From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1756912AbdGLHqT (ORCPT <rfc822;w@1wt.eu>);
        Wed, 12 Jul 2017 03:46:19 -0400
Received: from merlin.infradead.org ([205.233.59.134]:59278 "EHLO
        merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1756657AbdGLHqR (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 12 Jul 2017 03:46:17 -0400
Date: Wed, 12 Jul 2017 09:45:55 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
        hannes@cmpxchg.org, mingo@redhat.com, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@fb.com, pjt@google.com,
        luto@amacapital.net, efault@gmx.de, torvalds@linux-foundation.org
Subject: Re: [PATCHSET for-4.13] cgroup: implement cgroup2 thread mode, v2
Message-ID: <20170712074555.slefkebvdpfjse34@hirez.programming.kicks-ass.net>
References: <20170612123150.scopfxela7v26dct@hirez.programming.kicks-ass.net>
 <20170612212753.GN19206@htj.duckdns.org>
 <20170627070143.GB4114@worktop>
 <20170630132324.GA18669@htj.duckdns.org>
 <20170710083200.poevcjo7x47hy5ni@hirez.programming.kicks-ass.net>
 <8f9c83d7-cadf-3a41-8e56-5828d5abfa26@redhat.com>
 <20170711121527.imshmmoe4cj7dkig@hirez.programming.kicks-ass.net>
 <a554d16c-af40-756e-a611-a453451c40a9@redhat.com>
 <20170711165233.xx6wko4pdxk4rb72@hirez.programming.kicks-ass.net>
 <0659619a-067d-b542-918c-e468c51feb23@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <0659619a-067d-b542-918c-e468c51feb23@redhat.com>
User-Agent: NeoMutt/20170609 (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Jul 11, 2017 at 05:12:39PM -0400, Waiman Long wrote:
> On 07/11/2017 12:52 PM, Peter Zijlstra wrote:
> > On Tue, Jul 11, 2017 at 10:14:42AM -0400, Waiman Long wrote:
> >
> >> The "join" was a special op for the children of cgroup root to join the
> >> root as part of a threaded subtree. The children can instead use the
> >> "enable" option to become a thread root which was the configuration
> >> shown above.  This behavior applied only to children of root. Down the
> >> hierarchy, you can't have configuration like:
> >>
> >>      R (t=0)
> >>     / \
> >>        D (t=1)
> >>       / \
> >>      T   D (t=1)
> > Why not?
> >
> > First you create:
> >
> >       R (t=0)
> >      / \
> >         D (t=1)
> >        / \
> >       T   T (t=1)
> >
> > Then you flip t=0 like:
> >
> >       R (t=0)
> >      / \
> >         D (t=1)
> >        / \
> >       T   D (t=0)
> >
> > And then you flip t=1 again:
> >
> >       R (t=0)
> >      / \
> >         D (t=1)
> >        / \
> >       T   D (t=1)
> 
> Tejun's thread mode patch has constraints on what operations are allowed
> and what aren't. For a threaded subtree, thread mode cannot be disabled
> in the middle of the tree.

Where in that scenario did I change anything in the middle? All
operations were on a leaf group.