memcg: force use_hierarchy if sane_behavior

Turn on use_hierarchy by default if sane_behavior is specified and
don't create .use_hierarchy file.

It is debatable whether to remove .use_hierarchy file or make it ro as
the former could make transition easier in certain cases; however, the
behavior changes which will be gated by sane_behavior are intensive
including changing basic meaning of certain control knobs in a few
controllers and I don't really think keeping this piece would make
things easier in any noticeable way, so let's remove it.

v2: Explain that mem_cgroup_bind() doesn't have to worry about
    children as suggested by Michal Hocko.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 64047ae7fde1..cda7eb2239e1 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -268,6 +268,9 @@ enum {
          *
          * - Remount is disallowed.
          *
+         * - memcg: use_hierarchy is on by default and the cgroup file for
+         *   the flag is not created.
+         *
          * The followings are planned changes.
          *
          * - release_agent will be disallowed once replacement notification