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From: Anthony Yznaga <anthony.yznaga@oracle.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: willy@infradead.org, corbet@lwn.net, tglx@linutronix.de,
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	kexec@lists.infradead.org
Subject: [RFC 41/43] XArray: add xas_export_node() and xas_import_node()
Date: Wed,  6 May 2020 17:42:07 -0700	[thread overview]
Message-ID: <1588812129-8596-42-git-send-email-anthony.yznaga@oracle.com> (raw)
In-Reply-To: <1588812129-8596-1-git-send-email-anthony.yznaga@oracle.com>

Contention on the xarray lock when multiple threads are adding to the
same xarray can be mitigated by providing a way to add entries in
bulk.

Allow a caller to allocate and populate an xarray node outside of
the target xarray and then only take the xarray lock long enough to
import the node into it.

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 Documentation/core-api/xarray.rst |   8 +++
 include/linux/xarray.h            |   2 +
 lib/test_xarray.c                 |  45 +++++++++++++++++
 lib/xarray.c                      | 100 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 155 insertions(+)

diff --git a/Documentation/core-api/xarray.rst b/Documentation/core-api/xarray.rst
index 640934b6f7b4..659e10df8901 100644
--- a/Documentation/core-api/xarray.rst
+++ b/Documentation/core-api/xarray.rst
@@ -444,6 +444,14 @@ called each time the XArray updates a node.  This is used by the page
 cache workingset code to maintain its list of nodes which contain only
 shadow entries.
 
+xas_export_node() is used to remove and return a node from an XArray
+while xas_import_node() is used to add a node to an XArray.  Together
+these can be used, for example, to reduce lock contention when multiple
+threads are updating an XArray by allowing a caller to allocate and
+populate a node outside of the target XArray in a local XArray, export
+the node, and then take the target XArray lock just long enough to import
+the node.
+
 Multi-Index Entries
 -------------------
 
diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 14c893433139..73bd8ccc4424 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -1504,6 +1504,8 @@ bool xas_nomem(struct xa_state *, gfp_t);
 void xas_pause(struct xa_state *);
 
 void xas_create_range(struct xa_state *);
+struct xa_node *xas_export_node(struct xa_state *xas);
+void xas_import_node(struct xa_state *xas, struct xa_node *node);
 
 /**
  * xas_reload() - Refetch an entry from the xarray.
diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index d4f97925dbd8..5cfaa1720cc1 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -1682,6 +1682,50 @@ static noinline void check_destroy(struct xarray *xa)
 #endif
 }
 
+static noinline void check_export_import_1(struct xarray *xa,
+		unsigned long index, unsigned int order)
+{
+	int xa_shift = order + XA_CHUNK_SHIFT - (order % XA_CHUNK_SHIFT);
+	XA_STATE(xas, xa, index);
+	struct xa_node *node;
+	unsigned long i;
+
+	xa_store_many_order(xa, index, xa_shift);
+
+	xas_lock(&xas);
+	xas_set_order(&xas, index, xa_shift);
+	node = xas_export_node(&xas);
+	xas_unlock(&xas);
+
+	XA_BUG_ON(xa, !xa_empty(xa));
+
+	do {
+		xas_lock(&xas);
+		xas_set_order(&xas, index, xa_shift);
+		xas_import_node(&xas, node);
+		xas_unlock(&xas);
+	} while (xas_nomem(&xas, GFP_KERNEL));
+
+	for (i = index; i < index + (1UL << xa_shift); i++)
+		xa_erase_index(xa, i);
+
+	XA_BUG_ON(xa, !xa_empty(xa));
+}
+
+static noinline void check_export_import(struct xarray *xa)
+{
+	unsigned int order;
+	unsigned int max_order = IS_ENABLED(CONFIG_XARRAY_MULTI) ? 12 : 1;
+
+	for (order = 0; order < max_order; order += XA_CHUNK_SHIFT) {
+		int xa_shift = order + XA_CHUNK_SHIFT;
+		unsigned long j;
+
+		for (j = 0; j < XA_CHUNK_SIZE; j++)
+			check_export_import_1(xa, j << xa_shift, order);
+	}
+}
+
 static DEFINE_XARRAY(array);
 
 static int xarray_checks(void)
@@ -1712,6 +1756,7 @@ static int xarray_checks(void)
 	check_workingset(&array, 0);
 	check_workingset(&array, 64);
 	check_workingset(&array, 4096);
+	check_export_import(&array);
 
 	printk("XArray: %u of %u tests passed\n", tests_passed, tests_run);
 	return (tests_run == tests_passed) ? 0 : -EINVAL;
diff --git a/lib/xarray.c b/lib/xarray.c
index e9e641d3c0c3..478925780e87 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -507,6 +507,30 @@ static void xas_delete_node(struct xa_state *xas)
 		xas_shrink(xas);
 }
 
