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Date:   Sun, 20 May 2018 10:57:22 +0300
From:   Vladimir Davydov <vdavydov.dev@gmail.com>
To:     Kirill Tkhai <ktkhai@virtuozzo.com>
Cc:     akpm@linux-foundation.org, shakeelb@google.com,
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Subject: Re: [PATCH v6 13/17] mm: Export mem_cgroup_is_root()
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On Fri, May 18, 2018 at 11:43:53AM +0300, Kirill Tkhai wrote:
> This will be used in next patch.
> 
> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> ---
>  include/linux/memcontrol.h |   10 ++++++++++
>  mm/memcontrol.c            |    5 -----
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 7ae1b94becf3..cd44c1fac22b 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -311,6 +311,11 @@ struct mem_cgroup {
>  
>  extern struct mem_cgroup *root_mem_cgroup;
>  
> +static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
> +{
> +	return (memcg == root_mem_cgroup);
> +}
> +
>  static inline bool mem_cgroup_disabled(void)
>  {
>  	return !cgroup_subsys_enabled(memory_cgrp_subsys);
> @@ -780,6 +785,11 @@ void mem_cgroup_split_huge_fixup(struct page *head);
>  
>  struct mem_cgroup;
>  
> +static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
> +{
> +	return false;
> +}
> +

This stub must return true as one can think of !MEMCG as of the case
when there's the only cgroup - the root.