qemu) info memory-devices
 Memory device [virtio-mem]: "vm0"
   memaddr: 0x140000000
   node: 0
   requested-size: 0
   size: 0
   max-size: 107374182400
   block-size: 2097152
   memdev: /objects/mem0
 Memory device [virtio-mem]: "vm1"
   memaddr: 0x1a40000000
   node: 1
   requested-size: 1073741824
   size: 1073741824
   max-size: 107374182400
   block-size: 2097152
   memdev: /objects/mem1

Add some memory to node 0:
 QEMU 4.2.50 monitor - type 'help' for more information
 (qemu) qom-set vm0 requested-size 1G

Remove some memory from node 1:
 QEMU 4.2.50 monitor - type 'help' for more information
 (qemu) qom-set vm1 requested-size 64M

Query the configuration again:
 QEMU 4.2.50 monitor - type 'help' for more information
 (qemu) info memory-devices
 Memory device [virtio-mem]: "vm0"
   memaddr: 0x140000000
   node: 0
   requested-size: 1073741824
   size: 1073741824
   max-size: 107374182400
   block-size: 2097152
   memdev: /objects/mem0
 Memory device [virtio-mem]: "vm1"
   memaddr: 0x1a40000000
   node: 1
   requested-size: 67108864
   size: 67108864
   max-size: 107374182400
   block-size: 2097152
   memdev: /objects/mem1

--------------------------------------------------------------------------
6. Q/A
--------------------------------------------------------------------------

Q: Why add/remove parts ("subblocks") of memory blocks/sections?
A: Flexibility (section size depends on the architecture) - e.g., some
   architectures have a section size of 2GB. Also, the memory block size
   is variable (e.g., on x86-64). I want to avoid any such restrictions.
   Some use cases want to add/remove memory in smaller granularity to a
   VM (e.g., the Hyper-V balloon also implements this) - especially smaller
   VMs like used for kata containers. Also, on memory unplug, it is more
   reliable to free-up and unplug multiple small chunks instead
   of one big chunk. E.g., if one page of a DIMM is either unmovable or
   pinned, the DIMM can't get unplugged. This approach is basically a
   compromise between DIMM-based memory hot(un)plug and balloon
   inflation/deflation, which works mostly on page granularity.

Q: Why care about memory blocks?
A: They are the way to tell user space about new memory. This way,
   memory can get onlined/offlined by user space. Also, e.g., kdump
   relies on udev events to reload kexec when memory blocks are
   onlined/offlined. Memory blocks are the "real" memory hot(un)plug
   granularity. Everything that's smaller has to be emulated "on top".

Q: Won't memory unplug of subblocks fragment memory?
A: Yes and no. Unplugging e.g., >=4MB subblocks on x86-64 will not really
   fragment memory like unplugging random pages like a balloon driver does.
   Buddy merging will not be limited. However, any allocation that requires
   bigger consecutive memory chunks (e.g., gigantic pages) might observe
   the fragmentation. Possible solutions: Allocate gigantic huge pages
   before unplugging memory, don't unplug memory, combine virtio-mem with
   DIMM based memory or bigger initial memory. Remember, a virtio-mem
   device will only unplug on the memory range it manages, not on other
   DIMMs. Unplug of single memory blocks will result in similar
   fragmentation in respect to gigantic huge pages.

Q: How reliable is memory unplug?
A: There are no guarantees on how much memory can get unplugged
   again. However, it is more likely to find 4MB chunks to unplug than
   e.g., 128MB chunks. If memory is terribly fragmented, there is nothing
   we can do - for now. I consider memory hotplug the first primary use
   of virtio-mem. Memory unplug might usually work, but we want to improve
   the performance and the amount of memory we can actually unplug later.

Q: Why not unplug from the ZONE_MOVABLE?
A: Unplugged memory chunks are unmovable. Unmovable data must not end up
   on the ZONE_MOVABLE - similar to gigantic pages - they will never be
   allocated from ZONE_MOVABLE. virtio-mem added memory can be onlined
   to the ZONE_MOVABLE, but subblocks will not get unplugged from it.

Q: How big should the initial (!virtio-mem) memory of a VM be?
A: virtio-mem memory will not go to the DMA zones. So to avoid running out
   of DMA memory, I suggest something like 2-3GB on x86-64. But many
   VMs can most probably deal with less DMA memory - depends on the use
   case.

[1] https://events.linuxfoundation.org/wp-content/uploads/2017/12/virtio-mem-Paravirtualized-Memory-David-Hildenbrand-Red-Hat-1.pdf
[2] https://lkml.kernel.org/r/20190919142228.5483-1-david@redhat.com
[3] https://lkml.kernel.org/r/547865a9-d6c2-7140-47e2-5af01e7d761d@redhat.com
[4] https://github.com/kata-containers/documentation/pull/592
[5] https://github.com/cloud-hypervisor/cloud-hypervisor/pull/837

Cc: Sebastien Boeuf <sebastien.boeuf@intel.com>
Cc: Samuel Ortiz <samuel.ortiz@intel.com>
Cc: Robert Bradford <robert.bradford@intel.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>

David Hildenbrand (10):
  virtio-mem: Paravirtualized memory hotplug
  virtio-mem: Allow to specify an ACPI PXM as nid
  virtio-mem: Paravirtualized memory hotunplug part 1
  virtio-mem: Paravirtualized memory hotunplug part 2
  mm: Allow to offline unmovable PageOffline() pages via
    MEM_GOING_OFFLINE
  virtio-mem: Allow to offline partially unplugged memory blocks
  mm/memory_hotplug: Introduce offline_and_remove_memory()
  virtio-mem: Offline and remove completely unplugged memory blocks
  virtio-mem: Better retry handling
  MAINTAINERS: Add myself as virtio-mem maintainer

 MAINTAINERS                     |    7 +
 drivers/acpi/numa/srat.c        |    1 +
 drivers/virtio/Kconfig          |   18 +
 drivers/virtio/Makefile         |    1 +
 drivers/virtio/virtio_mem.c     | 1910 +++++++++++++++++++++++++++++++
 include/linux/memory_hotplug.h  |    1 +
 include/linux/page-flags.h      |   10 +
 include/uapi/linux/virtio_ids.h |    1 +
 include/uapi/linux/virtio_mem.h |  208 ++++
 mm/memory_hotplug.c             |   81 +-
 mm/page_alloc.c                 |   26 +
 mm/page_isolation.c             |    9 +
 12 files changed, 2263 insertions(+), 10 deletions(-)
 create mode 100644 drivers/virtio/virtio_mem.c
 create mode 100644 include/uapi/linux/virtio_mem.h

-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 01/10] virtio-mem: Paravirtualized memory hotplug
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-04-15  5:59   ` Pankaj Gupta
  2020-03-11 17:14 ` [PATCH v2 02/10] virtio-mem: Allow to specify an ACPI PXM as nid David Hildenbrand
                   ` (10 subsequent siblings)
  11 siblings, 1 reply; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Jason Wang, Oscar Salvador, Igor Mammedov, Dave Young,
	Dan Williams, Pavel Tatashin, Stefan Hajnoczi, Vlastimil Babka,
	Rafael J. Wysocki, Len Brown, linux-acpi

Each virtio-mem device owns exactly one memory region. It is responsible
for adding/removing memory from that memory region on request.

When the device driver starts up, the requested amount of memory is
queried and then plugged to Linux. On request, further memory can be
plugged or unplugged. This patch only implements the plugging part.

On x86-64, memory can currently be plugged in 4MB ("subblock") granularity.
When required, a new memory block will be added (e.g., usually 128MB on
x86-64) in order to plug more subblocks. Only x86-64 was tested for now.

The online_page callback is used to keep unplugged subblocks offline
when onlining memory - similar to the Hyper-V balloon driver. Unplugged
pages are marked PG_offline, to tell dump tools (e.g., makedumpfile) to
skip them.

User space is usually responsible for onlining the added memory. The
memory hotplug notifier is used to synchronize virtio-mem activity
against memory onlining/offlining.

Each virtio-mem device can belong to a NUMA node, which allows us to
easily add/remove small chunks of memory to/from a specific NUMA node by
using multiple virtio-mem devices. Something that works even when the
guest has no idea about the NUMA topology.

One way to view virtio-mem is as a "resizable DIMM" or a DIMM with many
"sub-DIMMS".

This patch directly introduces the basic infrastructure to implement memory
unplug. Especially the memory block states and subblock bitmaps will be
heavily used there.

Notes:
- In case memory is to be onlined by user space, we limit the amount of
  offline memory blocks, to not run out of memory. This is esp. an
  issue if memory is added faster than it is getting onlined.
- Suspend/Hibernate is not supported due to the way virtio-mem devices
  behave. Limited support might be possible in the future.
- Reloading the device driver is not supported.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Len Brown <lenb@kernel.org>
Cc: linux-acpi@vger.kernel.org
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/Kconfig          |   17 +
 drivers/virtio/Makefile         |    1 +
 drivers/virtio/virtio_mem.c     | 1526 +++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_ids.h |    1 +
 include/uapi/linux/virtio_mem.h |  200 ++++
 5 files changed, 1745 insertions(+)
 create mode 100644 drivers/virtio/virtio_mem.c
 create mode 100644 include/uapi/linux/virtio_mem.h

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 4b2dd8259ff5..95ea2094a6b4 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -65,6 +65,23 @@ config VIRTIO_BALLOON
 
 	 If unsure, say M.
 
