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From: Robin Holt <holt@sgi.com>
To: Andrea Arcangeli <andrea@qumranet.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>,
	Christoph Lameter <clameter@sgi.com>,
	akpm@linux-foundation.org, Robin Holt <holt@sgi.com>,
	Avi Kivity <avi@qumranet.com>, Izik Eidus <izike@qumranet.com>,
	kvm-devel@lists.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	general@lists.openfabrics.org,
	Steve Wise <swise@opengridcomputing.com>,
	Roland Dreier <rdreier@cisco.com>,
	Kanoj Sarcar <kanojsarcar@yahoo.com>,
	steiner@sgi.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, daniel.blueman@quadrics.com
Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges
Date: Tue, 19 Feb 2008 21:00:31 -0600	[thread overview]
Message-ID: <20080220030031.GC11364@sgi.com> (raw)
In-Reply-To: <20080220010038.GQ7128@v2.random>

On Wed, Feb 20, 2008 at 02:00:38AM +0100, Andrea Arcangeli wrote:
> On Wed, Feb 20, 2008 at 10:08:49AM +1100, Nick Piggin wrote:
> > You can't sleep inside rcu_read_lock()!
> > 
> > I must say that for a patch that is up to v8 or whatever and is
> > posted twice a week to such a big cc list, it is kind of slack to
> > not even test it and expect other people to review it.
> 
> Well, xpmem requirements are complex. As as side effect of the
> simplicity of my approach, my patch is 100% safe since #v1. Now it
> also works for GRU and it cluster invalidates.
> 
> > Also, what we are going to need here are not skeleton drivers
> > that just do all the *easy* bits (of registering their callbacks),
> > but actual fully working examples that do everything that any
> > real driver will need to do. If not for the sanity of the driver
> 
> I've a fully working scenario for my patch, infact I didn't post the
> mmu notifier patch until I got KVM to swap 100% reliably to be sure I
> would post something that works well. mmu notifiers are already used
> in KVM for:
> 
> 1) 100% reliable and efficient swapping of guest physical memory
> 2) copy-on-writes of writeprotect faults after ksm page sharing of guest
>    physical memory
> 3) ballooning using madvise to give the guest memory back to the host
> 
> My implementation is the most handy because it requires zero changes
> to the ksm code too (no explicit mmu notifier calls after
> ptep_clear_flush) and it's also 100% safe (no mess with schedules over
> rcu_read_lock), no "atomic" parameters, and it doesn't open a window
> where sptes have a view on older pages and linux pte has view on newer
> pages (this can happen with remap_file_pages with my KVM swapping
> patch to use V8 Christoph's patch).
> 
> > Also, how to you resolve the case where you are not allowed to sleep?
> > I would have thought either you have to handle it, in which case nobody
> > needs to sleep; or you can't handle it, in which case the code is
> > broken.
> 
> I also asked exactly this, glad you reasked this too.

Currently, we BUG_ON having a PFN in our tables and not being able
to sleep.  These are mappings which MPT has never supported in the past
and XPMEM was already not allowing page faults for VMAs which are not
anonymous so it should never happen.  If the file-backed operations can
ever get changed to allow for sleeping and a customer has a need for it,
we would need to change XPMEM to allow those types of faults to succeed.

Thanks,
Robin

  reply	other threads:[~2008-02-20  3:00 UTC|newest]

