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

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Message-ID: <20100513105204.GT3296@balbir.in.ibm.com>
Date:	Thu, 13 May 2010 16:22:04 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Dhaval Giani <dhaval.giani@...il.com>
Cc:	Paul Menage <menage@...gle.com>, peterz@...radead.org,
	lennart@...ttering.net, jsafrane@...hat.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC] Have sane default values for cpusets

* Dhaval Giani <dhaval.giani@...il.com> [2010-05-13 12:26:30]:

> On Wed, May 12, 2010 at 9:59 PM, Dhaval Giani <dhaval.giani@...il.com> wrote:
> > On Wed, May 12, 2010 at 9:36 PM, Paul Menage <menage@...gle.com> wrote:
> >> On Wed, May 12, 2010 at 12:29 PM, Dhaval Giani <dhaval.giani@...il.com> wrote:
> >>>> I think the idea is reasonable - the only way that I could see it
> >>>> breaking someone would be code that currently does something like:
> >>>>
> >>>> mkdir A
> >>>> mkdir B
> >>>> echo 1 > A/mem_exclusive
> >>>> echo 1 > B/mem_exclusive
> >>>> echo $mems_for_a > A/mems
> >>>> echo $mems_for_b > B/mems
> >>>>
> >>>> The attempts to set the mem_exclusive flags would fail, since A and B
> >>>> would both have all of the parent's mems.
> >>>>
> >>>
> >>> But would this not fail otherwise?
> >>>
> >>
> >> Assuming that mems_for_a and mems_for_b were disjoint, it would be
> >> fine currently.
> >>
> >
> > Ah my bad. I misread mems_for_a as taking the value from the parent.
> > You are right, that was a case I missed.
> >
> > Hmm, so how do we fix this? Any solutions? Not fixing the kernel
> > pushes the problem to the userspace, making it hard for tons of more
> > applications to use cgroups without jumping through a lot of hoops.
> >
> 
> OK, how about this. Introduce a new option, nodefaults (or some such
> name) which would retain the existing behaviour while the default
> mount options would moutn cpuset with the defaults. Also, make
> 
> mount -t cpuset cpuset /cpuset
> 
> equivalent to
> 
> mount -t cgroup -onoprefix,nodefaults,cpuset cpuset /cpuset
>

Does something like cpusetinherits make more sense.

-- 
	Three Cheers,
	Balbir
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