linux-kernel - Re: [PATCH -mm v2 5/8] slub: make slab

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Message-ID: <20140612100344.GB19221@esperanza>
Date:	Thu, 12 Jun 2014 14:03:46 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	<akpm@...ux-foundation.org>, <cl@...ux.com>, <rientjes@...gle.com>,
	<penberg@...nel.org>, <hannes@...xchg.org>, <mhocko@...e.cz>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH -mm v2 5/8] slub: make slab_free non-preemptable

Hi,

On Thu, Jun 12, 2014 at 03:58:42PM +0900, Joonsoo Kim wrote:
> On Fri, Jun 06, 2014 at 05:22:42PM +0400, Vladimir Davydov wrote:
> > @@ -2673,18 +2673,11 @@ static __always_inline void slab_free(struct kmem_cache *s,
> >  
> >  	slab_free_hook(s, x);
> >  
> > -redo:
> > -	/*
> > -	 * Determine the currently cpus per cpu slab.
> > -	 * The cpu may change afterward. However that does not matter since
> > -	 * data is retrieved via this pointer. If we are on the same cpu
> > -	 * during the cmpxchg then the free will succedd.
> > -	 */
> >  	preempt_disable();
> 
> Could you add some code comment why this preempt_disable/enable() is
> needed? We don't have any clue that kmemcg depends on these things
> on code, so someone cannot understand why it is here.
> 
> If possible, please add similar code comment on slab_alloc in mm/slab.c.

Sure.

Thanks.
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