linux-kernel - Re: [PATCH 04 of 12] Moves all mmu notifier methods outside the PT lock (first and not last

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Date:	Wed, 23 Apr 2008 18:15:45 +0200
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Robin Holt <holt@....com>
Cc:	Christoph Lameter <clameter@....com>,
	Nick Piggin <npiggin@...e.de>, Jack Steiner <steiner@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	kvm-devel@...ts.sourceforge.net,
	Kanoj Sarcar <kanojsarcar@...oo.com>,
	Roland Dreier <rdreier@...co.com>,
	Steve Wise <swise@...ngridcomputing.com>,
	linux-kernel@...r.kernel.org, Avi Kivity <avi@...ranet.com>,
	linux-mm@...ck.org, general@...ts.openfabrics.org,
	Hugh Dickins <hugh@...itas.com>, akpm@...ux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 04 of 12] Moves all mmu notifier methods outside the PT
	lock (first and not last

On Wed, Apr 23, 2008 at 10:45:36AM -0500, Robin Holt wrote:
> XPMEM has passed all regression tests using your version 12 notifiers.

That's great news, thanks! I'd greatly appreciate if you could test
#v13 too as I posted it. It already passed GRU and KVM regressions
tests and it should work fine for XPMEM too. You can ignore the purely
cosmetical error I managed to introduce in mm_lock_cmp (I implemented
a BUG_ON that would have trigger if that wasn't a purely cosmetical
issue, and it clearly doesn't trigger so you can be sure it's
only cosmetical ;).

Once I get confirmation that everyone is ok with #v13 I'll push a #v14
before Saturday with that cosmetical error cleaned up and
mmu_notifier_unregister moved at the end (XPMEM will have unregister
don't worry). I expect the 1/13 of #v14 to go in -mm and then 2.6.26.

> I have a bug in xpmem which shows up on our 8x oversubscription tests,
> but that is clearly my bug to figure out.  Unfortunately it only shows

This is what I meant.

As opposed we don't have any known bug left in this area, infact we
need mmu_notifiers to _fix_ issues I identified that can't be fixed
efficiently without mmu notifiers, and we need the mmu notifier to go
productive ASAP.

> up on a 128 processor machine so I have 1024 stack traces to sort
> through each time it fails.  Does take a bit of time and a lot of
> concentration.

Sure, hope you find it soon!

> SGI is under an equally strict timeline.  We really needed the sleeping
> version into 2.6.26.  We may still be able to get this accepted by
> vendor distros if we make 2.6.27.

I don't think vendor distro are less likely to take the patches 2-12
if 1/N (aka mmu-notifier-core) is merged in 2.6.26 especially at the
light of kabi.
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