linux-kernel - Re: [PATCH v4 23/25] memcg: propagate kmem limiting information to children

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Date:	Mon, 18 Jun 2012 16:43:39 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	<linux-mm@...ck.org>, Pekka Enberg <penberg@...nel.org>,
	Cristoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	<cgroups@...r.kernel.org>, <devel@...nvz.org>,
	<linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v4 23/25] memcg: propagate kmem limiting information to
 children

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.



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