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

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Date:   Tue, 18 Jul 2017 13:23:14 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>
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

On 07/18/2017 01:10 PM, Tejun Heo wrote:
> 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.
I am not advocating on removing the invalid state now as I note about
sibling cgroups. I am just saying that there is no point in not doing an
automatic conversion to threaded for newly created children of threaded
cgroups (not thread root). I don't see any cons in doing that.

Cheers,
Longman