linux-kernel - Re: [PATCH 1/4] Simplify and comment on anon_vma re-use for anon_vma

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Date:	Tue, 13 Apr 2010 13:04:58 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Borislav Petkov <bp@...en8.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	sgunderson@...foot.com
Subject: Re: [PATCH 1/4] Simplify and comment on anon_vma re-use for 
	anon_vma_prepare()

On Tue, Apr 13, 2010 at 5:22 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> From: Linus Torvalds <torvalds@...ux-foundation.org>
> Date: Sat, 10 Apr 2010 10:36:19 -0700
> Subject: [PATCH 1/4] Simplify and comment on anon_vma re-use for anon_vma_prepare()
>
> This changes the anon_vma reuse case to require that we only reuse
> simple anon_vma's - ie the case when the vma only has a single anon_vma
> associated with it.
>
> This means that a reuse of an anon_vma from an adjacent vma will always
> guarantee that both vma's are associated not onyl with the same
> anon_vma, they will also have the same anon_vma chain (of just a single
> entry in this case).
>
> And since anon_vma re-use was the only case where the same anon_vma
> might be associated with different chains of anon_vma's, we now have the
> case that every vma that shares the same vma will always also have the

same vma => same anon_vma.

> same chain.  That makes it much easier to think about merging vma's that
> share the same anon_vma's: you can always just drop the other anon_vma
> chain in anon_vma_merge() since you know that they are always identical.
>
> This also splits up the function to validate the anon_vma re-use, and
> adds a lot of commentary about the possible races.
>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>



-- 
Kind regards,
Minchan Kim
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