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

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Hello, Peter.

On Mon, Jul 17, 2017 at 04:14:09PM +0200, Peter Zijlstra wrote:
> AFAICT this is not in fact what I suggested... :/

Heh, sorry about misattributing that.  I was mostly referring to the
overall idea of marking each cgroup domain or threaded rather than
subtree.

> My proposal did not have that invalid state. It would simply refuse to
> change the type from thread to domain in the case where the parent is
> not a domain.
> 
> Also, my proposal maintained the normal property inheritance rules. A
> child cgroup's creation 'type' would be that of its parent and not
> always be 'domain'.

But aren't both of the above get weird when the parent can host both
domain and threaded children?

	 R
       / 
      A(D)

If you create another child B under R, it's naturally gonna be a
domain.  Let's say you turn that to threaded.

	 R
       /   \
     A(D) B(T)

And now try to create another child C, should that be a domain or
threaded?

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 think whether we fail the transition or put the cgroup in an
invalid state is all that material.  The simpler the better.

> Let me read more (and more careful) to see if there's other things.

Sure thing.

Thanks!

-- 
tejun

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[PATCHSET for-4.13] cgroup: implement cgroup2 thread mode, v3 Tejun Heo <tj@kernel.org> - 2017-07-17 04:10 +0200
  [PATCH 2/6] cgroup: add @flags to css_task_iter_start() and implement CSS_TASK_ITER_PROCS Tejun Heo <tj@kernel.org> - 2017-07-17 04:10 +0200
  [PATCH 1/6] cgroup: reorganize cgroup.procs / task write path Tejun Heo <tj@kernel.org> - 2017-07-17 04:10 +0200
  [PATCH 3/6] cgroup: introduce cgroup->dom_cgrp and threaded css_set handling Tejun Heo <tj@kernel.org> - 2017-07-17 04:10 +0200
  [PATCH 6/6] cgroup: update debug controller to print out thread mode information Tejun Heo <tj@kernel.org> - 2017-07-17 04:10 +0200
    Re: [PATCH 6/6] cgroup: update debug controller to print out thread  mode information Waiman Long <longman@redhat.com> - 2017-07-17 23:20 +0200
  [PATCH 5/6] cgroup: implement cgroup v2 thread support Tejun Heo <tj@kernel.org> - 2017-07-17 04:10 +0200
    Re: [PATCH 5/6] cgroup: implement cgroup v2 thread support Peter Zijlstra <peterz@infradead.org> - 2017-07-17 16:20 +0200
      Re: [PATCH 5/6] cgroup: implement cgroup v2 thread support Tejun Heo <tj@kernel.org> - 2017-07-17 16:30 +0200
      Re: [PATCH 5/6] cgroup: implement cgroup v2 thread support Waiman Long <longman@redhat.com> - 2017-07-17 23:00 +0200
    Re: [PATCH 5/6] cgroup: implement cgroup v2 thread support Waiman Long <longman@redhat.com> - 2017-07-17 23:20 +0200
  [PATCH 4/6] cgroup: implement CSS_TASK_ITER_THREADED Tejun Heo <tj@kernel.org> - 2017-07-17 04:10 +0200
  Re: [PATCHSET for-4.13] cgroup: implement cgroup2 thread mode, v3 Waiman Long <longman@redhat.com> - 2017-07-17 16:50 +0200
    Re: [PATCHSET for-4.13] cgroup: implement cgroup2 thread mode, v3 Tejun Heo <tj@kernel.org> - 2017-07-17 17:00 +0200

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