Recently Shakeel reported a issue which also confused me several 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 of un-needed warnings. So, ignore all such warnings from memory.max. 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 from OOM kill. 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 a try. Basically why setting memory.max to 0 is better than setting memory.high to 0 before deletion. The reason is remote charging. High reclaim does not work for remote memcg and the usage can go till max or global pressure. [shakeelb@xxxxxxxxxx: improve commit log] Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Roman Gushchin <guro@xxxxxx> Cc: Greg Thelen <gthelen@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
