linux-kernel - Re: [PATCH 17/23] kmem controller charge/uncharge infrastructure

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Date:	Tue, 24 Apr 2012 13:21:43 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Glauber Costa <glommer@...allels.com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, devel@...nvz.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 17/23] kmem controller charge/uncharge infrastructure

On Tue, 24 Apr 2012, Frederic Weisbecker wrote:

> > This seems horribly inconsistent with memcg charging of user memory since 
> > it charges to p->mm->owner and you're charging to p.  So a thread attached 
> > to a memcg can charge user memory to one memcg while charging slab to 
> > another memcg?
> 
> Charging to the thread rather than the process seem to me the right behaviour:
> you can have two threads of a same process attached to different cgroups.
> 
> Perhaps it is the user memory memcg that needs to be fixed?
> 

No, because memory is represented by mm_struct, not task_struct, so you 
must charge to p->mm->owner to allow for moving threads amongst memcgs 
later for memory.move_charge_at_immigrate.  You shouldn't be able to 
charge two different memcgs for memory represented by a single mm.

> > > +
> > > +	if (!mem_cgroup_kmem_enabled(memcg))
> > > +		goto out;
> > > +
> > > +	mem_cgroup_get(memcg);
> > > +	ret = memcg_charge_kmem(memcg, gfp, size) == 0;
> > > +	if (ret)
> > > +		mem_cgroup_put(memcg);
> > > +out:
> > > +	rcu_read_unlock();
> > > +	return ret;
> > > +}
> > > +EXPORT_SYMBOL(__mem_cgroup_charge_kmem);
> > > +
> > > +void __mem_cgroup_uncharge_kmem(size_t size)
> > > +{
> > > +	struct mem_cgroup *memcg;
> > > +
> > > +	rcu_read_lock();
> > > +	memcg = mem_cgroup_from_task(current);
> > > +
> > > +	if (!mem_cgroup_kmem_enabled(memcg))
> > > +		goto out;
> > > +
> > > +	mem_cgroup_put(memcg);
> > > +	memcg_uncharge_kmem(memcg, size);
> > > +out:
> > > +	rcu_read_unlock();
> > > +}
> > > +EXPORT_SYMBOL(__mem_cgroup_uncharge_kmem);
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