From: Tejun Heo <tj@kernel.org> To: Waiman Long <llong@redhat.com> Cc: "Zefan Li" <lizefan.x@bytedance.com>, "Johannes Weiner" <hannes@cmpxchg.org>, "Jonathan Corbet" <corbet@lwn.net>, "Shuah Khan" <shuah@kernel.org>, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, "Andrew Morton" <akpm@linux-foundation.org>, "Roman Gushchin" <guro@fb.com>, "Phil Auld" <pauld@redhat.com>, "Peter Zijlstra" <peterz@infradead.org>, "Juri Lelli" <juri.lelli@redhat.com>, "Frederic Weisbecker" <frederic@kernel.org>, "Marcelo Tosatti" <mtosatti@redhat.com>, "Michal Koutný" <mkoutny@suse.com> Subject: Re: [PATCH v4 4/6] cgroup/cpuset: Allow non-top parent partition root to distribute out all CPUs Date: Thu, 12 Aug 2021 11:51:27 -1000 [thread overview] Message-ID: <YRWX3z6Nl41GsXR8@slm.duckdns.org> (raw) In-Reply-To: <ef02d96b-325c-87f6-a6a3-d840feefef24@redhat.com> On Wed, Aug 11, 2021 at 02:46:24PM -0400, Waiman Long wrote: > On 8/11/21 2:21 PM, Tejun Heo wrote: > > On Wed, Aug 11, 2021 at 02:18:17PM -0400, Waiman Long wrote: > > > I don't think that is true. A task can reside anywhere in the cgroup > > > hierarchy. I have encountered no problem moving tasks around. > > Oh, that shouldn't be happening with controllers enabled. Can you please > > share a repro? > > I have done further testing. Enabling controllers won't prohibit moving a > task into a parent cgroup as long as the child cgroups have no tasks. Once Should be "as long as there's no child cgroups". root@test /s/f/cgroup# mkdir test root@test /s/f/cgroup# mkdir -p test/A root@test /s/f/cgroup# echo +io > test/cgroup.subtree_control root@test /s/f/cgroup# echo $fish_pid > test/cgroup.procs write: Device or resource busy > the child cgroup has task, moving another task to the parent is not allowed > (-EBUSY). Similarly if a parent cgroup has tasks, you can't put new tasks > into the child cgroup. I don't realize that we have such constraints as I You can't enable controller from a populated cgroup: root@test /s/f/cgroup# mkdir test root@test /s/f/cgroup# echo +io > test/cgroup.subtree_control root@test /s/f/cgroup# echo $fish_pid > test/cgroup.procs > usually do my testing with a cgroup hierarchy with no tasks initially. > Anyway, a new lesson learned. The invariant is that from each controller's POV, all cgroups with processes in them are leaves. This is all pretty well documented in cgroup-v2.rst. Thanks. -- tejun
WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> To: Waiman Long <llong-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Cc: "Zefan Li" <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, "Johannes Weiner" <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, "Jonathan Corbet" <corbet-T1hC0tSOHrs@public.gmane.org>, "Shuah Khan" <shuah-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kselftest-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, "Andrew Morton" <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, "Roman Gushchin" <guro-b10kYP2dOMg@public.gmane.org>, "Phil Auld" <pauld-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "Peter Zijlstra" <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, "Juri Lelli" <juri.lelli-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "Frederic Weisbecker" <frederic-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, "Marcelo Tosatti" <mtosatti-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "Michal Koutný" <mkoutny-IBi9RG/b67k@public.gmane.org> Subject: Re: [PATCH v4 4/6] cgroup/cpuset: Allow non-top parent partition root to distribute out all CPUs Date: Thu, 12 Aug 2021 11:51:27 -1000 [thread overview] Message-ID: <YRWX3z6Nl41GsXR8@slm.duckdns.org> (raw) In-Reply-To: <ef02d96b-325c-87f6-a6a3-d840feefef24-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> On Wed, Aug 11, 2021 at 02:46:24PM -0400, Waiman Long wrote: > On 8/11/21 2:21 PM, Tejun Heo wrote: > > On Wed, Aug 11, 2021 at 02:18:17PM -0400, Waiman Long wrote: > > > I don't think that is true. A task can reside anywhere in the cgroup > > > hierarchy. I have encountered no problem moving tasks around. > > Oh, that shouldn't be happening with controllers enabled. Can you please > > share a repro? > > I have done further testing. Enabling controllers won't prohibit moving a > task into a parent cgroup as long as the child cgroups have no tasks. Once Should be "as long as there's no child cgroups". root@test /s/f/cgroup# mkdir test root@test /s/f/cgroup# mkdir -p test/A root@test /s/f/cgroup# echo +io > test/cgroup.subtree_control root@test /s/f/cgroup# echo $fish_pid > test/cgroup.procs write: Device or resource busy > the child cgroup has task, moving another task to the parent is not allowed > (-EBUSY). Similarly if a parent cgroup has tasks, you can't put new tasks > into the child cgroup. I don't realize that we have such constraints as I You can't enable controller from a populated cgroup: root@test /s/f/cgroup# mkdir test root@test /s/f/cgroup# echo +io > test/cgroup.subtree_control root@test /s/f/cgroup# echo $fish_pid > test/cgroup.procs > usually do my testing with a cgroup hierarchy with no tasks initially. > Anyway, a new lesson learned. The invariant is that from each controller's POV, all cgroups with processes in them are leaves. This is all pretty well documented in cgroup-v2.rst. Thanks. -- tejun
next prev parent reply other threads:[~2021-08-12 21:51 UTC|newest] Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-08-11 3:06 [PATCH-cgroup v4 0/6] cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus Waiman Long 2021-08-11 3:06 ` [PATCH v4 1/6] cgroup/cpuset: Enable event notification when partition state changes Waiman Long 2021-08-11 3:06 ` Waiman Long 2021-08-11 18:04 ` Tejun Heo 2021-08-11 18:04 ` Tejun Heo 2021-08-11 3:06 ` [PATCH v4 2/6] cgroup/cpuset: Properly handle partition root tree Waiman Long 2021-08-11 18:08 ` Tejun Heo 2021-08-11 19:27 ` Waiman Long 2021-08-11 19:27 ` Waiman Long 2021-08-12 22:18 ` Tejun Heo 2021-08-12 22:18 ` Tejun Heo 2021-08-12 22:56 ` Waiman Long 2021-08-12 22:56 ` Waiman Long 2021-08-13 16:07 ` Tejun Heo 2021-08-11 3:06 ` [PATCH v4 3/6] cgroup/cpuset: Add a new isolated cpus.partition type Waiman Long 2021-08-11 3:06 ` [PATCH v4 4/6] cgroup/cpuset: Allow non-top parent partition root to distribute out all CPUs Waiman Long 2021-08-11 18:13 ` Tejun Heo 2021-08-11 18:13 ` Tejun Heo 2021-08-11 18:18 ` Waiman Long 2021-08-11 18:21 ` Tejun Heo 2021-08-11 18:21 ` Tejun Heo 2021-08-11 18:46 ` Waiman Long 2021-08-11 18:46 ` Waiman Long 2021-08-12 21:51 ` Tejun Heo [this message] 2021-08-12 21:51 ` Tejun Heo 2021-08-11 3:06 ` [PATCH v4 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst Waiman Long 2021-08-11 18:15 ` Tejun Heo 2021-08-11 18:19 ` Waiman Long 2021-08-11 18:19 ` Waiman Long 2021-08-11 3:06 ` [PATCH v4 6/6] kselftest/cgroup: Add cpuset v2 partition root state test Waiman Long
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