linux-kernel - Re: [PATCH 3/5] track the root (oldest) anon

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Message-ID: <4BEB1732.1010503@redhat.com>
Date:	Wed, 12 May 2010 17:01:38 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mel@....ul.ie>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux-MM <linux-mm@...ck.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 3/5] track the root (oldest) anon_vma

On 05/12/2010 04:59 PM, Mel Gorman wrote:
> On Wed, May 12, 2010 at 01:39:58PM -0400, Rik van Riel wrote:
>> Subject: track the root (oldest) anon_vma
>>
>> Track the root (oldest) anon_vma in each anon_vma tree.   Because we only
>> take the lock on the root anon_vma, we cannot use the lock on higher-up
>> anon_vmas to lock anything.  This makes it impossible to do an indirect
>> lookup of the root anon_vma, since the data structures could go away from
>> under us.
>>
>> However, a direct pointer is safe because the root anon_vma is always the
>> last one that gets freed on munmap or exit, by virtue of the same_vma list
>> order and unlink_anon_vmas walking the list forward.
>>
>
> Shouldn't this be "usually the last one that gets freed" because of the
> ref-counting by KSM aspect? Minor nit anyway.

It needs to be the last one that gets freed.  Patch 5/5 makes
sure that it is when KSM refcounting is involved.

>> Signed-off-by: Rik van Riel<riel@...hat.com>
>
> Otherwise
>
> Acked-by: Mel Gorman<mel@....ul.ie>

Thank you for reviewing these patches.

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