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

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Message-ID: <50D3947F.2060503@oracle.com>
Date:	Thu, 20 Dec 2012 17:43:11 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Mel Gorman <mgorman@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Petr Holasek <pholasek@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] ksm: make rmap walks more scalable

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

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