On Wed 11-06-14 11:20:30, Johannes Weiner wrote: > On Wed, Jun 11, 2014 at 10:00:23AM +0200, Michal Hocko wrote: > > If there is no memcg eligible for reclaim because all groups under the > > reclaimed hierarchy are within their guarantee then the global direct > > reclaim would end up in the endless loop because zones in the zonelists > > are not considered unreclaimable (as per all_unreclaimable) and so the > > OOM killer would never fire and direct reclaim would be triggered > > without no chance to reclaim anything. > > > > This is not possible yet because reclaim falls back to ignore low_limit > > when nobody is eligible for reclaim. Following patch will allow to set > > the fallback mode to hard guarantee, though, so this is a preparatory > > patch. > > > > Memcg reclaim doesn't suffer from this because the OOM killer is > > triggered after few unsuccessful attempts of the reclaim. > > > > Fix this by checking the number of scanned pages which is obviously 0 if > > nobody is eligible and also check that the whole tree hierarchy is not > > eligible and tell OOM it can go ahead. > > > > Signed-off-by: Michal Hocko <mhocko@xxxxxxx> > > --- > > mm/vmscan.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 8041b0667673..99137aecd95f 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -2570,6 +2570,13 @@ out: > > if (aborted_reclaim) > > return 1; > > > > + /* > > + * If the target memcg is not eligible for reclaim then we have no option > > + * but OOM > > + */ > > + if (!sc->nr_scanned && mem_cgroup_all_within_guarantee(sc->target_mem_cgroup)) > > + return 0; > > We can't just sprinkle `for each memcg in hierarchy` loops like this, > they can get really expensive. Yeah, I know. This one gets called only when nothing was scanned which shoudln't happen without the hard guarantee. And as said in other email we can optimize mem_cgroup_all_within_guarantee to skip all subtrees that are within their guarantee. > It's pretty stupid to not have a return value on shrink_zone(), which > could easily indicate whether a zone was reclaimable, and instead have > another iteration over the same zonelist and the same memcg hierarchy > afterwards to figure out if shrink_zone() was successful or not. I know it is stupid but this is the easiest way right now. We can/should refactor shrink_zones to forward that information. I was playing with sticking that infortmation into scan_control but that was even uglier. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>