+config VIRTIO_MEM
+	tristate "Virtio mem driver"
+	default m
+	depends on X86_64
+	depends on VIRTIO
+	depends on MEMORY_HOTPLUG_SPARSE
+	depends on MEMORY_HOTREMOVE
+	help
+	 This driver provides access to virtio-mem paravirtualized memory
+	 devices, allowing to hotplug and hotunplug memory.
+
+	 This driver is was only tested under x86-64, but should
+	 theoretically work on all architectures that support memory
+	 hotplug and hotremove.
+
+	 If unsure, say M.
+
 config VIRTIO_INPUT
 	tristate "Virtio input driver"
 	depends on VIRTIO
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 3a2b5c5dcf46..906d5a00ac85 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -6,3 +6,4 @@ virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
 virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
 obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
 obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
+obj-$(CONFIG_VIRTIO_MEM) += virtio_mem.o
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
new file mode 100644
index 000000000000..803e1426f80b
--- /dev/null
+++ b/drivers/virtio/virtio_mem.c
@@ -0,0 +1,1526 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Virtio-mem device driver.
+ *
+ * Copyright Red Hat, Inc. 2020
+ *
+ * Author(s): David Hildenbrand <david@redhat.com>
+ */
+
+#include <linux/virtio.h>
+#include <linux/virtio_mem.h>
+#include <linux/workqueue.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/memory_hotplug.h>
+#include <linux/memory.h>
+#include <linux/hrtimer.h>
+#include <linux/crash_dump.h>
+#include <linux/mutex.h>
+#include <linux/bitmap.h>
+#include <linux/lockdep.h>
+
+enum virtio_mem_mb_state {
+	/* Unplugged, not added to Linux. Can be reused later. */
+	VIRTIO_MEM_MB_STATE_UNUSED = 0,
+	/* (Partially) plugged, not added to Linux. Error on add_memory(). */
+	VIRTIO_MEM_MB_STATE_PLUGGED,
+	/* Fully plugged, fully added to Linux, offline. */
+	VIRTIO_MEM_MB_STATE_OFFLINE,
+	/* Partially plugged, fully added to Linux, offline. */
+	VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL,
+	/* Fully plugged, fully added to Linux, online (!ZONE_MOVABLE). */
+	VIRTIO_MEM_MB_STATE_ONLINE,
+	/* Partially plugged, fully added to Linux, online (!ZONE_MOVABLE). */
+	VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL,
+	/*
+	 * Fully plugged, fully added to Linux, online (ZONE_MOVABLE).
+	 * We are not allowed to allocate (unplug) parts of this block that
+	 * are not movable (similar to gigantic pages). We will never allow
+	 * to online OFFLINE_PARTIAL to ZONE_MOVABLE (as they would contain
+	 * unmovable parts).
+	 */
+	VIRTIO_MEM_MB_STATE_ONLINE_MOVABLE,
+	VIRTIO_MEM_MB_STATE_COUNT
+};
+
+struct virtio_mem {
+	struct virtio_device *vdev;
+
+	/* We might first have to unplug all memory when starting up. */
+	bool unplug_all_required;
+
+	/* Workqueue that processes the plug/unplug requests. */
+	struct work_struct wq;
+	atomic_t config_changed;
+
+	/* Virtqueue for guest->host requests. */
+	struct virtqueue *vq;
+
+	/* Wait for a host response to a guest request. */
+	wait_queue_head_t host_resp;
+
+	/* Space for one guest request and the host response. */
+	struct virtio_mem_req req;
+	struct virtio_mem_resp resp;
+
+	/* The current size of the device. */
+	uint64_t plugged_size;
+	/* The requested size of the device. */
+	uint64_t requested_size;
+
+	/* The device block size (for communicating with the device). */
+	uint32_t device_block_size;
+	/* Physical start address of the memory region. */
+	uint64_t addr;
+
+	/* The subblock size. */
+	uint32_t subblock_size;
+	/* The number of subblocks per memory block. */
+	uint32_t nb_sb_per_mb;
+
+	/* Id of the first memory block of this device. */
+	unsigned long first_mb_id;
+	/* Id of the last memory block of this device. */
+	unsigned long last_mb_id;
+	/* Id of the last usable memory block of this device. */
+	unsigned long last_usable_mb_id;
+	/* Id of the next memory bock to prepare when needed. */
+	unsigned long next_mb_id;
+
+	/* Summary of all memory block states. */
+	unsigned long nb_mb_state[VIRTIO_MEM_MB_STATE_COUNT];
+#define VIRTIO_MEM_NB_OFFLINE_THRESHOLD		10
+
+	/*
+	 * One byte state per memory block.
+	 *
+	 * Allocated via vmalloc(). When preparing new blocks, resized
+	 * (alloc+copy+free) when needed (crossing pages with the next mb).
+	 * (when crossing pages).
+	 *
+	 * With 128MB memory blocks, we have states for 512GB of memory in one
+	 * page.
+	 */
+	uint8_t *mb_state;
+
+	/*
+	 * $nb_sb_per_mb bit per memory block. Handled similar to mb_state.
+	 *
+	 * With 4MB subblocks, we manage 128GB of memory in one page.
+	 */
+	unsigned long *sb_bitmap;
+
+	/*
+	 * Mutex that protects the nb_mb_state, mb_state, and sb_bitmap.
+	 *
+	 * When this lock is held the pointers can't change, ONLINE and
+	 * OFFLINE blocks can't change the state and no subblocks will get
+	 * plugged.
+	 */
+	struct mutex hotplug_mutex;
+	bool hotplug_active;
+
+	/* An error occurred we cannot handle - stop processing requests. */
+	bool broken;
+
+	/* The driver is being removed. */
+	spinlock_t removal_lock;
+	bool removing;
+
+	/* Timer for retrying to plug/unplug memory. */
+	struct hrtimer retry_timer;
+#define VIRTIO_MEM_RETRY_TIMER_MS		30000
+
+	/* Memory notifier (online/offline events). */
+	struct notifier_block memory_notifier;
+
+	/* Next device in the list of virtio-mem devices. */
+	struct list_head next;
+};
+
+/*
+ * We have to share a single online_page callback among all virtio-mem
+ * devices. We use RCU to iterate the list in the callback.
+ */
+static DEFINE_MUTEX(virtio_mem_mutex);
+static LIST_HEAD(virtio_mem_devices);
+
+static void virtio_mem_online_page_cb(struct page *page, unsigned int order);
+
+/*
+ * Register a virtio-mem device so it will be considered for the online_page
+ * callback.
+ */
+static int register_virtio_mem_device(struct virtio_mem *vm)
+{
+	int rc = 0;
+
+	/* First device registers the callback. */
+	mutex_lock(&virtio_mem_mutex);
+	if (list_empty(&virtio_mem_devices))
+		rc = set_online_page_callback(&virtio_mem_online_page_cb);
+	if (!rc)
+		list_add_rcu(&vm->next, &virtio_mem_devices);
+	mutex_unlock(&virtio_mem_mutex);
+
+	return rc;
+}
+
+/*
+ * Unregister a virtio-mem device so it will no longer be considered for the
+ * online_page callback.
+ */
+static void unregister_virtio_mem_device(struct virtio_mem *vm)
+{
+	/* Last device unregisters the callback. */
+	mutex_lock(&virtio_mem_mutex);
+	list_del_rcu(&vm->next);
+	if (list_empty(&virtio_mem_devices))
+		restore_online_page_callback(&virtio_mem_online_page_cb);
+	mutex_unlock(&virtio_mem_mutex);
+
+	synchronize_rcu();
+}
+
+/*
+ * Calculate the memory block id of a given address.
+ */
+static unsigned long virtio_mem_phys_to_mb_id(unsigned long addr)
+{
+	return addr / memory_block_size_bytes();
+}
+
+/*
+ * Calculate the physical start address of a given memory block id.
+ */
+static unsigned long virtio_mem_mb_id_to_phys(unsigned long mb_id)
+{
+	return mb_id * memory_block_size_bytes();
+}
+
+/*
+ * Calculate the subblock id of a given address.
+ */
+static unsigned long virtio_mem_phys_to_sb_id(struct virtio_mem *vm,
+					      unsigned long addr)
+{
+	const unsigned long mb_id = virtio_mem_phys_to_mb_id(addr);
+	const unsigned long mb_addr = virtio_mem_mb_id_to_phys(mb_id);
+
+	return (addr - mb_addr) / vm->subblock_size;
+}
+
+/*
+ * Set the state of a memory block, taking care of the state counter.
+ */
+static void virtio_mem_mb_set_state(struct virtio_mem *vm, unsigned long mb_id,
+				    enum virtio_mem_mb_state state)
+{
+	const unsigned long idx = mb_id - vm->first_mb_id;
+	enum virtio_mem_mb_state old_state;
+
+	old_state = vm->mb_state[idx];
+	vm->mb_state[idx] = state;
+
+	BUG_ON(vm->nb_mb_state[old_state] == 0);
+	vm->nb_mb_state[old_state]--;
+	vm->nb_mb_state[state]++;
+}
+
+/*
+ * Get the state of a memory block.
+ */
+static enum virtio_mem_mb_state virtio_mem_mb_get_state(struct virtio_mem *vm,
+							unsigned long mb_id)
+{
+	const unsigned long idx = mb_id - vm->first_mb_id;
+
+	return vm->mb_state[idx];
+}
+
+/*
+ * Prepare the state array for the next memory block.
+ */
+static int virtio_mem_mb_state_prepare_next_mb(struct virtio_mem *vm)
+{
+	unsigned long old_bytes = vm->next_mb_id - vm->first_mb_id + 1;
+	unsigned long new_bytes = vm->next_mb_id - vm->first_mb_id + 2;
+	int old_pages = PFN_UP(old_bytes);
+	int new_pages = PFN_UP(new_bytes);
+	uint8_t *new_mb_state;
+
+	if (vm->mb_state && old_pages == new_pages)
+		return 0;
+
+	new_mb_state = vzalloc(new_pages * PAGE_SIZE);
+	if (!new_mb_state)
+		return -ENOMEM;
+
+	mutex_lock(&vm->hotplug_mutex);
+	if (vm->mb_state)
+		memcpy(new_mb_state, vm->mb_state, old_pages * PAGE_SIZE);
+	vfree(vm->mb_state);
+	vm->mb_state = new_mb_state;
+	mutex_unlock(&vm->hotplug_mutex);
+
+	return 0;
+}
+
+#define virtio_mem_for_each_mb_state(_vm, _mb_id, _state) \
+	for (_mb_id = _vm->first_mb_id; \
+	     _mb_id < _vm->next_mb_id && _vm->nb_mb_state[_state]; \
+	     _mb_id++) \
+		if (virtio_mem_mb_get_state(_vm, _mb_id) == _state)
+
+/*
+ * Mark all selected subblocks plugged.
+ *
+ * Will not modify the state of the memory block.
+ */
+static void virtio_mem_mb_set_sb_plugged(struct virtio_mem *vm,
+					 unsigned long mb_id, int sb_id,
+					 int count)
+{
+	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;
+
+	__bitmap_set(vm->sb_bitmap, bit, count);
+}
+
+/*
+ * Mark all selected subblocks unplugged.
+ *
+ * Will not modify the state of the memory block.
+ */
+static void virtio_mem_mb_set_sb_unplugged(struct virtio_mem *vm,
+					   unsigned long mb_id, int sb_id,
+					   int count)
+{
+	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;
+
+	__bitmap_clear(vm->sb_bitmap, bit, count);
+}
+
+/*
+ * Test if all selected subblocks are plugged.
+ */
+static bool virtio_mem_mb_test_sb_plugged(struct virtio_mem *vm,
+					  unsigned long mb_id, int sb_id,
+					  int count)
+{
+	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;
+
+	if (count == 1)
+		return test_bit(bit, vm->sb_bitmap);
+
+	/* TODO: Helper similar to bitmap_set() */
+	return find_next_zero_bit(vm->sb_bitmap, bit + count, bit) >=
+	       bit + count;
+}
+
+/*
+ * Find the first plugged subblock. Returns vm->nb_sb_per_mb in case there is
+ * none.
+ */
+static int virtio_mem_mb_first_plugged_sb(struct virtio_mem *vm,
+					  unsigned long mb_id)
+{
+	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb;
+
+	return find_next_bit(vm->sb_bitmap, bit + vm->nb_sb_per_mb, bit) - bit;
+}
+
+/*
+ * Find the first unplugged subblock. Returns vm->nb_sb_per_mb in case there is
+ * none.
+ */
+static int virtio_mem_mb_first_unplugged_sb(struct virtio_mem *vm,
+					    unsigned long mb_id)
+{
+	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb;
+
+	return find_next_zero_bit(vm->sb_bitmap, bit + vm->nb_sb_per_mb, bit) -
+	       bit;
+}
+
+/*
+ * Prepare the subblock bitmap for the next memory block.
+ */
+static int virtio_mem_sb_bitmap_prepare_next_mb(struct virtio_mem *vm)
+{
+	const unsigned long old_nb_mb = vm->next_mb_id - vm->first_mb_id;
+	const unsigned long old_nb_bits = old_nb_mb * vm->nb_sb_per_mb;
+	const unsigned long new_nb_bits = (old_nb_mb + 1) * vm->nb_sb_per_mb;
+	int old_pages = PFN_UP(BITS_TO_LONGS(old_nb_bits) * sizeof(long));
+	int new_pages = PFN_UP(BITS_TO_LONGS(new_nb_bits) * sizeof(long));
+	unsigned long *new_sb_bitmap, *old_sb_bitmap;
+
+	if (vm->sb_bitmap && old_pages == new_pages)
+		return 0;
+
+	new_sb_bitmap = vzalloc(new_pages * PAGE_SIZE);
+	if (!new_sb_bitmap)
+		return -ENOMEM;
+
+	mutex_lock(&vm->hotplug_mutex);
+	if (new_sb_bitmap)
+		memcpy(new_sb_bitmap, vm->sb_bitmap, old_pages * PAGE_SIZE);
+
+	old_sb_bitmap = vm->sb_bitmap;
+	vm->sb_bitmap = new_sb_bitmap;
+	mutex_unlock(&vm->hotplug_mutex);
+
+	vfree(old_sb_bitmap);
+	return 0;
+}
+
+/*
+ * Try to add a memory block to Linux. This will usually only fail
+ * if out of memory.
+ *
+ * Must not be called with the vm->hotplug_mutex held (possible deadlock with
+ * onlining code).
+ *
+ * Will not modify the state of the memory block.
+ */
+static int virtio_mem_mb_add(struct virtio_mem *vm, unsigned long mb_id)
+{
+	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
+	int nid = memory_add_physaddr_to_nid(addr);
+
+	dev_dbg(&vm->vdev->dev, "adding memory block: %lu\n", mb_id);
+	return add_memory(nid, addr, memory_block_size_bytes());
+}
+
+/*
+ * Try to remove a memory block from Linux. Will only fail if the memory block
+ * is not offline.
+ *
+ * Must not be called with the vm->hotplug_mutex held (possible deadlock with
+ * onlining code).
+ *
+ * Will not modify the state of the memory block.
+ */
+static int virtio_mem_mb_remove(struct virtio_mem *vm, unsigned long mb_id)
+{
+	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
+	int nid = memory_add_physaddr_to_nid(addr);
+
+	dev_dbg(&vm->vdev->dev, "removing memory block: %lu\n", mb_id);
+	return remove_memory(nid, addr, memory_block_size_bytes());
+}
+
+/*
+ * Trigger the workqueue so the device can perform its magic.
+ */
+static void virtio_mem_retry(struct virtio_mem *vm)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&vm->removal_lock, flags);
+	if (!vm->removing)
+		queue_work(system_freezable_wq, &vm->wq);
+	spin_unlock_irqrestore(&vm->removal_lock, flags);
+}
+
+/*
+ * Test if a virtio-mem device overlaps with the given range. Can be called
+ * from (notifier) callbacks lockless.
+ */
+static bool virtio_mem_overlaps_range(struct virtio_mem *vm,
+				      unsigned long start, unsigned long size)
+{
+	const unsigned long end = start + size;
+	unsigned long dev_start = virtio_mem_mb_id_to_phys(vm->first_mb_id);
+	unsigned long dev_end = virtio_mem_mb_id_to_phys(vm->last_mb_id) +
+				memory_block_size_bytes();
+
+	return start < dev_end && dev_start < end;
+}
+
+/*
+ * Test if a virtio-mem device owns a memory block. Can be called from
+ * (notifier) callbacks lockless.
+ */
+static bool virtio_mem_owned_mb(struct virtio_mem *vm, unsigned long mb_id)
+{
+	return mb_id >= vm->first_mb_id && mb_id <= vm->last_mb_id;
+}
+
+static int virtio_mem_notify_going_online(struct virtio_mem *vm,
+					  unsigned long mb_id,
+					  enum zone_type zone)
+{
+	switch (virtio_mem_mb_get_state(vm, mb_id)) {
+	case VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL:
+		/*
+		 * We won't allow to online a partially plugged memory block
+		 * to the MOVABLE zone - it would contain unmovable parts.
+		 */
+		if (zone == ZONE_MOVABLE) {
+			dev_warn_ratelimited(&vm->vdev->dev,
+					     "memory block has holes, MOVABLE not supported\n");
+			return NOTIFY_BAD;
+		}
+		return NOTIFY_OK;
+	case VIRTIO_MEM_MB_STATE_OFFLINE:
+		return NOTIFY_OK;
+	default:
+		break;
+	}
+	dev_warn_ratelimited(&vm->vdev->dev,
+			     "memory block onlining denied\n");
+	return NOTIFY_BAD;
+}
+
+static void virtio_mem_notify_offline(struct virtio_mem *vm,
+				      unsigned long mb_id)
+{
+	switch (virtio_mem_mb_get_state(vm, mb_id)) {
+	case VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL:
+		virtio_mem_mb_set_state(vm, mb_id,
+					VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL);
+		break;
+	case VIRTIO_MEM_MB_STATE_ONLINE:
+	case VIRTIO_MEM_MB_STATE_ONLINE_MOVABLE:
+		virtio_mem_mb_set_state(vm, mb_id,
+					VIRTIO_MEM_MB_STATE_OFFLINE);
+		break;
+	default:
+		BUG();
+		break;
+	}
+}
+
+static void virtio_mem_notify_online(struct virtio_mem *vm, unsigned long mb_id,
+				     enum zone_type zone)
+{
+	unsigned long nb_offline;
+
+	switch (virtio_mem_mb_get_state(vm, mb_id)) {
+	case VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL:
+		BUG_ON(zone == ZONE_MOVABLE);
+		virtio_mem_mb_set_state(vm, mb_id,
+					VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL);
+		break;
+	case VIRTIO_MEM_MB_STATE_OFFLINE:
+		if (zone == ZONE_MOVABLE)
+			virtio_mem_mb_set_state(vm, mb_id,
+					    VIRTIO_MEM_MB_STATE_ONLINE_MOVABLE);
+		else
+			virtio_mem_mb_set_state(vm, mb_id,
+						VIRTIO_MEM_MB_STATE_ONLINE);
+		break;
+	default:
+		BUG();
+		break;
+	}
+	nb_offline = vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE] +
+		     vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL];
+
+	/* see if we can add new blocks now that we onlined one block */
+	if (nb_offline == VIRTIO_MEM_NB_OFFLINE_THRESHOLD - 1)
+		virtio_mem_retry(vm);
+}
+
+/*
+ * This callback will either be called synchronously from add_memory() or
+ * asynchronously (e.g., triggered via user space). We have to be careful
+ * with locking when calling add_memory().
+ */
+static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
+					 unsigned long action, void *arg)
+{
+	struct virtio_mem *vm = container_of(nb, struct virtio_mem,
+					     memory_notifier);
+	struct memory_notify *mhp = arg;
+	const unsigned long start = PFN_PHYS(mhp->start_pfn);
+	const unsigned long size = PFN_PHYS(mhp->nr_pages);
+	const unsigned long mb_id = virtio_mem_phys_to_mb_id(start);
+	enum zone_type zone;
+	int rc = NOTIFY_OK;
+
+	if (!virtio_mem_overlaps_range(vm, start, size))
+		return NOTIFY_DONE;
+
+	/*
+	 * Memory is onlined/offlined in memory block granularity. We cannot
+	 * cross virtio-mem device boundaries and memory block boundaries. Bail
+	 * out if this ever changes.
+	 */
+	if (WARN_ON_ONCE(size != memory_block_size_bytes() ||
+			 !IS_ALIGNED(start, memory_block_size_bytes())))
+		return NOTIFY_BAD;
+
+	/*
+	 * Avoid circular locking lockdep warnings. We lock the mutex
+	 * e.g., in MEM_GOING_ONLINE and unlock it in MEM_ONLINE. The
+	 * blocking_notifier_call_chain() has it's own lock, which gets unlocked
+	 * between both notifier calls and will bail out. False positive.
+	 */
+	lockdep_off();
+
+	switch (action) {
+	case MEM_GOING_OFFLINE:
+		mutex_lock(&vm->hotplug_mutex);
+		if (vm->removing) {
+			rc = notifier_to_errno(-EBUSY);
+			mutex_unlock(&vm->hotplug_mutex);
+			break;
+		}
+		vm->hotplug_active = true;
+		break;
+	case MEM_GOING_ONLINE:
+		mutex_lock(&vm->hotplug_mutex);
+		if (vm->removing) {
+			rc = notifier_to_errno(-EBUSY);
+			mutex_unlock(&vm->hotplug_mutex);
+			break;
+		}
+		vm->hotplug_active = true;
+		zone = page_zonenum(pfn_to_page(mhp->start_pfn));
+		rc = virtio_mem_notify_going_online(vm, mb_id, zone);
+		break;
+	case MEM_OFFLINE:
+		virtio_mem_notify_offline(vm, mb_id);
+		vm->hotplug_active = false;
+		mutex_unlock(&vm->hotplug_mutex);
+		break;
+	case MEM_ONLINE:
+		zone = page_zonenum(pfn_to_page(mhp->start_pfn));
+		virtio_mem_notify_online(vm, mb_id, zone);
+		vm->hotplug_active = false;
+		mutex_unlock(&vm->hotplug_mutex);
+		break;
+	case MEM_CANCEL_OFFLINE:
+	case MEM_CANCEL_ONLINE:
+		if (!vm->hotplug_active)
+			break;
+		vm->hotplug_active = false;
+		mutex_unlock(&vm->hotplug_mutex);
+		break;
+	default:
+		break;
+	}
+
+	lockdep_on();
+
+	return rc;
+}
+
+/*
+ * Set a range of pages PG_offline.
+ */
+static void virtio_mem_set_fake_offline(unsigned long pfn,
+					unsigned int nr_pages)
+{
+	for (; nr_pages--; pfn++)
+		__SetPageOffline(pfn_to_page(pfn));
+}
+
+/*
+ * Clear PG_offline from a range of pages.
+ */
+static void virtio_mem_clear_fake_offline(unsigned long pfn,
+					  unsigned int nr_pages)
+{
+	for (; nr_pages--; pfn++)
+		__ClearPageOffline(pfn_to_page(pfn));
+}
+
+/*
+ * Release a range of fake-offline pages to the buddy, effectively
+ * fake-onlining them.
+ */
+static void virtio_mem_fake_online(unsigned long pfn, unsigned int nr_pages)
+{
+	const int order = MAX_ORDER - 1;
+	int i;
+
+	/*
+	 * We are always called with subblock granularity, which is at least
+	 * aligned to MAX_ORDER - 1.
+	 */
+	virtio_mem_clear_fake_offline(pfn, nr_pages);
+
+	for (i = 0; i < nr_pages; i += 1 << order)
+		generic_online_page(pfn_to_page(pfn + i), order);
+}
+
+static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
+{
+	const unsigned long addr = page_to_phys(page);
+	const unsigned long mb_id = virtio_mem_phys_to_mb_id(addr);
+	struct virtio_mem *vm;
+	int sb_id;
+
+	/*
+	 * We exploit here that subblocks have at least MAX_ORDER - 1
+	 * size/alignment and that this callback is is called with such a
+	 * size/alignment. So we cannot cross subblocks and therefore
+	 * also not memory blocks.
+	 */
+	rcu_read_lock();
+	list_for_each_entry_rcu(vm, &virtio_mem_devices, next) {
+		if (!virtio_mem_owned_mb(vm, mb_id))
+			continue;
+
+		sb_id = virtio_mem_phys_to_sb_id(vm, addr);
+		/*
+		 * If plugged, online the pages, otherwise, set them fake
+		 * offline (PageOffline).
+		 */
+		if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
+			generic_online_page(page, order);
+		else
+			virtio_mem_set_fake_offline(PFN_DOWN(addr), 1 << order);
+		rcu_read_unlock();
+		return;
+	}
+	rcu_read_unlock();
+
+	/* not virtio-mem memory, but e.g., a DIMM. online it */
+	generic_online_page(page, order);
+}
+
+static uint64_t virtio_mem_send_request(struct virtio_mem *vm,
+					const struct virtio_mem_req *req)
+{
+	struct scatterlist *sgs[2], sg_req, sg_resp;
+	unsigned int len;
+	int rc;
+
+	/* don't use the request residing on the stack (vaddr) */
+	vm->req = *req;
+
+	/* out: buffer for request */
+	sg_init_one(&sg_req, &vm->req, sizeof(vm->req));
+	sgs[0] = &sg_req;
+
+	/* in: buffer for response */
+	sg_init_one(&sg_resp, &vm->resp, sizeof(vm->resp));
+	sgs[1] = &sg_resp;
+
+	rc = virtqueue_add_sgs(vm->vq, sgs, 1, 1, vm, GFP_KERNEL);
+	if (rc < 0)
+		return rc;
+
+	virtqueue_kick(vm->vq);
+
+	/* wait for a response */
+	wait_event(vm->host_resp, virtqueue_get_buf(vm->vq, &len));
+
+	return virtio16_to_cpu(vm->vdev, vm->resp.type);
+}
+
+static int virtio_mem_send_plug_request(struct virtio_mem *vm, uint64_t addr,
+					uint64_t size)
+{
+	const uint64_t nb_vm_blocks = size / vm->device_block_size;
+	const struct virtio_mem_req req = {
+		.type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_PLUG),
+		.u.plug.addr = cpu_to_virtio64(vm->vdev, addr),
+		.u.plug.nb_blocks = cpu_to_virtio16(vm->vdev, nb_vm_blocks),
+	};
+
+	if (atomic_read(&vm->config_changed))
+		return -EAGAIN;
+
+	switch (virtio_mem_send_request(vm, &req)) {
+	case VIRTIO_MEM_RESP_ACK:
+		vm->plugged_size += size;
+		return 0;
+	case VIRTIO_MEM_RESP_NACK:
+		return -EAGAIN;
+	case VIRTIO_MEM_RESP_BUSY:
+		return -EBUSY;
+	case VIRTIO_MEM_RESP_ERROR:
+		return -EINVAL;
+	default:
+		return -ENOMEM;
+	}
+}
+
+static int virtio_mem_send_unplug_request(struct virtio_mem *vm, uint64_t addr,
+					  uint64_t size)
+{
+	const uint64_t nb_vm_blocks = size / vm->device_block_size;
+	const struct virtio_mem_req req = {
+		.type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_UNPLUG),
+		.u.unplug.addr = cpu_to_virtio64(vm->vdev, addr),
+		.u.unplug.nb_blocks = cpu_to_virtio16(vm->vdev, nb_vm_blocks),
+	};
+
+	if (atomic_read(&vm->config_changed))
+		return -EAGAIN;
+
+	switch (virtio_mem_send_request(vm, &req)) {
+	case VIRTIO_MEM_RESP_ACK:
+		vm->plugged_size -= size;
+		return 0;
+	case VIRTIO_MEM_RESP_BUSY:
+		return -EBUSY;
+	case VIRTIO_MEM_RESP_ERROR:
+		return -EINVAL;
+	default:
+		return -ENOMEM;
+	}
+}
+
+static int virtio_mem_send_unplug_all_request(struct virtio_mem *vm)
+{
+	const struct virtio_mem_req req = {
+		.type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_UNPLUG_ALL),
+	};
+
+	switch (virtio_mem_send_request(vm, &req)) {
+	case VIRTIO_MEM_RESP_ACK:
+		vm->unplug_all_required = false;
+		vm->plugged_size = 0;
+		/* usable region might have shrunk */
+		atomic_set(&vm->config_changed, 1);
+		return 0;
+	case VIRTIO_MEM_RESP_BUSY:
+		return -EBUSY;
+	default:
+		return -ENOMEM;
+	}
+}
+
+/*
+ * Plug selected subblocks. Updates the plugged state, but not the state
+ * of the memory block.
+ */
+static int virtio_mem_mb_plug_sb(struct virtio_mem *vm, unsigned long mb_id,
+				 int sb_id, int count)
+{
+	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id) +
+			      sb_id * vm->subblock_size;
+	const uint64_t size = count * vm->subblock_size;
+	int rc;
+
+	dev_dbg(&vm->vdev->dev, "plugging memory block: %lu : %i - %i\n", mb_id,
+		sb_id, sb_id + count - 1);
+
+	rc = virtio_mem_send_plug_request(vm, addr, size);
+	if (!rc)
+		virtio_mem_mb_set_sb_plugged(vm, mb_id, sb_id, count);
+	return rc;
+}
+
+/*
+ * Unplug selected subblocks. Updates the plugged state, but not the state
+ * of the memory block.
+ */
+static int virtio_mem_mb_unplug_sb(struct virtio_mem *vm, unsigned long mb_id,
+				   int sb_id, int count)
+{
+	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id) +
+			      sb_id * vm->subblock_size;
+	const uint64_t size = count * vm->subblock_size;
+	int rc;
+
+	dev_dbg(&vm->vdev->dev, "unplugging memory block: %lu : %i - %i\n",
+		mb_id, sb_id, sb_id + count - 1);
+
+	rc = virtio_mem_send_unplug_request(vm, addr, size);
+	if (!rc)
+		virtio_mem_mb_set_sb_unplugged(vm, mb_id, sb_id, count);
+	return rc;
+}
+
+/*
+ * Unplug the desired number of plugged subblocks of a offline or not-added
+ * memory block. Will fail if any subblock cannot get unplugged (instead of
+ * skipping it).
+ *
+ * Will not modify the state of the memory block.
+ *
+ * Note: can fail after some subblocks were unplugged.
+ */
+static int virtio_mem_mb_unplug_any_sb(struct virtio_mem *vm,
+				       unsigned long mb_id, uint64_t *nb_sb)
+{
+	int sb_id, count;
+	int rc;
+
+	while (*nb_sb) {
+		sb_id = virtio_mem_mb_first_plugged_sb(vm, mb_id);
+		if (sb_id >= vm->nb_sb_per_mb)
+			break;
+		count = 1;
+		while (count < *nb_sb &&
+		       sb_id + count  < vm->nb_sb_per_mb &&
+		       virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id + count,
+						     1))
+			count++;
+
+		rc = virtio_mem_mb_unplug_sb(vm, mb_id, sb_id, count);
+		if (rc)
+			return rc;
+		*nb_sb -= count;
+	}
+
+	return 0;
+}
+
+/*
+ * Unplug all plugged subblocks of an offline or not-added memory block.
+ *
+ * Will not modify the state of the memory block.
+ *
+ * Note: can fail after some subblocks were unplugged.
+ */
+static int virtio_mem_mb_unplug(struct virtio_mem *vm, unsigned long mb_id)
+{
+	uint64_t nb_sb = vm->nb_sb_per_mb;
+
+	return virtio_mem_mb_unplug_any_sb(vm, mb_id, &nb_sb);
+}
+
+/*
+ * Prepare tracking data for the next memory block.
+ */
+static int virtio_mem_prepare_next_mb(struct virtio_mem *vm,
+				      unsigned long *mb_id)
+{
+	int rc;
+
+	if (vm->next_mb_id > vm->last_usable_mb_id)
+		return -ENOSPC;
+
+	/* Resize the state array if required. */
+	rc = virtio_mem_mb_state_prepare_next_mb(vm);
+	if (rc)
+		return rc;
+
+	/* Resize the subblock bitmap if required. */
+	rc = virtio_mem_sb_bitmap_prepare_next_mb(vm);
+	if (rc)
+		return rc;
+
+	vm->nb_mb_state[VIRTIO_MEM_MB_STATE_UNUSED]++;
+	*mb_id = vm->next_mb_id++;
+	return 0;
+}
+
+/*
+ * Don't add too many blocks that are not onlined yet to avoid running OOM.
+ */
+static bool virtio_mem_too_many_mb_offline(struct virtio_mem *vm)
+{
+	unsigned long nb_offline;
+
+	nb_offline = vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE] +
+		     vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL];
+	return nb_offline >= VIRTIO_MEM_NB_OFFLINE_THRESHOLD;
+}
+
+/*
+ * Try to plug the desired number of subblocks and add the memory block
+ * to Linux.
+ *
+ * Will modify the state of the memory block.
+ */
+static int virtio_mem_mb_plug_and_add(struct virtio_mem *vm,
+				      unsigned long mb_id,
+				      uint64_t *nb_sb)
+{
+	const int count = min_t(int, *nb_sb, vm->nb_sb_per_mb);
+	int rc, rc2;
+
+	if (WARN_ON_ONCE(!count))
+		return -EINVAL;
+
+	/*
+	 * Plug the requested number of subblocks before adding it to linux,
+	 * so that onlining will directly online all plugged subblocks.
+	 */
+	rc = virtio_mem_mb_plug_sb(vm, mb_id, 0, count);
+	if (rc)
+		return rc;
+
+	/*
+	 * Mark the block properly offline before adding it to Linux,
+	 * so the memory notifiers will find the block in the right state.
+	 */
+	if (count == vm->nb_sb_per_mb)
+		virtio_mem_mb_set_state(vm, mb_id,
+					VIRTIO_MEM_MB_STATE_OFFLINE);
+	else
+		virtio_mem_mb_set_state(vm, mb_id,
+					VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL);
+
+	/* Add the memory block to linux - if that fails, try to unplug. */
+	rc = virtio_mem_mb_add(vm, mb_id);
+	if (rc) {
+		enum virtio_mem_mb_state new_state = VIRTIO_MEM_MB_STATE_UNUSED;
+
+		dev_err(&vm->vdev->dev,
+			"adding memory block %lu failed with %d\n", mb_id, rc);
+		rc2 = virtio_mem_mb_unplug_sb(vm, mb_id, 0, count);
+
+		/*
+		 * TODO: Linux MM does not properly clean up yet in all cases
+		 * where adding of memory failed - especially on -ENOMEM.
+		 */
+		if (rc2)
+			new_state = VIRTIO_MEM_MB_STATE_PLUGGED;
+		virtio_mem_mb_set_state(vm, mb_id, new_state);
+		return rc;
+	}
+
+	*nb_sb -= count;
+	return 0;
+}
+
+/*
+ * Try to plug the desired number of subblocks of a memory block that
+ * is already added to Linux.
+ *
+ * Will modify the state of the memory block.
+ *
+ * Note: Can fail after some subblocks were successfully plugged.
+ */
+static int virtio_mem_mb_plug_any_sb(struct virtio_mem *vm, unsigned long mb_id,
+				     uint64_t *nb_sb, bool online)
+{
+	unsigned long pfn, nr_pages;
+	int sb_id, count;
+	int rc;
+
+	if (WARN_ON_ONCE(!*nb_sb))
+		return -EINVAL;
+
+	while (*nb_sb) {
+		sb_id = virtio_mem_mb_first_unplugged_sb(vm, mb_id);
+		if (sb_id >= vm->nb_sb_per_mb)
+			break;
+		count = 1;
+		while (count < *nb_sb &&
+		       sb_id + count < vm->nb_sb_per_mb &&
+		       !virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id + count,
+						      1))
+			count++;
+
+		rc = virtio_mem_mb_plug_sb(vm, mb_id, sb_id, count);
+		if (rc)
+			return rc;
+		*nb_sb -= count;
+		if (!online)
+			continue;
+
+		/* fake-online the pages if the memory block is online */
+		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
+			       sb_id * vm->subblock_size);
+		nr_pages = PFN_DOWN(count * vm->subblock_size);
+		virtio_mem_fake_online(pfn, nr_pages);
+	}
+
+	if (virtio_mem_mb_test_sb_plugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
+		if (online)
+			virtio_mem_mb_set_state(vm, mb_id,
+						VIRTIO_MEM_MB_STATE_ONLINE);
+		else
+			virtio_mem_mb_set_state(vm, mb_id,
+						VIRTIO_MEM_MB_STATE_OFFLINE);
+	}
+
+	return rc;
+}
+
+/*
+ * Try to plug the requested amount of memory.
+ */
+static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff)
+{
+	uint64_t nb_sb = diff / vm->subblock_size;
+	unsigned long mb_id;
+	int rc;
+
+	if (!nb_sb)
+		return 0;
+
+	/* Don't race with onlining/offlining */
+	mutex_lock(&vm->hotplug_mutex);
+
+	/* Try to plug subblocks of partially plugged online blocks. */
+	virtio_mem_for_each_mb_state(vm, mb_id,
+				     VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL) {
+		rc = virtio_mem_mb_plug_any_sb(vm, mb_id, &nb_sb, true);
+		if (rc || !nb_sb)
+			goto out_unlock;
+		cond_resched();
+	}
+
+	/* Try to plug subblocks of partially plugged offline blocks. */
+	virtio_mem_for_each_mb_state(vm, mb_id,
+				     VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL) {
+		rc = virtio_mem_mb_plug_any_sb(vm, mb_id, &nb_sb, false);
+		if (rc || !nb_sb)
+			goto out_unlock;
+		cond_resched();
+	}
+
+	/*
+	 * We won't be working on online/offline memory blocks from this point,
+	 * so we can't race with memory onlining/offlining. Drop the mutex.
+	 */
+	mutex_unlock(&vm->hotplug_mutex);
+
+	/* Try to plug and add unused blocks */
+	virtio_mem_for_each_mb_state(vm, mb_id, VIRTIO_MEM_MB_STATE_UNUSED) {
+		if (virtio_mem_too_many_mb_offline(vm))
+			return -ENOSPC;
+
+		rc = virtio_mem_mb_plug_and_add(vm, mb_id, &nb_sb);
+		if (rc || !nb_sb)
+			return rc;
+		cond_resched();
+	}
+
+	/* Try to prepare, plug and add new blocks */
+	while (nb_sb) {
+		if (virtio_mem_too_many_mb_offline(vm))
+			return -ENOSPC;
+
+		rc = virtio_mem_prepare_next_mb(vm, &mb_id);
+		if (rc)
+			return rc;
+		rc = virtio_mem_mb_plug_and_add(vm, mb_id, &nb_sb);
+		if (rc)
+			return rc;
+		cond_resched();
+	}
+
+	return 0;
+out_unlock:
+	mutex_unlock(&vm->hotplug_mutex);
+	return rc;
+}
+
+/*
+ * Try to unplug all blocks that couldn't be unplugged before, for example,
+ * because the hypervisor was busy.
+ */
+static int virtio_mem_unplug_pending_mb(struct virtio_mem *vm)
+{
+	unsigned long mb_id;
+	int rc;
+
+	virtio_mem_for_each_mb_state(vm, mb_id, VIRTIO_MEM_MB_STATE_PLUGGED) {
+		rc = virtio_mem_mb_unplug(vm, mb_id);
+		if (rc)
+			return rc;
+		virtio_mem_mb_set_state(vm, mb_id, VIRTIO_MEM_MB_STATE_UNUSED);
+	}
+
+	return 0;
+}
+
+/*
+ * Update all parts of the config that could have changed.
+ */
+static void virtio_mem_refresh_config(struct virtio_mem *vm)
+{
+	const uint64_t phys_limit = 1UL << MAX_PHYSMEM_BITS;
+	uint64_t new_plugged_size, usable_region_size, end_addr;
+
+	/* the plugged_size is just a reflection of what _we_ did previously */
+	virtio_cread(vm->vdev, struct virtio_mem_config, plugged_size,
+		     &new_plugged_size);
+	if (WARN_ON_ONCE(new_plugged_size != vm->plugged_size))
+		vm->plugged_size = new_plugged_size;
+
+	/* calculate the last usable memory block id */
+	virtio_cread(vm->vdev, struct virtio_mem_config,
+		     usable_region_size, &usable_region_size);
+	end_addr = vm->addr + usable_region_size;
+	end_addr = min(end_addr, phys_limit);
+	vm->last_usable_mb_id = virtio_mem_phys_to_mb_id(end_addr) - 1;
+
+	/* see if there is a request to change the size */
+	virtio_cread(vm->vdev, struct virtio_mem_config, requested_size,
+		     &vm->requested_size);
+
+	dev_info(&vm->vdev->dev, "plugged size: 0x%llx", vm->plugged_size);
+	dev_info(&vm->vdev->dev, "requested size: 0x%llx", vm->requested_size);
+}
+
+/*
+ * Workqueue function for handling plug/unplug requests and config updates.
+ */
+static void virtio_mem_run_wq(struct work_struct *work)
+{
+	struct virtio_mem *vm = container_of(work, struct virtio_mem, wq);
+	uint64_t diff;
+	int rc;
+
+	hrtimer_cancel(&vm->retry_timer);
+
+	if (vm->broken)
+		return;
+
+retry:
+	rc = 0;
+
+	/* Make sure we start with a clean state if there are leftovers. */
+	if (unlikely(vm->unplug_all_required))
+		rc = virtio_mem_send_unplug_all_request(vm);
+
+	if (atomic_read(&vm->config_changed)) {
+		atomic_set(&vm->config_changed, 0);
+		virtio_mem_refresh_config(vm);
+	}
+
+	/* Unplug any leftovers from previous runs */
+	if (!rc)
+		rc = virtio_mem_unplug_pending_mb(vm);
+
+	if (!rc && vm->requested_size != vm->plugged_size) {
+		if (vm->requested_size > vm->plugged_size) {
+			diff = vm->requested_size - vm->plugged_size;
+			rc = virtio_mem_plug_request(vm, diff);
+		}
+		/* TODO: try to unplug memory */
+	}
+
+	switch (rc) {
+	case 0:
+		break;
+	case -ENOSPC:
+		/*
+		 * We cannot add any more memory (alignment, physical limit)
+		 * or we have too many offline memory blocks.
+		 */
+		break;
+	case -EBUSY:
+		/*
+		 * The hypervisor cannot process our request right now
+		 * (e.g., out of memory, migrating).
+		 */
+	case -ENOMEM:
+		/* Out of memory, try again later. */
+		hrtimer_start(&vm->retry_timer,
+			      ms_to_ktime(VIRTIO_MEM_RETRY_TIMER_MS),
+			      HRTIMER_MODE_REL);
+		break;
+	case -EAGAIN:
+		/* Retry immediately (e.g., the config changed). */
+		goto retry;
+	default:
+		/* Unknown error, mark as broken */
+		dev_err(&vm->vdev->dev,
+			"unknown error, marking device broken: %d\n", rc);
+		vm->broken = true;
+	}
+}
+
+static enum hrtimer_restart virtio_mem_timer_expired(struct hrtimer *timer)
+{
+	struct virtio_mem *vm = container_of(timer, struct virtio_mem,
+					     retry_timer);
+
+	virtio_mem_retry(vm);
+	return HRTIMER_NORESTART;
+}
+
+static void virtio_mem_handle_response(struct virtqueue *vq)
+{
+	struct virtio_mem *vm = vq->vdev->priv;
+
+	wake_up(&vm->host_resp);
+}
+
+static int virtio_mem_init_vq(struct virtio_mem *vm)
+{
+	struct virtqueue *vq;
+
+	vq = virtio_find_single_vq(vm->vdev, virtio_mem_handle_response,
+				   "guest-request");
+	if (IS_ERR(vq))
+		return PTR_ERR(vq);
+	vm->vq = vq;
+
+	return 0;
+}
+
+/*
+ * Test if any memory in the range is present in Linux.
+ */
+static bool virtio_mem_any_memory_present(unsigned long start,
+					  unsigned long size)
+{
+	const unsigned long start_pfn = PFN_DOWN(start);
+	const unsigned long end_pfn = PFN_UP(start + size);
+	unsigned long pfn;
+
+	for (pfn = start_pfn; pfn != end_pfn; pfn++)
+		if (present_section_nr(pfn_to_section_nr(pfn)))
+			return true;
+
+	return false;
+}
+
+static int virtio_mem_init(struct virtio_mem *vm)
+{
+	const uint64_t phys_limit = 1UL << MAX_PHYSMEM_BITS;
+	uint64_t region_size;
+
+	if (!vm->vdev->config->get) {
+		dev_err(&vm->vdev->dev, "config access disabled\n");
+		return -EINVAL;
+	}
+
+	/*
+	 * We don't want to (un)plug or reuse any memory when in kdump. The
+	 * memory is still accessible (but not mapped).
+	 */
+	if (is_kdump_kernel()) {
+		dev_warn(&vm->vdev->dev, "disabled in kdump kernel\n");
+		return -EBUSY;
+	}
+
+	/* Fetch all properties that can't change. */
+	virtio_cread(vm->vdev, struct virtio_mem_config, plugged_size,
+		     &vm->plugged_size);
+	virtio_cread(vm->vdev, struct virtio_mem_config, block_size,
+		     &vm->device_block_size);
+	virtio_cread(vm->vdev, struct virtio_mem_config, addr, &vm->addr);
+	virtio_cread(vm->vdev, struct virtio_mem_config, region_size,
+		     &region_size);
+
+	/*
+	 * If we still have memory plugged, we might have to unplug all
+	 * memory first. However, if somebody simply unloaded the driver
+	 * we would have to reinitialize the old state - something we don't
+	 * support yet. Detect if we have any memory in the area present.
+	 */
+	if (vm->plugged_size) {
+		uint64_t usable_region_size;
+
+		virtio_cread(vm->vdev, struct virtio_mem_config,
+			     usable_region_size, &usable_region_size);
+
+		if (virtio_mem_any_memory_present(vm->addr,
+						  usable_region_size)) {
+			dev_err(&vm->vdev->dev,
+				"reloading the driver is not supported\n");
+			return -EINVAL;
+		}
+		/*
+		 * Note: it might happen that the device is busy and
+		 * unplugging all memory might take some time.
+		 */
+		dev_info(&vm->vdev->dev, "unplugging all memory required\n");
+		vm->unplug_all_required = 1;
+	}
+
+	/*
+	 * We always hotplug memory in memory block granularity. This way,
+	 * we have to wait for exactly one memory block to online.
+	 */
+	if (vm->device_block_size > memory_block_size_bytes()) {
+		dev_err(&vm->vdev->dev,
+			"The block size is not supported (too big).\n");
+		return -EINVAL;
+	}
+
+	/* bad device setup - warn only */
+	if (!IS_ALIGNED(vm->addr, memory_block_size_bytes()))
+		dev_warn(&vm->vdev->dev,
+			 "The alignment of the physical start address can make some memory unusable.\n");
+	if (!IS_ALIGNED(vm->addr + region_size, memory_block_size_bytes()))
+		dev_warn(&vm->vdev->dev,
+			 "The alignment of the physical end address can make some memory unusable.\n");
+	if (vm->addr + region_size > phys_limit)
+		dev_warn(&vm->vdev->dev,
+			 "Some memory is not addressable. This can make some memory unusable.\n");
+
+	/*
+	 * Calculate the subblock size:
+	 * - At least MAX_ORDER - 1 / pageblock_order.
+	 * - At least the device block size.
+	 * In the worst case, a single subblock per memory block.
+	 */
+	vm->subblock_size = PAGE_SIZE * 1u << max_t(uint32_t, MAX_ORDER - 1,
+						    pageblock_order);
+	vm->subblock_size = max_t(uint32_t, vm->device_block_size,
+				  vm->subblock_size);
+	vm->nb_sb_per_mb = memory_block_size_bytes() / vm->subblock_size;
+
+	/* Round up to the next full memory block */
+	vm->first_mb_id = virtio_mem_phys_to_mb_id(vm->addr - 1 +
+						   memory_block_size_bytes());
+	vm->next_mb_id = vm->first_mb_id;
+	vm->last_mb_id = virtio_mem_phys_to_mb_id(vm->addr + region_size) - 1;
+
+	dev_info(&vm->vdev->dev, "start address: 0x%llx", vm->addr);
+	dev_info(&vm->vdev->dev, "region size: 0x%llx", region_size);
+	dev_info(&vm->vdev->dev, "device block size: 0x%x",
+		 vm->device_block_size);
+	dev_info(&vm->vdev->dev, "memory block size: 0x%lx",
+		 memory_block_size_bytes());
+	dev_info(&vm->vdev->dev, "subblock size: 0x%x",
+		 vm->subblock_size);
+
+	return 0;
+}
+
+static int virtio_mem_probe(struct virtio_device *vdev)
+{
+	struct virtio_mem *vm;
+	int rc = -EINVAL;
+
+	vdev->priv = vm = kzalloc(sizeof(*vm), GFP_KERNEL);
+	if (!vm)
+		return -ENOMEM;
+
+	init_waitqueue_head(&vm->host_resp);
+	vm->vdev = vdev;
+	INIT_WORK(&vm->wq, virtio_mem_run_wq);
+	mutex_init(&vm->hotplug_mutex);
+	INIT_LIST_HEAD(&vm->next);
+	spin_lock_init(&vm->removal_lock);
+	hrtimer_init(&vm->retry_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	vm->retry_timer.function = virtio_mem_timer_expired;
+
+	/* register the virtqueue */
+	rc = virtio_mem_init_vq(vm);
+	if (rc)
+		goto out_free_vm;
+
+	/* initialize the device by querying the config */
+	rc = virtio_mem_init(vm);
+	if (rc)
+		goto out_del_vq;
+
+	/* register callbacks */
+	vm->memory_notifier.notifier_call = virtio_mem_memory_notifier_cb;
+	rc = register_memory_notifier(&vm->memory_notifier);
+	if (rc)
+		goto out_del_vq;
+	rc = register_virtio_mem_device(vm);
+	if (rc)
+		goto out_unreg_mem;
+
+	virtio_device_ready(vdev);
+
+	/* trigger a config update to start processing the requested_size */
+	atomic_set(&vm->config_changed, 1);
+	queue_work(system_freezable_wq, &vm->wq);
+
+	return 0;
+out_unreg_mem:
+	unregister_memory_notifier(&vm->memory_notifier);
+out_del_vq:
+	vdev->config->del_vqs(vdev);
+out_free_vm:
+	kfree(vm);
+	vdev->priv = NULL;
+
+	return rc;
+}
+
+static void virtio_mem_remove(struct virtio_device *vdev)
+{
+	struct virtio_mem *vm = vdev->priv;
+	unsigned long mb_id;
+	int rc;
+
+	/*
+	 * Make sure the workqueue won't be triggered anymore and no memory
+	 * blocks can be onlined/offlined until we're finished here.
+	 */
+	mutex_lock(&vm->hotplug_mutex);
+	spin_lock_irq(&vm->removal_lock);
+	vm->removing = true;
+	spin_unlock_irq(&vm->removal_lock);
+	mutex_unlock(&vm->hotplug_mutex);
+
+	/* wait until the workqueue stopped */
+	cancel_work_sync(&vm->wq);
+	hrtimer_cancel(&vm->retry_timer);
+
+	/*
+	 * After we unregistered our callbacks, user space can online partially
+	 * plugged offline blocks. Make sure to remove them.
+	 */
+	virtio_mem_for_each_mb_state(vm, mb_id,
+				     VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL) {
+		rc = virtio_mem_mb_remove(vm, mb_id);
+		BUG_ON(rc);
+	}
+
+	/* unregister callbacks */
+	unregister_virtio_mem_device(vm);
+	unregister_memory_notifier(&vm->memory_notifier);
+
+	/*
+	 * There is no way we could reliably remove all memory we have added to
+	 * the system. And there is no way to stop the driver/device from going
+	 * away.
+	 */
+	if (vm->plugged_size)
+		dev_warn(&vdev->dev, "device still has memory plugged\n");
+
+	/* remove all tracking data - no locking needed */
+	vfree(vm->mb_state);
+	vfree(vm->sb_bitmap);
+
+	/* reset the device and cleanup the queues */
+	vdev->config->reset(vdev);
+	vdev->config->del_vqs(vdev);
+
+	kfree(vm);
+	vdev->priv = NULL;
+}
+
+static void virtio_mem_config_changed(struct virtio_device *vdev)
+{
+	struct virtio_mem *vm = vdev->priv;
+
+	atomic_set(&vm->config_changed, 1);
+	virtio_mem_retry(vm);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int virtio_mem_freeze(struct virtio_device *vdev)
+{
+	/*
+	 * When restarting the VM, all memory is usually unplugged. Don't
+	 * allow to suspend/hibernate.
+	 */
+	dev_err(&vdev->dev, "save/restore not supported.\n");
+	return -EPERM;
+}
+
+static int virtio_mem_restore(struct virtio_device *vdev)
+{
+	return -EPERM;
+}
+#endif
+
+static struct virtio_device_id virtio_mem_id_table[] = {
+	{ VIRTIO_ID_MEM, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+
+static struct virtio_driver virtio_mem_driver = {
+	.driver.name = KBUILD_MODNAME,
+	.driver.owner = THIS_MODULE,
+	.id_table = virtio_mem_id_table,
+	.probe = virtio_mem_probe,
+	.remove = virtio_mem_remove,
+	.config_changed = virtio_mem_config_changed,
+#ifdef CONFIG_PM_SLEEP
+	.freeze	=	virtio_mem_freeze,
+	.restore =	virtio_mem_restore,
+#endif
+};
+
+module_virtio_driver(virtio_mem_driver);
+MODULE_DEVICE_TABLE(virtio, virtio_mem_id_table);
+MODULE_AUTHOR("David Hildenbrand <david@redhat.com>");
+MODULE_DESCRIPTION("Virtio-mem driver");
+MODULE_LICENSE("GPL");
diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
index 585e07b27333..934e0b444454 100644
--- a/include/uapi/linux/virtio_ids.h
+++ b/include/uapi/linux/virtio_ids.h
@@ -44,6 +44,7 @@
 #define VIRTIO_ID_VSOCK        19 /* virtio vsock transport */
 #define VIRTIO_ID_CRYPTO       20 /* virtio crypto */
 #define VIRTIO_ID_IOMMU        23 /* virtio IOMMU */
+#define VIRTIO_ID_MEM          24 /* virtio mem */
 #define VIRTIO_ID_FS           26 /* virtio filesystem */
 #define VIRTIO_ID_PMEM         27 /* virtio pmem */
 
