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

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Message-ID: <alpine.LFD.2.02.1208161006430.2133@tux.localdomain>
Date:	Thu, 16 Aug 2012 10:06:50 +0300 (EEST)
From:	Pekka Enberg <penberg@...nel.org>
To:	Joonsoo Kim <js1304@...il.com>
cc:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 2/3] slub: reduce failure of this_cpu_cmpxchg in
 put_cpu_partial() after unfreezing

On Sat, 23 Jun 2012, Joonsoo Kim 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);

Applied, thanks!
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