linux-kernel - Re: [PATCH v2 06/11] memcg: kmem controller infrastructure

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Message-ID: <502A2FE5.4060809@parallels.com>
Date:	Tue, 14 Aug 2012 15:00:53 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, <devel@...nvz.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v2 06/11] memcg: kmem controller infrastructure

On 08/10/2012 09:27 PM, Kamezawa Hiroyuki wrote:
>> +bool __memcg_kmem_new_page(gfp_t gfp, void *_handle, int order)
>> > +{
>> > +	struct mem_cgroup *memcg;
>> > +	struct mem_cgroup **handle = (struct mem_cgroup **)_handle;
>> > +	bool ret = true;
>> > +	size_t size;
>> > +	struct task_struct *p;
>> > +
>> > +	*handle = NULL;
>> > +	rcu_read_lock();
>> > +	p = rcu_dereference(current->mm->owner);
>> > +	memcg = mem_cgroup_from_task(p);
>> > +	if (!memcg_kmem_enabled(memcg))
>> > +		goto out;
>> > +
>> > +	mem_cgroup_get(memcg);
>> > +
> This mem_cgroup_get() will be a potentioal performance problem.
> Don't you have good idea to avoid accessing atomic counter here ?
> I think some kind of percpu counter or a feature to disable "move task"
> will be a help.
> 
> 

I have just sent out a proposal to deal with this. I tried the trick of
marking only the first charge and last uncharge, and it works quite
alright at the cost of a bit test on most calls to memcg_kmem_charge.

Please let me know what you think.

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