linux-kernel - Re: [PATCH 01/10] slab/slub: struct memcg

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Message-ID: <5010482B.1040009@parallels.com>
Date:	Wed, 25 Jul 2012 23:25:31 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Greg Thelen <gthelen@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>, <devel@...nvz.org>,
	<cgroups@...r.kernel.org>, Suleiman Souhlal <suleiman@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 01/10] slab/slub: struct memcg_params

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@...allels.com>
>> Signed-off-by: Suleiman Souhlal <suleiman@...gle.com>
>> CC: Christoph Lameter <cl@...ux.com>
>> CC: Pekka Enberg <penberg@...helsinki.fi>
>> CC: Michal Hocko <mhocko@...e.cz>
>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>> CC: Johannes Weiner <hannes@...xchg.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.
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