linux-kernel - Re: [PATCH v3] cpuset: Enable cpuset controller in default hierarchy

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Date:   Thu, 26 Oct 2017 22:59:16 +0200
From:   Christian Brauner <christian.brauner@...onical.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        Mike Galbraith <efault@....de>,
        Stéphane Graber <stgraber@...ntu.com>,
        Serge Hallyn <serge@...lyn.com>
Subject: Re: [PATCH v3] cpuset: Enable cpuset controller in default hierarchy

On Thu, Oct 26, 2017 at 02:12:01PM -0400, Waiman Long wrote:
> On 10/26/2017 10:39 AM, Tejun Heo wrote:
> > Hello, Waiman.
> >
> > On Wed, Oct 25, 2017 at 11:50:34AM -0400, Waiman Long wrote:
> >> Ping! Any comment on this patch?

Fwiw, I just saw this patch today for some weird reason.

> > Sorry about the lack of response.  Here are my two thoughts.
> >
> > 1. I'm not really sure about the memory part.  Mostly because of the
> >    way it's configured and enforced is completely out of step with how
> >    mm behaves in general.  I'd like to get more input from mm folks on
> >    this.
> 
> Yes, I also have doubt about which of the additional features are being
> actively used. That is why the current patch exposes only the memory_migrate
> flag in addition to the core *cpus and *mems control files. All the
> other v1 features are not exposed waiting for further investigation and
> feedback. One way to get more feedback is to have something that people
> can play with. Maybe we could somehow tag it as experimental so that we
> can change the interface later on, when necessary, if you have concern
> about setting the APIs in stone.

This sounds like a reasonable approach to me. The cpuset controller is quite
important from a userspace (especially container) perspective. So making this
an experimental feature for a while to gather feedback seems worth it. I'd be
happy to carry/receive some experimental patches in a liblxc branch for cgroup
v2 to see where the current cpuset controller implementation currently gets us
and send/discuss patches where needed.

> 
> > 2. I want to think more about how we expose the effective settings.
> >    Not that anything is wrong with what cpuset does, but more that I
> >    wanna ensure that it's something we can follow in other cases where
> >    we have similar hierarchical property propagation.
> 
> Currently, the effective setting is exposed via the effective_cpus and
> effective_mems control files. Unlike other controllers that control
> resources, cpuset is unique in the sense that it is propagating
> hierarchical constraints on CPUs and memory nodes down the tree. I
> understand your desire to have a unified framework that can be applied
> to most controllers, but I doubt cpuset is a good model in this regard.
> 
> Cheers,
> Longman
>