linux-kernel - Re: [PATCH] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous

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Date:	Tue, 31 May 2011 09:32:15 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	akpm@...ux-foundation.org, Ury Stankevich <urykhy@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, stable@...nel.org
Subject: Re: [PATCH] mm: compaction: Abort compaction if too many pages are
 isolated and caller is asynchronous

On Tue, May 31, 2011 at 01:14:15AM +0900, Minchan Kim wrote:
> On Mon, May 30, 2011 at 02:13:00PM +0100, Mel Gorman wrote:
> > Asynchronous compaction is used when promoting to huge pages. This is
> > all very nice but if there are a number of processes in compacting
> > memory, a large number of pages can be isolated. An "asynchronous"
> > process can stall for long periods of time as a result with a user
> > reporting that firefox can stall for 10s of seconds. This patch aborts
> > asynchronous compaction if too many pages are isolated as it's better to
> > fail a hugepage promotion than stall a process.
> > 
> > If accepted, this should also be considered for 2.6.39-stable. It should
> > also be considered for 2.6.38-stable but ideally [11bc82d6: mm:
> > compaction: Use async migration for __GFP_NO_KSWAPD and enforce no
> > writeback] would be applied to 2.6.38 before consideration.
> > 
> > Reported-and-Tested-by: Ury Stankevich <urykhy@...il.com>
> > Signed-off-by: Mel Gorman <mgorman@...e.de>
> Reviewed-by: Minchan Kim <minchan.kim@...il.com>
> 

Thanks

> I have a nitpick below.
> Otherwise, looks good to me.
> 
> > ---
> >  mm/compaction.c |   32 ++++++++++++++++++++++++++------
> >  1 files changed, 26 insertions(+), 6 deletions(-)
> > 
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 021a296..331a2ee 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -240,11 +240,20 @@ static bool too_many_isolated(struct zone *zone)
> >  	return isolated > (inactive + active) / 2;
> >  }
> >  
> > +/* possible outcome of isolate_migratepages */
> > +typedef enum {
> > +	ISOLATE_ABORT,		/* Abort compaction now */
> > +	ISOLATE_NONE,		/* No pages isolated, continue scanning */
> > +	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
> > +} isolate_migrate_t;
> > +
> >  /*
> >   * Isolate all pages that can be migrated from the block pointed to by
> >   * the migrate scanner within compact_control.
> > + *
> > + * Returns false if compaction should abort at this point due to congestion.
> 
> false? I think it would be better to use explicit word, ISOLATE_ABORT.
> 

Oops, thanks for pointing that out. I'll post a V2 once it has been
figured out why NR_ISOLATE_* is getting screwed up on !CONFIG_SMP.

-- 
Mel Gorman
SUSE Labs
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