diff --git a/include/uapi/linux/virtio_mem.h b/include/uapi/linux/virtio_mem.h
new file mode 100644
index 000000000000..1bfade78bdfd
--- /dev/null
+++ b/include/uapi/linux/virtio_mem.h
@@ -0,0 +1,200 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+/*
+ * Virtio Mem Device
+ *
+ * Copyright Red Hat, Inc. 2020
+ *
+ * Authors:
+ *     David Hildenbrand <david@redhat.com>
+ *
+ * This header is BSD licensed so anyone can use the definitions
+ * to implement compatible drivers/servers:
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of IBM nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _LINUX_VIRTIO_MEM_H
+#define _LINUX_VIRTIO_MEM_H
+
+#include <linux/types.h>
+#include <linux/virtio_types.h>
+#include <linux/virtio_ids.h>
+#include <linux/virtio_config.h>
+
+/*
+ * Each virtio-mem device manages a dedicated region in physical address
+ * space. Each device can belong to a single NUMA node, multiple devices
+ * for a single NUMA node are possible. A virtio-mem device is like a
+ * "resizable DIMM" consisting of small memory blocks that can be plugged
+ * or unplugged. The device driver is responsible for (un)plugging memory
+ * blocks on demand.
+ *
+ * Virtio-mem devices can only operate on their assigned memory region in
+ * order to (un)plug memory. A device cannot (un)plug memory belonging to
+ * other devices.
+ *
+ * The "region_size" corresponds to the maximum amount of memory that can
+ * be provided by a device. The "size" corresponds to the amount of memory
+ * that is currently plugged. "requested_size" corresponds to a request
+ * from the device to the device driver to (un)plug blocks. The
+ * device driver should try to (un)plug blocks in order to reach the
+ * "requested_size". It is impossible to plug more memory than requested.
+ *
+ * The "usable_region_size" represents the memory region that can actually
+ * be used to (un)plug memory. It is always at least as big as the
+ * "requested_size" and will grow dynamically. It will only shrink when
+ * explicitly triggered (VIRTIO_MEM_REQ_UNPLUG).
+ *
+ * There are no guarantees what will happen if unplugged memory is
+ * read/written. Such memory should, in general, not be touched. E.g.,
+ * even writing might succeed, but the values will simply be discarded at
+ * random points in time.
+ *
+ * It can happen that the device cannot process a request, because it is
+ * busy. The device driver has to retry later.
+ *
+ * Usually, during system resets all memory will get unplugged, so the
+ * device driver can start with a clean state. However, in specific
+ * scenarios (if the device is busy) it can happen that the device still
+ * has memory plugged. The device driver can request to unplug all memory
+ * (VIRTIO_MEM_REQ_UNPLUG) - which might take a while to succeed if the
+ * device is busy.
+ */
+
+/* --- virtio-mem: guest -> host requests --- */
+
+/* request to plug memory blocks */
+#define VIRTIO_MEM_REQ_PLUG			0
+/* request to unplug memory blocks */
+#define VIRTIO_MEM_REQ_UNPLUG			1
+/* request to unplug all blocks and shrink the usable size */
+#define VIRTIO_MEM_REQ_UNPLUG_ALL		2
+/* request information about the plugged state of memory blocks */
+#define VIRTIO_MEM_REQ_STATE			3
+
+struct virtio_mem_req_plug {
+	__virtio64 addr;
+	__virtio16 nb_blocks;
+};
+
+struct virtio_mem_req_unplug {
+	__virtio64 addr;
+	__virtio16 nb_blocks;
+};
+
+struct virtio_mem_req_state {
+	__virtio64 addr;
+	__virtio16 nb_blocks;
+};
+
+struct virtio_mem_req {
+	__virtio16 type;
+	__virtio16 padding[3];
+
+	union {
+		struct virtio_mem_req_plug plug;
+		struct virtio_mem_req_unplug unplug;
+		struct virtio_mem_req_state state;
+	} u;
+};
+
+
+/* --- virtio-mem: host -> guest response --- */
+
+/*
+ * Request processed successfully, applicable for
+ * - VIRTIO_MEM_REQ_PLUG
+ * - VIRTIO_MEM_REQ_UNPLUG
+ * - VIRTIO_MEM_REQ_UNPLUG_ALL
+ * - VIRTIO_MEM_REQ_STATE
+ */
+#define VIRTIO_MEM_RESP_ACK			0
+/*
+ * Request denied - e.g. trying to plug more than requested, applicable for
+ * - VIRTIO_MEM_REQ_PLUG
+ */
+#define VIRTIO_MEM_RESP_NACK			1
+/*
+ * Request cannot be processed right now, try again later, applicable for
+ * - VIRTIO_MEM_REQ_PLUG
+ * - VIRTIO_MEM_REQ_UNPLUG
+ * - VIRTIO_MEM_REQ_UNPLUG_ALL
+ */
+#define VIRTIO_MEM_RESP_BUSY			2
+/*
+ * Error in request (e.g. addresses/alignment), applicable for
+ * - VIRTIO_MEM_REQ_PLUG
+ * - VIRTIO_MEM_REQ_UNPLUG
+ * - VIRTIO_MEM_REQ_STATE
+ */
+#define VIRTIO_MEM_RESP_ERROR			3
+
+
+/* State of memory blocks is "plugged" */
+#define VIRTIO_MEM_STATE_PLUGGED		0
+/* State of memory blocks is "unplugged" */
+#define VIRTIO_MEM_STATE_UNPLUGGED		1
+/* State of memory blocks is "mixed" */
+#define VIRTIO_MEM_STATE_MIXED			2
+
+struct virtio_mem_resp_state {
+	__virtio16 state;
+};
+
+struct virtio_mem_resp {
+	__virtio16 type;
+	__virtio16 padding[3];
+
+	union {
+		struct virtio_mem_resp_state state;
+	} u;
+};
+
+/* --- virtio-mem: configuration --- */
+
+struct virtio_mem_config {
+	/* Block size and alignment. Cannot change. */
+	__u32 block_size;
+	__u32 padding;
+	/* Start address of the memory region. Cannot change. */
+	__u64 addr;
+	/* Region size (maximum). Cannot change. */
+	__u64 region_size;
+	/*
+	 * Currently usable region size. Can grow up to region_size. Can
+	 * shrink due to VIRTIO_MEM_REQ_UNPLUG_ALL (in which case no config
+	 * update will be sent).
+	 */
+	__u64 usable_region_size;
+	/*
+	 * Currently used size. Changes due to plug/unplug requests, but no
+	 * config updates will be sent.
+	 */
+	__u64 plugged_size;
+	/* Requested size. New plug requests cannot exceed it. Can change. */
+	__u64 requested_size;
+};
+
+#endif /* _LINUX_VIRTIO_MEM_H */
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 02/10] virtio-mem: Allow to specify an ACPI PXM as nid
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
  2020-03-11 17:14 ` [PATCH v2 01/10] virtio-mem: Paravirtualized memory hotplug David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-03-30 11:04   ` Pankaj Gupta
  2020-03-11 17:14 ` [PATCH v2 03/10] virtio-mem: Paravirtualized memory hotunplug part 1 David Hildenbrand
                   ` (9 subsequent siblings)
  11 siblings, 1 reply; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Michal Hocko, Rafael J. Wysocki, Jason Wang, Oscar Salvador,
	Igor Mammedov, Dave Young, Dan Williams, Pavel Tatashin,
	Stefan Hajnoczi, Vlastimil Babka, Len Brown, linux-acpi

We want to allow to specify (similar as for a DIMM), to which node a
virtio-mem device (and, therefore, its memory) belongs. Add a new
virtio-mem feature flag and export pxm_to_node, so it can be used in kernel
module context.

