linux-kernel - Re: [PATCH 2/2] mm,migration: Fix race between shift_arg_pages and rmap_walk by guaranteeing rmap_walk finds PTEs created within the temporary stack

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Message-ID: <alpine.LFD.2.00.1005091827500.3711@i5.linux-foundation.org>
Date:	Sun, 9 May 2010 18:30:51 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] mm,migration: Fix race between shift_arg_pages and
 rmap_walk by guaranteeing rmap_walk finds PTEs created within the temporary
 stack

On Mon, 10 May 2010, KAMEZAWA Hiroyuki wrote:
> 
> But, move_page_tables()'s failure is not a big problem.

Well, yes and no.

It's not a problem because it fails, but because it does the allocation. 
Which means that we can't protect the thing with the (natural) anon_vma 
locking.

> Considering cost, as Mel shows, "don't migrate apges in exec's stack" seems
> reasonable. But, I still doubt this check.

Well, I actually always liked Mel's patch, the one he calls "magic". I 
think it's _less_ magic than the crazy "let's create another vma and 
anon_vma chain just because migration has it's thumb up its ass".

So I never disliked that patch. I'm perfectly happy with a "don't migrate 
these pages at all, because they are in a half-way state in the middle of 
execve stack magic".

		Linus
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