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: <20100511161516.GU26611@csn.ul.ie>
Date:	Tue, 11 May 2010 17:15:16 +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 10:56:00AM -0500, Christoph Lameter wrote:
> On Tue, 11 May 2010, Mel Gorman wrote:
> 
> > Or just identify the temporary stack from the migration side instead of
> > adding to the cost of exec?
> 
> Adding one off checks to a generic mechanism isnt really clean
> programming. Using the provided means of disabling a generic mechanism is.
> 

Andrea's solution is likely lighter than yours as it is one kmalloc and
an insertion into the VM as opposed to a page table walk with reference
counting. Better yet, it exists as a patch that has been tested and it
fits in with the generic mechanism by guaranteeing that rmap_walk finds
all the migration PTEs during the second walk.

The problem remains the same - that class of solution increases the cost of
a common operation (exec) to keep a much less operation (migration) happy.

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