On Sat, May 2, 2020 at 7:35 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote: > > Recently Shakeel reported a issue which also confused me serveral months > earlier. Bellow is his report - > > Lowering memory.max can trigger an oom-kill if the reclaim does not > succeed. However if oom-killer does not find a process for killing, it > dumps a lot of warnings. > > Deleting a memcg does not reclaim memory from it and the memory can > linger till there is a memory pressure. One normal way to proactively > reclaim such memory is to set memory.max to 0 just before deleting the > memcg. However if some of the memcg's memory is pinned by others, this > operation can trigger an oom-kill without any process and thus can log a > lot un-needed warnings. So, ignore all such warnings from memory.max. lot *of* un-needed > > [shakeelb@xxxxxxxxxx: commit log above] > > A better way to avoid this issue is to avoid trying to kill a process if > memcg is not populated. > Note that OOM is different with OOM kill. different *from* > OOM is a status that the > system or memcg is out of memory, while OOM kill is a result that a > process inside this memcg is killed when this memcg is in OOM status. > That is the same reason why there're both MEMCG_OOM event and > MEMCG_OOM_KILL event. If we have already known that there's nothing to > kill, i.e. the memcg is not populated, then we don't need to have a try. need to try I think adding the discussion of memory.high is also useful in the commit message. Basically why setting memory.max to 0 is better than setting memory.high to 0 before deletion. The reason is remote charging. > > Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: Roman Gushchin <guro@xxxxxx> > Cc: Greg Thelen <gthelen@xxxxxxxxxx> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> > --- > mm/memcontrol.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 985edce98491..29afe3df9d98 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6102,6 +6102,10 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, > } > > memcg_memory_event(memcg, MEMCG_OOM); > + > + if (!cgroup_is_populated(memcg->css.cgroup)) > + break; > + > if (!mem_cgroup_oom_kill(memcg, GFP_KERNEL, 0)) > break; > } > -- > 2.18.2 >
