linux-kernel - Re: [PATCH] ksm: make rmap walks more scalable

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Date:	Fri, 21 Dec 2012 01:36:49 +0100
From:	Petr Holasek <pholasek@...hat.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] ksm: make rmap walks more scalable

On Thu, 20 Dec 2012, Sasha Levin wrote:
> On 12/20/2012 05:37 PM, Hugh Dickins wrote:
> > On Thu, 20 Dec 2012, Sasha Levin wrote:
> >> On 12/19/2012 08:44 PM, Hugh Dickins wrote:
> >>> The rmap walks in ksm.c are like those in rmap.c:
> >>> they can safely be done with anon_vma_lock_read().
> >>>
> >>> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> >>> ---
> >>
> >> Hi Hugh,
> >>
> >> This patch didn't fix the ksm oopses I'm seeing.
> > 
> > I wouldn't expect it to (and should certainly have mentioned oopses
> > in the commit message if I'd intended): this patch was merely an
> > optimization/clarification of a commit gone in for 3.8-rc1.
> > 
> > Understandable misunderstanding: you took my Cc too seriously,
> > I just thought I'd better keep Petr in the loop on current changes
> > to ksm.c, and foolishly kept you in too ;)
> > 
> > Your oopses are on linux-next, which as of 20121220 still had Petr's
> > nice but buggy NUMA KSM patch in: it should go away when Stephen gets
> > a fresh mm update from Andrew, then reappear once his v6 goes into mm.
> > 
> > To stop these oopses in get_mergeable_page (inlined in
> > unstable_tree_search_insert) you need the patch I showed on
> > Tuesday, which I hope he'll merge in for his v6.  That doesn't fix
> > all of the problems, but hopefully all that you'll encounter before
> > I've devised a fix for the separate stale stable_nodes issue.
> 
> My bad! I thought that this is the finalized version of the patch from
> Tuesday and was surprised when the oops was still there :)
> 
> fwiw I'll use this to report that I'm not seeing any unexpected behaviour
> with this patch applied.
> 
> 
> Thanks,
> Sasha
> 

Hugh, big thanks for your Tuesday fix, I am not able to reproduce reported
oops any more. I will continue with testing overnight and submit v6 version
tomorrow if there won't be any problem.

Should I also add [PATCH] ksm: make rmap walks more scalable into v6 or
can I rely on it?

thanks,
Petr H
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