linux-ext4 - Re: [PATCH 3/3] mm: slub: Default slub_max

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Date:	Fri, 13 May 2011 11:14:29 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Colin King <colin.king@...onical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@...il.com>,
	Jan Kara <jack@...e.cz>, Chris Mason <chris.mason@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	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 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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