linux-kernel - Re: [PATCH v10 2/9] cpuset: Add new v2 cpuset.sched.domain

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Message-ID: <20180621092013.GU2494@hirez.programming.kicks-ass.net>
Date:   Thu, 21 Jun 2018 11:20:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.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,
        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 v10 2/9] cpuset: Add new v2 cpuset.sched.domain_root flag

On Thu, Jun 21, 2018 at 03:58:06PM +0800, Waiman Long wrote:

> As for the inconsistency between the real root and the container root,
> this is true for almost all the controllers. So it is a generic problem.
> One possible solution is to create a kind a pseudo root cgroup for the
> container that looks and feels like a real root. But is there really a
> need to do that?

I don't really know. I thought the idea was to make containers
indistinguishable from a real system. Now I know we're really rather far
away from that in reality, and I really have no clue how important all
that is.

It all depends on how exactly this works; is it like I assumed, that
this file is owned by the parent instead of the current directory? And
that if you namespace this, you have an effective read-only file?

Then fixing the inconsistency is trivial; simply provide a read-only
file for the actual root cgroup too.

And if the solution is trivial, I don't see a good reason not to do it.