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Date: Mon, 24 Sep 2012 12:17:37 +0400
From: Glauber Costa <glommer@parallels.com>
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To: Tejun Heo <tj@kernel.org>
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        <kamezawa.hiroyu@jp.fujitsu.com>, <devel@openvz.org>,
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        Pekka Enberg <penberg@cs.helsinki.fi>, Michal Hocko <mhocko@suse.cz>,
        Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH v3 06/16] memcg: infrastructure to match an allocation
 to the right cache
References: <1347977530-29755-1-git-send-email-glommer@parallels.com> <1347977530-29755-7-git-send-email-glommer@parallels.com> <20120921205236.GT7264@google.com>
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On 09/22/2012 12:52 AM, Tejun Heo wrote:
> Missed some stuff.
> 
> On Tue, Sep 18, 2012 at 06:12:00PM +0400, Glauber Costa wrote:
>> +static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
>> +						  struct kmem_cache *cachep)
>> +{
> ...
>> +	memcg->slabs[idx] = new_cachep;
> ...
>> +struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep,
>> +					  gfp_t gfp)
>> +{
> ...
>> +	return memcg->slabs[idx];
> 
> I think you need memory barriers for the above pair.
> 
> Thanks.
> 

Why is that?

We'll either see a value, or NULL. If we see NULL, we assume the cache
is not yet created. Not a big deal.