From: Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0
Date: Mon, 16 May 2011 09:42:30 +0100
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Cc: Christoph Lameter <cl@linux.com>,
	Pekka Enberg <penberg@kernel.org>,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	Dave Jones <davej@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Colin King <colin.king@canonical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@gmail.com>,
	Jan Kara <jack@suse.cz>, Chris Mason <chris.mason@oracle.com>,
	Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-ext4 <linux-ext4@vger.kernel.org>
To: Andrea Arcangeli <aarcange@redhat.com>
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On Sun, May 15, 2011 at 06:39:06PM +0200, Andrea Arcangeli wrote:
> On Fri, May 13, 2011 at 10:49:58AM +0100, Mel Gorman wrote:
> > On Thu, May 12, 2011 at 08:00:18PM +0200, Andrea Arcangeli wrote:
> > > <SNIP>
> > >
> > > BTW, it comes to mind in patch 2, SLUB should clear __GFP_REPEAT too
> > > (not only __GFP_NOFAIL). Clearing __GFP_WAIT may be worth it or not
> > > with COMPACTION=y, definitely good idea to clear __GFP_WAIT unless
> > > lumpy is restricted to __GFP_REPEAT|__GFP_NOFAIL.
> > 
> > This is in V2 (unreleased, testing in progress and was running
> > overnight). I noticed that clearing __GFP_REPEAT is required for
> > reclaim/compaction if direct reclaimers from SLUB are to return false in
> > should_continue_reclaim() and bail out from high-order allocation
> > properly. As it is, there is a possibility for slub high-order direct
> > reclaimers to loop in reclaim/compaction for a long time. This is
> > only important when CONFIG_COMPACTION=y.
> 
> Agreed. However I don't expect anyone to allocate from slub(/slab)
> with __GFP_REPEAT so it's probably only theoretical but more correct
> indeed ;).

Networking layer does specify __GFP_REPEAT.

-- 
Mel Gorman
SUSE Labs

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