linux-kernel - Re: [PATCH v6 5/8] slub: only IPI CPUs that have per cpu obj to flush

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Date:	Wed, 18 Jan 2012 14:09:14 +0200
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	Milton Miller <miltonm@....com>
Cc:	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Mel Gorman <mel@....ul.ie>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	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>, Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Sasha Levin <levinsasha928@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v6 5/8] slub: only IPI CPUs that have per cpu obj to flush

On Wed, Jan 11, 2012 at 9:04 AM, Milton Miller <miltonm@....com> wrote:

>
> > mm/slub.c | 10 +++++++++-
> > 1 files changed, 9 insertions(+), 1 deletions(-)
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 09ccee8..31833d6 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -2013,9 +2013,17 @@ static void flush_cpu_slab(void *d)
> > __flush_cpu_slab(s, smp_processor_id());
> > }
> >
> > +static int has_cpu_slab(int cpu, void *info)
> > +{
> > + struct kmem_cache *s = info;
> > + struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
> > +
> > + return !!(c->page);
>
> __flush_cpu_slab is careful to test that the the per_cpu_ptr is not
> NULL before referencing the page field.  free_percpu likewise ignores
> NULL pointers.  We need to check !!(c && c->page) here.
>
This is indeed what I did in the first iterations but Christoph indicated that
c could never be NULL in his review of the patch. See :
https://lkml.org/lkml/2011/11/15/207

I integrated all the other review comment of this patch though. Thanks!
Gilad

--
Gilad Ben-Yossef
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gilad@...yossef.com
Israel Cell: +972-52-8260388
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http://benyossef.com

"Unfortunately, cache misses are an equal opportunity pain provider."
-- Mike Galbraith, LKML
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