On 08/29/2017 11:24 AM, Tejun Heo wrote: > Hello, Peter. > > On Tue, Aug 29, 2017 at 04:32:52PM +0200, Peter Zijlstra wrote: >> So I mostly like. On accounting it only adds to the immediate cgroup (if >> it has a parent, aka !root). >> >> On update it does a DFS of all sub-groups and propagates the deltas up >> to the requested group. > ... >> What I don't get is why you need cgroup_cpu_stat_updated(). That is, I >> see you use it to keep the keep the DFS 'stack' up-to-date, but what I >> don't see is why you'd need that. > That is to make reading stats O(number of descendants which have been > active since last read) instad of O(number of all descendants) as > there can be a lot of not-too-active cgroups in a system. Stat > reading can be frequent, so the combination can get really bad. By > keeping the updated list separate, increasing read frequency decreases > the cost of each read. > > Also, please note that a system may end up with a lot of cgroups > without the user intending to. memcg drains removed cgroups lazily > and the number of draining cgroups can reach very high numbers if the > system isn't under memory pressure. The plan is to add basic stats > for other resources too and keeping it scalable w.r.t. idle cgroups > allows using the same mechanism for all resources. I think it will be good to put the rationale behind this function as a comment in the code. Cheers, Longman -- 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
