linux-kernel - Re: [PATCH v11 7/9] cpuset: Expose cpus.effective and mems.effective on cgroup v2 root

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Message-ID: <20180720114549.GY72677@devbig577.frc2.facebook.com>
Date:   Fri, 20 Jul 2018 04:45:49 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Waiman Long <longman@...hat.com>, 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,
        Mike Galbraith <efault@....de>, torvalds@...ux-foundation.org,
        Roman Gushchin <guro@...com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH v11 7/9] cpuset: Expose cpus.effective and mems.effective
 on cgroup v2 root

Hello,

On Fri, Jul 20, 2018 at 01:31:21PM +0200, Peter Zijlstra wrote:
> On Thu, Jul 19, 2018 at 09:52:01AM -0700, Tejun Heo wrote:
> > On Thu, Jul 19, 2018 at 11:52:46AM -0400, Waiman Long wrote:
> > > BTW, the way the partition is currently implemented right now is that a
> > > child cannot be a partition root unless its parent is a partition root
> > > itself. That is to avoid turning on partition to affect ancestors
> > > further up the hierarchy than just the parent. So in the case of a
> > > container, it cannot allocate sub-partitions underneath it unless it is
> > > a partition itself. Will that solve your concern?
> > 
> > Hmm... so a given ancestor must be able to both
> > 
> > 1. control which cpus are moved into a partition in all of its
> >    subtree.
> 
> By virtue of the partition file being owned by the parent, this is
> already achived, no?

The currently proposed implementation is somewhere in the middle.  It
kinda gets there by restricting a partition to be a child of another
partition, which may be okay but it does make the whole delegation
mechanism less useful.

> > 2. take away any given cpu from ist subtree.
> 
> I really hate this obsession of yours and doubly so for partitions. But
> why would this currently not be allowed?

Well, sorry that you hate it.  It's a fundamental architectural
constraint.  If it can't satisfy that, it should't be in cgroup.

Thanks.

-- 
tejun