On Thu, Aug 24, 2017 at 03:48:59PM +0200, Michal Hocko wrote: > On Thu 24-08-17 13:51:13, Roman Gushchin wrote: > > On Thu, Aug 24, 2017 at 02:10:54PM +0200, Michal Hocko wrote: > > > On Wed 23-08-17 17:52:00, Roman Gushchin wrote: > > > > Introduce a per-memory-cgroup oom_priority setting: an integer number > > > > within the [-10000, 10000] range, which defines the order in which > > > > the OOM killer selects victim memory cgroups. > > > > > > Why do we need a range here? > > > > No specific reason, both [INT_MIN, INT_MAX] and [-10000, 10000] will > > work equally. > > Then do not enforce a range because this just reduces possible usecases > (e.g. timestamp one...). I agree. > > > We should be able to predefine an OOM killing order for > > any reasonable amount of cgroups. > > > > > > > > > OOM killer prefers memory cgroups with larger priority if they are > > > > populated with eligible tasks. > > > > > > So this is basically orthogonal to the score based selection and the > > > real size is only the tiebreaker for same priorities? Could you describe > > > the usecase? Becasuse to me this sounds like a separate oom killer > > > strategy. I can imagine somebody might be interested (e.g. always kill > > > the oldest memcgs...) but an explicit range wouldn't fly with such a > > > usecase very well. > > > > The usecase: you have a machine with several containerized workloads > > of different importance, and some system-level stuff, also in (memory) > > cgroups. > > In case of global memory shortage, some workloads should be killed in > > a first order, others should be killed only if there is no other option. > > Several workloads can have equal importance. Size-based tiebreaking > > is very useful to catch memory leakers amongst them. > > OK, please document that in the changelog. Sure. > > > > That brings me back to my original suggestion. Wouldn't a "register an > > > oom strategy" approach much better than blending things together and > > > then have to wrap heads around different combinations of tunables? > > > > Well, I believe that 90% of this patchset is still relevant; > > agreed and didn't say otherwise. > > > the only > > thing you might want to customize/replace size-based tiebreaking with > > something else (like timestamp-based tiebreaking, mentioned by David earlier). > > > What about tunables, there are two, and they are completely orthogonal: > > 1) oom_priority allows to define an order, in which cgroups will be OOMed > > 2) oom_kill_all defines if all or just one task should be killed > > > > So, I don't think it's a too complex interface. > > > > Again, I'm not against oom strategy approach, it just looks as a much bigger > > project, and I do not see a big need. > > Well, I was thinking that our current oom victim selection code is > quite extensible already. Your patches will teach it kill the whole > group semantic which is already very useful. Now we can talk about the > selection criteria and this is something to be replaceable. Because even > the current discussion has shown that different people might and will > have different requirements. Can we structure the code in such a way > that new comparison algorithm would be simple to add without reworking > the whole selection logic? I'd say that extended oom_priority range and potentially customizable memcg_oom_badness() should do the job for memcgroups. We can extract a part of the oom_badness() into something like this: unsigned long task_oom_badness(struct task_struct *p) { /* * The baseline for the badness score is the proportion of RAM that each * task's rss, pagetable and swap space use. */ return get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) + atomic_long_read(&p->mm->nr_ptes) + mm_nr_pmds(p->mm); } Also, it would be nice to introduce an oom_priority for tasks, as David suggested. > > > Do you have an example, which can't be effectively handled by an approach > > I'm suggesting? > > No, I do not have any which would be _explicitly_ requested but I do > envision new requirements will emerge. The most probable one would be > kill the youngest container because that would imply the least amount of > work wasted. I agree, this a nice feature. It can be implemented in userspace by setting oom_priority. Thanks! Roman -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>