Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource group and PRIO_RGRP

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource group and PRIO_RGRP
Date	2016-04-09 18:10 +0200
Message-ID	<rm3Cq-7IV-7@gated-at.bofh.it> (permalink)
References	(4 earlier) <rlcHL-pI-1@gated-at.bofh.it> <rldaN-RS-1@gated-at.bofh.it> <rlo6e-o4-17@gated-at.bofh.it> <rloIV-Ti-3@gated-at.bofh.it> <rlL2O-Ou-19@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, Apr 08, 2016 at 04:11:35PM -0400, Tejun Heo wrote:
> > Yes, I'm familiar with the problem; but simply mandating leaf only nodes
> > is not a solution, for the very simple fact that there are tasks in the
> > root cgroup that cannot ever be moved out, so we _must_ be able to deal
> > with !leaf nodes containing tasks.
> 
> As Johannes already pointed out, the root cgroup has always been
> special.

The root of the tree isn't special except for 2 properties.

 - it _is_ a root; iow, it doesn't have any incoming edges.
   This also means it doesn't have a parent; nor can have a weight,
   since that is an edge propery, not a node property.

 - it always exists; for without a root there is no tree.

Making it _more_ special is silly.

> > Maybe, but so far I've only heard people complain this v2 thing didn't
> > work for them, and as far as I can see the whole v2 model is internally
> > inconsistent and impossible to implement.
> 
> I suppose we live in different bubbles.  Can you please elaborate
> which parts of cgroup v2 model are internally inconsistent and
> impossible to implement?  I'd be happy to rectify the situation.

The fact that we have to deal with tasks in the root cgroup while not
allowing tasks in any other node is internally inconsistent.

If I can deal with tasks in one node (root) I can equally deal with
tasks in any other node in exactly the same manner.

Making it different is actually _more_ code.

Thread

Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Tejun Heo <tj@kernel.org> - 2016-04-06 18:00 +0200
  Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Peter Zijlstra <peterz@infradead.org> - 2016-04-07 08:50 +0200
    Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Johannes Weiner <hannes@cmpxchg.org> - 2016-04-07 09:40 +0200
      Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Peter Zijlstra <peterz@infradead.org> - 2016-04-07 10:10 +0200
        Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Johannes Weiner <hannes@cmpxchg.org> - 2016-04-07 11:30 +0200
          Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Peter Zijlstra <peterz@infradead.org> - 2016-04-07 12:50 +0200
        Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Tejun Heo <tj@kernel.org> - 2016-04-07 21:50 +0200
          Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Peter Zijlstra <peterz@infradead.org> - 2016-04-07 22:30 +0200
            Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Tejun Heo <tj@kernel.org> - 2016-04-08 22:20 +0200
              Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-09 08:20 +0200
              Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Peter Zijlstra <peterz@infradead.org> - 2016-04-09 15:40 +0200
                Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Tejun Heo <tj@kernel.org> - 2016-04-13 00:30 +0200
                Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-13 09:50 +0200
                Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Tejun Heo <tj@kernel.org> - 2016-04-13 18:10 +0200
                Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-13 21:20 +0200
                Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-14 08:10 +0200
                Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Tejun Heo <tj@kernel.org> - 2016-04-14 22:00 +0200
                Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-15 04:50 +0200
              Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Peter Zijlstra <peterz@infradead.org> - 2016-04-09 18:10 +0200
      Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-07 10:10 +0200
      Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Peter Zijlstra <peterz@infradead.org> - 2016-04-07 10:30 +0200
        Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Johannes Weiner <hannes@cmpxchg.org> - 2016-04-07 21:10 +0200
          Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Peter Zijlstra <peterz@infradead.org> - 2016-04-07 21:40 +0200
            Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Johannes Weiner <hannes@cmpxchg.org> - 2016-04-07 22:30 +0200
              Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource  group and PRIO_RGRP Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-08 05:20 +0200

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