[Devel] Re: [PATCH 09/11] memcg: propagate kmem limiting information to children

[Andrew Morton]

On Tue, 26 Jun 2012 02:36:27 +0400
Glauber Costa <glommer at parallels.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!