From: Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0
Date: Fri, 13 May 2011 11:14:29 +0100
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Cc: Andrew Morton <akpm@linux-foundation.org>,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	Colin King <colin.king@canonical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@gmail.com>,
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	Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>,
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To: David Rientjes <rientjes@google.com>
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On Wed, May 11, 2011 at 03:27:11PM -0700, David Rientjes wrote:
> On Wed, 11 May 2011, Mel Gorman wrote:
> 
> > I agree with you that there are situations where plenty of memory
> > means that that it'll perform much better. However, indications are
> > that it breaks down with high CPU usage when memory is low.  Worse,
> > once fragmentation becomes a problem, large amounts of UNMOVABLE and
> > RECLAIMABLE will make it progressively more expensive to find the
> > necessary pages. Perhaps with patches 1 and 2, this is not as much
> > of a problem but figures in the leader indicated that for a simple
> > workload with large amounts of files and data exceeding physical
> > memory that it was better off not to use high orders at all which
> > is a situation I'd expect to be encountered by more users than
> > performance-sensitive applications.
> > 
> > In other words, we're taking one hit or the other.
> > 
> 
> Seems like the ideal solution would then be to find how to best set the 
> default, and that can probably only be done with the size of the smallest 
> node since it has a higher liklihood of encountering a large amount of 
> unreclaimable slab when memory is low.
> 

Ideally yes, but glancing through this thread and thinking on it a bit
more, I'm going to drop this patch. As pointed out, SLUB with high
orders has been in use with distributions already so the breakage is
elsewhere. Patches 1 and 2 still make some sense but they're not the
root cause.

> <SNIP>

-- 
Mel Gorman
SUSE Labs

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