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From: Tejun Heo <tj@kernel.org>
To: Glauber Costa <glommer@parallels.com>
Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	kamezawa.hiroyu@jp.fujitsu.com, devel@openvz.org,
	linux-mm@kvack.org, Suleiman Souhlal <suleiman@google.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Mel Gorman <mgorman@suse.de>,
	David Rientjes <rientjes@google.com>,
	Christoph Lameter <cl@linux.com>,
	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
Date: Mon, 24 Sep 2012 10:58:01 -0700	[thread overview]
Message-ID: <20120924175801.GE7694@google.com> (raw)
In-Reply-To: <50601721.6040805@parallels.com>

On Mon, Sep 24, 2012 at 12:17:37PM +0400, Glauber Costa wrote:
> 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.

Because when you see !NULL cache pointer you want to be able to see
the cache fully initialized.  You need wmb between cache creation and
pointer assignment and at least read_barrier_depends() between
fetching the cache pointer and dereferencing it.

Thanks.

-- 
tejun

  reply	other threads:[~2012-09-24 17:58 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-18 14:11 [PATCH v3 00/16] slab accounting for memcg Glauber Costa
2012-09-18 14:11 ` [PATCH v3 01/16] slab/slub: struct memcg_params Glauber Costa
2012-09-18 14:11 ` [PATCH v3 02/16] slub: use free_page instead of put_page for freeing kmalloc allocation Glauber Costa
2012-09-18 14:11 ` [PATCH v3 03/16] slab: Ignore the cflgs bit in cache creation Glauber Costa
2012-09-18 15:20   ` Christoph Lameter
2012-09-21 17:33   ` Tejun Heo
2012-09-18 14:11 ` [PATCH v3 04/16] provide a common place for initcall processing in kmem_cache Glauber Costa
2012-09-18 15:22   ` Christoph Lameter
2012-09-18 14:11 ` [PATCH v3 05/16] consider a memcg parameter in kmem_create_cache Glauber Costa
2012-09-21 18:14   ` Tejun Heo
2012-09-24  8:12     ` Glauber Costa
2012-09-24 12:41       ` Christoph
2012-09-24 12:41         ` Glauber Costa
2012-09-24 13:42           ` Christoph Lameter
2012-09-24 13:44             ` Glauber Costa
2012-09-24 13:56               ` Christoph Lameter
2012-09-24 13:57                 ` Glauber Costa
2012-09-24 15:38                   ` Pekka Enberg
2012-09-24 15:36                     ` Glauber Costa
2012-09-24 17:38                       ` Christoph Lameter
2012-09-24 17:39                     ` Christoph Lameter
2012-10-02 14:46   ` Michal Hocko
2012-09-18 14:12 ` [PATCH v3 06/16] memcg: infrastructure to match an allocation to the right cache Glauber Costa
2012-09-21 18:32   ` Tejun Heo
2012-09-24  8:46     ` Glauber Costa
2012-09-24 17:56       ` Tejun Heo
2012-09-25 13:57         ` Glauber Costa
2012-09-25 16:28           ` Christoph Lameter
2012-09-21 20:52   ` Tejun Heo
2012-09-24  8:17     ` Glauber Costa
2012-09-24 17:58       ` Tejun Heo [this message]
2012-09-18 14:12 ` [PATCH v3 07/16] memcg: skip memcg kmem allocations in specified code regions Glauber Costa
2012-09-21 19:59   ` Tejun Heo
2012-09-24  9:09     ` Glauber Costa
2012-09-24 17:47       ` Tejun Heo
2012-09-18 14:12 ` [PATCH v3 08/16] slab: allow enable_cpu_cache to use preset values for its tunables Glauber Costa
2012-09-18 15:25   ` Christoph Lameter
2012-09-19  7:44     ` Glauber Costa
2012-09-21  9:29   ` Pekka Enberg
2012-09-18 14:12 ` [PATCH v3 09/16] sl[au]b: always get the cache from its page in kfree Glauber Costa
2012-09-18 15:28   ` Christoph Lameter
2012-09-19  7:42     ` Glauber Costa
2012-09-19 14:14       ` Christoph Lameter
2012-09-21  9:33       ` Pekka Enberg
2012-09-21  9:30         ` Glauber Costa
2012-09-21  9:41           ` Pekka Enberg
2012-09-21 20:07             ` Tejun Heo
2012-09-21 20:14               ` Pekka Enberg
2012-09-21 20:16                 ` Tejun Heo
2012-09-18 14:12 ` [PATCH v3 10/16] sl[au]b: Allocate objects from memcg cache Glauber Costa
2012-09-18 14:12 ` [PATCH v3 11/16] memcg: destroy memcg caches Glauber Costa
2012-09-21 20:22   ` Tejun Heo
2012-09-18 14:12 ` [PATCH v3 12/16] memcg/sl[au]b Track all the memcg children of a kmem_cache Glauber Costa
2012-09-21 20:31   ` Tejun Heo
2012-09-18 14:12 ` [PATCH v3 13/16] slab: slab-specific propagation changes Glauber Costa
2012-09-18 17:00   ` Christoph Lameter
2012-09-19  7:41     ` Glauber Costa
2012-09-18 14:12 ` [PATCH v3 14/16] slub: slub-specific " Glauber Costa
2012-09-18 14:12 ` [PATCH v3 15/16] memcg/sl[au]b: shrink dead caches Glauber Costa
2012-09-18 17:02   ` Christoph Lameter
2012-09-19  7:40     ` Glauber Costa
2012-09-21  4:48   ` JoonSoo Kim
2012-09-21  8:40     ` Glauber Costa
2012-09-21  9:28       ` JoonSoo Kim
2012-09-21  9:31         ` Glauber Costa
2012-09-21 20:40   ` Tejun Heo
2012-09-24  8:25     ` Glauber Costa
2012-09-24 17:43       ` Tejun Heo
2012-09-18 14:12 ` [PATCH v3 16/16] Add documentation about the kmem controller Glauber Costa
2012-09-21  9:40 ` [PATCH v3 00/16] slab accounting for memcg Pekka Enberg
2012-09-21  9:43   ` Glauber Costa
2012-09-21 20:46 ` Tejun Heo
2012-09-21 20:47   ` Tejun Heo
2012-09-24  8:15   ` Glauber Costa

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