linux-kernel - Re: [patch] slub: default min_partial to at least highest cpus per node

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Message-ID: <alpine.DEB.2.00.0904071456130.32000@chino.kir.corp.google.com>
Date:	Tue, 7 Apr 2009 15:01:45 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
cc:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] slub: default min_partial to at least highest cpus per
  node

On Tue, 7 Apr 2009, Pekka Enberg wrote:

> Yeah, something more dynamic makes sense. But we probably need to do
> ilog2(nr_cpu_ids) or something; otherwise we will have very long partial lists
> on big iron machines (think 4096 cpus here).
> 

The suggestion was to replace MAX_PARTIAL with nr_cpu_ids, not as the 
default value for n->min_partial, which is ilog2(size).  To exceed the 
current value of MAX_PARTIAL, which is 10, size would need to be 2K or 
greater.

I agree that the default n->min_partial would be better represented in 
terms of cpus than object size.  ilog2(nr_cpu_ids) certainly seems 
appropriate and free partial slabs can always be reclaimed by utilizing 
/sys/kernel/slab/cache/shrink.

The 4096 cpu example is certainly realistic, but probably not UMA.
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