linux-kernel - Re: -mm merge plans -- anti-fragmentation

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Message-ID: <20070710132459.GB9426@skynet.ie>
Date:	Tue, 10 Jul 2007 14:24:59 +0100
From:	mel@...net.ie (Mel Gorman)
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, npiggin@...e.de,
	kenchen@...gle.com, jschopp@...tin.ibm.com, apw@...dowen.org,
	kamezawa.hiroyu@...fujitsu.com, y-goto@...fujitsu.com,
	clameter@....com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: -mm merge plans -- anti-fragmentation

On (10/07/07 13:04), Peter Zijlstra didst pronounce:
> On Tue, 2007-07-10 at 11:20 +0100, Mel Gorman wrote:
> 
> <snip>
> 
> > > lumpy-reclaim-v4.patch
> > 
> > This patch is really what lumpy reclaim is. I believe Peter has looked
> > at this and was happy enough at the time although he is cc'd here again
> > in case this has changed. This is mainly useful with either grouping
> > pages by mobility or the ZONE_MOVABLE stuff. However, at the time the
> > patch was proposed, there was a feeling that it might help jumbo frame
> > allocation on e1000's and maybe if fsblock optimistically uses
> > contiguous pages it would have an application. I would like to see it go
> > through to see does it help e1000 at least.
> 
> I'm not seeing how this will help e1000 (and other jumbo drivers). They
> typically allocate using GFP_ATOMIC, so in order to satisfy those you'd
> need to either have a higher order watermark or do atomic defrag of the
> free space.
> 

It does help somewhat indirectly and in an unsatisfactory manner. When the
higher watermarks are breached, the atomic allocation will still succeeed
but kswapd will be poked to reclaim at a given order. This is similar to
the problems SLUB hits when it uses high-orders frequently.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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