linux-kernel - Re: [PATCH v4.15-rc9] sched, cgroup: Don't reject lower cpu.max on ancestors

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Message-ID: <20180201195710.GK1121507@devbig577.frc2.facebook.com>
Date:   Thu, 1 Feb 2018 11:57:10 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v4.15-rc9] sched, cgroup: Don't reject lower cpu.max on
 ancestors

Hello,

On Thu, Feb 01, 2018 at 05:49:42PM +0100, Peter Zijlstra wrote:
> > Well, they're upper limits, not strict allocations.  The current
> > behavior implemented by cpu isn't either a strict allocation or upper
> > limits.  It disallows a child from having a value higher than the
> > parent (allocation-ish) but the sum of the children is allowed to
> > exceed the parent's (limit-ish).
> 
> True; but its still weird to have the parent 'promise' something and
> then retract that 'promise' later.

Yeah, depending on how you look at it, it can feel weird.  It's just
that viewing these absolute resource limits (cpu.max,
memory.{high,max}, io.max, pids.max) as upper bounds seems to be the
best abstraction in terms of capturing what they do and making uses of
them in a robust way.

> > We had this sort of input validations in different controllers all in
> > their own ways.  In most cases, these aren't well thought out and we
> > can't support things like delegation without aligning controller
> > behaviors.
> 
> I suppose.. 
> 
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Will route it through cgroup fixes branch in a week or so.

Thanks a lot.

-- 
tejun