linux-kernel - Re: [patch 2/2] slub: add min

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Message-Id: <1235384784.6216.34.camel@penberg-laptop>
Date:	Mon, 23 Feb 2009 12:26:24 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] slub: add min_partial sysfs tunable

Hi David,

On Mon, 23 Feb 2009, Pekka Enberg wrote:
> > The patches look good but the description is bit lacking. Does this
> > actually fix up something? Why don't we fix the limit calculations
> > instead?
> > 
> > I'm a sucker for numbers so I'm easily fooled into merging patches with
> > statements of the form "this shaves off N bytes/kb/mb on XYZ systems".

On Mon, 2009-02-23 at 01:58 -0800, David Rientjes wrote:
> The memory savings from simply moving min_partial from struct 
> kmem_cache_node to struct kmem_cache is obviously not significant (unless 
> maybe you're from SGI or something), at the largest it's
> 
> 	# allocated caches * (MAX_NUMNODES - 1) * sizeof(unsigned long)
> 
> The true savings occurs when userspace reduces the number of partial slabs 
> that would otherwise be wasted, especially on machines with a large 
> number of nodes (ia64 with CONFIG_NODES_SHIFT at 10 for default?).  As 
> well as the kernel estimates ideal values for n->min_partial and ensures 
> it's within a sane range, userspace has no other input other than writing 
> to /sys/kernel/slab/cache/shrink.

Applied with the above explanation added to the changelog. Thanks!

			Pekka

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