linux-kernel - Re: [PATCH/RFC] Have sane default values for cpusets

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Message-ID: <AANLkTikEyJ8q9GkpyZo0OUY4MLM_soWEviiBG2R6H-mY@mail.gmail.com>
Date:	Wed, 12 May 2010 19:42:20 +0200
From:	Dhaval Giani <dhaval.giani@...il.com>
To:	James Kosin <jkosin@...comgrp.com>
Cc:	Jan Safranek <jsafrane@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, menage@...gle.com,
	balbir@...ux.vnet.ibm.com, lennart@...ttering.net,
	tglx@...utronix.de
Subject: Re: [PATCH/RFC] Have sane default values for cpusets

On Wed, May 12, 2010 at 7:38 PM, James Kosin <jkosin@...comgrp.com> wrote:
> On 5/12/2010 10:40 AM, Jan Safranek wrote:
>
> On 05/12/2010 04:20 PM, Peter Zijlstra wrote:
>
> On Wed, 2010-05-12 at 16:13 +0200, Dhaval Giani wrote:
>
> What you are saying is that an application
> programmer who wants to just use memory cgroups should also care about
> cpusets and just about countless other cgroup subsystems that can
> exist.
>
> That's exactly what he says if he mounts them together.
>
> No, the programmer does not mount anything. Programmer writes application
> which wants to create a subgroup. System admin is the one who decides what
> is mounted how. And the programmer (=me) needs a way how to reliably create
> a subgroup, without knowing details about all controllers. E.g. 'blkio'
> controller is quite new one, old applications do now know anything about it,
> yet according to your idea, the application *must* provide sane defaults to
> it.
>
> Jan
>
>
> Jan,
>
> I think sane defaults should be enforced only if the application actively
> uses the device.  Your right in that you don't want to have to guess as to
> which devices are mounted as long as you don't touch the devices that aren't
> mounted everything should be okay and work for the specific device or mount
> you are working with  (which by the way you need to know!!!)....
>

I seem to get the impression that there is a miscommunication here. We
are talking about the cgroups feature here (more details are available
at http://www.mjmwired.net/kernel/Documentation/cgroups.txt ). We
really are not talking about devices, but about specific cgroup
subsystems which can be mounted together, and are not under the
control of the programmer.

> PS: Providing a set of defaults on creation may lead to a security
> problem... just an afterthought.
>

Which is why you have *sane* defaults.

Dhaval
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