Messages in this thread | | | Date | Tue, 25 Oct 2011 13:40:14 +0800 | From | Li Zefan <> | Subject | Re: A Plumber’s Wish List for Linux |
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Lennart Poettering wrote: > On Sat, 22.10.11 12:21, Frederic Weisbecker (fweisbec@gmail.com) wrote: > >> If you really need to stop any forks in a cgroup, then a cgroup core feature >> handling that very single purpose would be better and more efficient. > > We'd be happy with that and this is what we originally suggested actually. > >> That said I'm not really sure why you're using cgroups in Systemd. > > We want to reliably label processes in a hierarchial way, so that this > is inherited by all child processes, cannot be overriden by unprivileged > code (subject to some classic Unix access control handling) and get > notifications when such a label stops referring to any process. We use > that for sticking the service name on a process, so that all CGI > processes of Apache are automatically assigned the same service as > apache itself. And we want a notification when all of apache's processes > die. And we also want to be able to kill Apache compeltely by killing > all its processes. > > cgroups provides us with all of that, though the last two items only in > a suboptimal way: notification of cgroups running empty is ugly, since > it is done by spawning a usermode helper (we'd prefer a netlink msg or > so), and the process killing is a bit racy. >
How about using eventfd? You can create an eventfd for the specific "tasks" file, and when the cgroup gets empty (no task in it), you'll get a notification.
It should be easy to implement, since cgroup already supports eventfd-based API.
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