Date: Tue, 26 Jun 2012 21:01:32 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
To: Glauber Costa <glommer@parallels.com>
cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Frederic Weisbecker <fweisbec@gmail.com>,
        Pekka Enberg <penberg@kernel.org>, Michal Hocko <mhocko@suse.cz>,
        Johannes Weiner <hannes@cmpxchg.org>, Christoph Lameter <cl@linux.com>,
        devel@openvz.org, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Tejun Heo <tj@kernel.org>, Pekka Enberg <penberg@cs.helsinki.fi>
Subject: Re: [PATCH 06/11] memcg: kmem controller infrastructure
In-Reply-To: <4FE97E31.3010201@parallels.com>
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On Tue, 26 Jun 2012, Glauber Costa wrote:

> > > @@ -416,6 +423,43 @@ static inline void sock_update_memcg(struct sock *sk)
> > >   static inline void sock_release_memcg(struct sock *sk)
> > >   {
> > >   }
> > > +
> > > +#define mem_cgroup_kmem_on 0
> > > +#define __mem_cgroup_new_kmem_page(a, b, c) false
> > > +#define __mem_cgroup_free_kmem_page(a,b )
> > > +#define __mem_cgroup_commit_kmem_page(a, b, c)
> > > +#define is_kmem_tracked_alloc (false)
> > >   #endif /* CONFIG_CGROUP_MEM_RES_CTLR_KMEM */
> > > +
> > > +static __always_inline
> > > +bool mem_cgroup_new_kmem_page(gfp_t gfp, void *handle, int order)
> > > +{
> > > +	if (!mem_cgroup_kmem_on)
> > > +		return true;
> > > +	if (!is_kmem_tracked_alloc)
> > > +		return true;
> > > +	if (!current->mm)
> > > +		return true;
> > > +	if (in_interrupt())
> > > +		return true;
> > 
> > You can't test for current->mm in irq context, so you need to check for
> > in_interrupt() first.
> >
> Right, thanks.
> 
> > Also, what prevents __mem_cgroup_new_kmem_page()
> > from being called for a kthread that has called use_mm() before
> > unuse_mm()?
> 
> Nothing, but I also don't see how to prevent that.

You can test for current->flags & PF_KTHREAD following the check for 
in_interrupt() and return true, it's what you were trying to do with the 
check for !current->mm.
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