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Date: Thu, 10 Nov 2011 15:37:32 -0800 (PST)
From: David Rientjes <rientjes@google.com>
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To: Andrew Morton <akpm@linux-foundation.org>
cc: Mel Gorman <mgorman@suse.de>, Minchan Kim <minchan.kim@gmail.com>,
        Jan Kara <jack@suse.cz>, Andy Isaacson <adi@hexapodia.org>,
        Johannes Weiner <jweiner@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH] mm: Do not stall in synchronous compaction for THP
 allocations
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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.