Acked-by: Michal Hocko <mhocko@suse.com> # for the export
Acked-by: "Rafael J. Wysocki" <rafael@kernel.org> # for the export
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Len Brown <lenb@kernel.org>
Cc: linux-acpi@vger.kernel.org
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/acpi/numa/srat.c        |  1 +
 drivers/virtio/virtio_mem.c     | 37 +++++++++++++++++++++++++++++++--
 include/uapi/linux/virtio_mem.h | 10 ++++++++-
 3 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
index 47b4969d9b93..5be5a977da1b 100644
--- a/drivers/acpi/numa/srat.c
+++ b/drivers/acpi/numa/srat.c
@@ -35,6 +35,7 @@ int pxm_to_node(int pxm)
 		return NUMA_NO_NODE;
 	return pxm_to_node_map[pxm];
 }
+EXPORT_SYMBOL(pxm_to_node);
 
 int node_to_pxm(int node)
 {
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 803e1426f80b..d8da656c9145 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -20,6 +20,8 @@
 #include <linux/bitmap.h>
 #include <linux/lockdep.h>
 
+#include <acpi/acpi_numa.h>
+
 enum virtio_mem_mb_state {
 	/* Unplugged, not added to Linux. Can be reused later. */
 	VIRTIO_MEM_MB_STATE_UNUSED = 0,
@@ -71,6 +73,8 @@ struct virtio_mem {
 
 	/* The device block size (for communicating with the device). */
 	uint32_t device_block_size;
+	/* The translated node id. NUMA_NO_NODE in case not specified. */
+	int nid;
 	/* Physical start address of the memory region. */
 	uint64_t addr;
 
@@ -386,7 +390,10 @@ static int virtio_mem_sb_bitmap_prepare_next_mb(struct virtio_mem *vm)
 static int virtio_mem_mb_add(struct virtio_mem *vm, unsigned long mb_id)
 {
 	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
-	int nid = memory_add_physaddr_to_nid(addr);
+	int nid = vm->nid;
+
+	if (nid == NUMA_NO_NODE)
+		nid = memory_add_physaddr_to_nid(addr);
 
 	dev_dbg(&vm->vdev->dev, "adding memory block: %lu\n", mb_id);
 	return add_memory(nid, addr, memory_block_size_bytes());
@@ -404,7 +411,10 @@ static int virtio_mem_mb_add(struct virtio_mem *vm, unsigned long mb_id)
 static int virtio_mem_mb_remove(struct virtio_mem *vm, unsigned long mb_id)
 {
 	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
-	int nid = memory_add_physaddr_to_nid(addr);
+	int nid = vm->nid;
+
+	if (nid == NUMA_NO_NODE)
+		nid = memory_add_physaddr_to_nid(addr);
 
 	dev_dbg(&vm->vdev->dev, "removing memory block: %lu\n", mb_id);
 	return remove_memory(nid, addr, memory_block_size_bytes());
@@ -423,6 +433,17 @@ static void virtio_mem_retry(struct virtio_mem *vm)
 	spin_unlock_irqrestore(&vm->removal_lock, flags);
 }
 
+static int virtio_mem_translate_node_id(struct virtio_mem *vm, uint16_t node_id)
+{
+	int node = NUMA_NO_NODE;
+
+#if defined(CONFIG_ACPI_NUMA)
+	if (virtio_has_feature(vm->vdev, VIRTIO_MEM_F_ACPI_PXM))
+		node = pxm_to_node(node_id);
+#endif
+	return node;
+}
+
 /*
  * Test if a virtio-mem device overlaps with the given range. Can be called
  * from (notifier) callbacks lockless.
@@ -1266,6 +1287,7 @@ static int virtio_mem_init(struct virtio_mem *vm)
 {
 	const uint64_t phys_limit = 1UL << MAX_PHYSMEM_BITS;
 	uint64_t region_size;
+	uint16_t node_id;
 
 	if (!vm->vdev->config->get) {
 		dev_err(&vm->vdev->dev, "config access disabled\n");
@@ -1286,6 +1308,9 @@ static int virtio_mem_init(struct virtio_mem *vm)
 		     &vm->plugged_size);
 	virtio_cread(vm->vdev, struct virtio_mem_config, block_size,
 		     &vm->device_block_size);
+	virtio_cread(vm->vdev, struct virtio_mem_config, node_id,
+		     &node_id);
+	vm->nid = virtio_mem_translate_node_id(vm, node_id);
 	virtio_cread(vm->vdev, struct virtio_mem_config, addr, &vm->addr);
 	virtio_cread(vm->vdev, struct virtio_mem_config, region_size,
 		     &region_size);
@@ -1501,12 +1526,20 @@ static int virtio_mem_restore(struct virtio_device *vdev)
 }
 #endif
 
+static unsigned int virtio_mem_features[] = {
+#if defined(CONFIG_NUMA) && defined(CONFIG_ACPI_NUMA)
+	VIRTIO_MEM_F_ACPI_PXM,
+#endif
+};
+
 static struct virtio_device_id virtio_mem_id_table[] = {
 	{ VIRTIO_ID_MEM, VIRTIO_DEV_ANY_ID },
 	{ 0 },
 };
 
 static struct virtio_driver virtio_mem_driver = {
+	.feature_table = virtio_mem_features,
+	.feature_table_size = ARRAY_SIZE(virtio_mem_features),
 	.driver.name = KBUILD_MODNAME,
 	.driver.owner = THIS_MODULE,
 	.id_table = virtio_mem_id_table,
diff --git a/include/uapi/linux/virtio_mem.h b/include/uapi/linux/virtio_mem.h
index 1bfade78bdfd..e0a9dc7397c3 100644
--- a/include/uapi/linux/virtio_mem.h
+++ b/include/uapi/linux/virtio_mem.h
@@ -83,6 +83,12 @@
  * device is busy.
  */
 
+/* --- virtio-mem: feature bits --- */
+
+/* node_id is an ACPI PXM and is valid */
+#define VIRTIO_MEM_F_ACPI_PXM		0
+
+
 /* --- virtio-mem: guest -> host requests --- */
 
 /* request to plug memory blocks */
@@ -177,7 +183,9 @@ struct virtio_mem_resp {
 struct virtio_mem_config {
 	/* Block size and alignment. Cannot change. */
 	__u32 block_size;
-	__u32 padding;
+	/* Valid with VIRTIO_MEM_F_ACPI_PXM. Cannot change. */
+	__u16 node_id;
+	__u16 padding;
 	/* Start address of the memory region. Cannot change. */
 	__u64 addr;
 	/* Region size (maximum). Cannot change. */
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 03/10] virtio-mem: Paravirtualized memory hotunplug part 1
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
  2020-03-11 17:14 ` [PATCH v2 01/10] virtio-mem: Paravirtualized memory hotplug David Hildenbrand
  2020-03-11 17:14 ` [PATCH v2 02/10] virtio-mem: Allow to specify an ACPI PXM as nid David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-03-11 17:14 ` [PATCH v2 04/10] virtio-mem: Paravirtualized memory hotunplug part 2 David Hildenbrand
                   ` (8 subsequent siblings)
  11 siblings, 0 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Jason Wang, Oscar Salvador, Igor Mammedov, Dave Young,
	Dan Williams, Pavel Tatashin, Stefan Hajnoczi, Vlastimil Babka

Unplugging subblocks of memory blocks that are offline is easy. All we
have to do is watch out for concurrent onlining activity.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/virtio_mem.c | 116 +++++++++++++++++++++++++++++++++++-
 1 file changed, 114 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index d8da656c9145..c1fc7f9c4acf 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -120,7 +120,7 @@ struct virtio_mem {
 	 *
 	 * When this lock is held the pointers can't change, ONLINE and
 	 * OFFLINE blocks can't change the state and no subblocks will get
-	 * plugged.
+	 * plugged/unplugged.
 	 */
 	struct mutex hotplug_mutex;
 	bool hotplug_active;
@@ -277,6 +277,12 @@ static int virtio_mem_mb_state_prepare_next_mb(struct virtio_mem *vm)
 	     _mb_id++) \
 		if (virtio_mem_mb_get_state(_vm, _mb_id) == _state)
 
+#define virtio_mem_for_each_mb_state_rev(_vm, _mb_id, _state) \
+	for (_mb_id = _vm->next_mb_id - 1; \
+	     _mb_id >= _vm->first_mb_id && _vm->nb_mb_state[_state]; \
+	     _mb_id--) \
+		if (virtio_mem_mb_get_state(_vm, _mb_id) == _state)
+
 /*
  * Mark all selected subblocks plugged.
  *
@@ -322,6 +328,19 @@ static bool virtio_mem_mb_test_sb_plugged(struct virtio_mem *vm,
 	       bit + count;
 }
 
+/*
+ * Test if all selected subblocks are unplugged.
+ */
+static bool virtio_mem_mb_test_sb_unplugged(struct virtio_mem *vm,
+					    unsigned long mb_id, int sb_id,
+					    int count)
+{
+	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;
+
+	/* TODO: Helper similar to bitmap_set() */
+	return find_next_bit(vm->sb_bitmap, bit + count, bit) >= bit + count;
+}
+
 /*
  * Find the first plugged subblock. Returns vm->nb_sb_per_mb in case there is
  * none.
@@ -511,6 +530,9 @@ static void virtio_mem_notify_offline(struct virtio_mem *vm,
 		BUG();
 		break;
 	}
+
+	/* trigger the workqueue, maybe we can now unplug memory. */
+	virtio_mem_retry(vm);
 }
 
 static void virtio_mem_notify_online(struct virtio_mem *vm, unsigned long mb_id,
@@ -1120,6 +1142,94 @@ static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff)
 	return rc;
 }
 
+/*
+ * Unplug the desired number of plugged subblocks of an offline memory block.
+ * Will fail if any subblock cannot get unplugged (instead of skipping it).
+ *
+ * Will modify the state of the memory block. Might temporarily drop the
+ * hotplug_mutex.
+ *
+ * Note: Can fail after some subblocks were successfully unplugged.
+ */
+static int virtio_mem_mb_unplug_any_sb_offline(struct virtio_mem *vm,
+					       unsigned long mb_id,
+					       uint64_t *nb_sb)
+{
+	int rc;
+
+	rc = virtio_mem_mb_unplug_any_sb(vm, mb_id, nb_sb);
+
+	/* some subblocks might have been unplugged even on failure */
+	if (!virtio_mem_mb_test_sb_plugged(vm, mb_id, 0, vm->nb_sb_per_mb))
+		virtio_mem_mb_set_state(vm, mb_id,
+					VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL);
+	if (rc)
+		return rc;
+
+	if (virtio_mem_mb_test_sb_unplugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
+		/*
+		 * Remove the block from Linux - this should never fail.
+		 * Hinder the block from getting onlined by marking it
+		 * unplugged. Temporarily drop the mutex, so
+		 * any pending GOING_ONLINE requests can be serviced/rejected.
+		 */
+		virtio_mem_mb_set_state(vm, mb_id,
+					VIRTIO_MEM_MB_STATE_UNUSED);
+
+		mutex_unlock(&vm->hotplug_mutex);
+		rc = virtio_mem_mb_remove(vm, mb_id);
+		BUG_ON(rc);
+		mutex_lock(&vm->hotplug_mutex);
+	}
+	return 0;
+}
+
+/*
+ * Try to unplug the requested amount of memory.
+ */
+static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
+{
+	uint64_t nb_sb = diff / vm->subblock_size;
+	unsigned long mb_id;
+	int rc;
+
+	if (!nb_sb)
+		return 0;
+
+	/*
+	 * We'll drop the mutex a couple of times when it is safe to do so.
+	 * This might result in some blocks switching the state (online/offline)
+	 * and we could miss them in this run - we will retry again later.
+	 */
+	mutex_lock(&vm->hotplug_mutex);
+
+	/* Try to unplug subblocks of partially plugged offline blocks. */
+	virtio_mem_for_each_mb_state_rev(vm, mb_id,
+					 VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL) {
+		rc = virtio_mem_mb_unplug_any_sb_offline(vm, mb_id,
+							 &nb_sb);
+		if (rc || !nb_sb)
+			goto out_unlock;
+		cond_resched();
+	}
+
+	/* Try to unplug subblocks of plugged offline blocks. */
+	virtio_mem_for_each_mb_state_rev(vm, mb_id,
+					 VIRTIO_MEM_MB_STATE_OFFLINE) {
+		rc = virtio_mem_mb_unplug_any_sb_offline(vm, mb_id,
+							 &nb_sb);
+		if (rc || !nb_sb)
+			goto out_unlock;
+		cond_resched();
+	}
+
+	mutex_unlock(&vm->hotplug_mutex);
+	return 0;
+out_unlock:
+	mutex_unlock(&vm->hotplug_mutex);
+	return rc;
+}
+
 /*
  * Try to unplug all blocks that couldn't be unplugged before, for example,
  * because the hypervisor was busy.
@@ -1202,8 +1312,10 @@ static void virtio_mem_run_wq(struct work_struct *work)
 		if (vm->requested_size > vm->plugged_size) {
 			diff = vm->requested_size - vm->plugged_size;
 			rc = virtio_mem_plug_request(vm, diff);
+		} else {
+			diff = vm->plugged_size - vm->requested_size;
+			rc = virtio_mem_unplug_request(vm, diff);
 		}
-		/* TODO: try to unplug memory */
 	}
 
 	switch (rc) {
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 04/10] virtio-mem: Paravirtualized memory hotunplug part 2
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
                   ` (2 preceding siblings ...)
  2020-03-11 17:14 ` [PATCH v2 03/10] virtio-mem: Paravirtualized memory hotunplug part 1 David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-03-11 17:14 ` [PATCH v2 05/10] mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE David Hildenbrand
                   ` (7 subsequent siblings)
  11 siblings, 0 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Michal Hocko, Jason Wang, Oscar Salvador, Igor Mammedov,
	Dave Young, Dan Williams, Pavel Tatashin, Stefan Hajnoczi,
	Vlastimil Babka, Mel Gorman, Mike Rapoport, Alexander Duyck,
	Alexander Potapenko

We also want to unplug online memory (contained in online memory blocks
and, therefore, managed by the buddy), and eventually replug it later.

When requested to unplug memory, we use alloc_contig_range() to allocate
subblocks in online memory blocks (so we are the owner) and send them to
our hypervisor. When requested to plug memory, we can replug such memory
using free_contig_range() after asking our hypervisor.

We also want to mark all allocated pages PG_offline, so nobody will
touch them. To differentiate pages that were never onlined when
onlining the memory block from pages allocated via alloc_contig_range(), we
use PageDirty(). Based on this flag, virtio_mem_fake_online() can either
online the pages for the first time or use free_contig_range().

It is worth noting that there are no guarantees on how much memory can
actually get unplugged again. All device memory might completely be
fragmented with unmovable data, such that no subblock can get unplugged.

We are not touching the ZONE_MOVABLE. If memory is onlined to the
ZONE_MOVABLE, it can only get unplugged after that memory was offlined
manually by user space. In normal operation, virtio-mem memory is
suggested to be onlined to ZONE_NORMAL. In the future, we will try to
make unplug more likely to succeed.

Add a module parameter to control if online memory shall be touched.

As we want to access alloc_contig_range()/free_contig_range() from
kernel module context, export the symbols.

Note: Whenever virtio-mem uses alloc_contig_range(), all affected pages
are on the same node, in the same zone, and contain no holes.

Acked-by: Michal Hocko <mhocko@suse.com> # to export contig range allocator API
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/Kconfig      |   1 +
 drivers/virtio/virtio_mem.c | 157 ++++++++++++++++++++++++++++++++----
 mm/page_alloc.c             |   2 +
 3 files changed, 146 insertions(+), 14 deletions(-)

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 95ea2094a6b4..6af35ffb9796 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -72,6 +72,7 @@ config VIRTIO_MEM
 	depends on VIRTIO
 	depends on MEMORY_HOTPLUG_SPARSE
 	depends on MEMORY_HOTREMOVE
+	select CONTIG_ALLOC
 	help
 	 This driver provides access to virtio-mem paravirtualized memory
 	 devices, allowing to hotplug and hotunplug memory.
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index c1fc7f9c4acf..5b26d57be551 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -22,6 +22,10 @@
 
 #include <acpi/acpi_numa.h>
 
+static bool unplug_online = true;
+module_param(unplug_online, bool, 0644);
+MODULE_PARM_DESC(unplug_online, "Try to unplug online memory");
+
 enum virtio_mem_mb_state {
 	/* Unplugged, not added to Linux. Can be reused later. */
 	VIRTIO_MEM_MB_STATE_UNUSED = 0,
@@ -652,23 +656,35 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
 }
 
 /*
- * Set a range of pages PG_offline.
+ * Set a range of pages PG_offline. Remember pages that were never onlined
+ * (via generic_online_page()) using PageDirty().
  */
 static void virtio_mem_set_fake_offline(unsigned long pfn,
-					unsigned int nr_pages)
+					unsigned int nr_pages, bool onlined)
 {
-	for (; nr_pages--; pfn++)
-		__SetPageOffline(pfn_to_page(pfn));
+	for (; nr_pages--; pfn++) {
+		struct page *page = pfn_to_page(pfn);
+
+		__SetPageOffline(page);
+		if (!onlined)
+			SetPageDirty(page);
+	}
 }
 
 /*
- * Clear PG_offline from a range of pages.
+ * Clear PG_offline from a range of pages. If the pages were never onlined,
+ * (via generic_online_page()), clear PageDirty().
  */
 static void virtio_mem_clear_fake_offline(unsigned long pfn,
-					  unsigned int nr_pages)
+					  unsigned int nr_pages, bool onlined)
 {
-	for (; nr_pages--; pfn++)
-		__ClearPageOffline(pfn_to_page(pfn));
+	for (; nr_pages--; pfn++) {
+		struct page *page = pfn_to_page(pfn);
+
+		__ClearPageOffline(page);
+		if (!onlined)
+			ClearPageDirty(page);
+	}
 }
 
 /*
@@ -684,10 +700,26 @@ static void virtio_mem_fake_online(unsigned long pfn, unsigned int nr_pages)
 	 * We are always called with subblock granularity, which is at least
 	 * aligned to MAX_ORDER - 1.
 	 */
-	virtio_mem_clear_fake_offline(pfn, nr_pages);
+	for (i = 0; i < nr_pages; i += 1 << order) {
+		struct page *page = pfn_to_page(pfn + i);
 
-	for (i = 0; i < nr_pages; i += 1 << order)
-		generic_online_page(pfn_to_page(pfn + i), order);
+		/*
+		 * If the page is PageDirty(), it was kept fake-offline when
+		 * onlining the memory block. Otherwise, it was allocated
+		 * using alloc_contig_range(). All pages in a subblock are
+		 * alike.
+		 */
+		if (PageDirty(page)) {
+			virtio_mem_clear_fake_offline(pfn + i, 1 << order,
+						      false);
+			generic_online_page(page, order);
+		} else {
+			virtio_mem_clear_fake_offline(pfn + i, 1 << order,
+						      true);
+			free_contig_range(pfn + i, 1 << order);
+			adjust_managed_page_count(page, 1 << order);
+		}
+	}
 }
 
 static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
@@ -716,7 +748,8 @@ static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
 		if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
 			generic_online_page(page, order);
 		else
-			virtio_mem_set_fake_offline(PFN_DOWN(addr), 1 << order);
+			virtio_mem_set_fake_offline(PFN_DOWN(addr), 1 << order,
+						    false);
 		rcu_read_unlock();
 		return;
 	}
@@ -1184,6 +1217,72 @@ static int virtio_mem_mb_unplug_any_sb_offline(struct virtio_mem *vm,
 	return 0;
 }
 
+/*
+ * Unplug the desired number of plugged subblocks of an online memory block.
+ * Will skip subblock that are busy.
+ *
+ * Will modify the state of the memory block.
+ *
+ * Note: Can fail after some subblocks were successfully unplugged. Can
+ *       return 0 even if subblocks were busy and could not get unplugged.
+ */
+static int virtio_mem_mb_unplug_any_sb_online(struct virtio_mem *vm,
+					      unsigned long mb_id,
+					      uint64_t *nb_sb)
+{
+	const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
+	unsigned long start_pfn;
+	int rc, sb_id;
+
+	/*
+	 * TODO: To increase the performance we want to try bigger, consecutive
+	 * subblocks first before falling back to single subblocks. Also,
+	 * we should sense via something like is_mem_section_removable()
+	 * first if it makes sense to go ahead any try to allocate.
+	 */
+	for (sb_id = 0; sb_id < vm->nb_sb_per_mb && *nb_sb; sb_id++) {
+		/* Find the next candidate subblock */
+		while (sb_id < vm->nb_sb_per_mb &&
+		       !virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
+			sb_id++;
+		if (sb_id >= vm->nb_sb_per_mb)
+			break;
+
+		start_pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
+				     sb_id * vm->subblock_size);
+		rc = alloc_contig_range(start_pfn, start_pfn + nr_pages,
+					MIGRATE_MOVABLE, GFP_KERNEL);
+		if (rc == -ENOMEM)
+			/* whoops, out of memory */
+			return rc;
+		if (rc)
+			/* memory busy, we can't unplug this chunk */
+			continue;
+
+		/* Mark it as fake-offline before unplugging it */
+		virtio_mem_set_fake_offline(start_pfn, nr_pages, true);
+		adjust_managed_page_count(pfn_to_page(start_pfn), -nr_pages);
+
+		/* Try to unplug the allocated memory */
+		rc = virtio_mem_mb_unplug_sb(vm, mb_id, sb_id, 1);
+		if (rc) {
+			/* Return the memory to the buddy. */
+			virtio_mem_fake_online(start_pfn, nr_pages);
+			return rc;
+		}
+
+		virtio_mem_mb_set_state(vm, mb_id,
+					VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL);
+		*nb_sb -= 1;
+	}
+
+	/*
+	 * TODO: Once all subblocks of a memory block were unplugged, we want
+	 * to offline the memory block and remove it.
+	 */
+	return 0;
+}
+
 /*
  * Try to unplug the requested amount of memory.
  */
@@ -1223,8 +1322,37 @@ static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
 		cond_resched();
 	}
 
