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. 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. -- 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>