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

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Message-ID: <CAOJsxLECbRHq=amSkNZGDx+rSMkE0Hd2VvCs=vyFcxPQpfxL_g@mail.gmail.com>
Date:	Mon, 26 Sep 2011 12:28:14 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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>,
	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 11:35 AM, Gilad Ben-Yossef <gilad@...yossef.com> wrote:
>> Right, having to do that for_each_oneline_cpu() loop only to then IPI
>> them can cause a massive cacheline bounce fest.. Ideally you'd want to
>> keep a cpumask per kmem_cache, although I bet the memory overhead of
>> that isn't attractive.
>>
>> Also, what Pekka says, having that alloc here isn't good either.
>
> Yes, the alloc in the flush_all path definitively needs to go. I
> wonder if just to resolve that allocating the mask per cpu and not in
> kmem_cache itself is not better - after all, all we need is a single
> mask per cpu when we wish to do a flush_all and no per cache. The
> memory overhead of that is slightly better. This doesn't cover the
> cahce bounce issue.

I'm fine with whatever works for you as long as you don't add a
kmalloc() call in flush_all().

                        Pekka
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