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From: Andy Lutomirski <luto@amacapital.net>
To: Tejun Heo <tj@kernel.org>, Linux API <linux-api@vger.kernel.org>
Cc: Li Zefan <lizefan@huawei.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Paul Turner <pjt@google.com>,
	Mike Galbraith <efault@gmx.de>,
	"open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	kernel-team@fb.com, lvenanci@redhat.com
Subject: Re: [PATCHSET for-4.11] cgroup: implement cgroup v2 thread mode
Date: Thu, 2 Feb 2017 13:32:19 -0800	[thread overview]
Message-ID: <CALCETrW6Mqj9VLogd0XaLgVAzEqsZ+VnZjN5NROCqr0ssdYaKg@mail.gmail.com> (raw)
In-Reply-To: <20170202200632.13992-1-tj@kernel.org>

On Thu, Feb 2, 2017 at 12:06 PM, Tejun Heo <tj@kernel.org> wrote:
> Hello,
>
> This patchset implements cgroup v2 thread mode.  It is largely based
> on the discussions that we had at the plumbers last year.  Here's the
> rough outline.

I like this, but I have some design questions:

>
> * Thread mode is explicitly enabled on a cgroup by writing "enable"
>   into "cgroup.threads" file.  The cgroup shouldn't have any child
>   cgroups or enabled controllers.

Why do you need to manually turn it on?  That is, couldn't it be
automatic based on what controllers are enabled?

>
> * Once enabled, arbitrary sub-hierarchy can be created and threads can
>   be put anywhere in the subtree by writing TIDs into "cgroup.threads"
>   file.  Process granularity and no-internal-process constraint don't
>   apply in a threaded subtree.

I'm a bit worried that this conflates two different things.  There's
thread support, i.e. allowing individual threads to be placed into
cgroups.  There's also more flexible sub-hierarchy support, i.e.
relaxing no-internal-process constraints.  For the "cpuacct"
controller, for example, both of these make sense.  But what if
someone writes a controller (directio, for example, just to make
something up) for which thread granularity makes sense but relaxing
no-internal-process constraints does not?

--Andy

WARNING: multiple messages have this Message-ID (diff)
From: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Cc: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>,
	Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
	Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Paul Turner <pjt-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Mike Galbraith <efault-Mmb7MZpHnFY@public.gmane.org>,
	"open list:CONTROL GROUP (CGROUP)"
	<cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	kernel-team-b10kYP2dOMg@public.gmane.org,
	lvenanci-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org
Subject: Re: [PATCHSET for-4.11] cgroup: implement cgroup v2 thread mode
Date: Thu, 2 Feb 2017 13:32:19 -0800	[thread overview]
Message-ID: <CALCETrW6Mqj9VLogd0XaLgVAzEqsZ+VnZjN5NROCqr0ssdYaKg@mail.gmail.com> (raw)
In-Reply-To: <20170202200632.13992-1-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>

On Thu, Feb 2, 2017 at 12:06 PM, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> Hello,
>
> This patchset implements cgroup v2 thread mode.  It is largely based
> on the discussions that we had at the plumbers last year.  Here's the
> rough outline.

I like this, but I have some design questions:

>
> * Thread mode is explicitly enabled on a cgroup by writing "enable"
>   into "cgroup.threads" file.  The cgroup shouldn't have any child
>   cgroups or enabled controllers.

Why do you need to manually turn it on?  That is, couldn't it be
automatic based on what controllers are enabled?

>
> * Once enabled, arbitrary sub-hierarchy can be created and threads can
>   be put anywhere in the subtree by writing TIDs into "cgroup.threads"
>   file.  Process granularity and no-internal-process constraint don't
>   apply in a threaded subtree.

I'm a bit worried that this conflates two different things.  There's
thread support, i.e. allowing individual threads to be placed into
cgroups.  There's also more flexible sub-hierarchy support, i.e.
relaxing no-internal-process constraints.  For the "cpuacct"
controller, for example, both of these make sense.  But what if
someone writes a controller (directio, for example, just to make
something up) for which thread granularity makes sense but relaxing
no-internal-process constraints does not?

