On Tue 09-04-13 17:57:54, Glauber Costa wrote:
> On 04/09/2013 04:13 PM, Michal Hocko wrote:
[...]
> > +static void shrink_zone(struct zone *zone, struct scan_control *sc)
> > +{
> > + bool do_soft_reclaim = mem_cgroup_should_soft_reclaim(sc);
> > + unsigned long nr_scanned = sc->nr_scanned;
> > + unsigned nr_shrunk;
> > +
> > + nr_shrunk = __shrink_zone(zone, sc, do_soft_reclaim);
> > +
> > + /*
> > + * No group is over the soft limit or those that are do not have
> > + * pages in the zone we are reclaiming so we have to reclaim everybody
> > + */
> > + if (do_soft_reclaim && (!nr_shrunk || sc->nr_scanned == nr_scanned)) {
> > + __shrink_zone(zone, sc, false);
> > + return;
> > + }
> > }
>
> If I read this correctly, you stop shrinking when you reach a group in
> which you manage to shrink some pages. Is it really what we want?
Well, this is what we do during standard reclaim __shrink_zone either
walks all children of the target_memcg or reclaim enough pages.
> We have no guarantee that we're now under the soft limit, so shouldn't
> we keep shrinking downwards until every parent of ours is within limits ?
I do not think we should reclaim until we are under soft limit because
our primary target is different - balance zones resp. get under hard
limit. Soft limit just helps us to point at victims (and newly also to
protect high class citizens).
So the second round is just a way to reclaim at least something if
the is nobody eligible for the soft game part. I can see some harder
conditions for the fallback (e.g. only fallback after certain priority
but let's keep this simple for now and do additional parts on top).
Thanks
--
Michal Hocko
SUSE Labs
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