On Wed 30-08-17 13:57:29, Roman Gushchin wrote: > On Wed, Aug 30, 2017 at 02:55:43PM +0200, Michal Hocko wrote: > > On Wed 30-08-17 13:44:59, Roman Gushchin wrote: > > > On Wed, Aug 30, 2017 at 02:36:55PM +0200, Michal Hocko wrote: > > > > On Tue 29-08-17 11:01:50, Roman Gushchin wrote: > > > > [...] > > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > > > > index b9cf3cf4a3d0..a69d23082abf 100644 > > > > > --- a/mm/memcontrol.c > > > > > +++ b/mm/memcontrol.c > > > > > @@ -1792,6 +1792,9 @@ static void refill_stock(struct mem_cgroup > > > > > *memcg, unsigned int nr_pages) > > > > > } > > > > > stock->nr_pages += nr_pages; > > > > > > > > > > + if (stock->nr_pages > CHARGE_BATCH) > > > > > + drain_stock(stock); > > > > > + > > > > > local_irq_restore(flags); > > > > > } > > > > > > > > Why do we need this? In other words, why cannot we rely on draining we > > > > already do? > > > > > > The existing draining depends on memory pressure, so to keep > > > the accounting (which we expose to a user) reasonable accurate > > > even without memory pressure, we need to limit the size of per-cpu stocks. > > > > Why don't we need this for regular page charges? Or maybe we do but that > > sounds like a seprate and an unrealted fix to me. > > Because we never refill more than CHARGE_BATCH.
You are right that a single process will not but try_charge is a preemptible context and so multiple processes might pass consume_stock and then charge a N*CHARGE_BATCH. But I agree that this is quite unlikely so a separate patch is probably not worth it. -- Michal Hocko SUSE Labs
