On Tue, Apr 15, 2014 at 7:48 PM, Li Zefan <lizefan@xxxxxxxxxx> wrote: > On 2014/4/15 5:44, Tejun Heo wrote: >> cgroup users often need a way to determine when a cgroup's >> subhierarchy becomes empty so that it can be cleaned up. cgroup >> currently provides release_agent for it; unfortunately, this mechanism >> is riddled with issues. >> >> * It delivers events by forking and execing a userland binary >> specified as the release_agent. This is a long deprecated method of >> notification delivery. It's extremely heavy, slow and cumbersome to >> integrate with larger infrastructure. >> >> * There is single monitoring point at the root. There's no way to >> delegate management of subtree. >> >> * The event isn't recursive. It triggers when a cgroup doesn't have >> any tasks or child cgroups. Events for internal nodes trigger only >> after all children are removed. This again makes it impossible to >> delegate management of subtree. >> >> * Events are filtered from the kernel side. "notify_on_release" file >> is used to subscribe to or suppress release event. This is >> unnecessarily complicated and probably done this way because event >> delivery itself was expensive. >> >> This patch implements interface file "cgroup.subtree_populated" which >> can be used to monitor whether the cgroup's subhierarchy has tasks in >> it or not. Its value is 0 if there is no task in the cgroup and its >> descendants; otherwise, 1, and kernfs_notify() notificaiton is >> triggers when the value changes, which can be monitored through poll >> and [di]notify. >> > > For the old notification mechanism, the path of the cgroup that becomes > empty will be passed to the user specified release agent. Like this: > > # cat /sbin/cpuset_release_agent > #!/bin/sh > rmdir /dev/cpuset/$1 > > How do we achieve this using inotify? > > - monitor all the cgroups, or > - monitor all the leaf cgroups, and travel cgrp->parent to delete all > empty cgroups. > - monitor root cgroup only, and travel the whole hierarchy to find > empy cgroups when it gets an fs event. > > Seems none of them is scalible. The manager would add all cgroups as watches to one inotify file descriptor, it should not be problem to do that. Kay _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
