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Subject[PATCH 0/7] cgroups: Allow to bind/unbind subsystems to/from non-trival hierarchy
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 in specific.

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.

---
Documentation/cgroups/cgroups.txt | 26 ++-
include/linux/cgroup.h | 25 +++-
kernel/cgroup.c | 305 +++++++++++++++++++++++++++++++------
kernel/cgroup_freezer.c | 19 ++-
kernel/sched.c | 1 +
net/sched/cls_cgroup.c | 1 +
security/device_cgroup.c | 1 +
7 files changed, 311 insertions(+), 67 deletions(-)

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