--Andy

  parent reply	other threads:[~2017-02-02 21:32 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-02 20:06 [PATCHSET for-4.11] cgroup: implement cgroup v2 thread mode Tejun Heo
2017-02-02 20:06 ` Tejun Heo
2017-02-02 20:06 ` [PATCH 1/5] cgroup: reorganize cgroup.procs / task write path Tejun Heo
2017-02-02 20:06 ` [PATCH 2/5] cgroup: add @flags to css_task_iter_start() and implement CSS_TASK_ITER_PROCS Tejun Heo
2017-02-02 20:06 ` [PATCH 3/5] cgroup: introduce cgroup->proc_cgrp and threaded css_set handling Tejun Heo
2017-02-02 20:06   ` Tejun Heo
2017-02-02 20:06 ` [PATCH 4/5] cgroup: implement CSS_TASK_ITER_THREADED Tejun Heo
2017-02-02 20:06 ` [PATCH 5/5] cgroup: implement cgroup v2 thread support Tejun Heo
2017-02-02 20:06   ` Tejun Heo
2017-02-02 21:32 ` Andy Lutomirski [this message]
2017-02-02 21:32   ` [PATCHSET for-4.11] cgroup: implement cgroup v2 thread mode Andy Lutomirski
2017-02-02 21:52   ` Tejun Heo
2017-02-02 21:52     ` Tejun Heo
2017-02-03 21:10     ` Andy Lutomirski
2017-02-03 21:10       ` Andy Lutomirski
2017-02-03 21:56       ` Tejun Heo
2017-02-06  9:50     ` Peter Zijlstra
2017-02-06  9:50       ` Peter Zijlstra
2017-02-03 20:20 ` Peter Zijlstra
2017-02-03 20:20   ` Peter Zijlstra
2017-02-03 20:59   ` Tejun Heo
2017-02-03 20:59     ` Tejun Heo
2017-02-06 12:49     ` Peter Zijlstra
2017-02-06 12:49       ` Peter Zijlstra
2017-02-08 23:08       ` Tejun Heo
2017-02-08 23:08         ` Tejun Heo
2017-02-09 10:29         ` Peter Zijlstra
2017-02-09 10:29           ` Peter Zijlstra
2017-02-10 15:45           ` Tejun Heo
2017-02-10 15:45             ` Tejun Heo
2017-02-10 17:51             ` Peter Zijlstra
2017-02-10 17:51               ` Peter Zijlstra
2017-02-12  5:05               ` Tejun Heo
2017-02-12  5:05                 ` Tejun Heo
2017-02-12  6:59                 ` Mike Galbraith
2017-02-12  6:59                   ` Mike Galbraith
2017-02-13  5:45                   ` Mike Galbraith
2017-03-13 19:26                     ` Tejun Heo
2017-03-13 19:26                       ` Tejun Heo
2017-03-14 14:45                       ` Mike Galbraith
2017-02-14 10:35                 ` Peter Zijlstra
2017-03-13 20:05                   ` Tejun Heo
2017-03-13 20:05                     ` Tejun Heo
2017-03-21 12:39                     ` Peter Zijlstra
2017-03-21 12:39                       ` Peter Zijlstra
2017-03-22 14:52                       ` Peter Zijlstra
2017-03-22 14:52                         ` Peter Zijlstra
2017-02-09 13:07 ` Paul Turner
2017-02-09 14:47   ` Peter Zijlstra
2017-02-09 15:08     ` Mike Galbraith
     [not found]     ` <CAPM31RJaJjFwenC36Abij+EdzO3KBm-DEjQ_crSmzrtrrn2N2A@mail.gmail.com>
2017-02-13  5:28       ` Mike Galbraith
2017-02-10 15:46   ` Tejun Heo
2017-02-10 15:46     ` Tejun Heo

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