linux-kernel - Re: [PATCH 5/5] slub: Only IPI CPUs that have per cpu obj to flush

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Date:	Mon, 26 Sep 2011 16:49:06 +0300
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Chris Metcalf <cmetcalf@...era.com>, linux-mm@...ck.org,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH 5/5] slub: Only IPI CPUs that have per cpu obj to flush

On Mon, Sep 26, 2011 at 3:05 PM, Gilad Ben-Yossef <gilad@...yossef.com> wrote:


>> The problem with a per-cpu cpumask is that you need to disable
>> preemption over the whole for_each_online_cpu() scan and that's not
>> really sane on very large machines as that can easily take a very long
>> time indeed.
>
> hmm... I might be thick, but why disable the preemption with the
> per-cpu cpumask at all?
...
>
> Does that makes sense or have I've gone over board with this concept? :-)

Scratch that. The cpumask must be per cache or the patch doesn't make
sense at all.
So sadly the only sane place to put it is in struct kmem_cache.

I think we can still update the cpumask field without caring about
preemption for the reasons
stated above, but the per cache memory overhead is still there I'm afraid.

Gilad

-- 
Gilad Ben-Yossef
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gilad@...yossef.com
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"I've seen things you people wouldn't believe. Goto statements used to
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