On Tue, Oct 31, 2017 at 10:50:43AM -0700, Shakeel Butt wrote: > On Tue, Oct 31, 2017 at 9:40 AM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > On Tue, Oct 31, 2017 at 08:04:19AM -0700, Shakeel Butt wrote: > >> > + > >> > +static void select_victim_memcg(struct mem_cgroup *root, struct oom_control *oc) > >> > +{ > >> > + struct mem_cgroup *iter; > >> > + > >> > + oc->chosen_memcg = NULL; > >> > + oc->chosen_points = 0; > >> > + > >> > + /* > >> > + * The oom_score is calculated for leaf memory cgroups (including > >> > + * the root memcg). > >> > + */ > >> > + rcu_read_lock(); > >> > + for_each_mem_cgroup_tree(iter, root) { > >> > + long score; > >> > + > >> > + if (memcg_has_children(iter) && iter != root_mem_cgroup) > >> > + continue; > >> > + > >> > >> Cgroup v2 does not support charge migration between memcgs. So, there > >> can be intermediate nodes which may contain the major charge of the > >> processes in their leave descendents. Skipping such intermediate nodes > >> will kind of protect such processes from oom-killer (lower on the list > >> to be killed). Is it ok to not handle such scenario? If yes, shouldn't > >> we document it? > > > > Tasks cannot be in intermediate nodes, so the only way you can end up > > in a situation like this is to start tasks fully, let them fault in > > their full workingset, then create child groups and move them there. > > > > That has attribution problems much wider than the OOM killer: any > > local limits you would set on a leaf cgroup like this ALSO won't > > control the memory of its tasks - as it's all sitting in the parent. > > > > We created the "no internal competition" rule exactly to prevent this > > situation. > > Rather than the "no internal competition" restriction I think "charge > migration" would have resolved that situation? Also "no internal > competition" restriction (I am assuming 'no internal competition' is > no tasks in internal nodes, please correct me if I am wrong) has made > "charge migration" hard to implement and thus not added in cgroup v2. > > I know this is parallel discussion and excuse my ignorance, what are > other reasons behind "no internal competition" specifically for memory > controller? Sorry, but this is completely off-topic. The rationale for this decisions is in Documentation/cgroup-v2.txt. -- 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