Re: A Plumber’s Wish List for Linux

From: Li Zefan
Date: Mon Oct 31 2011 - 21:26:14 EST

Lennart Poettering wrote:
> On Tue, 25.10.11 13:40, Li Zefan (lizf@xxxxxxxxxxxxxx) wrote:
>>> 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.
> I am quite convinced that using eventfd() like this is quite ugly. The
> current evetnfd() logic is not recursive anyway, hence wouldn't help us
> much.

I remember in an earlier email you stated you want to be able to kill all tasks
in a cgroup and its children, and you used the word "recursive", but what do you
mean by ""recursive" for empty cgroup notification, do you expect the listener
to recieve a message if a cgroup or any of its children becomes empty?
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