linux-kernel - Re: [PATCH 5/6] cgroup: implement cgroup v2 thread support

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Message-ID: <20170718171034.GE585283@devbig577.frc2.facebook.com>
Date:   Tue, 18 Jul 2017 13:10:34 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, lizefan@...wei.com,
        hannes@...xchg.org, 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,
        guro@...com
Subject: Re: [PATCH 5/6] cgroup: implement cgroup v2 thread support

Hello, Waiman.

On Tue, Jul 18, 2017 at 10:37:41AM -0400, Waiman Long wrote:
> Thinking about it some more. There is a place for invalid domain. It is
> not the child of a threaded cgroup. It is the siblings of a threaded
> cgroup whose parent is not root.
> 
>        Root - A (domain) - B (domain)
>                          \ C (domain)
> 
> With "echo threaded > B/cgroup.type":
> 
>        Root - A (threaded domain) - B (threaded)
>                                   \ C (domain, invalid)

Yes, I noted that when I was replying to Peter.

> Any children of a threaded cgroup should be threaded.

It's really difficult to discuss if you just declare that something
should be a certain way without giving rationale for thinking so.

If we could get rid of the invalid state completely that way, I'd
completely agree with you but that isn't the case here as you noted
yourself, so the choice between the two isn't something trivially
clear.  Both choices come with their pros and cons.  We can absoultely
discuss them comparing the pros and cons.

Thanks.

-- 
tejun