linux-kernel - [PATCH v2 0/6] cgroups: Bindable cgroup subsystems

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Message-ID: <4D088BB5.30903@cn.fujitsu.com>
Date:	Wed, 15 Dec 2010 17:34:45 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Paul Menage <menage@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Hiroyuki KAMEZAWA <kamezawa.hiroyu@...fujitsu.com>,
	Matt Helsley <matthltc@...ibm.com>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	containers@...ts.linux-foundation.org
Subject: [PATCH v2 0/6] cgroups: Bindable cgroup subsystems

Stephane posted a patchset to add perf_cgroup subsystem, so perf can
be used to monitor all threads belonging to a cgroup.

But if you already mounted a cgroup hierarchy but without perf_cgroup
and the hierarchy has sub-cgroups, you can't bind perf_cgroup to it,
and thus you're not able to use per-cgroup perf feature.

This patchset alleviates the pain, and then a subsytem can be
bound/unbound to/from a hierarchy which has sub-cgroups in it.

Some subsystems still can't take advantage of this patchset, memcgroup
and cpuset for example.

For cpuset, if a hierarchy has a sub-cgroup and the cgroup has tasks,
we can't decide sub-cgroup's cpuset.mems and cpuset.cpus automatically
if we try to bind cpuset to this hierarchy.

For memcgroup, memcgroup uses css_get/put(), and due to some complexity,
for now bindable subsystems should not use css_get/put().

Usage:

# mount -t cgroup -o cpuset xxx /mnt
# mkdir /mnt/tmp
# echo $$ > /mnt/tmp/tasks

(add cpuacct to the hierarchy)
# mount -o remount,cpuset,cpuacct xxx /mnt

(remove it from the hierarchy)
# mount -o remount,cpuset xxx /mnt

There's another limitation, cpuacct should not be bound to any mounted
hierarchy before the above operation. But that's not a problem, as you
can remove it from a hierarchy and bind it to another one.

Changelog v2:

- Fix some bugs.
- Spit can_bind flag to bindable and unbindable flags
- Provide a __css_tryget() so a bindable subsystem can pin a cgroup
  via it.
- ...

---
 Documentation/cgroups/cgroups.txt |   37 +++-
 include/linux/cgroup.h            |   39 +++-
 kernel/cgroup.c                   |  391 +++++++++++++++++++++++++++++++------
 kernel/cgroup_freezer.c           |    1 +
 kernel/sched.c                    |    2 +
 security/device_cgroup.c          |    2 +
 6 files changed, 398 insertions(+), 74 deletions(-)
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