This doesn't apply on top of mmotm cleanly. You are missing http://lkml.kernel.org/r/20170807113839.16695-3-mhocko@xxxxxxxxxx On Wed 23-08-17 17:51:59, Roman Gushchin wrote: > Traditionally, the OOM killer is operating on a process level. > Under oom conditions, it finds a process with the highest oom score > and kills it. > > This behavior doesn't suit well the system with many running > containers: > > 1) There is no fairness between containers. A small container with > few large processes will be chosen over a large one with huge > number of small processes. > > 2) Containers often do not expect that some random process inside > will be killed. In many cases much safer behavior is to kill > all tasks in the container. Traditionally, this was implemented > in userspace, but doing it in the kernel has some advantages, > especially in a case of a system-wide OOM. > > 3) Per-process oom_score_adj affects global OOM, so it's a breache > in the isolation. Please explain more. I guess you mean that an untrusted memcg could hide itself from the global OOM killer by reducing the oom scores? Well you need CAP_SYS_RESOURCE do reduce the current oom_score{_adj} as David has already pointed out. I also agree that we absolutely must not kill an oom disabled task. I am pretty sure somebody is using OOM_SCORE_ADJ_MIN as a protection from an untrusted SIGKILL and inconsistent state as a result. Those applications simply shouldn't behave differently in the global and container contexts. If nothing else we have to skip OOM_SCORE_ADJ_MIN tasks during the kill. > To address these issues, cgroup-aware OOM killer is introduced. > > Under OOM conditions, it tries to find the biggest memory consumer, > and free memory by killing corresponding task(s). The difference > the "traditional" OOM killer is that it can treat memory cgroups > as memory consumers as well as single processes. > > By default, it will look for the biggest leaf cgroup, and kill > the largest task inside. Why? I believe that the semantic should be as simple as kill the largest oom killable entity. And the entity is either a process or a memcg which is marked that way. Why should we mix things and select a memcg to kill a process inside it? More on that below. > 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. If anything you wouldn't have to treat the root memcg any special. It will be like any other memcg which doesn't have oom_kill_all_tasks... [...] > +static long memcg_oom_badness(struct mem_cgroup *memcg, > + const nodemask_t *nodemask) > +{ > + long points = 0; > + int nid; > + pg_data_t *pgdat; > + > + for_each_node_state(nid, N_MEMORY) { > + if (nodemask && !node_isset(nid, *nodemask)) > + continue; > + > + points += mem_cgroup_node_nr_lru_pages(memcg, nid, > + LRU_ALL_ANON | BIT(LRU_UNEVICTABLE)); > + > + pgdat = NODE_DATA(nid); > + points += lruvec_page_state(mem_cgroup_lruvec(pgdat, memcg), > + NR_SLAB_UNRECLAIMABLE); > + } > + > + points += memcg_page_state(memcg, MEMCG_KERNEL_STACK_KB) / > + (PAGE_SIZE / 1024); > + points += memcg_page_state(memcg, MEMCG_SOCK); > + points += memcg_page_state(memcg, MEMCG_SWAP); > + > + return points; I guess I have asked already and we haven't reached any consensus. I do not like how you treat memcgs and tasks differently. Why cannot we have a memcg score a sum of all its tasks? How do you want to compare memcg score with tasks score? This just smells like the outcome of a weird semantic that you try to select the largest group I have mentioned above. This is a rather fundamental concern and I believe we should find a consensus on it before going any further. I believe that users shouldn't see any difference in the OOM behavior when memcg v2 is used and there is no kill-all memcg. If there is such a memcg then we should treat only those specially. But you might have really strong usecases which haven't been presented or I've missed their importance. -- 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
