On Tue, Aug 08, 2017 at 04:24:32PM -0700, David Rientjes wrote: > On Wed, 26 Jul 2017, Roman Gushchin wrote: > > > +Cgroup-aware OOM Killer > > +~~~~~~~~~~~~~~~~~~~~~~~ > > + > > +Cgroup v2 memory controller implements a cgroup-aware OOM killer. > > +It means that it treats memory cgroups as first class OOM entities. > > + > > +Under OOM conditions the memory controller tries to make the best > > +choise of a victim, hierarchically looking for the largest memory > > +consumer. By default, it will look for the biggest task in the > > +biggest leaf cgroup. > > + > > +Be default, all cgroups have oom_priority 0, and OOM killer will > > +chose the largest cgroup recursively on each level. For non-root > > +cgroups it's possible to change the oom_priority, and it will cause > > +the OOM killer to look athe the priority value first, and compare > > +sizes only of cgroups with equal priority. > > + > > +But a user can change this behavior by enabling the per-cgroup > > +oom_kill_all_tasks option. If set, it causes the OOM killer treat > > +the whole cgroup as an indivisible memory consumer. In case if it's > > +selected as on OOM victim, all belonging tasks will be killed. > > + > > +Tasks in the root cgroup are treated as independent memory consumers, > > +and are compared with other memory consumers (e.g. leaf cgroups). > > +The root cgroup doesn't support the oom_kill_all_tasks feature. > > + > > +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. > > + > > IO > > -- > > Thanks very much for following through with this. > > As described in http://marc.info/?l=linux-kernel&m=149980660611610 this is > very similar to what we do for priority based oom killing. > > I'm wondering your comments on extending it one step further, however: > include process priority as part of the selection rather than simply memcg > priority. > > memory.oom_priority will dictate which memcg the kill will originate from, > but processes have no ability to specify that they should actually be > killed as opposed to a leaf memcg. I'm not sure how important this is for > your usecase, but we have found it useful to be able to specify process > priority as part of the decisionmaking. > > At each level of consideration, we simply kill a process with lower > /proc/pid/oom_priority if there are no memcgs with a lower > memory.oom_priority. This allows us to define the exact process that will > be oom killed, absent oom_kill_all_tasks, and not require that the process > be attached to leaf memcg. Most notably these are processes that are best > effort: stats collection, logging, etc. I'm focused on cgroup v2 interface, that means, that there are no processes belonging to non-leaf cgroups. So, cgroups are compared only with root-cgroup processes, and I'm not sure we really need a way to prioritize them. > > Do you think it would be helpful to introduce per-process oom priority as > well? I'm not against per-process oom_priority, and it might be a good idea to replace the existing oom_score_adj with it at some point. I might be wrong, but I think users mostly using the extereme oom_score_adj values; no one really needs the tiebreaking based on some percentages of the total memory. And oom_priority will be just a simpler and more clear way to express the same intention. But it's not directly related to this patchset, and it's more arguable, so I think it can be done later. -- 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
