On Tue, Jul 7, 2009 at 5:56 PM, KAMEZAWA Hiroyuki<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > I know people likes to wait for file descriptor to get notification in these days. > Can't we have "event" file descriptor in cgroup layer and make it reusable for > other purposes ? I agree - rather than having to add a separate "wait for value to cross X threshold" file for each numeric usage value that people might be concerned about, it would be better to have a generic way to do it for any file. Given that this is a userspace API, it would be better to work out at least the generic API first, even if the initial implementation isn't generic. Properties that it should support include: - notification when a value crosses above or below a given threshold (which would include binary cases such as OOM notification where the value cross from "not-OOM" to "OOM" - independent thresholds for different waiters - epoll support (by using eventfd?) - automatic wakeup when a cgroup is removed - maybe optional wakeup when a thread attach occurs? - not require more than read permissions on the file containing the value being monitored I guess there are a few possible ways this could be exposed to userspace: 1) new ioctl on cgroups files. simple but probably not popular 2) new system call. maybe the cleanest, but involves changing every arch and is hard to script 3) new per-cgroup file to control these e.g: - create an eventfd - open the control file to be monitored - write the "<event_fd>, <control_fd> <threshold> to cgroup.event_control to link them together flexible and scriptable but maybe a clumsy interface in general Paul _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
