linux-kernel - Re: [PATCH 2/2] mm: fix race between shift_arg_pages and rmap

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Message-ID: <alpine.LFD.2.00.1005030935100.5478@i5.linux-foundation.org>
Date:	Mon, 3 May 2010 09:37:17 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
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 2/2] mm: fix race between shift_arg_pages and rmap_walk



On Mon, 3 May 2010, Linus Torvalds wrote:
> 
> It looks like it makes execve() do a totally insane "create and then 
> immediately destroy temporary vma and anon_vma chain" for a case that is 
> unlikely to ever matter. 
> 
> In fact, for a case that isn't even normally _enabled_, namely migration.
> 
> Why would we want to slow down execve() for that?

Alternate suggestions:

 - clean up the patch so that it is explicitly abouy migration, and 
   doesn't even get enabled for anything else.

 - make the migration code take the VM lock for writing (why doesn't it 
   already?) and never race with things like this in the first place.

 - explain why the new code isn't any slower.

Hmm?

		Linus
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