+	if (!unplug_online) {
+		mutex_unlock(&vm->hotplug_mutex);
+		return 0;
+	}
+
+	/* Try to unplug subblocks of partially plugged online blocks. */
+	virtio_mem_for_each_mb_state_rev(vm, mb_id,
+					 VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL) {
+		rc = virtio_mem_mb_unplug_any_sb_online(vm, mb_id,
+							&nb_sb);
+		if (rc || !nb_sb)
+			goto out_unlock;
+		mutex_unlock(&vm->hotplug_mutex);
+		cond_resched();
+		mutex_lock(&vm->hotplug_mutex);
+	}
+
+	/* Try to unplug subblocks of plugged online blocks. */
+	virtio_mem_for_each_mb_state_rev(vm, mb_id,
+					 VIRTIO_MEM_MB_STATE_ONLINE) {
+		rc = virtio_mem_mb_unplug_any_sb_online(vm, mb_id,
+							&nb_sb);
+		if (rc || !nb_sb)
+			goto out_unlock;
+		mutex_unlock(&vm->hotplug_mutex);
+		cond_resched();
+		mutex_lock(&vm->hotplug_mutex);
+	}
+
 	mutex_unlock(&vm->hotplug_mutex);
-	return 0;
+	return nb_sb ? -EBUSY : 0;
 out_unlock:
 	mutex_unlock(&vm->hotplug_mutex);
 	return rc;
@@ -1330,7 +1458,8 @@ static void virtio_mem_run_wq(struct work_struct *work)
 	case -EBUSY:
 		/*
 		 * The hypervisor cannot process our request right now
-		 * (e.g., out of memory, migrating).
+		 * (e.g., out of memory, migrating) or we cannot free up
+		 * any memory to unplug it (all plugged memory is busy).
 		 */
 	case -ENOMEM:
 		/* Out of memory, try again later. */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 79e950d76ffc..8d7be3f33e26 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8597,6 +8597,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 				pfn_max_align_up(end), migratetype);
 	return ret;
 }
+EXPORT_SYMBOL(alloc_contig_range);
 
 static int __alloc_contig_pages(unsigned long start_pfn,
 				unsigned long nr_pages, gfp_t gfp_mask)
@@ -8712,6 +8713,7 @@ void free_contig_range(unsigned long pfn, unsigned int nr_pages)
 	}
 	WARN(count != 0, "%d pages are still in use!\n", count);
 }
+EXPORT_SYMBOL(free_contig_range);
 
 /*
  * The zone indicated has a new number of managed_pages; batch sizes and percpu
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 05/10] mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
                   ` (3 preceding siblings ...)
  2020-03-11 17:14 ` [PATCH v2 04/10] virtio-mem: Paravirtualized memory hotunplug part 2 David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-04-14 16:34   ` Michael S. Tsirkin
  2020-03-11 17:14 ` [PATCH v2 06/10] virtio-mem: Allow to offline partially unplugged memory blocks David Hildenbrand
                   ` (6 subsequent siblings)
  11 siblings, 1 reply; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Alexander Duyck, Michal Hocko, Juergen Gross,
	Konrad Rzeszutek Wilk, Pavel Tatashin, Vlastimil Babka,
	Johannes Weiner, Anthony Yznaga, Oscar Salvador, Mel Gorman,
	Mike Rapoport, Dan Williams, Anshuman Khandual, Qian Cai,
	Pingfan Liu

virtio-mem wants to allow to offline memory blocks of which some parts
were unplugged (allocated via alloc_contig_range()), especially, to later
offline and remove completely unplugged memory blocks. The important part
is that PageOffline() has to remain set until the section is offline, so
these pages will never get accessed (e.g., when dumping). The pages should
not be handed back to the buddy (which would require clearing PageOffline()
and result in issues if offlining fails and the pages are suddenly in the
buddy).

Let's allow to do that by allowing to isolate any PageOffline() page
when offlining. This way, we can reach the memory hotplug notifier
MEM_GOING_OFFLINE, where the driver can signal that he is fine with
offlining this page by dropping its reference count. PageOffline() pages
with a reference count of 0 can then be skipped when offlining the
pages (like if they were free, however they are not in the buddy).

Anybody who uses PageOffline() pages and does not agree to offline them
(e.g., Hyper-V balloon, XEN balloon, VMWare balloon for 2MB pages) will not
decrement the reference count and make offlining fail when trying to
migrate such an unmovable page. So there should be no observable change.
Same applies to balloon compaction users (movable PageOffline() pages), the
pages will simply be migrated.

Note 1: If offlining fails, a driver has to increment the reference
	count again in MEM_CANCEL_OFFLINE.

Note 2: A driver that makes use of this has to be aware that re-onlining
	the memory block has to be handled by hooking into onlining code
	(online_page_callback_t), resetting the page PageOffline() and
	not giving them to the buddy.

Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Pavel Tatashin <pavel.tatashin@microsoft.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Anthony Yznaga <anthony.yznaga@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Pingfan Liu <kernelfans@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 include/linux/page-flags.h | 10 +++++++++
 mm/memory_hotplug.c        | 44 +++++++++++++++++++++++++++++---------
 mm/page_alloc.c            | 24 +++++++++++++++++++++
 mm/page_isolation.c        |  9 ++++++++
 4 files changed, 77 insertions(+), 10 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 49c2697046b9..fd6d4670ccc3 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -772,6 +772,16 @@ PAGE_TYPE_OPS(Buddy, buddy)
  * not onlined when onlining the section).
  * The content of these pages is effectively stale. Such pages should not
  * be touched (read/write/dump/save) except by their owner.
+ *
+ * If a driver wants to allow to offline unmovable PageOffline() pages without
+ * putting them back to the buddy, it can do so via the memory notifier by
+ * decrementing the reference count in MEM_GOING_OFFLINE and incrementing the
+ * reference count in MEM_CANCEL_OFFLINE. When offlining, the PageOffline()
+ * pages (now with a reference count of zero) are treated like free pages,
+ * allowing the containing memory block to get offlined. A driver that
+ * relies on this feature is aware that re-onlining the memory block will
+ * require to re-set the pages PageOffline() and not giving them to the
+ * buddy via online_page_callback_t.
  */
 PAGE_TYPE_OPS(Offline, offline)
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 1a00b5a37ef6..ab1c31e67fd1 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1221,11 +1221,17 @@ struct zone *test_pages_in_a_zone(unsigned long start_pfn,
 
 /*
  * Scan pfn range [start,end) to find movable/migratable pages (LRU pages,
- * non-lru movable pages and hugepages). We scan pfn because it's much
- * easier than scanning over linked list. This function returns the pfn
- * of the first found movable page if it's found, otherwise 0.
+ * non-lru movable pages and hugepages). Will skip over most unmovable
+ * pages (esp., pages that can be skipped when offlining), but bail out on
+ * definitely unmovable pages.
+ *
+ * Returns:
+ *	0 in case a movable page is found and movable_pfn was updated.
+ *	-ENOENT in case no movable page was found.
+ *	-EBUSY in case a definitely unmovable page was found.
  */
-static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
+static int scan_movable_pages(unsigned long start, unsigned long end,
+			      unsigned long *movable_pfn)
 {
 	unsigned long pfn;
 
@@ -1237,18 +1243,30 @@ static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
 			continue;
 		page = pfn_to_page(pfn);
 		if (PageLRU(page))
-			return pfn;
+			goto found;
 		if (__PageMovable(page))
-			return pfn;
+			goto found;
+
+		/*
+		 * PageOffline() pages that are not marked __PageMovable() and
+		 * have a reference count > 0 (after MEM_GOING_OFFLINE) are
+		 * definitely unmovable. If their reference count would be 0,
+		 * they could at least be skipped when offlining memory.
+		 */
+		if (PageOffline(page) && page_count(page))
+			return -EBUSY;
 
 		if (!PageHuge(page))
 			continue;
 		head = compound_head(page);
 		if (page_huge_active(head))
-			return pfn;
+			goto found;
 		skip = compound_nr(head) - (page - head);
 		pfn += skip - 1;
 	}
+	return -ENOENT;
+found:
+	*movable_pfn = pfn;
 	return 0;
 }
 
@@ -1515,7 +1533,8 @@ static int __ref __offline_pages(unsigned long start_pfn,
 	}
 
 	do {
-		for (pfn = start_pfn; pfn;) {
+		pfn = start_pfn;
+		do {
 			if (signal_pending(current)) {
 				ret = -EINTR;
 				reason = "signal backoff";
@@ -1525,14 +1544,19 @@ static int __ref __offline_pages(unsigned long start_pfn,
 			cond_resched();
 			lru_add_drain_all();
 
-			pfn = scan_movable_pages(pfn, end_pfn);
-			if (pfn) {
+			ret = scan_movable_pages(pfn, end_pfn, &pfn);
+			if (!ret) {
 				/*
 				 * TODO: fatal migration failures should bail
 				 * out
 				 */
 				do_migrate_range(pfn, end_pfn);
 			}
+		} while (!ret);
+
+		if (ret != -ENOENT) {
+			reason = "unmovable page";
+			goto failed_removal_isolated;
 		}
 
 		/*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8d7be3f33e26..baa60222215f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8366,6 +8366,19 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
 		if ((flags & MEMORY_OFFLINE) && PageHWPoison(page))
 			continue;
 
+		/*
+		 * We treat all PageOffline() pages as movable when offlining
+		 * to give drivers a chance to decrement their reference count
+		 * in MEM_GOING_OFFLINE in order to indicate that these pages
+		 * can be offlined as there are no direct references anymore.
+		 * For actually unmovable PageOffline() where the driver does
+		 * not support this, we will fail later when trying to actually
+		 * move these pages that still have a reference count > 0.
+		 * (false negatives in this function only)
+		 */
+		if ((flags & MEMORY_OFFLINE) && PageOffline(page))
+			continue;
+
 		if (__PageMovable(page) || PageLRU(page))
 			continue;
 
@@ -8786,6 +8799,17 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 			offlined_pages++;
 			continue;
 		}
+		/*
+		 * At this point all remaining PageOffline() pages have a
+		 * reference count of 0 and can simply be skipped.
+		 */
+		if (PageOffline(page)) {
+			BUG_ON(page_count(page));
+			BUG_ON(PageBuddy(page));
+			pfn++;
+			offlined_pages++;
+			continue;
+		}
 
 		BUG_ON(page_count(page));
 		BUG_ON(!PageBuddy(page));
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 2c11a38d6e87..f6d07c5f0d34 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -151,6 +151,7 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
  *			a bit mask)
  *			MEMORY_OFFLINE - isolate to offline (!allocate) memory
  *					 e.g., skip over PageHWPoison() pages
+ *					 and PageOffline() pages.
  *			REPORT_FAILURE - report details about the failure to
  *			isolate the range
  *
@@ -259,6 +260,14 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
 		else if ((flags & MEMORY_OFFLINE) && PageHWPoison(page))
 			/* A HWPoisoned page cannot be also PageBuddy */
 			pfn++;
+		else if ((flags & MEMORY_OFFLINE) && PageOffline(page) &&
+			 !page_count(page))
+			/*
+			 * The responsible driver agreed to skip PageOffline()
+			 * pages when offlining memory by dropping its
+			 * reference in MEM_GOING_OFFLINE.
+			 */
+			pfn++;
 		else
 			break;
 	}
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 06/10] virtio-mem: Allow to offline partially unplugged memory blocks
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
                   ` (4 preceding siblings ...)
  2020-03-11 17:14 ` [PATCH v2 05/10] mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-03-11 17:14 ` [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory() David Hildenbrand
                   ` (5 subsequent siblings)
  11 siblings, 0 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Jason Wang, Oscar Salvador, Igor Mammedov, Dave Young,
	Dan Williams, Pavel Tatashin, Stefan Hajnoczi, Vlastimil Babka

Dropping the reference count of PageOffline() pages during MEM_GOING_ONLINE
allows offlining code to skip them. However, we also have to clear
PG_reserved, because PG_reserved pages get detected as unmovable right
away. Take care of restoring the reference count when offlining is
canceled.

Clarify why we don't have to perform any action when unloading the
driver. Also, let's add a warning if anybody is still holding a
reference to unplugged pages when offlining.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/virtio_mem.c | 68 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 67 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 5b26d57be551..35f20232770c 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -570,6 +570,57 @@ static void virtio_mem_notify_online(struct virtio_mem *vm, unsigned long mb_id,
 		virtio_mem_retry(vm);
 }
 
+static void virtio_mem_notify_going_offline(struct virtio_mem *vm,
+					    unsigned long mb_id)
+{
+	const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
+	struct page *page;
+	unsigned long pfn;
+	int sb_id, i;
+
+	for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
+		if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
+			continue;
+		/*
+		 * Drop our reference to the pages so the memory can get
+		 * offlined and add the unplugged pages to the managed
+		 * page counters (so offlining code can correctly subtract
+		 * them again).
+		 */
+		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
+			       sb_id * vm->subblock_size);
+		adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
+		for (i = 0; i < nr_pages; i++) {
+			page = pfn_to_page(pfn + i);
+			if (WARN_ON(!page_ref_dec_and_test(page)))
+				dump_page(page, "unplugged page referenced");
+		}
+	}
+}
+
+static void virtio_mem_notify_cancel_offline(struct virtio_mem *vm,
+					     unsigned long mb_id)
+{
+	const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
+	unsigned long pfn;
+	int sb_id, i;
+
+	for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
+		if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
+			continue;
+		/*
+		 * Get the reference we dropped when going offline and
+		 * subtract the unplugged pages from the managed page
+		 * counters.
+		 */
+		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
+			       sb_id * vm->subblock_size);
+		adjust_managed_page_count(pfn_to_page(pfn), -nr_pages);
+		for (i = 0; i < nr_pages; i++)
+			page_ref_inc(pfn_to_page(pfn + i));
+	}
+}
+
 /*
  * This callback will either be called synchronously from add_memory() or
  * asynchronously (e.g., triggered via user space). We have to be careful
@@ -616,6 +667,7 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
 			break;
 		}
 		vm->hotplug_active = true;
+		virtio_mem_notify_going_offline(vm, mb_id);
 		break;
 	case MEM_GOING_ONLINE:
 		mutex_lock(&vm->hotplug_mutex);
@@ -640,6 +692,12 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
 		mutex_unlock(&vm->hotplug_mutex);
 		break;
 	case MEM_CANCEL_OFFLINE:
+		if (!vm->hotplug_active)
+			break;
+		virtio_mem_notify_cancel_offline(vm, mb_id);
+		vm->hotplug_active = false;
+		mutex_unlock(&vm->hotplug_mutex);
+		break;
 	case MEM_CANCEL_ONLINE:
 		if (!vm->hotplug_active)
 			break;
@@ -666,8 +724,11 @@ static void virtio_mem_set_fake_offline(unsigned long pfn,
 		struct page *page = pfn_to_page(pfn);
 
 		__SetPageOffline(page);
-		if (!onlined)
+		if (!onlined) {
 			SetPageDirty(page);
+			/* FIXME: remove after cleanups */
+			ClearPageReserved(page);
+		}
 	}
 }
 
@@ -1717,6 +1778,11 @@ static void virtio_mem_remove(struct virtio_device *vdev)
 		rc = virtio_mem_mb_remove(vm, mb_id);
 		BUG_ON(rc);
 	}
+	/*
+	 * After we unregistered our callbacks, user space can no longer
+	 * offline partially plugged online memory blocks. No need to worry
+	 * about them.
+	 */
 
 	/* unregister callbacks */
 	unregister_virtio_mem_device(vm);
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory()
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
                   ` (5 preceding siblings ...)
  2020-03-11 17:14 ` [PATCH v2 06/10] virtio-mem: Allow to offline partially unplugged memory blocks David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-03-11 17:19   ` David Hildenbrand
  2020-04-15  7:35   ` Pankaj Gupta
  2020-03-11 17:14 ` [PATCH v2 08/10] virtio-mem: Offline and remove completely unplugged memory blocks David Hildenbrand
                   ` (4 subsequent siblings)
  11 siblings, 2 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Oscar Salvador, Michal Hocko, Pavel Tatashin, Wei Yang,
	Dan Williams, Qian Cai

virtio-mem wants to offline and remove a memory block once it unplugged
all subblocks (e.g., using alloc_contig_range()). Let's provide
an interface to do that from a driver. virtio-mem already supports to
offline partially unplugged memory blocks. Offlining a fully unplugged
memory block will not require to migrate any pages. All unplugged
subblocks are PageOffline() and have a reference count of 0 - so
offlining code will simply skip them.

All we need is an interface to offline and remove the memory from kernel
module context, where we don't have access to the memory block devices
(esp. find_memory_block() and device_offline()) and the device hotplug
lock.

To keep things simple, allow to only work on a single memory block.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Oscar Salvador <osalvador@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 include/linux/memory_hotplug.h |  1 +
 mm/memory_hotplug.c            | 37 ++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index f4d59155f3d4..a98aa16dbfa1 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -311,6 +311,7 @@ extern void try_offline_node(int nid);
 extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
 extern int remove_memory(int nid, u64 start, u64 size);
 extern void __remove_memory(int nid, u64 start, u64 size);
+extern int offline_and_remove_memory(int nid, u64 start, u64 size);
 
 #else
 static inline bool is_mem_section_removable(unsigned long pfn,
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index ab1c31e67fd1..d0d337918a15 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1818,4 +1818,41 @@ int remove_memory(int nid, u64 start, u64 size)
 	return rc;
 }
 EXPORT_SYMBOL_GPL(remove_memory);
+
+/*
+ * Try to offline and remove a memory block. Might take a long time to
+ * finish in case memory is still in use. Primarily useful for memory devices
+ * that logically unplugged all memory (so it's no longer in use) and want to
+ * offline + remove the memory block.
+ */
+int offline_and_remove_memory(int nid, u64 start, u64 size)
+{
+	struct memory_block *mem;
+	int rc = -EINVAL;
+
+	if (!IS_ALIGNED(start, memory_block_size_bytes()) ||
+	    size != memory_block_size_bytes())
+		return rc;
+
+	lock_device_hotplug();
+	mem = find_memory_block(__pfn_to_section(PFN_DOWN(start)));
+	if (mem)
+		rc = device_offline(&mem->dev);
+	/* Ignore if the device is already offline. */
+	if (rc > 0)
+		rc = 0;
+
+	/*
+	 * In case we succeeded to offline the memory block, remove it.
+	 * This cannot fail as it cannot get onlined in the meantime.
+	 */
+	if (!rc) {
+		rc = try_remove_memory(nid, start, size);
+		WARN_ON_ONCE(rc);
+	}
+	unlock_device_hotplug();
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(offline_and_remove_memory);
 #endif /* CONFIG_MEMORY_HOTREMOVE */
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 08/10] virtio-mem: Offline and remove completely unplugged memory blocks
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
                   ` (6 preceding siblings ...)
  2020-03-11 17:14 ` [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory() David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-04-15  7:42   ` Pankaj Gupta
  2020-03-11 17:14 ` [PATCH v2 09/10] virtio-mem: Better retry handling David Hildenbrand
                   ` (3 subsequent siblings)
  11 siblings, 1 reply; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Jason Wang, Oscar Salvador, Igor Mammedov, Dave Young,
	Dan Williams, Pavel Tatashin, Stefan Hajnoczi, Vlastimil Babka

Let's offline+remove memory blocks once all subblocks are unplugged. We
can use the new Linux MM interface for that. As no memory is in use
anymore, this shouldn't take a long time and shouldn't fail. There might
be corner cases where the offlining could still fail (especially, if
another notifier NACKs the offlining request).

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/virtio_mem.c | 47 +++++++++++++++++++++++++++++++++----
 1 file changed, 43 insertions(+), 4 deletions(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 35f20232770c..aa322e7732a4 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -443,6 +443,28 @@ static int virtio_mem_mb_remove(struct virtio_mem *vm, unsigned long mb_id)
 	return remove_memory(nid, addr, memory_block_size_bytes());
 }
 
+/*
+ * Try to offline and remove a memory block from Linux.
+ *
+ * Must not be called with the vm->hotplug_mutex held (possible deadlock with
+ * onlining code).
+ *
+ * Will not modify the state of the memory block.
+ */
+static int virtio_mem_mb_offline_and_remove(struct virtio_mem *vm,
+					    unsigned long mb_id)
+{
+	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
+	int nid = vm->nid;
+
+	if (nid == NUMA_NO_NODE)
+		nid = memory_add_physaddr_to_nid(addr);
+
+	dev_dbg(&vm->vdev->dev, "offlining and removing memory block: %lu\n",
+		mb_id);
+	return offline_and_remove_memory(nid, addr, memory_block_size_bytes());
+}
+
 /*
  * Trigger the workqueue so the device can perform its magic.
  */
@@ -535,7 +557,13 @@ static void virtio_mem_notify_offline(struct virtio_mem *vm,
 		break;
 	}
 
-	/* trigger the workqueue, maybe we can now unplug memory. */
+	/*
+	 * Trigger the workqueue, maybe we can now unplug memory. Also,
+	 * when we offline and remove a memory block, this will re-trigger
+	 * us immediately - which is often nice because the removal of
+	 * the memory block (e.g., memmap) might have freed up memory
+	 * on other memory blocks we manage.
+	 */
 	virtio_mem_retry(vm);
 }
 
@@ -1282,7 +1310,8 @@ static int virtio_mem_mb_unplug_any_sb_offline(struct virtio_mem *vm,
  * Unplug the desired number of plugged subblocks of an online memory block.
  * Will skip subblock that are busy.
  *
- * Will modify the state of the memory block.
+ * Will modify the state of the memory block. Might temporarily drop the
+ * hotplug_mutex.
  *
  * Note: Can fail after some subblocks were successfully unplugged. Can
  *       return 0 even if subblocks were busy and could not get unplugged.
@@ -1338,9 +1367,19 @@ static int virtio_mem_mb_unplug_any_sb_online(struct virtio_mem *vm,
 	}
 
 	/*
-	 * TODO: Once all subblocks of a memory block were unplugged, we want
-	 * to offline the memory block and remove it.
+	 * Once all subblocks of a memory block were unplugged, offline and
+	 * remove it. This will usually not fail, as no memory is in use
+	 * anymore - however some other notifiers might NACK the request.
 	 */
+	if (virtio_mem_mb_test_sb_unplugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
+		mutex_unlock(&vm->hotplug_mutex);
+		rc = virtio_mem_mb_offline_and_remove(vm, mb_id);
+		mutex_lock(&vm->hotplug_mutex);
+		if (!rc)
+			virtio_mem_mb_set_state(vm, mb_id,
+						VIRTIO_MEM_MB_STATE_UNUSED);
+	}
+
 	return 0;
 }
 
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 09/10] virtio-mem: Better retry handling
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
                   ` (7 preceding siblings ...)
  2020-03-11 17:14 ` [PATCH v2 08/10] virtio-mem: Offline and remove completely unplugged memory blocks David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-03-11 17:14 ` [PATCH v2 10/10] MAINTAINERS: Add myself as virtio-mem maintainer David Hildenbrand
                   ` (2 subsequent siblings)
  11 siblings, 0 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand,
	Jason Wang, Oscar Salvador, Igor Mammedov, Dave Young,
	Dan Williams, Pavel Tatashin, Stefan Hajnoczi, Vlastimil Babka

Let's start with a retry interval of 5 seconds and double the time until
we reach 5 minutes, in case we keep getting errors. Reset the retry
interval in case we succeeded.

