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

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Message-ID: <alpine.LFD.2.00.1005030928350.5478@i5.linux-foundation.org>
Date:	Mon, 3 May 2010 09:34:14 -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, Rik van Riel wrote:
> 
> migrate.c requires rmap to be able to find all ptes mapping a page at
> all times, otherwise the migration entry can be instantiated, but it
> can't be removed if the second rmap_walk fails to find the page.

Please correct me if I'm wrong, but this patch looks like pure and utter 
garbage.

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?

		Linus
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