linux-kernel - Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped anonymous pages

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Date:	Tue, 23 Mar 2010 18:04:18 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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 02/11] mm,migration: Do not try to migrate unmapped
	anonymous pages

On Tue, Mar 23, 2010 at 12:22:57PM -0500, Christoph Lameter wrote:
> On Tue, 23 Mar 2010, Mel Gorman wrote:
> 
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 98eaaf2..6eb1efe 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -603,6 +603,19 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
> >  	 */
> >  	if (PageAnon(page)) {
> >  		rcu_read_lock();
> > +
> > +		/*
> > +		 * If the page has no mappings any more, just bail. An
> > +		 * unmapped anon page is likely to be freed soon but worse,
> > +		 * it's possible its anon_vma disappeared between when
> > +		 * the page was isolated and when we reached here while
> > +		 * the RCU lock was not held
> > +		 */
> > +		if (!page_mapcount(page)) {
> > +			rcu_read_unlock();
> > +			goto uncharge;
> > +		}
> > +
> >  		rcu_locked = 1;
> >  		anon_vma = page_anon_vma(page);
> >  		atomic_inc(&anon_vma->migrate_refcount);
> 
> A way to make this simpler would be to move "rcu_locked = 1" before the
> if statement and then do
> 
> if (!page_mapcount(page))
> 	goto rcu_unlock;
> 

True. Fixed.

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