On Tue, Sep 19, 2017 at 01:54:48PM -0700, David Rientjes wrote: > On Fri, 15 Sep 2017, Roman Gushchin wrote: > > > > > > But then you just enforce a structural restriction on your configuration > > > > > because > > > > > root > > > > > / \ > > > > > A D > > > > > /\ > > > > > B C > > > > > > > > > > is a different thing than > > > > > root > > > > > / | \ > > > > > B C D > > > > > > > > > > > > > I actually don't have a strong argument against an approach to select > > > > largest leaf or kill-all-set memcg. I think, in practice there will be > > > > no much difference. > > > > > > > > The only real concern I have is that then we have to do the same with > > > > oom_priorities (select largest priority tree-wide), and this will limit > > > > an ability to enforce the priority by parent cgroup. > > > > > > > > > > Yes, oom_priority cannot select the largest priority tree-wide for exactly > > > that reason. We need the ability to control from which subtree the kill > > > occurs in ancestor cgroups. If multiple jobs are allocated their own > > > cgroups and they can own memory.oom_priority for their own subcontainers, > > > this becomes quite powerful so they can define their own oom priorities. > > > Otherwise, they can easily override the oom priorities of other cgroups. > > > > I believe, it's a solvable problem: we can require CAP_SYS_RESOURCE to set > > the oom_priority below parent's value, or something like this. > > > > But it looks more complex, and I'm not sure there are real examples, > > when we have to compare memcgs, which are on different levels > > (or in different subtrees). > > > > It's actually much more complex because in our environment we'd need an > "activity manager" with CAP_SYS_RESOURCE to control oom priorities of user > subcontainers when today it need only be concerned with top-level memory > cgroups. Users can create their own hierarchies with their own oom > priorities at will, it doesn't alter the selection heuristic for another > other user running on the same system and gives them full control over the > selection in their own subtree. We shouldn't need to have a system-wide > daemon with CAP_SYS_RESOURCE be required to manage subcontainers when > nothing else requires it. I believe it's also much easier to document: > oom_priority is considered for all sibling cgroups at each level of the > hierarchy and the cgroup with the lowest priority value gets iterated. I do agree actually. System-wide OOM priorities make no sense. Always compare sibling cgroups, either by priority or size, seems to be simple, clear and powerful enough for all reasonable use cases. Am I right, that it's exactly what you've used internally? This is a perfect confirmation, I believe. 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
