Re: [PATCH v2 4/4] memcg: force use_hierarchy if sane_behavior

[Michal Hocko <mhocko@suse.cz>]

On Mon 15-04-13 13:40:16, Tejun Heo wrote:
> 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.

Thanks a lot Tejun!

> 
> 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>
> ---
> Applying to cgroup/for-3.10.
> 
> Thanks!
> 
>  include/linux/cgroup.h |    3 +++
>  mm/memcontrol.c        |   17 +++++++++++++++++
>  2 files changed, 20 insertions(+)
> 
> --- 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
> --- 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 +6785,21 @@ static void mem_cgroup_move_task(struct
>  }
>  #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.  cgroup core
> +	 * guarantees that @root doesn't have any children, so turning it
> +	 * on for the root memcg is enough.
> +	 */
> +	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 +6810,7 @@ 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,

-- 
Michal Hocko
SUSE Labs