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

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Message-Id: <20100513093828.1cd022db.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 13 May 2010 09:38:28 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Rik van Riel <riel@...hat.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 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.



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