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

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Date:	Tue, 16 Nov 2010 15:17:57 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Lennart Poettering <mzxreary@...inter.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>,
	Oleg Nesterov <oleg@...hat.com>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

On Tue, Nov 16, 2010 at 11:56:33AM -0800, Paul Menage wrote:
> On Tue, Nov 16, 2010 at 11:45 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > In a system daemon? Good luck with that. It's a nightmare. Maybe you
> > could just poll all the cgroups, and try to remove them once a minute,
> > and if they are empty it works. Or something like that. But what a
> > hacky thing it would be.
> 
> There's an existing cgroups API - release_agent and notify_on_release
> - whereby the kernel will spawn a userspace command once a given
> cgroup is completely empty. It's intended for pretty much exactly this
> purpose.

Yes. And it seems to be working just fine for me. I modiefied Lennart's
script a bit to achieve that.

Addition to my .bashrc.

if [ "$PS1" ] ; then
        mkdir -m 0700 -p /cgroup/cpu/$$
        echo 1 > /cgroup/cpu/$$/notify_on_release
        echo $$ > /cgroup/cpu/$$/tasks
fi

I created one file /bin/rmcgroup to clean up the cgroup.

#!/bin/bash
rmdir /cgroup/cpu/$1

And did following to mount cgroup and setup empty group notification.

mount -t cgroup -o cpu none /cgroup/cpu
echo "/bin/rmcgroup" > /cgroup/cpu/release_agent

And it works fine. Upon ssh to my box, a cpu cgroup is automatically
created and upon exiting the shell, this group is automatically destroyed.

So API/interface for automatically reclaiming the cgroup once it is empty 
seems to be pretty simple and works.

Thanks
Vivek
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