The two main reasons for having to retry are
- The hypervisor is busy and cannot process our request
- We cannot reach the desired requested_size (esp., not enough memory can
  get unplugged because we can't allocate any subblocks).

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/virtio_mem.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index aa322e7732a4..48e96702d4ce 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -138,7 +138,9 @@ struct virtio_mem {
 
 	/* Timer for retrying to plug/unplug memory. */
 	struct hrtimer retry_timer;
-#define VIRTIO_MEM_RETRY_TIMER_MS		30000
+	unsigned int retry_timer_ms;
+#define VIRTIO_MEM_RETRY_TIMER_MIN_MS		50000
+#define VIRTIO_MEM_RETRY_TIMER_MAX_MS		300000
 
 	/* Memory notifier (online/offline events). */
 	struct notifier_block memory_notifier;
@@ -1548,6 +1550,7 @@ static void virtio_mem_run_wq(struct work_struct *work)
 
 	switch (rc) {
 	case 0:
+		vm->retry_timer_ms = VIRTIO_MEM_RETRY_TIMER_MIN_MS;
 		break;
 	case -ENOSPC:
 		/*
@@ -1563,8 +1566,7 @@ static void virtio_mem_run_wq(struct work_struct *work)
 		 */
 	case -ENOMEM:
 		/* Out of memory, try again later. */
-		hrtimer_start(&vm->retry_timer,
-			      ms_to_ktime(VIRTIO_MEM_RETRY_TIMER_MS),
+		hrtimer_start(&vm->retry_timer, ms_to_ktime(vm->retry_timer_ms),
 			      HRTIMER_MODE_REL);
 		break;
 	case -EAGAIN:
@@ -1584,6 +1586,8 @@ static enum hrtimer_restart virtio_mem_timer_expired(struct hrtimer *timer)
 					     retry_timer);
 
 	virtio_mem_retry(vm);
+	vm->retry_timer_ms = min_t(unsigned int, vm->retry_timer_ms * 2,
+				   VIRTIO_MEM_RETRY_TIMER_MAX_MS);
 	return HRTIMER_NORESTART;
 }
 
@@ -1750,6 +1754,7 @@ static int virtio_mem_probe(struct virtio_device *vdev)
 	spin_lock_init(&vm->removal_lock);
 	hrtimer_init(&vm->retry_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	vm->retry_timer.function = virtio_mem_timer_expired;
+	vm->retry_timer_ms = VIRTIO_MEM_RETRY_TIMER_MIN_MS;
 
 	/* register the virtqueue */
 	rc = virtio_mem_init_vq(vm);
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* [PATCH v2 10/10] MAINTAINERS: Add myself as virtio-mem maintainer
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
                   ` (8 preceding siblings ...)
  2020-03-11 17:14 ` [PATCH v2 09/10] virtio-mem: Better retry handling David Hildenbrand
@ 2020-03-11 17:14 ` David Hildenbrand
  2020-03-27 16:58 ` [PATCH v2 00/10] virtio-mem: paravirtualized memory Pankaj Gupta
  2020-03-29 12:42 ` Michael S. Tsirkin
  11 siblings, 0 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, David Hildenbrand

Let's make sure patches/bug reports find the right person.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 MAINTAINERS | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index f6dcd1233935..ee0e7cbca5c6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17937,6 +17937,13 @@ S:	Maintained
 F:	drivers/iommu/virtio-iommu.c
 F:	include/uapi/linux/virtio_iommu.h
 
+VIRTIO MEM DRIVER
+M:	David Hildenbrand <david@redhat.com>
+L:	virtualization@lists.linux-foundation.org
+S:	Maintained
+F:	drivers/virtio/virtio_mem.c
+F:	include/uapi/linux/virtio_mem.h
+
 VIRTUAL BOX GUEST DEVICE DRIVER
 M:	Hans de Goede <hdegoede@redhat.com>
 M:	Arnd Bergmann <arnd@arndb.de>
-- 
2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory()
  2020-03-11 17:14 ` [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory() David Hildenbrand
@ 2020-03-11 17:19   ` David Hildenbrand
  2020-04-14 16:35     ` Michael S. Tsirkin
  2020-04-15  7:35   ` Pankaj Gupta
  1 sibling, 1 reply; 30+ messages in thread
From: David Hildenbrand @ 2020-03-11 17:19 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, Oscar Salvador, Michal Hocko,
	Pavel Tatashin, Wei Yang, Dan Williams, Qian Cai

On 11.03.20 18:14, David Hildenbrand wrote:
> virtio-mem wants to offline and remove a memory block once it unplugged
> all subblocks (e.g., using alloc_contig_range()). Let's provide
> an interface to do that from a driver. virtio-mem already supports to
> offline partially unplugged memory blocks. Offlining a fully unplugged
> memory block will not require to migrate any pages. All unplugged
> subblocks are PageOffline() and have a reference count of 0 - so
> offlining code will simply skip them.
> 
> All we need is an interface to offline and remove the memory from kernel
> module context, where we don't have access to the memory block devices
> (esp. find_memory_block() and device_offline()) and the device hotplug
> lock.
> 
> To keep things simple, allow to only work on a single memory block.
> 

Lost the ACK from Michael

Acked-by: Michal Hocko <mhocko@suse.com> [1]

[1] https://lkml.kernel.org/r/20200302142737.GP4380@dhcp22.suse.cz

-- 
Thanks,

David / dhildenb


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
                   ` (9 preceding siblings ...)
  2020-03-11 17:14 ` [PATCH v2 10/10] MAINTAINERS: Add myself as virtio-mem maintainer David Hildenbrand
@ 2020-03-27 16:58 ` Pankaj Gupta
  2020-03-27 17:03   ` David Hildenbrand
  2020-03-29 12:42 ` Michael S. Tsirkin
  11 siblings, 1 reply; 30+ messages in thread
From: Pankaj Gupta @ 2020-03-27 16:58 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Michael S . Tsirkin,
	Sebastien Boeuf, Samuel Ortiz, Robert Bradford, Luiz Capitulino,
	teawater, Igor Mammedov, Dr . David Alan Gilbert,
	Alexander Duyck, Alexander Potapenko, Anshuman Khandual,
	Anthony Yznaga, Dan Williams, Dave Young, Jason Wang,
	Johannes Weiner, Juergen Gross, Konrad Rzeszutek Wilk, Len Brown,
	Mel Gorman, Michal Hocko, Mike Rapoport, Oscar Salvador,
	Oscar Salvador, Pavel Tatashin, Pavel Tatashin, Pingfan Liu,
	Qian Cai, Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

Hi David,

Trying to test the series with the Qemu branch(virtio-mem) mentioned.
Unfortunately,
not able to hotplug memory. Is anything changed from your previous posting
or I am doing something wrong?

After giving value to "requested-size", I see size as zero.

(qemu) qom-set vm0 requested-size 10G
(qemu) info memory-devices
Memory device [virtio-mem]: "vm0"
  memaddr: 0x240000000
  node: 0
  requested-size: 10737418240
  size: 0
  max-size: 107374182400
  block-size: 2097152
  memdev: /objects/mem0

Guest kernel: 5.6.0-rc4
Using same Qemu commandline arguments mentioned in cover-letter.

Thanks,
Pankaj

^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-03-27 16:58 ` [PATCH v2 00/10] virtio-mem: paravirtualized memory Pankaj Gupta
@ 2020-03-27 17:03   ` David Hildenbrand
  2020-03-27 17:07     ` David Hildenbrand
  2020-03-29 15:41     ` Pankaj Gupta
  0 siblings, 2 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-27 17:03 UTC (permalink / raw)
  To: Pankaj Gupta
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Michael S . Tsirkin,
	Sebastien Boeuf, Samuel Ortiz, Robert Bradford, Luiz Capitulino,
	teawater, Igor Mammedov, Dr . David Alan Gilbert,
	Alexander Duyck, Alexander Potapenko, Anshuman Khandual,
	Anthony Yznaga, Dan Williams, Dave Young, Jason Wang,
	Johannes Weiner, Juergen Gross, Konrad Rzeszutek Wilk, Len Brown,
	Mel Gorman, Michal Hocko, Mike Rapoport, Oscar Salvador,
	Oscar Salvador, Pavel Tatashin, Pavel Tatashin, Pingfan Liu,
	Qian Cai, Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

On 27.03.20 17:58, Pankaj Gupta wrote:
> Hi David,
> 
> Trying to test the series with the Qemu branch(virtio-mem) mentioned.
> Unfortunately,
> not able to hotplug memory. Is anything changed from your previous posting
> or I am doing something wrong?
> 
> After giving value to "requested-size", I see size as zero.
> 
> (qemu) qom-set vm0 requested-size 10G
> (qemu) info memory-devices
> Memory device [virtio-mem]: "vm0"
>   memaddr: 0x240000000
>   node: 0
>   requested-size: 10737418240
>   size: 0
>   max-size: 107374182400
>   block-size: 2097152
>   memdev: /objects/mem0
> 
> Guest kernel: 5.6.0-rc4
> Using same Qemu commandline arguments mentioned in cover-letter.

Are you booting from an initrd? Are you compiling virtio-mem as a kernel
module or into the kernel binary?

Make sure that the virtio-mem driver will actually be loaded. (lsmod  |
grep virtio-mem).

Also, double check if there are any virtio-mem dmesg errors/warnings.

-- 
Thanks,

David / dhildenb


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-03-27 17:03   ` David Hildenbrand
@ 2020-03-27 17:07     ` David Hildenbrand
  2020-03-29 15:41     ` Pankaj Gupta
  1 sibling, 0 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-27 17:07 UTC (permalink / raw)
  To: Pankaj Gupta
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Michael S . Tsirkin,
	Sebastien Boeuf, Samuel Ortiz, Robert Bradford, Luiz Capitulino,
	teawater, Igor Mammedov, Dr . David Alan Gilbert,
	Alexander Duyck, Alexander Potapenko, Anshuman Khandual,
	Anthony Yznaga, Dan Williams, Dave Young, Jason Wang,
	Johannes Weiner, Juergen Gross, Konrad Rzeszutek Wilk, Len Brown,
	Mel Gorman, Michal Hocko, Mike Rapoport, Oscar Salvador,
	Oscar Salvador, Pavel Tatashin, Pavel Tatashin, Pingfan Liu,
	Qian Cai, Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

On 27.03.20 18:03, David Hildenbrand wrote:
> On 27.03.20 17:58, Pankaj Gupta wrote:
>> Hi David,
>>
>> Trying to test the series with the Qemu branch(virtio-mem) mentioned.
>> Unfortunately,
>> not able to hotplug memory. Is anything changed from your previous posting
>> or I am doing something wrong?
>>
>> After giving value to "requested-size", I see size as zero.
>>
>> (qemu) qom-set vm0 requested-size 10G
>> (qemu) info memory-devices
>> Memory device [virtio-mem]: "vm0"
>>   memaddr: 0x240000000
>>   node: 0
>>   requested-size: 10737418240
>>   size: 0
>>   max-size: 107374182400
>>   block-size: 2097152
>>   memdev: /objects/mem0
>>
>> Guest kernel: 5.6.0-rc4
>> Using same Qemu commandline arguments mentioned in cover-letter.
> 
> Are you booting from an initrd? Are you compiling virtio-mem as a kernel
> module or into the kernel binary?
> 
> Make sure that the virtio-mem driver will actually be loaded. (lsmod  |
> grep virtio-mem).

"virtio_mem", of course :)

> 
> Also, double check if there are any virtio-mem dmesg errors/warnings.
> 


-- 
Thanks,

David / dhildenb


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
                   ` (10 preceding siblings ...)
  2020-03-27 16:58 ` [PATCH v2 00/10] virtio-mem: paravirtualized memory Pankaj Gupta
@ 2020-03-29 12:42 ` Michael S. Tsirkin
  2020-03-30  8:16   ` David Hildenbrand
  2020-04-14  9:15   ` David Hildenbrand
  11 siblings, 2 replies; 30+ messages in thread
From: Michael S. Tsirkin @ 2020-03-29 12:42 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Sebastien Boeuf, Samuel Ortiz,
	Robert Bradford, Luiz Capitulino, Pankaj Gupta, teawater,
	Igor Mammedov, Dr . David Alan Gilbert, Alexander Duyck,
	Alexander Potapenko, Anshuman Khandual, Anthony Yznaga,
	Dan Williams, Dave Young, Jason Wang, Johannes Weiner,
	Juergen Gross, Konrad Rzeszutek Wilk, Len Brown, Mel Gorman,
	Michal Hocko, Mike Rapoport, Oscar Salvador, Oscar Salvador,
	Pavel Tatashin, Pavel Tatashin, Pingfan Liu, Qian Cai,
	Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

On Wed, Mar 11, 2020 at 06:14:12PM +0100, David Hildenbrand wrote:
> This series is based on latest linux-next. The patches are located at:
>     https://github.com/davidhildenbrand/linux.git virtio-mem-v2
> 
> I now have acks for all !virtio-mem changes. I'll be happy to get review
> feedback, testing reports, etc. for the virtio-mem changes. If there are
> no further comments, I guess this is good to go as a v1 soon.

I'd like to queue it for merge after the release. If you feel it's ready
please ping me after the release to help make sure it didn't get
dropped.  I see there were some reports about people having trouble
using this, pls keep working on this meanwhile.

Thanks!


> The basic idea of virtio-mem is to provide a flexible,
> cross-architecture memory hot(un)plug solution that avoids many limitations
> imposed by existing technologies, architectures, and interfaces. More
> details can be found below and in linked material.
> 
> It's currently only enabled for x86-64, however, should theoretically work
> on any architecture that supports virtio and implements memory hot(un)plug
> under Linux - like s390x, powerpc64, and arm64. On x86-64, it is currently
> possible to add/remove memory to the system in >= 4MB granularity.
> Memory hotplug works very reliably. For memory unplug, there are no
> guarantees how much memory can actually get unplugged, it depends on the
> setup (especially: fragmentation of physical memory).
> 
> I am currently getting the QEMU side into shape (which will be posted as
> RFC soon, see below for a link to the current state). Experimental Kata
> support is in the works [4]. Also, a cloud-hypervisor implementation is
> under discussion [5].
> 
> --------------------------------------------------------------------------
> 1. virtio-mem
> --------------------------------------------------------------------------
> 
> The basic idea behind virtio-mem was presented at KVM Forum 2018. The
> slides can be found at [1]. The previous RFC can be found at [2]. The
> first RFC can be found at [3]. However, the concept evolved over time. The
> KVM Forum slides roughly match the current design.
> 
> Patch #2 ("virtio-mem: Paravirtualized memory hotplug") contains quite some
> information, especially in "include/uapi/linux/virtio_mem.h":
> 
>     Each virtio-mem device manages a dedicated region in physical address
>     space. Each device can belong to a single NUMA node, multiple devices
>     for a single NUMA node are possible. A virtio-mem device is like a
>     "resizable DIMM" consisting of small memory blocks that can be plugged
>     or unplugged. The device driver is responsible for (un)plugging memory
>     blocks on demand.
> 
>     Virtio-mem devices can only operate on their assigned memory region in
>     order to (un)plug memory. A device cannot (un)plug memory belonging to
>     other devices.
> 
>     The "region_size" corresponds to the maximum amount of memory that can
>     be provided by a device. The "size" corresponds to the amount of memory
>     that is currently plugged. "requested_size" corresponds to a request
>     from the device to the device driver to (un)plug blocks. The
>     device driver should try to (un)plug blocks in order to reach the
>     "requested_size". It is impossible to plug more memory than requested.
> 
>     The "usable_region_size" represents the memory region that can actually
>     be used to (un)plug memory. It is always at least as big as the
>     "requested_size" and will grow dynamically. It will only shrink when
>     explicitly triggered (VIRTIO_MEM_REQ_UNPLUG).
> 
>     There are no guarantees what will happen if unplugged memory is
>     read/written. Such memory should, in general, not be touched. E.g.,
>     even writing might succeed, but the values will simply be discarded at
>     random points in time.
> 
>     It can happen that the device cannot process a request, because it is
>     busy. The device driver has to retry later.
> 
>     Usually, during system resets all memory will get unplugged, so the
>     device driver can start with a clean state. However, in specific
>     scenarios (if the device is busy) it can happen that the device still
>     has memory plugged. The device driver can request to unplug all memory
>     (VIRTIO_MEM_REQ_UNPLUG) - which might take a while to succeed if the
>     device is busy.
> 
> --------------------------------------------------------------------------
> 2. Linux Implementation
> --------------------------------------------------------------------------
> 
> Memory blocks (e.g., 128MB) are added/removed on demand. Within these
> memory blocks, subblocks (e.g., 4MB) are plugged/unplugged. The sizes
> depend on the target architecture, MAX_ORDER, pageblock_order, and
> the block size of a virtio-mem device.
> 
> add_memory()/try_remove_memory() is used to add/remove memory blocks.
> virtio-mem will not online memory blocks itself. This has to be done by
> user space, or configured into the kernel
> (CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE). virtio-mem will only unplug memory
> that was online to the ZONE_NORMAL. Memory is suggested to be onlined to
> the ZONE_NORMAL for now.
> 
> The memory hotplug notifier is used to properly synchronize against
> onlining/offlining of memory blocks and to track the states of memory
> blocks (including the zone memory blocks are onlined to).
> 
> The set_online_page() callback is used to keep unplugged subblocks
> of a memory block fake-offline when onlining the memory block.
> generic_online_page() is used to fake-online plugged subblocks. This
> handling is similar to the Hyper-V balloon driver.
> 
> PG_offline is used to mark unplugged subblocks as offline, so e.g.,
> dumping tools (makedumpfile) will skip these pages. This is similar to
> other balloon drivers like virtio-balloon and Hyper-V.
> 
> Memory offlining code is extended to allow drivers to drop their reference
> to PG_offline pages when MEM_GOING_OFFLINE, so these pages can be skipped
> when offlining memory blocks. This allows to offline memory blocks that
> have partially unplugged (allocated e.g., via alloc_contig_range())
> subblocks - or are completely unplugged.
> 
> alloc_contig_range()/free_contig_range() [now exposed] is used to
> unplug/plug subblocks of memory blocks the are already exposed to Linux.
> 
> offline_and_remove_memory() [new] is used to offline a fully unplugged
> memory block and remove it from Linux.
> 
> --------------------------------------------------------------------------
> 3. Changes v1 -> v2
> --------------------------------------------------------------------------
> 
> - "virtio-mem: Paravirtualized memory hotplug"
> -- Use "__u64" and friends in uapi header
> -- Split out ACPI PXM handling
> - "virtio-mem: Allow to specify an ACPI PXM as nid"
> -- Squash of the ACPI PXM handling and previous "ACPI: NUMA: export
>    pxm_to_node"
> - "virtio-mem: Paravirtualized memory hotunplug part 2"
> -- Squashed previous "mm: Export alloc_contig_range() /
>    free_contig_range()"
> - "virtio-mem: Allow to offline partially unplugged memory blocks"
> -- WARN and dump_page() in case somebody has a reference to an unplugged
>    page
> - "virtio-mem: Better retry handling"
> -- Use retry interval of 5s -> 5m
> - Tweaked some patch descriptions
> 
> --------------------------------------------------------------------------
> 4. Future work
> --------------------------------------------------------------------------
> 
> One of the next TODO things besides the QEMU part is writing a virtio-mem
> spec - however, that might still take some time.
> 
> virtio-mem extensions (via new feature flags):
> - Indicate the guest status (e.g., initialized, working, all memory is
>   busy when unplugging, too many memory blocks are offline when plugging,
>   etc.)
> - Guest-triggered shrinking of the usable region (e.g., whenever the
>   highest memory block is removed).
> - Exchange of plugged<->unplugged block for defragmentation.
> 
> Memory hotplug:
> - Reduce the amount of memory resources if that tunes out to be an
>   issue. Or try to speed up relevant code paths to deal with many
>   resources.
> - Allocate vmemmap from added memory.
> 
> Memory hotunplug:
> - Performance improvements:
> -- Sense (lockless) if it make sense to try alloc_contig_range() at all
>    before directly trying to isolate and taking locks.
> -- Try to unplug bigger chunks within a memory block first.
> - Make unplug more likely to succeed:
> -- There are various idea to limit fragmentation on memory block
>    granularity. (e.g., ZONE_PREFER_MOVABLE and smart balancing)
> -- Allocate vmemmap from added memory.
> - OOM handling, e.g., via an OOM handler/shrinker.
> - Defragmentation
> - Support for < MAX_ORDER - 1 blocks (esp. pageblock_order)
> 
> --------------------------------------------------------------------------
> 5. Example Usage
> --------------------------------------------------------------------------
> 
> A QEMU implementation (without protection of unplugged memory, but with
> resizable memory regions and optimized migration) is available at (kept
> updated):
>     https://github.com/davidhildenbrand/qemu.git virtio-mem
> 
> Start QEMU with two virtio-mem devices (one per NUMA node):
>  $ qemu-system-x86_64 -m 4G,maxmem=204G \
>   -smp sockets=2,cores=2 \
>   -numa node,nodeid=0,cpus=0-1 -numa node,nodeid=1,cpus=2-3 \
>   [...]
>   -object memory-backend-ram,id=mem0,size=100G,managed-size=on \
>   -device virtio-mem-pci,id=vm0,memdev=mem0,node=0,requested-size=0M \
>   -object memory-backend-ram,id=mem1,size=100G,managed-size=on \
>   -device virtio-mem-pci,id=vm1,memdev=mem1,node=1,requested-size=1G
> 
> Query the configuration:
>  QEMU 4.2.50 monitor - type 'help' for more information
>  (qemu) info memory-devices
>  Memory device [virtio-mem]: "vm0"
>    memaddr: 0x140000000
>    node: 0
>    requested-size: 0
>    size: 0
>    max-size: 107374182400
>    block-size: 2097152
>    memdev: /objects/mem0
>  Memory device [virtio-mem]: "vm1"
>    memaddr: 0x1a40000000
>    node: 1
>    requested-size: 1073741824
>    size: 1073741824
>    max-size: 107374182400
>    block-size: 2097152
>    memdev: /objects/mem1
> 
> Add some memory to node 0:
>  QEMU 4.2.50 monitor - type 'help' for more information
>  (qemu) qom-set vm0 requested-size 1G
> 
> Remove some memory from node 1:
>  QEMU 4.2.50 monitor - type 'help' for more information
>  (qemu) qom-set vm1 requested-size 64M
> 
> Query the configuration again:
>  QEMU 4.2.50 monitor - type 'help' for more information
>  (qemu) info memory-devices
>  Memory device [virtio-mem]: "vm0"
>    memaddr: 0x140000000
>    node: 0
>    requested-size: 1073741824
>    size: 1073741824
>    max-size: 107374182400
>    block-size: 2097152
>    memdev: /objects/mem0
>  Memory device [virtio-mem]: "vm1"
>    memaddr: 0x1a40000000
>    node: 1
>    requested-size: 67108864
>    size: 67108864
>    max-size: 107374182400
>    block-size: 2097152
>    memdev: /objects/mem1
> 
> --------------------------------------------------------------------------
> 6. Q/A
> --------------------------------------------------------------------------
> 
> Q: Why add/remove parts ("subblocks") of memory blocks/sections?
> A: Flexibility (section size depends on the architecture) - e.g., some
>    architectures have a section size of 2GB. Also, the memory block size
>    is variable (e.g., on x86-64). I want to avoid any such restrictions.
>    Some use cases want to add/remove memory in smaller granularity to a
>    VM (e.g., the Hyper-V balloon also implements this) - especially smaller
>    VMs like used for kata containers. Also, on memory unplug, it is more
>    reliable to free-up and unplug multiple small chunks instead
>    of one big chunk. E.g., if one page of a DIMM is either unmovable or
>    pinned, the DIMM can't get unplugged. This approach is basically a
>    compromise between DIMM-based memory hot(un)plug and balloon
>    inflation/deflation, which works mostly on page granularity.
> 
> Q: Why care about memory blocks?
> A: They are the way to tell user space about new memory. This way,
>    memory can get onlined/offlined by user space. Also, e.g., kdump
>    relies on udev events to reload kexec when memory blocks are
>    onlined/offlined. Memory blocks are the "real" memory hot(un)plug
>    granularity. Everything that's smaller has to be emulated "on top".
> 
> Q: Won't memory unplug of subblocks fragment memory?
> A: Yes and no. Unplugging e.g., >=4MB subblocks on x86-64 will not really
>    fragment memory like unplugging random pages like a balloon driver does.
>    Buddy merging will not be limited. However, any allocation that requires
>    bigger consecutive memory chunks (e.g., gigantic pages) might observe
>    the fragmentation. Possible solutions: Allocate gigantic huge pages
>    before unplugging memory, don't unplug memory, combine virtio-mem with
>    DIMM based memory or bigger initial memory. Remember, a virtio-mem
>    device will only unplug on the memory range it manages, not on other
>    DIMMs. Unplug of single memory blocks will result in similar
>    fragmentation in respect to gigantic huge pages.
> 
> Q: How reliable is memory unplug?
> A: There are no guarantees on how much memory can get unplugged
>    again. However, it is more likely to find 4MB chunks to unplug than
>    e.g., 128MB chunks. If memory is terribly fragmented, there is nothing
>    we can do - for now. I consider memory hotplug the first primary use
>    of virtio-mem. Memory unplug might usually work, but we want to improve
>    the performance and the amount of memory we can actually unplug later.
> 
> Q: Why not unplug from the ZONE_MOVABLE?
> A: Unplugged memory chunks are unmovable. Unmovable data must not end up
>    on the ZONE_MOVABLE - similar to gigantic pages - they will never be
>    allocated from ZONE_MOVABLE. virtio-mem added memory can be onlined
>    to the ZONE_MOVABLE, but subblocks will not get unplugged from it.
> 
> Q: How big should the initial (!virtio-mem) memory of a VM be?
> A: virtio-mem memory will not go to the DMA zones. So to avoid running out
>    of DMA memory, I suggest something like 2-3GB on x86-64. But many
>    VMs can most probably deal with less DMA memory - depends on the use
>    case.
> 
> [1] https://events.linuxfoundation.org/wp-content/uploads/2017/12/virtio-mem-Paravirtualized-Memory-David-Hildenbrand-Red-Hat-1.pdf
> [2] https://lkml.kernel.org/r/20190919142228.5483-1-david@redhat.com
> [3] https://lkml.kernel.org/r/547865a9-d6c2-7140-47e2-5af01e7d761d@redhat.com
> [4] https://github.com/kata-containers/documentation/pull/592
> [5] https://github.com/cloud-hypervisor/cloud-hypervisor/pull/837
> 
> Cc: Sebastien Boeuf <sebastien.boeuf@intel.com>
> Cc: Samuel Ortiz <samuel.ortiz@intel.com>
> Cc: Robert Bradford <robert.bradford@intel.com>
> Cc: Luiz Capitulino <lcapitulino@redhat.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Cc: teawater <teawaterz@linux.alibaba.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> David Hildenbrand (10):
>   virtio-mem: Paravirtualized memory hotplug
>   virtio-mem: Allow to specify an ACPI PXM as nid
>   virtio-mem: Paravirtualized memory hotunplug part 1
>   virtio-mem: Paravirtualized memory hotunplug part 2
>   mm: Allow to offline unmovable PageOffline() pages via
>     MEM_GOING_OFFLINE
>   virtio-mem: Allow to offline partially unplugged memory blocks
>   mm/memory_hotplug: Introduce offline_and_remove_memory()
>   virtio-mem: Offline and remove completely unplugged memory blocks
>   virtio-mem: Better retry handling
>   MAINTAINERS: Add myself as virtio-mem maintainer
> 
>  MAINTAINERS                     |    7 +
>  drivers/acpi/numa/srat.c        |    1 +
>  drivers/virtio/Kconfig          |   18 +
>  drivers/virtio/Makefile         |    1 +
>  drivers/virtio/virtio_mem.c     | 1910 +++++++++++++++++++++++++++++++
>  include/linux/memory_hotplug.h  |    1 +
>  include/linux/page-flags.h      |   10 +
>  include/uapi/linux/virtio_ids.h |    1 +
>  include/uapi/linux/virtio_mem.h |  208 ++++
>  mm/memory_hotplug.c             |   81 +-
>  mm/page_alloc.c                 |   26 +
>  mm/page_isolation.c             |    9 +
>  12 files changed, 2263 insertions(+), 10 deletions(-)
>  create mode 100644 drivers/virtio/virtio_mem.c
>  create mode 100644 include/uapi/linux/virtio_mem.h
> 
> -- 
> 2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-03-27 17:03   ` David Hildenbrand
  2020-03-27 17:07     ` David Hildenbrand
@ 2020-03-29 15:41     ` Pankaj Gupta
  2020-03-30  8:42       ` David Hildenbrand
  1 sibling, 1 reply; 30+ messages in thread
From: Pankaj Gupta @ 2020-03-29 15:41 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Michael S . Tsirkin,
	Sebastien Boeuf, Samuel Ortiz, Robert Bradford, Luiz Capitulino,
	teawater, Igor Mammedov, Dr . David Alan Gilbert,
	Alexander Duyck, Alexander Potapenko, Anshuman Khandual,
	Anthony Yznaga, Dan Williams, Dave Young, Jason Wang,
	Johannes Weiner, Juergen Gross, Konrad Rzeszutek Wilk, Len Brown,
	Mel Gorman, Michal Hocko, Mike Rapoport, Oscar Salvador,
	Oscar Salvador, Pavel Tatashin, Pavel Tatashin, Pingfan Liu,
	Qian Cai, Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

