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Date: Tue, 19 Jun 2012 09:16:20 +0900
From: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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To: Glauber Costa <glommer@parallels.com>
CC: linux-mm@kvack.org, Pekka Enberg <penberg@kernel.org>,
        Cristoph Lameter <cl@linux.com>, David Rientjes <rientjes@google.com>,
        cgroups@vger.kernel.org, devel@openvz.org,
        linux-kernel@vger.kernel.org, Frederic Weisbecker <fweisbec@gmail.com>,
        Suleiman Souhlal <suleiman@google.com>,
        Pekka Enberg <penberg@cs.helsinki.fi>, Michal Hocko <mhocko@suse.cz>,
        Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH v4 23/25] memcg: propagate kmem limiting information to
 children
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(2012/06/18 21:43), Glauber Costa wrote:
> On 06/18/2012 04:37 PM, Kamezawa Hiroyuki wrote:
>> (2012/06/18 19:28), Glauber Costa wrote:
>>> The current memcg slab cache management fails to present satisfatory hierarchical
>>> behavior in the following scenario:
>>>
>>> ->   /cgroups/memory/A/B/C
>>>
>>> * kmem limit set at A
>>> * A and B empty taskwise
>>> * bash in C does find /
>>>
>>> Because kmem_accounted is a boolean that was not set for C, no accounting
>>> would be done. This is, however, not what we expect.
>>>
>>
>> Hmm....do we need this new routines even while we have mem_cgroup_iter() ?
>>
>> Doesn't this work ?
>>
>> 	struct mem_cgroup {
>> 		.....
>> 		bool kmem_accounted_this;
>> 		atomic_t kmem_accounted;
>> 		....
>> 	}
>>
>> at set limit
>>
>> 	....set_limit(memcg) {
>>
>> 		if (newly accounted) {
>> 			mem_cgroup_iter() {
>> 				atomic_inc(&iter->kmem_accounted)
>> 			}
>> 		} else {
>> 			mem_cgroup_iter() {
>> 				atomic_dec(&iter->kmem_accounted);
>> 			}
>> 	}
>>
>>
>> hm ? Then, you can see kmem is accounted or not by atomic_read(&memcg->kmem_accounted);
>>
> 
> Accounted by itself / parent is still useful, and I see no reason to use
> an atomic + bool if we can use a pair of bits.
> 
> As for the routine, I guess mem_cgroup_iter will work... It does a lot
> more than I need, but for the sake of using what's already in there, I
> can switch to it with no problems.
> 

Hmm. please start from reusing existing routines.
If it's not enough, some enhancement for generic cgroup  will be welcomed
rather than completely new one only for memcg.

Thanks,
-Kame