Thread overview: 129+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-15  6:48 [patch 0/6] MMU Notifiers V7 Christoph Lameter
2008-02-15  6:49 ` [patch 1/6] mmu_notifier: Core code Christoph Lameter
2008-02-16  3:37   ` Andrew Morton
2008-02-16  8:45     ` Avi Kivity
2008-02-16  8:56       ` Andrew Morton
2008-02-16  9:21         ` Avi Kivity
2008-02-16 10:41     ` Brice Goglin
2008-02-16 10:58       ` Andrew Morton
2008-02-16 19:31         ` Christoph Lameter
2008-02-16 19:21     ` Christoph Lameter
2008-02-17  3:01       ` Andrea Arcangeli
2008-02-17 12:24         ` Robin Holt
2008-02-17  5:04     ` Doug Maxey
2008-02-18 22:33   ` Roland Dreier
2008-02-15  6:49 ` [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges Christoph Lameter
2008-02-16  3:37   ` Andrew Morton
2008-02-16 19:26     ` Christoph Lameter
2008-02-19  8:54   ` Nick Piggin
2008-02-19 13:34     ` Andrea Arcangeli
2008-02-27 22:23       ` Christoph Lameter
2008-02-27 23:57         ` Andrea Arcangeli
2008-02-19 23:08   ` Nick Piggin
2008-02-20  1:00     ` Andrea Arcangeli
2008-02-20  3:00       ` Robin Holt [this message]
2008-02-20  3:11         ` Nick Piggin
2008-02-20  3:19           ` Robin Holt
2008-02-27 22:39       ` Christoph Lameter
2008-02-28  0:38         ` Andrea Arcangeli
2008-02-27 22:35     ` Christoph Lameter
2008-02-27 22:42       ` Jack Steiner
2008-02-28  0:10       ` Christoph Lameter
2008-02-28  0:11       ` Andrea Arcangeli
2008-02-28  0:14         ` Christoph Lameter
2008-02-28  0:52           ` Andrea Arcangeli
2008-02-28  1:03             ` Christoph Lameter
2008-02-28  1:10               ` Andrea Arcangeli
2008-02-28 18:43                 ` Christoph Lameter
2008-02-29  0:55                   ` Andrea Arcangeli
2008-02-29  0:59                     ` Christoph Lameter
2008-02-29 13:13                       ` Andrea Arcangeli
2008-02-29 19:55                         ` Christoph Lameter
2008-02-29 20:17                           ` Andrea Arcangeli
2008-02-29 21:03                             ` Christoph Lameter
2008-02-29 21:23                               ` Andrea Arcangeli
2008-02-29 21:29                                 ` Christoph Lameter
2008-02-29 21:34                                 ` Christoph Lameter
2008-02-29 21:48                                   ` Andrea Arcangeli
2008-02-29 22:12                                     ` Christoph Lameter
2008-02-29 22:41                                       ` Andrea Arcangeli
2008-02-28 10:53             ` Robin Holt
2008-03-03  5:11       ` Nick Piggin
2008-03-03 19:28         ` Christoph Lameter
2008-03-03 19:50           ` Nick Piggin
2008-03-04 18:58             ` Christoph Lameter
2008-03-05  0:52               ` Nick Piggin
2008-02-15  6:49 ` [patch 3/6] mmu_notifier: invalidate_page callbacks Christoph Lameter
2008-02-16  3:37   ` Andrew Morton
2008-02-16 11:07     ` Andrea Arcangeli
2008-02-16 19:22     ` Christoph Lameter
2008-02-16 19:54       ` Avi Kivity
2008-02-19  8:46       ` Nick Piggin
2008-02-19 13:30         ` Andrea Arcangeli
2008-02-18  1:51     ` Nick Piggin
2008-02-15  6:49 ` [patch 4/6] mmu_notifier: Skeleton driver for a simple mmu_notifier Christoph Lameter
2008-02-15  6:49 ` [patch 5/6] mmu_notifier: Support for drivers with revers maps (f.e. for XPmem) Christoph Lameter
2008-02-16  3:37   ` Andrew Morton
2008-02-16 19:28     ` Christoph Lameter
2008-02-19 23:55   ` Nick Piggin
2008-02-20  3:12     ` Robin Holt
2008-02-20  3:51       ` Nick Piggin
2008-02-20  9:00         ` Robin Holt
2008-02-20  9:05           ` Robin Holt
2008-02-21  4:20           ` Nick Piggin
2008-02-21 10:58             ` Robin Holt
2008-02-26  6:11               ` Nick Piggin
2008-02-26  7:21                 ` [ofa-general] " Gleb Natapov
2008-02-26  8:52                   ` Nick Piggin
2008-02-26  9:38                     ` Gleb Natapov
2008-02-26  9:52                       ` KOSAKI Motohiro
2008-02-26 12:28                     ` Robin Holt
2008-02-26 12:29                 ` Robin Holt
2008-02-27 22:43     ` Christoph Lameter
2008-02-28  0:42       ` Andrea Arcangeli
2008-02-28  1:01         ` Christoph Lameter
2008-02-15  6:49 ` [patch 6/6] mmu_rmap_notifier: Skeleton for complex driver that uses its own rmaps Christoph Lameter
2008-02-16 10:48 ` [PATCH] KVM swapping with MMU Notifiers V7 Andrea Arcangeli
2008-02-16 11:08   ` Andrew Morton
2008-02-18 12:17     ` Andrea Arcangeli
2008-02-16 11:51   ` Robin Holt
2008-02-18 12:35     ` Andrea Arcangeli
  -- strict thread matches above, loose matches on Subject: below --
2008-02-08 22:06 [patch 0/6] MMU Notifiers V6 Christoph Lameter
2008-02-08 22:06 ` [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges Christoph Lameter
2008-01-30  2:29 [patch 0/6] [RFC] MMU Notifiers V3 Christoph Lameter
2008-01-30  2:29 ` [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges Christoph Lameter
2008-01-28 20:28 [patch 0/6] [RFC] MMU Notifiers V2 Christoph Lameter
2008-01-28 20:28 ` [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges Christoph Lameter
2008-01-29 16:20   ` Andrea Arcangeli
2008-01-29 18:28     ` Andrea Arcangeli
2008-01-29 20:30       ` Christoph Lameter
2008-01-29 21:36         ` Andrea Arcangeli
2008-01-29 21:53           ` Christoph Lameter
2008-01-29 22:35             ` Andrea Arcangeli
2008-01-29 22:55               ` Christoph Lameter
2008-01-29 23:43                 ` Andrea Arcangeli
2008-01-30  0:34                   ` Christoph Lameter
2008-01-29 19:55     ` Christoph Lameter
2008-01-29 21:17       ` Andrea Arcangeli
2008-01-29 21:35         ` Christoph Lameter
2008-01-29 22:02           ` Andrea Arcangeli
2008-01-29 22:39             ` Christoph Lameter
2008-01-30  0:00               ` Andrea Arcangeli
2008-01-30  0:05                 ` Andrea Arcangeli
2008-01-30  0:22                   ` Christoph Lameter
2008-01-30  0:59                     ` Andrea Arcangeli
2008-01-30  8:26                       ` Peter Zijlstra
2008-01-30  0:20                 ` Christoph Lameter
2008-01-30  0:28                   ` Jack Steiner
2008-01-30  0:35                     ` Christoph Lameter
2008-01-30 13:37                     ` Andrea Arcangeli
2008-01-30 14:43                       ` Jack Steiner
2008-01-30 19:41                         ` Christoph Lameter
2008-01-30 20:29                           ` Jack Steiner
2008-01-30 20:55                             ` Christoph Lameter
2008-01-30 16:11                 ` Robin Holt
2008-01-30 17:04                   ` Andrea Arcangeli
2008-01-30 17:30                     ` Robin Holt
2008-01-30 18:25                       ` Andrea Arcangeli
2008-01-30 19:50                         ` Christoph Lameter
2008-01-30 22:18                           ` Robin Holt
2008-01-30 23:52                           ` Andrea Arcangeli
2008-01-31  0:01                             ` Christoph Lameter
2008-01-30 19:35                   ` Christoph Lameter

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