linux-kernel - Re: [PATCH 09/11] memcg: propagate kmem limiting information to children

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Date:	Mon, 25 Jun 2012 16:21:58 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Tejun Heo <tj@...nel.org>, <cgroups@...r.kernel.org>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	"Frederic Weisbecker" <fweisbec@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	"Pekka Enberg" <penberg@...nel.org>, Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>, <devel@...nvz.org>,
	<kamezawa.hiroyu@...fujitsu.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH 09/11] memcg: propagate kmem limiting information to
 children

On Tue, 26 Jun 2012 02:36:27 +0400
Glauber Costa <glommer@...allels.com> wrote:

> On 06/25/2012 10:29 PM, Tejun Heo wrote:
> > Feeling like a nit pervert but..
> >
> > On Mon, Jun 25, 2012 at 06:15:26PM +0400, Glauber Costa wrote:
> >> @@ -287,7 +287,11 @@ struct mem_cgroup {
> >>   	 * Should the accounting and control be hierarchical, per subtree?
> >>   	 */
> >>   	bool use_hierarchy;
> >> -	bool kmem_accounted;
> >> +	/*
> >> +	 * bit0: accounted by this cgroup
> >> +	 * bit1: accounted by a parent.
> >> +	 */
> >> +	volatile unsigned long kmem_accounted;
> >
> > Is the volatile declaration really necessary?  Why is it necessary?
> > Why no comment explaining it?
> 
> Seems to be required by set_bit and friends. gcc will complain if it is 
> not volatile (take a look at the bit function headers)

That would be a broken gcc.  We run test_bit()/set_bit() and friends
against plain old `unsigned long' in thousands of places.  There's
nothing special about this one!


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