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

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Message-ID: <20101120011330.GB4183@tango.0pointer.de>
Date:	Sat, 20 Nov 2010 02:13:30 +0100
From:	Lennart Poettering <mzxreary@...inter.de>
To:	Ben Gamari <bgamari.foss@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, tytso@....edu,
	a.p.zijlstra@...llo.nl, debiandev@...il.com,
	alan@...rguk.ukuu.org.uk, dhaval.giani@...il.com, efault@....de,
	vgoyal@...hat.com, oleg@...hat.com, markus@...ppelsdorf.de,
	mathieu.desnoyers@...icios.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, balbir@...ux.vnet.ibm.com
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

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

> 
> On Fri, 19 Nov 2010 09:51:14 -0800, Linus Torvalds <torvalds@...ux-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.
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