linux-kernel - Re: [PATCH 2/2] mm,migration: Avoid race between shift_arg_pages() and rmap_walk() during migration by not migrating temporary stacks

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Message-ID: <alpine.DEB.2.00.1005110857350.1500@router.home>
Date:	Tue, 11 May 2010 08:59:12 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Mel Gorman <mel@....ul.ie>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/2] mm,migration: Avoid race between shift_arg_pages()
 and rmap_walk() during migration by not migrating temporary stacks

On Mon, 10 May 2010, Mel Gorman wrote:

> > A simple way to disallow migration of pages is to increment the refcount
> > of a page.
> I guess it could be done by walking the page-tables in advance of the move
> and elevating the page count of any pages faulted and then finding those
> pages afterwards.  The fail path would be a bit of a pain though if the page
> tables are partially moved though. It's unnecessarily complicated when the
> temporary stack can be easily avoided.

Faulting during exec? Dont we hold mmap_sem for write? A get_user_pages()
or so on the range will increment the refcount.
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