linux-kernel - Re: [PATCH 04/14] mm,migration: Allow the migration of PageSwapCache pages

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Date:	Mon, 26 Apr 2010 17:54:08 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mel@....ul.ie>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 04/14] mm,migration: Allow the migration of	PageSwapCache
  pages

On 04/24/2010 07:59 AM, Mel Gorman wrote:
> On Sat, Apr 24, 2010 at 01:13:40PM +0200, Andrea Arcangeli wrote:

>> Also keep in mind expand_downwards which also adjusts
>> vm_start/vm_pgoff the same way (and without mmap_sem write mode).
>
> Will keep it in mind. It's taking the anon_vma lock but once again,
> there might be more than one anon_vma to worry about and the proper
> locking still isn't massively clear to me.

The locking for the anon_vma_chain->same_vma list is
essentially the same as what was used before in mmap
and anon_vma_prepare.

Either the mmap_sem is held for write, or the mmap_sem
is held for reading and the page_table_lock is held.

What exactly is the problem that migration is seeing?

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