linux-kernel - Re: [this_cpu_xx V6 7/7] this_cpu: slub aggressive use of this

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Date:	Wed, 14 Oct 2009 19:14:26 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Mel Gorman <mel@....ul.ie>, David Rientjes <rientjes@...gle.com>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>
Subject: Re: [this_cpu_xx V6 7/7] this_cpu: slub aggressive use of this_cpu 
	operations in the hotpaths

Hi Christoph,

On Wed, 14 Oct 2009, Pekka Enberg wrote:
>> SLAB is able to queue lots of large objects but SLUB can't do that because it
>> has no queues. In SLUB, each CPU gets a page assigned to it that serves as a
>> "queue" but the size of the queue gets smaller as object size approaches page
>> size.
>>
>> We try to offset that with higher order allocations but IIRC we don't increase
>> the order linearly with object size and cap it to some reasonable maximum.

On Wed, Oct 14, 2009 at 6:56 PM, Christoph Lameter
<cl@...ux-foundation.org> wrote:
> You can test to see if larger pages have an influence by passing
>
> slub_max_order=6
>
> or so on the kernel command line.
>
> You can force a large page use in slub by setting
>
> slub_min_order=3
>
> f.e.
>
> Or you can force a mininum number of objecxcts in slub through f.e.
>
> slub_min_objects=50
>
> slub_max_order=6 slub_min_objects=50
>
> should result in pretty large slabs with lots of in page objects that
> allow slub to queue better.

Yeah, that should help but it's probably not something we can do for
mainline. I'm not sure how we can fix SLUB to support large objects
out-of-the-box as efficiently as SLAB does.

                        Pekka
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