+static void xas_unlink_node(struct xa_state *xas)
+{
+	struct xa_node *node = xas->xa_node;
+	struct xa_node *parent;
+
+	parent = xa_parent_locked(xas->xa, node);
+	xas->xa_node = parent;
+	xas->xa_offset = node->offset;
+
+	if (!parent) {
+		xas->xa->xa_head = NULL;
+		xas->xa_node = XAS_BOUNDS;
+		return;
+	}
+
+	parent->slots[xas->xa_offset] = NULL;
+	parent->count--;
+	XA_NODE_BUG_ON(parent, parent->count > XA_CHUNK_SIZE);
+
+	xas_update(xas, parent);
+
+	xas_delete_node(xas);
+}
+
 /**
  * xas_free_nodes() - Free this node and all nodes that it references
  * @xas: Array operation state.
@@ -1540,6 +1564,82 @@ static void xas_set_range(struct xa_state *xas, unsigned long first,
 }
 
 /**
+ * xas_export_node() - remove and return a node from an XArray
+ * @xas: XArray operation state
+ *
+ * The range covered by @xas must be aligned to and cover a single node
+ * at any level of the tree.
+ *
+ * Return: On success, returns the removed node.  If the range is invalid,
+ * returns %NULL and sets -EINVAL in @xas.  Otherwise returns %NULL if the
+ * node does not exist.
+ */
+struct xa_node *xas_export_node(struct xa_state *xas)
+{
+	struct xa_node *node;
+
+	if (!xas->xa_shift || xas->xa_sibs) {
+		xas_set_err(xas, -EINVAL);
+		return NULL;
+	}
+
+	xas->xa_shift -= XA_CHUNK_SHIFT;
+
+	if (!xas_find(xas, xas->xa_index))
+		return NULL;
+	node = xas->xa_node;
+	xas_unlink_node(xas);
+	node->parent = NULL;
+
+	return node;
+}
+
+/**
+ * xas_import_node() - add a node to an XArray
+ * @xas: XArray operation state
+ * @node: The node to add
+ *
+ * The range covered by @xas must be aligned to and cover a single node
+ * at any level of the tree.  No nodes should already exist within the
+ * range.
+ * Sets an error in @xas if the range is invalid or xas_create() fails
+ */
+void xas_import_node(struct xa_state *xas, struct xa_node *node)
+{
+	struct xa_node *parent = NULL;
+	void __rcu **slot = &xas->xa->xa_head;
+	int count = 0;
+
+	if (!xas->xa_shift || xas->xa_sibs) {
+		xas_set_err(xas, -EINVAL);
+		return;
+	}
+
+	if (xas->xa_index || xa_head_locked(xas->xa)) {
+		xas_set_order(xas, xas->xa_index, node->shift + XA_CHUNK_SHIFT);
+		xas_create(xas, true);
+
+		if (xas_invalid(xas))
+			return;
+
+		parent = xas->xa_node;
+	}
+
+	if (parent) {
+		slot = &parent->slots[xas->xa_offset];
+		node->offset = xas->xa_offset;
+		count++;
+	}
+
+	RCU_INIT_POINTER(node->parent, parent);
+	node->array = xas->xa;
+
+	rcu_assign_pointer(*slot, xa_mk_node(node));
+
+	update_node(xas, parent, count, 0);
+}
+
+/**
  * xa_store_range() - Store this entry at a range of indices in the XArray.
  * @xa: XArray.
  * @first: First index to affect.
-- 
2.13.3


