On Thu 03-01-19 11:49:32, Yang Shi wrote: > > > On 1/3/19 11:23 AM, Michal Hocko wrote: > > On Thu 03-01-19 11:10:00, Yang Shi wrote: > > > > > > On 1/3/19 10:53 AM, Michal Hocko wrote: > > > > On Thu 03-01-19 10:40:54, Yang Shi wrote: > > > > > On 1/3/19 10:13 AM, Michal Hocko wrote: > > [...] > > > > > > Is there any reason for your scripts to be strictly sequential here? In > > > > > > other words why cannot you offload those expensive operations to a > > > > > > detached context in _userspace_? > > > > > I would say it has not to be strictly sequential. The above script is just > > > > > an example to illustrate the pattern. But, sometimes it may hit such pattern > > > > > due to the complicated cluster scheduling and container scheduling in the > > > > > production environment, for example the creation process might be scheduled > > > > > to the same CPU which is doing force_empty. I have to say I don't know too > > > > > much about the internals of the container scheduling. > > > > In that case I do not see a strong reason to implement the offloding > > > > into the kernel. It is an additional code and semantic to maintain. > > > Yes, it does introduce some additional code and semantic, but IMHO, it is > > > quite simple and very straight forward, isn't it? Just utilize the existing > > > css offline worker. And, that a couple of lines of code do improve some > > > throughput issues for some real usecases. > > I do not really care it is few LOC. It is more important that it is > > conflating force_empty into offlining logic. There was a good reason to > > remove reparenting/emptying the memcg during the offline. Considering > > that you can offload force_empty from userspace trivially then I do not > > see any reason to implement it in the kernel. > > Er, I may not articulate in the earlier email, force_empty can not be > offloaded from userspace *trivially*. IOWs the container scheduler may > unexpectedly overcommit something due to the stall of synchronous force > empty, which can't be figured out by userspace before it actually happens. > The scheduler doesn't know how long force_empty would take. If the > force_empty could be offloaded by kernel, it would make scheduler's life > much easier. This is not something userspace could do. What exactly prevents ( echo 1 > $memecg/force_empty rmdir $memcg ) & so that this sequence doesn't really block anything? -- Michal Hocko SUSE Labs
