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

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Message-ID: <4BEB630B.8070805@redhat.com>
Date:	Wed, 12 May 2010 22:25:15 -0400
From:	Rik van Riel <riel@...hat.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux-MM <linux-mm@...ck.org>,
	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 08:38 PM, KAMEZAWA Hiroyuki wrote:
> On Wed, 12 May 2010 13:39:58 -0400
> Rik van Riel<riel@...hat.com>  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.
>>
>> Signed-off-by: Rik van Riel<riel@...hat.com>
>
>
> Acked-by: KAMEZAWA Hiroyuki<kamezawa.hiroyu@...fujitsu.com>
>
> I welcome this. Thank you!
>
> Reading 4/5, I felt I'm grad if you add a Documentation or very-precise-comment
> about the new anon_vma rules and the _meaning_ of anon_vma_root_lock.
> I cannot fully convice myself that I understand them all.

Please send me a list of all the questions that come up
when you read the patches, and I'll prepare a patch 6/5
with just documentation :)

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