On Mon 29-01-18 11:11:39, Tejun Heo wrote: > Hello, Michal. > > On Mon, Jan 29, 2018 at 11:46:57AM +0100, Michal Hocko wrote: > > @@ -1292,7 +1292,11 @@ the memory controller considers only cgroups belonging to the sub-tree > > of the OOM'ing cgroup. > > > > The root cgroup is treated as a leaf memory cgroup, so it's compared > > -with other leaf memory cgroups and cgroups with oom_group option set. > > +with other leaf memory cgroups and cgroups with oom_group option > > +set. Due to internal implementation restrictions the size of the root > > +cgroup is a cumulative sum of oom_badness of all its tasks (in other > > +words oom_score_adj of each task is obeyed). This might change in the > > +future. > > Thanks, we can definitely use more documentation. However, it's a bit > difficult to follow. Maybe expand it to a separate paragraph on the > current behavior with a clear warning that the default OOM heuristics > is subject to changes? Does this sound any better? >From ea4fa9c36d3ec2cf13d1949169924a1a54b9fcd6 Mon Sep 17 00:00:00 2001 From: Michal Hocko <mhocko@xxxxxxxx> Date: Tue, 30 Jan 2018 09:54:15 +0100 Subject: [PATCH] oom, memcg: clarify root memcg oom accounting David Rientjes has pointed out that the current way how the root memcg is accounted for the cgroup aware OOM killer is undocumented. Unlike regular cgroups there is no accounting going on in the root memcg (mostly for performance reasons). Therefore we are suming up oom_badness of its tasks. This might result in an over accounting because of the oom_score_adj setting. Document this for now. Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> --- Documentation/cgroup-v2.txt | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt index 2eaed1e2243d..67bdf19f8e5b 100644 --- a/Documentation/cgroup-v2.txt +++ b/Documentation/cgroup-v2.txt @@ -1291,8 +1291,14 @@ This affects both system- and cgroup-wide OOMs. For a cgroup-wide OOM the memory controller considers only cgroups belonging to the sub-tree of the OOM'ing cgroup. -The root cgroup is treated as a leaf memory cgroup, so it's compared -with other leaf memory cgroups and cgroups with oom_group option set. +Leaf cgroups are compared based on their cumulative memory usage. The +root cgroup is treated as a leaf memory cgroup as well, so it's +compared with other leaf memory cgroups. Due to internal implementation +restrictions the size of the root cgroup is a cumulative sum of +oom_badness of all its tasks (in other words oom_score_adj of each task +is obeyed). Relying on oom_score_adj (appart from OOM_SCORE_ADJ_MIN) +can lead to overestimating of the root cgroup consumption and it is +therefore discouraged. This might change in the future, though. If there are no cgroups with the enabled memory controller, the OOM killer is using the "traditional" process-based approach. -- 2.15.1 -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
