linux-kernel - Re: [PATCH] mm: Do not stall in synchronous compaction for THP allocations

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Date:	Fri, 11 Nov 2011 10:14:14 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>, Jan Kara <jack@...e.cz>,
	Andy Isaacson <adi@...apodia.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: Do not stall in synchronous compaction for THP
 allocations

On Thu, Nov 10, 2011 at 03:37:32PM -0800, David Rientjes wrote:
> On Thu, 10 Nov 2011, Andrew Morton wrote:
> 
> > > This patch once again prevents sync migration for transparent
> > > hugepage allocations as it is preferable to fail a THP allocation
> > > than stall.
> > 
> > Who said?  ;) Presumably some people would prefer to get lots of
> > huge pages for their 1000-hour compute job, and waiting a bit to get
> > those pages is acceptable.
> > 
> 
> Indeed.  It seems like the behavior would better be controlled with 
> /sys/kernel/mm/transparent_hugepage/defrag which is set aside specifically 
> to control defragmentation for transparent hugepages and for that 
> synchronous compaction should certainly apply.

With khugepaged in place, it's adding a tunable that is unnecessary and
will not be used. Even if such a tuneable was created, the default
behaviour should be "do not stall".

-- 
Mel Gorman
SUSE Labs
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