On Thu, Aug 24, 2017 at 02:58:11PM +0200, Michal Hocko wrote: > On Thu 24-08-17 13:28:46, Roman Gushchin wrote: > > Hi Michal! > > > There is nothing like a "better victim". We are pretty much in a > catastrophic situation when we try to survive by killing a userspace. Not necessary, it can be a cgroup OOM. > We try to kill the largest because that assumes that we return the > most memory from it. Now I do understand that you want to treat the > memcg as a single killable entity but I find it really questionable > to do a per-memcg metric and then do not treat it like that and kill > only a single task. Just imagine a single memcg with zillions of taks > each very small and you select it as the largest while a small taks > itself doesn't help to help to get us out of the OOM. I don't think it's different from a non-containerized state: if you have a zillion of small tasks in the system, you'll meet the same issues. > > > 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? > > > > It sounds like a more expensive way to get almost the same with less accuracy. > > Why it's better? > > because then you are comparing apples to apples? Well, I can say that I compare some number of pages against some other number of pages. And the relation between a page and memcg is more obvious, than a relation between a page and a process. Both ways are not ideal, and sum of the processes is not ideal too. Especially, if you take oom_score_adj into account. Will you respect it? I've started actually with such approach, but then found it weird. > Besides that you have > to check each task for over-killing anyway. So I do not see any > performance merits here. It's an implementation detail, and we can hopefully get rid of it at some point. > > > > How do you want to compare memcg score with tasks score? > > > > I have to do it for tasks in root cgroups, but it shouldn't be a common case. > > How come? I can easily imagine a setup where only some memcgs which > really do need a kill-all semantic while all others can live with single > task killed perfectly fine. I mean taking a unified cgroup hierarchy into an account, there should not be lot of tasks in the root cgroup, if any. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
