[Devel] Re: [PATCH 01/10] slab/slub: struct memcg_params

[Glauber Costa]

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 at parallels.com>
>> Signed-off-by: Suleiman Souhlal <suleiman at google.com>
>> CC: Christoph Lameter <cl at linux.com>
>> CC: Pekka Enberg <penberg at cs.helsinki.fi>
>> CC: Michal Hocko <mhocko at suse.cz>
>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
>> CC: Johannes Weiner <hannes at 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.