> > Hi David,
> >
> > Trying to test the series with the Qemu branch(virtio-mem) mentioned.
> > Unfortunately,
> > not able to hotplug memory. Is anything changed from your previous posting
> > or I am doing something wrong?
> >
> > After giving value to "requested-size", I see size as zero.
> >
> > (qemu) qom-set vm0 requested-size 10G
> > (qemu) info memory-devices
> > Memory device [virtio-mem]: "vm0"
> >   memaddr: 0x240000000
> >   node: 0
> >   requested-size: 10737418240
> >   size: 0
> >   max-size: 107374182400
> >   block-size: 2097152
> >   memdev: /objects/mem0
> >
> > Guest kernel: 5.6.0-rc4
> > Using same Qemu commandline arguments mentioned in cover-letter.
>
> Are you booting from an initrd? Are you compiling virtio-mem as a kernel
> module or into the kernel binary?
Ah was booting into wrong kernel version. Sorry! for the noise.

Working perfectly for me. Tried various cmbinations for both
hotplug/unplug with multiple
NUMA nodes and verified result in guest.

For the series, you can add:
Tested-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>


>
> --
> Thanks,
>
> David / dhildenb
>

^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-03-29 12:42 ` Michael S. Tsirkin
@ 2020-03-30  8:16   ` David Hildenbrand
  2020-04-14  9:15   ` David Hildenbrand
  1 sibling, 0 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-30  8:16 UTC (permalink / raw)
  To: Michael S. Tsirkin
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Sebastien Boeuf, Samuel Ortiz,
	Robert Bradford, Luiz Capitulino, Pankaj Gupta, teawater,
	Igor Mammedov, Dr . David Alan Gilbert, Alexander Duyck,
	Alexander Potapenko, Anshuman Khandual, Anthony Yznaga,
	Dan Williams, Dave Young, Jason Wang, Johannes Weiner,
	Juergen Gross, Konrad Rzeszutek Wilk, Len Brown, Mel Gorman,
	Michal Hocko, Mike Rapoport, Oscar Salvador, Oscar Salvador,
	Pavel Tatashin, Pavel Tatashin, Pingfan Liu, Qian Cai,
	Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

On 29.03.20 14:42, Michael S. Tsirkin wrote:
> On Wed, Mar 11, 2020 at 06:14:12PM +0100, David Hildenbrand wrote:
>> This series is based on latest linux-next. The patches are located at:
>>     https://github.com/davidhildenbrand/linux.git virtio-mem-v2
>>
>> I now have acks for all !virtio-mem changes. I'll be happy to get review
>> feedback, testing reports, etc. for the virtio-mem changes. If there are
>> no further comments, I guess this is good to go as a v1 soon.
> 
> I'd like to queue it for merge after the release. If you feel it's ready
> please ping me after the release to help make sure it didn't get
> dropped.  I see there were some reports about people having trouble
> using this, pls keep working on this meanwhile.
> 

Yes, will ping you. The cloud-hypervisor implementation has already been
merged. I'll be posting the initial QEMU version once the next release
is close.

Thanks!

> Thanks!


-- 
Thanks,

David / dhildenb


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-03-29 15:41     ` Pankaj Gupta
@ 2020-03-30  8:42       ` David Hildenbrand
  0 siblings, 0 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-03-30  8:42 UTC (permalink / raw)
  To: Pankaj Gupta
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Michael S . Tsirkin,
	Sebastien Boeuf, Samuel Ortiz, Robert Bradford, Luiz Capitulino,
	teawater, Igor Mammedov, Dr . David Alan Gilbert,
	Alexander Duyck, Alexander Potapenko, Anshuman Khandual,
	Anthony Yznaga, Dan Williams, Dave Young, Jason Wang,
	Johannes Weiner, Juergen Gross, Konrad Rzeszutek Wilk, Len Brown,
	Mel Gorman, Michal Hocko, Mike Rapoport, Oscar Salvador,
	Oscar Salvador, Pavel Tatashin, Pavel Tatashin, Pingfan Liu,
	Qian Cai, Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

On 29.03.20 17:41, Pankaj Gupta wrote:
>>> Hi David,
>>>
>>> Trying to test the series with the Qemu branch(virtio-mem) mentioned.
>>> Unfortunately,
>>> not able to hotplug memory. Is anything changed from your previous posting
>>> or I am doing something wrong?
>>>
>>> After giving value to "requested-size", I see size as zero.
>>>
>>> (qemu) qom-set vm0 requested-size 10G
>>> (qemu) info memory-devices
>>> Memory device [virtio-mem]: "vm0"
>>>   memaddr: 0x240000000
>>>   node: 0
>>>   requested-size: 10737418240
>>>   size: 0
>>>   max-size: 107374182400
>>>   block-size: 2097152
>>>   memdev: /objects/mem0
>>>
>>> Guest kernel: 5.6.0-rc4
>>> Using same Qemu commandline arguments mentioned in cover-letter.
>>
>> Are you booting from an initrd? Are you compiling virtio-mem as a kernel
>> module or into the kernel binary?
> Ah was booting into wrong kernel version. Sorry! for the noise.
> 
> Working perfectly for me. Tried various cmbinations for both
> hotplug/unplug with multiple
> NUMA nodes and verified result in guest.
> 
> For the series, you can add:
> Tested-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

Awesome, thanks!

-- 
Thanks,

David / dhildenb


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 02/10] virtio-mem: Allow to specify an ACPI PXM as nid
  2020-03-11 17:14 ` [PATCH v2 02/10] virtio-mem: Allow to specify an ACPI PXM as nid David Hildenbrand
@ 2020-03-30 11:04   ` Pankaj Gupta
  0 siblings, 0 replies; 30+ messages in thread
From: Pankaj Gupta @ 2020-03-30 11:04 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: linux-kernel, linux-mm, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, Michal Hocko,
	Rafael J. Wysocki, Jason Wang, Oscar Salvador, Igor Mammedov,
	Dave Young, Dan Williams, Pavel Tatashin, Stefan Hajnoczi,
	Vlastimil Babka, Len Brown, linux-acpi

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-03-29 12:42 ` Michael S. Tsirkin
  2020-03-30  8:16   ` David Hildenbrand
@ 2020-04-14  9:15   ` David Hildenbrand
  2020-04-14 16:28     ` Michael S. Tsirkin
  1 sibling, 1 reply; 30+ messages in thread
From: David Hildenbrand @ 2020-04-14  9:15 UTC (permalink / raw)
  To: Michael S. Tsirkin
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Sebastien Boeuf, Samuel Ortiz,
	Robert Bradford, Luiz Capitulino, Pankaj Gupta, teawater,
	Igor Mammedov, Dr . David Alan Gilbert, Alexander Duyck,
	Alexander Potapenko, Anshuman Khandual, Anthony Yznaga,
	Dan Williams, Dave Young, Jason Wang, Johannes Weiner,
	Juergen Gross, Konrad Rzeszutek Wilk, Len Brown, Mel Gorman,
	Michal Hocko, Mike Rapoport, Oscar Salvador, Oscar Salvador,
	Pavel Tatashin, Pavel Tatashin, Pingfan Liu, Qian Cai,
	Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

On 29.03.20 14:42, Michael S. Tsirkin wrote:
> On Wed, Mar 11, 2020 at 06:14:12PM +0100, David Hildenbrand wrote:
>> This series is based on latest linux-next. The patches are located at:
>>     https://github.com/davidhildenbrand/linux.git virtio-mem-v2
>>
>> I now have acks for all !virtio-mem changes. I'll be happy to get review
>> feedback, testing reports, etc. for the virtio-mem changes. If there are
>> no further comments, I guess this is good to go as a v1 soon.
> 
> I'd like to queue it for merge after the release. If you feel it's ready
> please ping me after the release to help make sure it didn't get
> dropped.  I see there were some reports about people having trouble
> using this, pls keep working on this meanwhile.

Hi Michael,

I think this is ready to go as a first version. There are a couple of
future work items related to kexec/kdump:
- Teach kexec-tools/kexec_file_load() to not place the kexec
  kernel/initrd onto virtio-mem added memory.
- Teach kexec-tools/kdump to consider a bigger number of memory
  resources for dumping.

In general, as virtio-mem adds a lot of memory resources, we might want
to tweak performance in that area as well. Future stuff.

So I suggest queuing this. If you need a resend, please let me know.

Cheers!

-- 
Thanks,

David / dhildenb


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-04-14  9:15   ` David Hildenbrand
@ 2020-04-14 16:28     ` Michael S. Tsirkin
  2020-04-14 18:39       ` David Hildenbrand
  0 siblings, 1 reply; 30+ messages in thread
From: Michael S. Tsirkin @ 2020-04-14 16:28 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Sebastien Boeuf, Samuel Ortiz,
	Robert Bradford, Luiz Capitulino, Pankaj Gupta, teawater,
	Igor Mammedov, Dr . David Alan Gilbert, Alexander Duyck,
	Alexander Potapenko, Anshuman Khandual, Anthony Yznaga,
	Dan Williams, Dave Young, Jason Wang, Johannes Weiner,
	Juergen Gross, Konrad Rzeszutek Wilk, Len Brown, Mel Gorman,
	Michal Hocko, Mike Rapoport, Oscar Salvador, Oscar Salvador,
	Pavel Tatashin, Pavel Tatashin, Pingfan Liu, Qian Cai,
	Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

On Tue, Apr 14, 2020 at 11:15:18AM +0200, David Hildenbrand wrote:
> On 29.03.20 14:42, Michael S. Tsirkin wrote:
> > On Wed, Mar 11, 2020 at 06:14:12PM +0100, David Hildenbrand wrote:
> >> This series is based on latest linux-next. The patches are located at:
> >>     https://github.com/davidhildenbrand/linux.git virtio-mem-v2
> >>
> >> I now have acks for all !virtio-mem changes. I'll be happy to get review
> >> feedback, testing reports, etc. for the virtio-mem changes. If there are
> >> no further comments, I guess this is good to go as a v1 soon.
> > 
> > I'd like to queue it for merge after the release. If you feel it's ready
> > please ping me after the release to help make sure it didn't get
> > dropped.  I see there were some reports about people having trouble
> > using this, pls keep working on this meanwhile.
> 
> Hi Michael,
> 
> I think this is ready to go as a first version. There are a couple of
> future work items related to kexec/kdump:
> - Teach kexec-tools/kexec_file_load() to not place the kexec
>   kernel/initrd onto virtio-mem added memory.
> - Teach kexec-tools/kdump to consider a bigger number of memory
>   resources for dumping.
> 
> In general, as virtio-mem adds a lot of memory resources, we might want
> to tweak performance in that area as well. Future stuff.
> 
> So I suggest queuing this. If you need a resend, please let me know.
> 
> Cheers!

Thanks!
I'll queue it for merge after the release. If possible please ping me
after the release to help make sure it didn't get dropped.




> -- 
> Thanks,
> 
> David / dhildenb


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 05/10] mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE
  2020-03-11 17:14 ` [PATCH v2 05/10] mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE David Hildenbrand
@ 2020-04-14 16:34   ` Michael S. Tsirkin
  2020-04-15  0:32     ` Andrew Morton
  0 siblings, 1 reply; 30+ messages in thread
From: Michael S. Tsirkin @ 2020-04-14 16:34 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Alexander Duyck, Michal Hocko,
	Juergen Gross, Konrad Rzeszutek Wilk, Pavel Tatashin,
	Vlastimil Babka, Johannes Weiner, Anthony Yznaga, Oscar Salvador,
	Mel Gorman, Mike Rapoport, Dan Williams, Anshuman Khandual,
	Qian Cai, Pingfan Liu

On Wed, Mar 11, 2020 at 06:14:17PM +0100, David Hildenbrand wrote:
> virtio-mem wants to allow to offline memory blocks of which some parts
> were unplugged (allocated via alloc_contig_range()), especially, to later
> offline and remove completely unplugged memory blocks. The important part
> is that PageOffline() has to remain set until the section is offline, so
> these pages will never get accessed (e.g., when dumping). The pages should
> not be handed back to the buddy (which would require clearing PageOffline()
> and result in issues if offlining fails and the pages are suddenly in the
> buddy).
> 
> Let's allow to do that by allowing to isolate any PageOffline() page
> when offlining. This way, we can reach the memory hotplug notifier
> MEM_GOING_OFFLINE, where the driver can signal that he is fine with
> offlining this page by dropping its reference count. PageOffline() pages
> with a reference count of 0 can then be skipped when offlining the
> pages (like if they were free, however they are not in the buddy).
> 
> Anybody who uses PageOffline() pages and does not agree to offline them
> (e.g., Hyper-V balloon, XEN balloon, VMWare balloon for 2MB pages) will not
> decrement the reference count and make offlining fail when trying to
> migrate such an unmovable page. So there should be no observable change.
> Same applies to balloon compaction users (movable PageOffline() pages), the
> pages will simply be migrated.
> 
> Note 1: If offlining fails, a driver has to increment the reference
> 	count again in MEM_CANCEL_OFFLINE.
> 
> Note 2: A driver that makes use of this has to be aware that re-onlining
> 	the memory block has to be handled by hooking into onlining code
> 	(online_page_callback_t), resetting the page PageOffline() and
> 	not giving them to the buddy.
> 
> Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Pavel Tatashin <pavel.tatashin@microsoft.com>
> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Anthony Yznaga <anthony.yznaga@oracle.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Qian Cai <cai@lca.pw>
> Cc: Pingfan Liu <kernelfans@gmail.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Andrew, could you please ack merging this through the vhost tree
together with the rest of the patches?



