Re: [PATCH] memcg: Add memory.pressure_level events

[Anton Vorontsov <anton@enomsg.org>]

Hi Greg,

Thanks for taking a look!

On Tue, Feb 12, 2013 at 10:42:51PM -0800, Greg Thelen wrote:
[...]
> > +static unsigned long vmpressure_calc_level(unsigned int win,
> > +					   unsigned int s, unsigned int r)
> 
> Should seems like the return type of this function should be enum
> vmpressure_levels?  If yes, then the 'return 0' below should be
> VMPRESSURE_LOW.  And it would be nice if there was a little comment
> describing the meaning of the win, s, and r parameters.  The "We
> calculate ..." comment below makes me think that win is the number of
> pages scanned, which makes me wonder what the s param is.

Got it, will make it clearer.

[...]
> > +static bool vmpressure_event(struct vmpressure *vmpr,
> > +			     unsigned long s, unsigned long r)
> > +{
> > +	struct vmpressure_event *ev;
> > +	int level = vmpressure_calc_level(vmpressure_win, s, r);
> > +	bool signalled = 0;
> s/bool/int/

Um... I surely can do this, but why do you think it is a good idea?

> > +
> > +	mutex_lock(&vmpr->events_lock);
> > +
> > +	list_for_each_entry(ev, &vmpr->events, node) {
> > +		if (level >= ev->level) {
> > +			eventfd_signal(ev->efd, 1);
> > +			signalled++;
> > +		}
> > +	}
> > +
> > +	mutex_unlock(&vmpr->events_lock);
> > +
> > +	return signalled;

[...]
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1982,6 +1982,10 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
> >  			}
> >  			memcg = mem_cgroup_iter(root, memcg, &reclaim);
> >  		} while (memcg);
> > +
> > +		vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
> > +			   sc->nr_scanned - nr_scanned, nr_reclaimed);
> 
> (sc->nr_scanned - nr_scanned) is the number of pages scanned in above
> while loop but nr_reclaimed is the starting position of the reclaim
> counter before the loop.  It seems like you want:
> 	vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
> 		   sc->nr_scanned - nr_scanned, 
> 		   sc->nr_reclaimed - nr_reclaimed);

Yeah, right you are. There actually was a merge conflict when I rebased my
patch onto linux-next, and it seems that I overlooked that the logic has
changed. So we might get a bit distorted pressure because of that.

Thanks for catching this!

Anton

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