linux-kernel - Re: [PATCH 1/2] mm: Take all anon_vma locks in anon_vma

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Message-ID: <4BDEFF9E.6080508@redhat.com>
Date:	Mon, 03 May 2010 12:53:50 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	akpm@...ux-foundation.org, Mel Gorman <mel@....ul.ie>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 1/2] mm: Take all anon_vma locks in anon_vma_lock

On 05/03/2010 12:41 PM, Linus Torvalds wrote:
> On Mon, 3 May 2010, Rik van Riel wrote:
>>
>> Both the page migration code and the transparent hugepage patches expect
>> 100% reliable rmap lookups and use page_lock_anon_vma(page) to prevent
>> races with mmap, munmap, expand_stack, etc.
>
> Pretty much same comments as for the other one. Why are we pandering to
> the case that is/should be unusual?

In this case, because the fix from the migration side is
difficult and fragile, while fixing things from the mmap
side is straightforward.

I believe the overhead of patch 1/2 should be minimal
as well, because the locks we take are the _depth_ of
the process tree (truncated every exec), not the width.


As for patch 2/2, Mel has an alternative approach for that:

http://lkml.org/lkml/2010/4/30/198

Does Mel's patch seem more reasonable to you?

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