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Date: Wed, 25 Jul 2012 23:25:31 +0400
From: Glauber Costa <glommer@parallels.com>
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To: "Kirill A. Shutemov" <kirill@shutemov.name>
CC: <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>, David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>, Greg Thelen <gthelen@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>,
        Frederic Weisbecker <fweisbec@gmail.com>, <devel@openvz.org>,
        <cgroups@vger.kernel.org>, Suleiman Souhlal <suleiman@google.com>,
        Pekka Enberg <penberg@cs.helsinki.fi>,
        Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH 01/10] slab/slub: struct memcg_params
References: <1343227101-14217-1-git-send-email-glommer@parallels.com> <1343227101-14217-2-git-send-email-glommer@parallels.com> <20120725192650.GA5163@shutemov.name>
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On 07/25/2012 11:26 PM, Kirill A. Shutemov wrote:
> On Wed, Jul 25, 2012 at 06:38:12PM +0400, Glauber Costa wrote:
>> For the kmem slab controller, we need to record some extra
>> information in the kmem_cache structure.
>>
>> Signed-off-by: Glauber Costa <glommer@parallels.com>
>> Signed-off-by: Suleiman Souhlal <suleiman@google.com>
>> CC: Christoph Lameter <cl@linux.com>
>> CC: Pekka Enberg <penberg@cs.helsinki.fi>
>> CC: Michal Hocko <mhocko@suse.cz>
>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> CC: Johannes Weiner <hannes@cmpxchg.org>
>> ---
>>  include/linux/slab.h     |    7 +++++++
>>  include/linux/slab_def.h |    4 ++++
>>  include/linux/slub_def.h |    3 +++
>>  3 files changed, 14 insertions(+)
>>
>> diff --git a/include/linux/slab.h b/include/linux/slab.h
>> index 0dd2dfa..3152bcd 100644
>> --- a/include/linux/slab.h
>> +++ b/include/linux/slab.h
>> @@ -177,6 +177,13 @@ unsigned int kmem_cache_size(struct kmem_cache *);
>>  #define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
>>  #endif
>>  
>> +#ifdef CONFIG_MEMCG_KMEM
>> +struct mem_cgroup_cache_params {
>> +	struct mem_cgroup *memcg;
>> +	int id;
>> +};
> 
> IIUC, we only need the id to make slab name unique.  Why can't we embed
> the id to struct mem_cgroup? Is it possible to have multiple slabs with
> the same combination of type, size, and memcg?
> 
Humm, The id does not serve this purpose (perhaps deserves a comment here)

The purpose of the id is that given a slab, we can access it's memcg
equivalent in constant time through the cache array in memcg.