Re: [patch 2/3] memcg: prevent endless loop when charging huge pages to near-limit group

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 31 Jan 2011 14:41:31 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Mon, 31 Jan 2011 15:03:54 +0100
> Johannes Weiner <hannes@cmpxchg.org> wrote:
> 
> > +static inline bool res_counter_check_margin(struct res_counter *cnt,
> > +					    unsigned long bytes)
> > +{
> > +	bool ret;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&cnt->lock, flags);
> > +	ret = cnt->limit - cnt->usage >= bytes;
> > +	spin_unlock_irqrestore(&cnt->lock, flags);
> > +	return ret;
> > +}
> > +
> >  static inline bool res_counter_check_under_soft_limit(struct res_counter *cnt)
> >  {
> >  	bool ret;
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 73ea323..c28072f 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -1111,6 +1111,15 @@ static bool mem_cgroup_check_under_limit(struct mem_cgroup *mem)
> >  	return false;
> >  }
> >  
> > +static bool mem_cgroup_check_margin(struct mem_cgroup *mem, unsigned long bytes)
> > +{
> > +	if (!res_counter_check_margin(&mem->res, bytes))
> > +		return false;
> > +	if (do_swap_account && !res_counter_check_margin(&mem->memsw, bytes))
> > +		return false;
> > +	return true;
> > +}
> 
> argh.
> 
> If you ever have a function with the string "check" in its name, it's a
> good sign that you did something wrong.
> 
> Check what?  Against what?  Returning what?
> 
> mem_cgroup_check_under_limit() isn't toooo bad - the name tells you
> what's being checked and tells you what to expect the return value to
> mean.
> 
> But "res_counter_check_margin" and "mem_cgroup_check_margin" are just
> awful.  Something like
> 
> 	bool res_counter_may_charge(counter, bytes)
> 
> would be much clearer.
> 
> If we really want to stick with the "check" names (perhaps as an ironic
> reference to res_counter's past mistakes) then please at least document
> the sorry things?
> 

Ah, I ack the concept of patch.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Johannes, could you change name ? I'm sorry.