On Thu 03-08-17 13:47:51, Roman Gushchin wrote: > On Wed, Aug 02, 2017 at 09:29:01AM +0200, Michal Hocko wrote: > > On Tue 01-08-17 19:13:52, Roman Gushchin wrote: > > > On Tue, Aug 01, 2017 at 07:03:03PM +0200, Michal Hocko wrote: > > > > On Tue 01-08-17 16:25:48, Roman Gushchin wrote: > > > > > On Tue, Aug 01, 2017 at 04:54:35PM +0200, Michal Hocko wrote: > > > > [...] > > > > > > I would reap out the oom_kill_process into a separate patch. > > > > > > > > > > It was a separate patch, I've merged it based on Vladimir's feedback. > > > > > No problems, I can divide it back. > > > > > > > > It would make the review slightly more easier > > > > > > > > > > > > -static void oom_kill_process(struct oom_control *oc, const char *message) > > > > > > > +static void __oom_kill_process(struct task_struct *victim) > > > > > > > > > > > > To the rest of the patch. I have to say I do not quite like how it is > > > > > > implemented. I was hoping for something much simpler which would hook > > > > > > into oom_evaluate_task. If a task belongs to a memcg with kill-all flag > > > > > > then we would update the cumulative memcg badness (more specifically the > > > > > > badness of the topmost parent with kill-all flag). Memcg will then > > > > > > compete with existing self contained tasks (oom_badness will have to > > > > > > tell whether points belong to a task or a memcg to allow the caller to > > > > > > deal with it). But it shouldn't be much more complex than that. > > > > > > > > > > I'm not sure, it will be any simpler. Basically I'm doing the same: > > > > > the difference is that you want to iterate over tasks and for each > > > > > task traverse the memcg tree, update per-cgroup oom score and find > > > > > the corresponding memcg(s) with the kill-all flag. I'm doing the opposite: > > > > > traverse the cgroup tree, and for each leaf cgroup iterate over processes. > > > > > > > > Yeah but this doesn't fit very well to the existing scheme so we would > > > > need two different schemes which is not ideal from maint. point of view. > > > > We also do not have to duplicate all the tricky checks we already do in > > > > oom_evaluate_task. So I would prefer if we could try to hook there and > > > > do the special handling there. > > > > > > I hope, that iterating over all tasks just to check if there are > > > in-flight OOM victims might be optimized at some point. > > > That means, we would be able to choose a victim much cheaper. > > > It's not easy, but it feels as a right direction to go. > > > > You would have to count per each oom domain and that sounds quite > > unfeasible to me. > > It's hard, but traversing the whole cgroup tree from bottom to top > for each task is just not scalable. We are talking about the oom path which is a slow path. Besides that memcg hierarchies will not be very deep usually (we are not talking about hundreds). > This is exactly why I've choosen a compromise right now: let's > iterate over all tasks, but do it by iterating over the cgroup tree. > > > > > > Also, adding new tricks to the oom_evaluate_task() will make the code > > > even more hairy. Some of the existing tricks are useless for memcg selection. > > > > Not sure what you mean but oom_evaluate_task has been usable for both > > global and memcg oom paths so far. I do not see any reason why this > > shouldn't hold for a different oom killing strategy. > > Yes, but in both cases we've evaluated tasks, not cgroups. > > > > > > > > Also, please note, that even without the kill-all flag the decision is made > > > > > on per-cgroup level (except tasks in the root cgroup). > > > > > > > > Yeah and I am not sure this is a reasonable behavior. Why should we > > > > consider memcgs which are not kill-all as a single entity? > > > > > > I think, it's reasonable to choose a cgroup/container to blow off based on > > > the cgroup oom_priority/size (including hierarchical settings), and then > > > kill one biggest or all tasks depending on cgroup settings. > > > > But that doesn't mean you have to treat even !kill-all memcgs like a > > single entity. In fact we should compare killable entities which is > > either a task or the whole memcg if configured that way. > > I believe it's absolutely valid user's intention to prioritize some > cgroups over other, even if only one task should be killed in case of OOM. This is mixing different concepts which I really dislike. The semantic is getting really fuzzy. How are you going to apply memcg priority when you are killing a single task? What portion of the memcgs priority does the task get? Then you have that root is special... No I really dislike this. We should start simple and compare killable entities. If you want to apply memcg priority then only on the whole memcgs. -- 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
