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: <20100511151142.GS26611@csn.ul.ie>
Date:	Tue, 11 May 2010 16:11:42 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux.com>
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 Tue, May 11, 2010 at 08:59:12AM -0500, Christoph Lameter wrote:
> 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?

Copying in arguments and the like

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

Or just identify the temporary stack from the migration side instead of
adding to the cost of exec?

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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