linux-kernel - Re: [RFC PATCH-cgroup 1/6] cgroup: Relax the no internal process constraint

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Message-ID: <6c115cf4-e229-413c-f63f-26fb8fd870d9@redhat.com>
Date:   Wed, 21 Jun 2017 17:50:09 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com, pjt@...gle.com,
        luto@...capital.net, efault@....de, torvalds@...ux-foundation.org
Subject: Re: [RFC PATCH-cgroup 1/6] cgroup: Relax the no internal process
 constraint

On 06/21/2017 05:39 PM, Tejun Heo wrote:
> Hello,
>
> On Wed, Jun 21, 2017 at 05:37:00PM -0400, Waiman Long wrote:
>>> What happens when we add domain handling to CPU so that it is both a
>>> domain and resource controller?  Even if that somehow can be resolved,
>>> wouldn't that come with a rather surprising userland behavior changes?
>>> Also, I'm not sure what we're achieving by doing this.  It doesn't
>>> really relax the restriction.  It just turns it off implicitly when
>>> certain conditions are met, which doesn't really allow any real
>>> capabilities and at least to me the behaviors feel more subtle and
>>> complicated than before.
>> I think CPU isn't a good example for that.
> Can you please elaborate?

CPU is probably the most prominent controller where deep hierarchy has a
performance cost. So I can't envision that it will forbid internal
process competition.
 
>> Another alternative is to treat no internal process as a controller
>> attribute. Then we don't need to worry about this intricate question and
>> let the  controllers decide if they will allow internal processes.
> Isn't that what "threaded" is?
>

That is exactly what this patch intends to do. However, you raised
concern that threaded may not be equivalent to the need of allowing
internal process. That is why I propose that. If your concern is only
about the documentation change, we can certainly fix that.

Cheers,
Longman