linux-kernel - Re: [PATCH v2 6/6] slub: only preallocate cpus_with

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Message-ID: <alpine.DEB.2.00.1110272304020.14619@router.home>
Date:	Thu, 27 Oct 2011 23:06:31 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>
Subject: Re: [PATCH v2 6/6] slub: only preallocate cpus_with_slabs if
 offstack

On Sun, 23 Oct 2011, Gilad Ben-Yossef wrote:

> We need a cpumask to track cpus with per cpu cache pages
> to know which cpu to whack during flush_all. For
> CONFIG_CPUMASK_OFFSTACK=n we allocate the mask on stack.
> For CONFIG_CPUMASK_OFFSTACK=y we don't want to call kmalloc
> on the flush_all path, so we preallocate per kmem_cache
> on cache creation and use it in flush_all.

I think the on stack alloc should be the default because we can then avoid
the field in kmem_cache and the associated logic with managing the field.
Can we do a GFP_ATOMIC allocation in flush_all()? If the alloc
fails then you can still fallback to send an IPI to all cpus.

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