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

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Date:   Fri, 22 Jun 2018 11:00:03 +0800
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 06/21/2018 05:20 PM, Peter Zijlstra wrote:
> 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.

That will certainly be the ideal.

> 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?

Yes, that is right.

> 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.

Do you mean providing a flag like READONLY_AT_ROOT so that it will be
read-only at the real root? That is an cgroup architectural decision
that needs input from Tejun. Anyway, this issue is not specific to this
patchset and I would like to break it out as a separate discussion
independent of this patchset.

Cheers,
Longman