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

[Michal Hocko]

On Fri 12-04-13 16:10:59, 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.

OK, as the feature has to be enabled explicitly I do not mind not
exporting the file.
I have one nit though. Can we extend the comment for mem_cgroup_bind
that it doesn't have to care about children because there are none
because rebind_subsystems wouldn't allow remounting otherwise?
It wasn't obvious, at least from me.

Other than that.
Acked-by: Michal Hocko <mhocko@xxxxxxx>

Thanks!

> Signed-off-by: Tejun Heo <tj@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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-- 
Michal Hocko
SUSE Labs
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