linux-kernel - Re: [PATCH 01/12] mm,migration: Take a reference to the anon

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Message-ID: <20100219135934.GF30258@csn.ul.ie>
Date:	Fri, 19 Feb 2010 13:59:35 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 01/12] mm,migration: Take a reference to the anon_vma
	before migrating

On Fri, Feb 19, 2010 at 09:12:44AM +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 18 Feb 2010 18:02:31 +0000
> Mel Gorman <mel@....ul.ie> wrote:
> 
> > rmap_walk_anon() does not use page_lock_anon_vma() for looking up and
> > locking an anon_vma and it does not appear to have sufficient locking to
> > ensure the anon_vma does not disappear from under it.
> > 
> > This patch copies an approach used by KSM to take a reference on the
> > anon_vma while pages are being migrated. This should prevent rmap_walk()
> > running into nasty surprises later because anon_vma has been freed.
> > 
> > Signed-off-by: Mel Gorman <mel@....ul.ie>
> 
> I have no objection to this direction. But after this patch, you can remove
> rcu_read_lock()/unlock() in unmap_and_move().
> ruc_read_lock() is for guarding against anon_vma replacement.
> 

Thanks. I expected that would be the case but was going to leave at
least one kernel release between when compaction went in and I did that.

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