> ---
>  include/linux/page-flags.h | 10 +++++++++
>  mm/memory_hotplug.c        | 44 +++++++++++++++++++++++++++++---------
>  mm/page_alloc.c            | 24 +++++++++++++++++++++
>  mm/page_isolation.c        |  9 ++++++++
>  4 files changed, 77 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 49c2697046b9..fd6d4670ccc3 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -772,6 +772,16 @@ PAGE_TYPE_OPS(Buddy, buddy)
>   * not onlined when onlining the section).
>   * The content of these pages is effectively stale. Such pages should not
>   * be touched (read/write/dump/save) except by their owner.
> + *
> + * If a driver wants to allow to offline unmovable PageOffline() pages without
> + * putting them back to the buddy, it can do so via the memory notifier by
> + * decrementing the reference count in MEM_GOING_OFFLINE and incrementing the
> + * reference count in MEM_CANCEL_OFFLINE. When offlining, the PageOffline()
> + * pages (now with a reference count of zero) are treated like free pages,
> + * allowing the containing memory block to get offlined. A driver that
> + * relies on this feature is aware that re-onlining the memory block will
> + * require to re-set the pages PageOffline() and not giving them to the
> + * buddy via online_page_callback_t.
>   */
>  PAGE_TYPE_OPS(Offline, offline)
>  
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 1a00b5a37ef6..ab1c31e67fd1 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1221,11 +1221,17 @@ struct zone *test_pages_in_a_zone(unsigned long start_pfn,
>  
>  /*
>   * Scan pfn range [start,end) to find movable/migratable pages (LRU pages,
> - * non-lru movable pages and hugepages). We scan pfn because it's much
> - * easier than scanning over linked list. This function returns the pfn
> - * of the first found movable page if it's found, otherwise 0.
> + * non-lru movable pages and hugepages). Will skip over most unmovable
> + * pages (esp., pages that can be skipped when offlining), but bail out on
> + * definitely unmovable pages.
> + *
> + * Returns:
> + *	0 in case a movable page is found and movable_pfn was updated.
> + *	-ENOENT in case no movable page was found.
> + *	-EBUSY in case a definitely unmovable page was found.
>   */
> -static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
> +static int scan_movable_pages(unsigned long start, unsigned long end,
> +			      unsigned long *movable_pfn)
>  {
>  	unsigned long pfn;
>  
> @@ -1237,18 +1243,30 @@ static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
>  			continue;
>  		page = pfn_to_page(pfn);
>  		if (PageLRU(page))
> -			return pfn;
> +			goto found;
>  		if (__PageMovable(page))
> -			return pfn;
> +			goto found;
> +
> +		/*
> +		 * PageOffline() pages that are not marked __PageMovable() and
> +		 * have a reference count > 0 (after MEM_GOING_OFFLINE) are
> +		 * definitely unmovable. If their reference count would be 0,
> +		 * they could at least be skipped when offlining memory.
> +		 */
> +		if (PageOffline(page) && page_count(page))
> +			return -EBUSY;
>  
>  		if (!PageHuge(page))
>  			continue;
>  		head = compound_head(page);
>  		if (page_huge_active(head))
> -			return pfn;
> +			goto found;
>  		skip = compound_nr(head) - (page - head);
>  		pfn += skip - 1;
>  	}
> +	return -ENOENT;
> +found:
> +	*movable_pfn = pfn;
>  	return 0;
>  }
>  
> @@ -1515,7 +1533,8 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  	}
>  
>  	do {
> -		for (pfn = start_pfn; pfn;) {
> +		pfn = start_pfn;
> +		do {
>  			if (signal_pending(current)) {
>  				ret = -EINTR;
>  				reason = "signal backoff";
> @@ -1525,14 +1544,19 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  			cond_resched();
>  			lru_add_drain_all();
>  
> -			pfn = scan_movable_pages(pfn, end_pfn);
> -			if (pfn) {
> +			ret = scan_movable_pages(pfn, end_pfn, &pfn);
> +			if (!ret) {
>  				/*
>  				 * TODO: fatal migration failures should bail
>  				 * out
>  				 */
>  				do_migrate_range(pfn, end_pfn);
>  			}
> +		} while (!ret);
> +
> +		if (ret != -ENOENT) {
> +			reason = "unmovable page";
> +			goto failed_removal_isolated;
>  		}
>  
>  		/*
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8d7be3f33e26..baa60222215f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8366,6 +8366,19 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>  		if ((flags & MEMORY_OFFLINE) && PageHWPoison(page))
>  			continue;
>  
> +		/*
> +		 * We treat all PageOffline() pages as movable when offlining
> +		 * to give drivers a chance to decrement their reference count
> +		 * in MEM_GOING_OFFLINE in order to indicate that these pages
> +		 * can be offlined as there are no direct references anymore.
> +		 * For actually unmovable PageOffline() where the driver does
> +		 * not support this, we will fail later when trying to actually
> +		 * move these pages that still have a reference count > 0.
> +		 * (false negatives in this function only)
> +		 */
> +		if ((flags & MEMORY_OFFLINE) && PageOffline(page))
> +			continue;
> +
>  		if (__PageMovable(page) || PageLRU(page))
>  			continue;
>  
> @@ -8786,6 +8799,17 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
>  			offlined_pages++;
>  			continue;
>  		}
> +		/*
> +		 * At this point all remaining PageOffline() pages have a
> +		 * reference count of 0 and can simply be skipped.
> +		 */
> +		if (PageOffline(page)) {
> +			BUG_ON(page_count(page));
> +			BUG_ON(PageBuddy(page));
> +			pfn++;
> +			offlined_pages++;
> +			continue;
> +		}
>  
>  		BUG_ON(page_count(page));
>  		BUG_ON(!PageBuddy(page));
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 2c11a38d6e87..f6d07c5f0d34 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -151,6 +151,7 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
>   *			a bit mask)
>   *			MEMORY_OFFLINE - isolate to offline (!allocate) memory
>   *					 e.g., skip over PageHWPoison() pages
> + *					 and PageOffline() pages.
>   *			REPORT_FAILURE - report details about the failure to
>   *			isolate the range
>   *
> @@ -259,6 +260,14 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
>  		else if ((flags & MEMORY_OFFLINE) && PageHWPoison(page))
>  			/* A HWPoisoned page cannot be also PageBuddy */
>  			pfn++;
> +		else if ((flags & MEMORY_OFFLINE) && PageOffline(page) &&
> +			 !page_count(page))
> +			/*
> +			 * The responsible driver agreed to skip PageOffline()
> +			 * pages when offlining memory by dropping its
> +			 * reference in MEM_GOING_OFFLINE.
> +			 */
> +			pfn++;
>  		else
>  			break;
>  	}
> -- 
> 2.24.1


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory()
  2020-03-11 17:19   ` David Hildenbrand
@ 2020-04-14 16:35     ` Michael S. Tsirkin
  2020-04-15  0:30       ` Andrew Morton
  0 siblings, 1 reply; 30+ messages in thread
From: Michael S. Tsirkin @ 2020-04-14 16:35 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Oscar Salvador, Michal Hocko,
	Pavel Tatashin, Wei Yang, Dan Williams, Qian Cai

On Wed, Mar 11, 2020 at 06:19:04PM +0100, David Hildenbrand wrote:
> On 11.03.20 18:14, David Hildenbrand wrote:
> > virtio-mem wants to offline and remove a memory block once it unplugged
> > all subblocks (e.g., using alloc_contig_range()). Let's provide
> > an interface to do that from a driver. virtio-mem already supports to
> > offline partially unplugged memory blocks. Offlining a fully unplugged
> > memory block will not require to migrate any pages. All unplugged
> > subblocks are PageOffline() and have a reference count of 0 - so
> > offlining code will simply skip them.
> > 
> > All we need is an interface to offline and remove the memory from kernel
> > module context, where we don't have access to the memory block devices
> > (esp. find_memory_block() and device_offline()) and the device hotplug
> > lock.
> > 
> > To keep things simple, allow to only work on a single memory block.
> > 
> 
> Lost the ACK from Michael
> 
> Acked-by: Michal Hocko <mhocko@suse.com> [1]
> 
> [1] https://lkml.kernel.org/r/20200302142737.GP4380@dhcp22.suse.cz


Andrew, could you pls ack merging this through the vhost tree,
with the rest of the patchset?

> -- 
> Thanks,
> 
> David / dhildenb


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 00/10] virtio-mem: paravirtualized memory
  2020-04-14 16:28     ` Michael S. Tsirkin
@ 2020-04-14 18:39       ` David Hildenbrand
  0 siblings, 0 replies; 30+ messages in thread
From: David Hildenbrand @ 2020-04-14 18:39 UTC (permalink / raw)
  To: Michael S. Tsirkin
  Cc: linux-kernel, linux-mm, virtio-dev, virtualization, kvm,
	Michal Hocko, Andrew Morton, Sebastien Boeuf, Samuel Ortiz,
	Robert Bradford, Luiz Capitulino, Pankaj Gupta, teawater,
	Igor Mammedov, Dr . David Alan Gilbert, Alexander Duyck,
	Alexander Potapenko, Anshuman Khandual, Anthony Yznaga,
	Dan Williams, Dave Young, Jason Wang, Johannes Weiner,
	Juergen Gross, Konrad Rzeszutek Wilk, Len Brown, Mel Gorman,
	Michal Hocko, Mike Rapoport, Oscar Salvador, Oscar Salvador,
	Pavel Tatashin, Pavel Tatashin, Pingfan Liu, Qian Cai,
	Rafael J. Wysocki, Rafael J. Wysocki, Stefan Hajnoczi,
	Vlastimil Babka, Wei Yang

On 14.04.20 18:28, Michael S. Tsirkin wrote:
> On Tue, Apr 14, 2020 at 11:15:18AM +0200, David Hildenbrand wrote:
>> On 29.03.20 14:42, Michael S. Tsirkin wrote:
>>> On Wed, Mar 11, 2020 at 06:14:12PM +0100, David Hildenbrand wrote:
>>>> This series is based on latest linux-next. The patches are located at:
>>>>     https://github.com/davidhildenbrand/linux.git virtio-mem-v2
>>>>
>>>> I now have acks for all !virtio-mem changes. I'll be happy to get review
>>>> feedback, testing reports, etc. for the virtio-mem changes. If there are
>>>> no further comments, I guess this is good to go as a v1 soon.
>>>
>>> I'd like to queue it for merge after the release. If you feel it's ready
>>> please ping me after the release to help make sure it didn't get
>>> dropped.  I see there were some reports about people having trouble
>>> using this, pls keep working on this meanwhile.
>>
>> Hi Michael,
>>
>> I think this is ready to go as a first version. There are a couple of
>> future work items related to kexec/kdump:
>> - Teach kexec-tools/kexec_file_load() to not place the kexec
>>   kernel/initrd onto virtio-mem added memory.
>> - Teach kexec-tools/kdump to consider a bigger number of memory
>>   resources for dumping.
>>
>> In general, as virtio-mem adds a lot of memory resources, we might want
>> to tweak performance in that area as well. Future stuff.
>>
>> So I suggest queuing this. If you need a resend, please let me know.
>>
>> Cheers!
> 
> Thanks!
> I'll queue it for merge after the release. If possible please ping me
> after the release to help make sure it didn't get dropped.

If we could get this into 5.8, that would be great (IOW, have it in
-next for a while before the 5.8 merge window opens).

Thanks!

-- 
Thanks,

David / dhildenb


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory()
  2020-04-14 16:35     ` Michael S. Tsirkin
@ 2020-04-15  0:30       ` Andrew Morton
  0 siblings, 0 replies; 30+ messages in thread
From: Andrew Morton @ 2020-04-15  0:30 UTC (permalink / raw)
  To: Michael S. Tsirkin
  Cc: David Hildenbrand, linux-kernel, linux-mm, virtio-dev,
	virtualization, kvm, Michal Hocko, Oscar Salvador, Michal Hocko,
	Pavel Tatashin, Wei Yang, Dan Williams, Qian Cai

On Tue, 14 Apr 2020 12:35:02 -0400 "Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Wed, Mar 11, 2020 at 06:19:04PM +0100, David Hildenbrand wrote:
> > On 11.03.20 18:14, David Hildenbrand wrote:
> > > virtio-mem wants to offline and remove a memory block once it unplugged
> > > all subblocks (e.g., using alloc_contig_range()). Let's provide
> > > an interface to do that from a driver. virtio-mem already supports to
> > > offline partially unplugged memory blocks. Offlining a fully unplugged
> > > memory block will not require to migrate any pages. All unplugged
> > > subblocks are PageOffline() and have a reference count of 0 - so
> > > offlining code will simply skip them.
> > > 
> > > All we need is an interface to offline and remove the memory from kernel
> > > module context, where we don't have access to the memory block devices
> > > (esp. find_memory_block() and device_offline()) and the device hotplug
> > > lock.
> > > 
> > > To keep things simple, allow to only work on a single memory block.
> > > 
> > 
> > Lost the ACK from Michael
> > 
> > Acked-by: Michal Hocko <mhocko@suse.com> [1]
> > 
> > [1] https://lkml.kernel.org/r/20200302142737.GP4380@dhcp22.suse.cz
> 
> 
> Andrew, could you pls ack merging this through the vhost tree,
> with the rest of the patchset?

I wish the device_offline() return value was documented :(

Yes, please go ahead and merge.

Acked-by: Andrew Morton <akpm@linux-foundation.org>


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 05/10] mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE
  2020-04-14 16:34   ` Michael S. Tsirkin
@ 2020-04-15  0:32     ` Andrew Morton
  0 siblings, 0 replies; 30+ messages in thread
From: Andrew Morton @ 2020-04-15  0:32 UTC (permalink / raw)
  To: Michael S. Tsirkin
  Cc: David Hildenbrand, linux-kernel, linux-mm, virtio-dev,
	virtualization, kvm, Michal Hocko, Alexander Duyck, Michal Hocko,
	Juergen Gross, Konrad Rzeszutek Wilk, Pavel Tatashin,
	Vlastimil Babka, Johannes Weiner, Anthony Yznaga, Oscar Salvador,
	Mel Gorman, Mike Rapoport, Dan Williams, Anshuman Khandual,
	Qian Cai, Pingfan Liu

On Tue, 14 Apr 2020 12:34:26 -0400 "Michael S. Tsirkin" <mst@redhat.com> wrote:

> Andrew, could you please ack merging this through the vhost tree
> together with the rest of the patches?

Acked-by: Andrew Morton <akpm@linux-foundation.org>


^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 01/10] virtio-mem: Paravirtualized memory hotplug
  2020-03-11 17:14 ` [PATCH v2 01/10] virtio-mem: Paravirtualized memory hotplug David Hildenbrand
@ 2020-04-15  5:59   ` Pankaj Gupta
  0 siblings, 0 replies; 30+ messages in thread
From: Pankaj Gupta @ 2020-04-15  5:59 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: LKML, Linux MM, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, Jason Wang, Oscar Salvador,
	Igor Mammedov, Dave Young, Dan Williams, Pavel Tatashin,
	Stefan Hajnoczi, Vlastimil Babka, Rafael J. Wysocki, Len Brown,
	linux-acpi

I spent quite some time to review and also tested this driver.
This looks good to me. Feel free to add.

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory()
  2020-03-11 17:14 ` [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory() David Hildenbrand
  2020-03-11 17:19   ` David Hildenbrand
@ 2020-04-15  7:35   ` Pankaj Gupta
  1 sibling, 0 replies; 30+ messages in thread
From: Pankaj Gupta @ 2020-04-15  7:35 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: LKML, Linux MM, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, Oscar Salvador, Michal Hocko,
	Pavel Tatashin, Wei Yang, Dan Williams, Qian Cai

> virtio-mem wants to offline and remove a memory block once it unplugged
> all subblocks (e.g., using alloc_contig_range()). Let's provide
> an interface to do that from a driver. virtio-mem already supports to
> offline partially unplugged memory blocks. Offlining a fully unplugged
> memory block will not require to migrate any pages. All unplugged
> subblocks are PageOffline() and have a reference count of 0 - so
> offlining code will simply skip them.
>
> All we need is an interface to offline and remove the memory from kernel
> module context, where we don't have access to the memory block devices
> (esp. find_memory_block() and device_offline()) and the device hotplug
> lock.
>
> To keep things simple, allow to only work on a single memory block.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Oscar Salvador <osalvador@suse.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Wei Yang <richard.weiyang@gmail.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Qian Cai <cai@lca.pw>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  include/linux/memory_hotplug.h |  1 +
>  mm/memory_hotplug.c            | 37 ++++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index f4d59155f3d4..a98aa16dbfa1 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -311,6 +311,7 @@ extern void try_offline_node(int nid);
>  extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
>  extern int remove_memory(int nid, u64 start, u64 size);
>  extern void __remove_memory(int nid, u64 start, u64 size);
> +extern int offline_and_remove_memory(int nid, u64 start, u64 size);
>
>  #else
>  static inline bool is_mem_section_removable(unsigned long pfn,
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index ab1c31e67fd1..d0d337918a15 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1818,4 +1818,41 @@ int remove_memory(int nid, u64 start, u64 size)
>         return rc;
>  }
>  EXPORT_SYMBOL_GPL(remove_memory);
> +
> +/*
> + * Try to offline and remove a memory block. Might take a long time to
> + * finish in case memory is still in use. Primarily useful for memory devices
> + * that logically unplugged all memory (so it's no longer in use) and want to
> + * offline + remove the memory block.
> + */
> +int offline_and_remove_memory(int nid, u64 start, u64 size)
> +{
> +       struct memory_block *mem;
> +       int rc = -EINVAL;
> +
> +       if (!IS_ALIGNED(start, memory_block_size_bytes()) ||
> +           size != memory_block_size_bytes())
> +               return rc;
> +
> +       lock_device_hotplug();
> +       mem = find_memory_block(__pfn_to_section(PFN_DOWN(start)));
> +       if (mem)
> +               rc = device_offline(&mem->dev);
> +       /* Ignore if the device is already offline. */
> +       if (rc > 0)
> +               rc = 0;
> +
> +       /*
> +        * In case we succeeded to offline the memory block, remove it.
> +        * This cannot fail as it cannot get onlined in the meantime.
> +        */
> +       if (!rc) {
> +               rc = try_remove_memory(nid, start, size);
> +               WARN_ON_ONCE(rc);
> +       }
> +       unlock_device_hotplug();
> +
> +       return rc;
> +}
> +EXPORT_SYMBOL_GPL(offline_and_remove_memory);
>  #endif /* CONFIG_MEMORY_HOTREMOVE */

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

^ permalink raw reply	[flat|nested] 30+ messages in thread

* Re: [PATCH v2 08/10] virtio-mem: Offline and remove completely unplugged memory blocks
  2020-03-11 17:14 ` [PATCH v2 08/10] virtio-mem: Offline and remove completely unplugged memory blocks David Hildenbrand
@ 2020-04-15  7:42   ` Pankaj Gupta
  0 siblings, 0 replies; 30+ messages in thread
From: Pankaj Gupta @ 2020-04-15  7:42 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: LKML, Linux MM, virtio-dev, virtualization, kvm, Michal Hocko,
	Andrew Morton, Michael S . Tsirkin, Jason Wang, Oscar Salvador,
	Igor Mammedov, Dave Young, Dan Williams, Pavel Tatashin,
	Stefan Hajnoczi, Vlastimil Babka

> Let's offline+remove memory blocks once all subblocks are unplugged. We
> can use the new Linux MM interface for that. As no memory is in use
> anymore, this shouldn't take a long time and shouldn't fail. There might
> be corner cases where the offlining could still fail (especially, if
> another notifier NACKs the offlining request).
>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  drivers/virtio/virtio_mem.c | 47 +++++++++++++++++++++++++++++++++----
>  1 file changed, 43 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
> index 35f20232770c..aa322e7732a4 100644
> --- a/drivers/virtio/virtio_mem.c
> +++ b/drivers/virtio/virtio_mem.c
> @@ -443,6 +443,28 @@ static int virtio_mem_mb_remove(struct virtio_mem *vm, unsigned long mb_id)
>         return remove_memory(nid, addr, memory_block_size_bytes());
>  }
>
> +/*
> + * Try to offline and remove a memory block from Linux.
> + *
> + * Must not be called with the vm->hotplug_mutex held (possible deadlock with
> + * onlining code).
> + *
> + * Will not modify the state of the memory block.
> + */
> +static int virtio_mem_mb_offline_and_remove(struct virtio_mem *vm,
> +                                           unsigned long mb_id)
> +{
> +       const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
> +       int nid = vm->nid;
> +
> +       if (nid == NUMA_NO_NODE)
> +               nid = memory_add_physaddr_to_nid(addr);
> +
> +       dev_dbg(&vm->vdev->dev, "offlining and removing memory block: %lu\n",
> +               mb_id);
> +       return offline_and_remove_memory(nid, addr, memory_block_size_bytes());
> +}
> +
>  /*
>   * Trigger the workqueue so the device can perform its magic.
>   */
> @@ -535,7 +557,13 @@ static void virtio_mem_notify_offline(struct virtio_mem *vm,
>                 break;
>         }
>
> -       /* trigger the workqueue, maybe we can now unplug memory. */
> +       /*
> +        * Trigger the workqueue, maybe we can now unplug memory. Also,
> +        * when we offline and remove a memory block, this will re-trigger
> +        * us immediately - which is often nice because the removal of
> +        * the memory block (e.g., memmap) might have freed up memory
> +        * on other memory blocks we manage.
> +        */
>         virtio_mem_retry(vm);
>  }
>
> @@ -1282,7 +1310,8 @@ static int virtio_mem_mb_unplug_any_sb_offline(struct virtio_mem *vm,
>   * Unplug the desired number of plugged subblocks of an online memory block.
>   * Will skip subblock that are busy.
>   *
> - * Will modify the state of the memory block.
> + * Will modify the state of the memory block. Might temporarily drop the
> + * hotplug_mutex.
>   *
>   * Note: Can fail after some subblocks were successfully unplugged. Can
>   *       return 0 even if subblocks were busy and could not get unplugged.
> @@ -1338,9 +1367,19 @@ static int virtio_mem_mb_unplug_any_sb_online(struct virtio_mem *vm,
>         }
>
>         /*
> -        * TODO: Once all subblocks of a memory block were unplugged, we want
> -        * to offline the memory block and remove it.
> +        * Once all subblocks of a memory block were unplugged, offline and
> +        * remove it. This will usually not fail, as no memory is in use
> +        * anymore - however some other notifiers might NACK the request.
>          */
> +       if (virtio_mem_mb_test_sb_unplugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
> +               mutex_unlock(&vm->hotplug_mutex);
> +               rc = virtio_mem_mb_offline_and_remove(vm, mb_id);
> +               mutex_lock(&vm->hotplug_mutex);
> +               if (!rc)
> +                       virtio_mem_mb_set_state(vm, mb_id,
> +                                               VIRTIO_MEM_MB_STATE_UNUSED);
> +       }
> +
>         return 0;
>  }
>

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

> --

^ permalink raw reply	[flat|nested] 30+ messages in thread

end of thread, other threads:[~2020-04-15  7:43 UTC | newest]

Thread overview: 30+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-11 17:14 [PATCH v2 00/10] virtio-mem: paravirtualized memory David Hildenbrand
2020-03-11 17:14 ` [PATCH v2 01/10] virtio-mem: Paravirtualized memory hotplug David Hildenbrand
2020-04-15  5:59   ` Pankaj Gupta
2020-03-11 17:14 ` [PATCH v2 02/10] virtio-mem: Allow to specify an ACPI PXM as nid David Hildenbrand
2020-03-30 11:04   ` Pankaj Gupta
2020-03-11 17:14 ` [PATCH v2 03/10] virtio-mem: Paravirtualized memory hotunplug part 1 David Hildenbrand
2020-03-11 17:14 ` [PATCH v2 04/10] virtio-mem: Paravirtualized memory hotunplug part 2 David Hildenbrand
2020-03-11 17:14 ` [PATCH v2 05/10] mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE David Hildenbrand
2020-04-14 16:34   ` Michael S. Tsirkin
2020-04-15  0:32     ` Andrew Morton
2020-03-11 17:14 ` [PATCH v2 06/10] virtio-mem: Allow to offline partially unplugged memory blocks David Hildenbrand
2020-03-11 17:14 ` [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory() David Hildenbrand
2020-03-11 17:19   ` David Hildenbrand
2020-04-14 16:35     ` Michael S. Tsirkin
2020-04-15  0:30       ` Andrew Morton
2020-04-15  7:35   ` Pankaj Gupta
2020-03-11 17:14 ` [PATCH v2 08/10] virtio-mem: Offline and remove completely unplugged memory blocks David Hildenbrand
2020-04-15  7:42   ` Pankaj Gupta
2020-03-11 17:14 ` [PATCH v2 09/10] virtio-mem: Better retry handling David Hildenbrand
2020-03-11 17:14 ` [PATCH v2 10/10] MAINTAINERS: Add myself as virtio-mem maintainer David Hildenbrand
2020-03-27 16:58 ` [PATCH v2 00/10] virtio-mem: paravirtualized memory Pankaj Gupta
2020-03-27 17:03   ` David Hildenbrand
2020-03-27 17:07     ` David Hildenbrand
2020-03-29 15:41     ` Pankaj Gupta
2020-03-30  8:42       ` David Hildenbrand
2020-03-29 12:42 ` Michael S. Tsirkin
2020-03-30  8:16   ` David Hildenbrand
2020-04-14  9:15   ` David Hildenbrand
2020-04-14 16:28     ` Michael S. Tsirkin
2020-04-14 18:39       ` David Hildenbrand

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