  parent reply	other threads:[~2020-05-07  0:48 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-07  0:41 [RFC 00/43] PKRAM: Preserved-over-Kexec RAM Anthony Yznaga
2020-05-07  0:41 ` [RFC 01/43] mm: add PKRAM API stubs and Kconfig Anthony Yznaga
2020-05-07  0:41 ` [RFC 02/43] mm: PKRAM: implement node load and save functions Anthony Yznaga
2020-05-07  0:41 ` [RFC 03/43] mm: PKRAM: implement object " Anthony Yznaga
2020-05-07  0:41 ` [RFC 04/43] mm: PKRAM: implement page stream operations Anthony Yznaga
2020-05-07  0:41 ` [RFC 05/43] mm: PKRAM: support preserving transparent hugepages Anthony Yznaga
2020-05-07  0:41 ` [RFC 06/43] mm: PKRAM: implement byte stream operations Anthony Yznaga
2020-05-07  0:41 ` [RFC 07/43] mm: PKRAM: link nodes by pfn before reboot Anthony Yznaga
2020-05-07  0:41 ` [RFC 08/43] mm: PKRAM: introduce super block Anthony Yznaga
2020-05-07  0:41 ` [RFC 09/43] PKRAM: build a physical mapping pagetable of pages to be preserved Anthony Yznaga
2020-05-07  0:41 ` [RFC 10/43] PKRAM: add code for walking the preserved pages pagetable Anthony Yznaga
2020-05-07  0:41 ` [RFC 11/43] PKRAM: pass the preserved pages pagetable to the next kernel Anthony Yznaga
2020-05-07  0:41 ` [RFC 12/43] mm: PKRAM: reserve preserved memory at boot Anthony Yznaga
2020-05-07  0:41 ` [RFC 13/43] mm: PKRAM: free preserved pages pagetable Anthony Yznaga
2020-05-07  0:41 ` [RFC 14/43] mm: memblock: PKRAM: prevent memblock resize from clobbering preserved pages Anthony Yznaga
2020-05-11 13:57   ` Mike Rapoport
2020-05-11 23:29     ` Anthony Yznaga
2020-05-07  0:41 ` [RFC 15/43] PKRAM: provide a way to ban pages from use by PKRAM Anthony Yznaga
2020-05-07  0:41 ` [RFC 16/43] kexec: PKRAM: prevent kexec clobbering preserved pages in some cases Anthony Yznaga
2020-05-07  0:41 ` [RFC 17/43] PKRAM: provide a way to check if a memory range has preserved pages Anthony Yznaga
2020-05-07  0:41 ` [RFC 18/43] kexec: PKRAM: avoid clobbering already " Anthony Yznaga
2020-05-07  0:41 ` [RFC 19/43] mm: PKRAM: allow preserved memory to be freed from userspace Anthony Yznaga
2020-05-07  0:41 ` [RFC 20/43] PKRAM: disable feature when running the kdump kernel Anthony Yznaga
2020-05-07  0:41 ` [RFC 21/43] x86/KASLR: PKRAM: support physical kaslr Anthony Yznaga
2020-05-07 17:51   ` Kees Cook
2020-05-07 18:41     ` Anthony Yznaga
2020-05-07  0:41 ` [RFC 22/43] mm: shmem: introduce shmem_insert_page Anthony Yznaga
2020-05-07  0:41 ` [RFC 23/43] mm: shmem: enable saving to PKRAM Anthony Yznaga
2020-05-07  0:41 ` [RFC 24/43] mm: shmem: prevent swapping of PKRAM-enabled tmpfs pages Anthony Yznaga
2020-05-07  0:41 ` [RFC 25/43] mm: shmem: specify the mm to use when inserting pages Anthony Yznaga
2020-05-07  0:41 ` [RFC 26/43] mm: shmem: when inserting, handle pages already charged to a memcg Anthony Yznaga
2020-05-07  0:41 ` [RFC 27/43] x86/mm/numa: add numa_isolate_memblocks() Anthony Yznaga
2020-05-07  0:41 ` [RFC 28/43] PKRAM: ensure memblocks with preserved pages init'd for numa Anthony Yznaga
2020-05-07  0:41 ` [RFC 29/43] memblock: PKRAM: mark memblocks that contain preserved pages Anthony Yznaga
2020-05-07  0:41 ` [RFC 30/43] memblock: add for_each_reserved_mem_range() Anthony Yznaga
2020-05-07  0:41 ` [RFC 31/43] memblock, mm: defer initialization of preserved pages Anthony Yznaga
2020-05-07  0:41 ` [RFC 32/43] shmem: PKRAM: preserve shmem files a chunk at a time Anthony Yznaga
2020-05-07  0:41 ` [RFC 33/43] PKRAM: atomically add and remove link pages Anthony Yznaga
2020-05-07  0:42 ` [RFC 34/43] shmem: PKRAM: multithread preserving and restoring shmem pages Anthony Yznaga
2020-05-07 16:30   ` Randy Dunlap
2020-05-07 17:59     ` Anthony Yznaga
2020-05-07  0:42 ` [RFC 35/43] shmem: introduce shmem_insert_pages() Anthony Yznaga
2020-05-07  0:42 ` [RFC 36/43] PKRAM: add support for loading pages in bulk Anthony Yznaga
2020-05-07  0:42 ` [RFC 37/43] shmem: PKRAM: enable bulk loading of preserved pages into shmem Anthony Yznaga
2020-05-07  0:42 ` [RFC 38/43] mm: implement splicing a list of pages to the LRU Anthony Yznaga
2020-05-07  0:42 ` [RFC 39/43] shmem: optimize adding pages to the LRU in shmem_insert_pages() Anthony Yznaga
2020-05-07  0:42 ` [RFC 40/43] shmem: initial support for adding multiple pages to pagecache Anthony Yznaga
2020-05-07  0:42 ` Anthony Yznaga [this message]
2020-05-07  0:42 ` [RFC 42/43] shmem: reduce time holding xa_lock when inserting pages Anthony Yznaga
2020-05-07  0:42 ` [RFC 43/43] PKRAM: improve index alignment of pkram_link entries Anthony Yznaga

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