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

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Message-ID: <20180720154454.GR2494@hirez.programming.kicks-ass.net>
Date:   Fri, 20 Jul 2018 17:44:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <tj@...nel.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

On Fri, Jul 20, 2018 at 04:45:49AM -0700, Tejun Heo wrote:

> > > 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.

So the implementation does not set ownership of the 'partition' file to
that of the parent directory? Because _that_ is what I understood from
Waiman (many versions ago). And that _does_ allow delegation to work
nicely.

> > > 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.

So is hierarchical behaviour; but you seem willing to forgo that.

Still, the question was, how is this (dispicable or not) behaviour not
allowed by the current implementation?