linux-kernel - Re: [PATCH] new cgroup controller "fork"

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Date:	Thu, 3 Nov 2011 19:51:08 +0100
From:	Max Kellermann <max@...mpel.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Glauber Costa <glommer@...allels.com>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] new cgroup controller "fork"

On 2011/11/03 19:21, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> > After little discussion, nobody seemed to be interested in it, and
> > nobody merged it.  I reposted it today, not knowing somebody else had
> > come up with a similar idea meanwhile.
> 
> I don't really see a meaningful use case for this. Why should millions of
> users have this stuff in their kernel. What's the general purpose use
> case we should all be excited about ?

Putting a reasonable limit on jobs that are expected to run only for a
limited amount of time, with a limited amount of total resources.  For
example: CGI, cron jobs, backup, munin plugins, virus scanners and
other email filters, procmail, ... - when the job is done, the group
can be deleted, and new instances will run in a new group.

With just RLIMIT_NPROC or task_counter, you can limit the total number
of processes, but it will not stop a fork bomb - it will only slow it
down.  The fork bomb will still bounce between 1 and the limit, and
consume lots of resources for forking and exiting.

(Glauber: the above should answer your last email, too)

Similar existing feature: RLIMIT_CPU.  Millions of users have it in
their kernels, but nobody uses it nowadays.  And it's not even
optional.

Btw. I have no problem with maintaining this patch (and a whole bunch
of others) in my proprietary git repository at work forever.  They're
very useful for my employer.  I'm just trying to be a good citizen by
sharing them.

Max
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