Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

[Lennart Poettering <mzxreary@0pointer.de>]

On Fri, 19.11.10 14:12, Ben Gamari (bgamari.foss@gmail.com) wrote:

> 
> On Fri, 19 Nov 2010 09:51:14 -0800, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > And the user level approach? I think it's fine too. If you run systemd
> > for other reasons (or if the gnome people add it to the task launcher
> > or whatever), doing it there isn't wrong. I personally think it's
> > somewhat disgusting to have a user-level callback with processes etc
> > just to clean up a group, but whatever.  As long as it's not common,
> > who cares?
> > 
> On that note, is there a good reason why the notify_on_release interface
> works the way it does? Wouldn't it be simpler if the cgroup simply
> provided a file on which a process (e.g. systemd) could block?

The notify_on_release interface is awful indeed. Feels like the old
hotplug interface where each module request by the kernel caused a
hotplug script to be spawned by the kernel.

However, I am not sure I like the idea of having pollable files like that,
because in the systemd case I am very much interested in getting
recursive notifications, i.e. I want to register once for getting
notifications for a full subtree instead of having to register for each
cgroup individually.

My personal favourite solution would be to get a netlink msg when a
cgroup runs empty. That way multiple programs could listen to the events
at the same time, and we'd have an easy way to subscribe to a whole
hierarchy of groups.

Lennart

-- 
Lennart Poettering - Red Hat, Inc.