linux-kernel - Re: [PATCH 3/3] mm: slub: Default slub_max

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Message-ID: <20110515163906.GB25981@random.random>
Date:	Sun, 15 May 2011 18:39:06 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Colin King <colin.king@...onical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@...il.com>,
	Jan Kara <jack@...e.cz>, Chris Mason <chris.mason@...cle.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0

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 ;).
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