linux-kernel - Re: [PATCH 2/3] slub: reduce failure of this_cpu_cmpxchg in put_cpu

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Date:	Thu, 5 Jul 2012 09:20:04 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Pekka Enberg <penberg@...nel.org>
cc:	Joonsoo Kim <js1304@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 2/3] slub: reduce failure of this_cpu_cmpxchg in
 put_cpu_partial() after unfreezing

On Wed, 4 Jul 2012, Pekka Enberg wrote:

> On Fri, Jun 22, 2012 at 9:22 PM, Joonsoo Kim <js1304@...il.com> wrote:
> > In current implementation, after unfreezing, we doesn't touch oldpage,
> > so it remain 'NOT NULL'. When we call this_cpu_cmpxchg()
> > with this old oldpage, this_cpu_cmpxchg() is mostly be failed.
> >
> > We can change value of oldpage to NULL after unfreezing,
> > because unfreeze_partial() ensure that all the cpu partial slabs is removed
> > from cpu partial list. In this time, we could expect that
> > this_cpu_cmpxchg is mostly succeed.
> >
> > Signed-off-by: Joonsoo Kim <js1304@...il.com>
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 92f1c0e..531d8ed 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -1968,6 +1968,7 @@ int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
> >                                 local_irq_save(flags);
> >                                 unfreeze_partials(s);
> >                                 local_irq_restore(flags);
> > +                               oldpage = NULL;
> >                                 pobjects = 0;
> >                                 pages = 0;
> >                                 stat(s, CPU_PARTIAL_DRAIN);
>
> Makes sense. Christoph, David?

Acked-by: Christoph Lameter <cl@...ux.com>

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