Quoting Tejun Heo (tj@xxxxxxxxxx):
> 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.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> include/linux/cgroup.h | 3 +++
> mm/memcontrol.c | 13 +++++++++++++
> 2 files changed, 16 insertions(+)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 9c300ad..c562e33 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -269,6 +269,9 @@ 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
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 9715c0c..a651131 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5814,6 +5814,7 @@ static struct cftype mem_cgroup_files[] = {
> },
> {
> .name = "use_hierarchy",
> + .flags = CFTYPE_INSANE,
> .write_u64 = mem_cgroup_hierarchy_write,
> .read_u64 = mem_cgroup_hierarchy_read,
> },
> @@ -6784,6 +6785,17 @@ static void mem_cgroup_move_task(struct cgroup *cont,
> }
> #endif
>
> +/*
> + * Cgroup retains root cgroups across [un]mount cycles making it necessary
> + * to verify sane_behavior flag on each mount attempt.
> + */
> +static void mem_cgroup_bind(struct cgroup *root)
> +{
> + /* use_hierarchy is forced with sane_behavior */
> + if (cgroup_sane_behavior(root))
> + mem_cgroup_from_cont(root)->use_hierarchy = true;
> +}
> +
> struct cgroup_subsys mem_cgroup_subsys = {
> .name = "memory",
> .subsys_id = mem_cgroup_subsys_id,
> @@ -6794,6 +6806,7 @@ struct cgroup_subsys mem_cgroup_subsys = {
> .can_attach = mem_cgroup_can_attach,
> .cancel_attach = mem_cgroup_cancel_attach,
> .attach = mem_cgroup_move_task,
> + .bind = mem_cgroup_bind,
> .base_cftypes = mem_cgroup_files,
> .early_init = 0,
> .use_id = 1,
> --
> 1.8.1.4
>
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