linux-kernel - Re: A Plumber’s Wish List for Linux

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Date:	Thu, 20 Oct 2011 01:31:11 +0200
From:	Lennart Poettering <mzxreary@...inter.de>
To:	Paul Menage <paul@...lmenage.org>
Cc:	Kay Sievers <kay.sievers@...y.org>, linux-kernel@...r.kernel.org,
	harald@...hat.com, david@...ar.dk, greg@...ah.com
Subject: Re: A Plumber’s Wish List for Linux

On Wed, 19.10.11 16:09, Paul Menage (paul@...lmenage.org) wrote:

> On Wed, Oct 19, 2011 at 4:03 PM, Lennart Poettering
> <mzxreary@...inter.de> wrote:
> >
> > For our systemd usecase a cgroup.signal file would not be useful. This
> > is because we actually kill all members of the service's cgroup plus the
> > main process of the service, which is usually also in the service's
> > cgroup but sometimes isn't (for example: when the user logs in, the
> > whole /sbin/login process ends up in the user's session cgroup, and is
> > removed from the original service cgroup). Since we want to avoid
> > killing the main service process twice in the case where it isn't in the
> > servce cgroup we'd hence prefer to have some fork throttling logic in
> > place, so that we can kill members flexibly in accordance with these
> > rules.
> 
> By fork-throttling, do you just mean "0 or unlimited", or would you
> actually want some kind of rate-limited throttling? If the former,
> than I agree with Frederick that his task counter should solve that
> problem.

Given that shutting down some services might involve forking off a few
things (think: a shell script handling shutdown which forks off a couple
of shell utilities) we'd want something that is between "from now on no
forking at all" and "unlimited forking". This could be done in many
different ways: we'd be happy if we could do time-based rate limiting,
but we'd also be fine with defining a certain budget of additional forks
a cgroup can do (i.e. "from now on you can do 50 more forks, then you'll
get EPERM).

Lennart

-- 
Lennart Poettering - Red Hat, Inc.
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