Date: Thu, 8 Nov 2007 10:59:29 -0800 (PST)
From: Christoph Lameter <clameter@sgi.com>
To: Mel Gorman <mel@skynet.ie>
cc: akpm@linux-foundatin.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch 07/23] SLUB: Add defrag_ratio field and sysfs support.
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Message-ID: <Pine.LNX.4.64.0711081057290.8954@schroedinger.engr.sgi.com>
References: <20071107011130.382244340@sgi.com> <20071107011228.102370371@sgi.com>
 <20071108150705.GD2591@skynet.ie>
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On Thu, 8 Nov 2007, Mel Gorman wrote:

> On (06/11/07 17:11), Christoph Lameter didst pronounce:
> > The defrag_ratio is used to set the threshold at which defragmentation
> > should be run on a slabcache.
> > 
> 
> I'm thick, I would like to see a quick note here on what defragmentation
> means. Also, this defrag_ratio seems to have a significantly different
> meaning to the other defrag_ratio which isn't helping my poor head at
> all.

Yes that is why they have different names. The remote_node_defrag ratio 
controls the amount of remote allocs we do to reduce fragmentation.
 
> "The defrag_ratio sets a threshold at which a slab will be vacated of all
> it's objects and the pages freed during memory reclaim."

Sortof. If a slab is beyond the threshold during reclaim then reclaim will 
attempt to free the remaining objects in the slab to reclaim the whole 
slab.
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