linux-kernel - Re: [PATCH v4] cpuset: Enable cpuset controller in default hierarchy

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Date:   Thu, 15 Mar 2018 03:49:01 +0100
From:   Mike Galbraith <efault@....de>
To:     Tejun Heo <tj@...nel.org>
Cc:     Waiman Long <longman@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kernel-team@...com, pjt@...gle.com, luto@...capital.net,
        torvalds@...ux-foundation.org, Roman Gushchin <guro@...com>
Subject: Re: [PATCH v4] cpuset: Enable cpuset controller in default hierarchy

On Wed, 2018-03-14 at 12:57 -0700, Tejun Heo wrote:
> Hello,
> 
> On Sat, Mar 10, 2018 at 04:47:28AM +0100, Mike Galbraith wrote:
> > Some form of cpu_exclusive (preferably exactly that, but something else
> > could replace it) is needed to define sets that must not overlap any
> > other set at creation time or any time thereafter.  A set with property
> > 'exclusive' is the enabler for fundamentally exclusive (but dynamic!)
> > set properties such as 'isolated' (etc etc).
> 
> I'm not sure cpu_exclusive makes sense.  A controller knob can either
> belong to the parent or the cgroup itself and cpu_exclusive doesn't
> make sense in either case.
> 
> 1. cpu_exclusive is owned by the parent as other usual resource
>    control knobs.  IOW, it's not delegatable.
> 
>    This is weird because it's asking the kernel to protect against its
>    own misconfiguration and there's nothing preventing cpu_exclusive
>    itself being cleared by the same entitya.
> 
> 2. cpu_exclusive is owned by the cgroup itself like memory.oom_group.
>    IOW, it's delegatable.
> 
>    This allows a cgroup to affect what its siblings can or cannot do,
>    which is broken.  Semantically, it doesn't make much sense either.
> 
> I don't think it's a good idea to add a kernel mechanism to prevent
> misconfiguration from a single entity.

Under the hood v2 details are entirely up to you.  My input ends at
please don't leave dynamic partitioning standing at the dock when v2
sails.

	-Mike