On Tue, Sep 05, 2017 at 05:12:51PM +0200, Michal Hocko wrote: > On Tue 05-09-17 15:30:21, Roman Gushchin wrote: > > On Tue, Sep 05, 2017 at 03:44:12PM +0200, Michal Hocko wrote: > [...] > > > Why is this an opt out rather than opt-in? IMHO the original oom logic > > > should be preserved by default and specific workloads should opt in for > > > the cgroup aware logic. Changing the global behavior depending on > > > whether cgroup v2 interface is in use is more than unexpected and IMHO > > > wrong approach to take. I think we should instead go with > > > oom_strategy=[alloc_task,biggest_task,cgroup] > > > > > > we currently have alloc_task (via sysctl_oom_kill_allocating_task) and > > > biggest_task which is the default. You are adding cgroup and the more I > > > think about the more I agree that it doesn't really make sense to try to > > > fit thew new semantic into the existing one (compare tasks to kill-all > > > memcgs). Just introduce a new strategy and define a new semantic from > > > scratch. Memcg priority and kill-all are a natural extension of this new > > > strategy. This will make the life easier and easier to understand by > > > users. > > > > > > Does that make sense to you? > > > > Absolutely. > > > > The only thing: I'm not sure that we have to preserve the existing logic > > as default option. For most users (except few very specific usecases), > > it should be at least as good, as the existing one. > > But this is really an unexpected change. Users even might not know that > they are using cgroup v2 and memcg is in use. > > > Making it opt-in means that corresponding code will be executed only > > by few users, who cares. > > Yeah, which is the way we should introduce new features no? > > > Then we should probably hide corresponding > > cgroup interface (oom_group and oom_priority knobs) by default, > > and it feels as unnecessary complication and is overall against > > cgroup v2 interface design. > > Why. If we care enough, we could simply return EINVAL when those knobs > are written while the corresponding strategy is not used. It doesn't look as a nice default interface. > > > > I think we should instead go with > > > oom_strategy=[alloc_task,biggest_task,cgroup] > > > > It would be a really nice interface; although I've no idea how to implement it: > > "alloc_task" is an existing sysctl, which we have to preserve; > > I would argue that we should simply deprecate and later drop the sysctl. > I _strongly_ suspect anybody is using this. If yes it is not that hard > to change the kernel command like rather than select the sysctl. I agree. And if so, why do we need a new interface for an useless feature? > > > while "cgroup" depends on cgroup v2. > > Which is not a big deal either. Simply fall back to default if there are > no cgroup v2. The implementation would have essentially the same effect > because there won't be any kill-all cgroups and so we will select the > largest task. I'd agree with you, if there are use cases (excluding pure legacy), when the per-process algorithm is preferable over the cgroup-aware OOM. I really doubt, and hope, that with oom_priorities the suggested algorithm should cover almost all reasonable use cases. Thanks! -- 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
