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

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Date:   Tue, 18 Jul 2017 13:54:56 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     lizefan@...wei.com, hannes@...xchg.org, mingo@...hat.com,
        longman@...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, Peter.

On Tue, Jul 18, 2017 at 07:28:01PM +0200, Peter Zijlstra wrote:
> > And now try to create another child C, should that be a domain or
> > threaded?
> 
> Domain of course, as R must be a domain, and hence all its children
> start out as such.

I don't think it's a matter of course as R also is the root of a
threaded subtree, but this is more or less bikeshedding.

> > If we only inherit from the second level on, which is in itself
> > already confusing, that still leads to invalid configs for non-root
> > thread roots.
> 
> I don't see how. I don't get the example Waiman gave, what is wrong
> with:
> 
> 	R (D)
> 	|
> 	A (D)
>        / \
>      C(D) B(T) 
> 
> ? Afaict that's a perfectly valid configuration.

Okay, we're kinda off the rails now.  Just to verify that we're on the
same page, are you also saying that the following should be a valid
configuration?

	R (D)
        |
	A (D and has processes in it and controllers enabled)
        |
        C (D and has processes in it) 

Thanks.

-- 
tejun