linux-kernel - Re: [PATCH RFC] fix RCU-callback-after-kmem_cache

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Date:	Tue, 30 Jun 2009 17:26:39 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	paulmck@...ux.vnet.ibm.com, Matt Mackall <mpm@...enic.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, jdb@...x.dk
Subject: Re: [PATCH RFC] fix RCU-callback-after-kmem_cache_destroy problem in 
	sl[aou]b

Hi Christoph,

On Tue, 30 Jun 2009, Pekka Enberg wrote:
>> I don't even claim to understand all the RCU details here but I don't
>> see why we should care about _kmem_cache_destroy()_ performance at
>> this level. Christoph, hmmm?

On Tue, Jun 30, 2009 at 5:20 PM, Christoph
Lameter<cl@...ux-foundation.org> wrote:
> Well it was surprising to me that kmem_cache_destroy() would perform rcu
> actions in the first place. RCU is usually handled externally and not
> within the slab allocator. The only reason that SLAB_DESTROY_BY_RCU exists
> is because the user cannot otherwise control the final release of memory
> to the page allocator.

Right. A quick grep for git logs reveals that it's been like that in
mm/slab.c at least since 2.6.12-rc2 so I think we should consider it
as part of the slab API and Paul's patch is an obvious bugfix to it.

                                           Pekka
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