linux-kernel - Re: [PATCH v3 1/6] mm: memcontrol: introduce mem_cgroup_ino() and mem_cgroup_get_from

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Date:   Sun, 22 May 2022 15:05:33 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Dave Chinner <dchinner@...hat.com>,
        linux-kernel@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...il.com>,
        Hillf Danton <hdanton@...a.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: Re: [PATCH v3 1/6] mm: memcontrol: introduce mem_cgroup_ino() and
 mem_cgroup_get_from_ino()

On Mon, May 09, 2022 at 11:38:15AM -0700, Roman Gushchin wrote:
> Shrinker debugfs requires a way to represent memory cgroups without
> using full paths, both for displaying information and getting input
> from a user.
> 
> Cgroup inode number is a perfect way, already used by bpf.
> 
> This commit adds a couple of helper functions which will be used
> to handle memcg-aware shrinkers.
> 
> Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
> ---
>  include/linux/memcontrol.h | 21 +++++++++++++++++++++
>  mm/memcontrol.c            | 23 +++++++++++++++++++++++
>  2 files changed, 44 insertions(+)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index fe580cb96683..a6de9e5c1549 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -831,6 +831,15 @@ static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
>  }
>  struct mem_cgroup *mem_cgroup_from_id(unsigned short id);
>  
> +#ifdef CONFIG_SHRINKER_DEBUG
> +static inline unsigned long mem_cgroup_ino(struct mem_cgroup *memcg)
> +{
> +	return memcg ? cgroup_ino(memcg->css.cgroup) : 0;
> +}
> +
> +struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino);
> +#endif
> +
>  static inline struct mem_cgroup *mem_cgroup_from_seq(struct seq_file *m)
>  {
>  	return mem_cgroup_from_css(seq_css(m));
> @@ -1324,6 +1333,18 @@ static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
>  	return NULL;
>  }
>  
> +#ifdef CONFIG_SHRINKER_DEBUG
> +static inline unsigned long mem_cgroup_ino(struct mem_cgroup *memcg)
> +{
> +	return 0;
> +}
> +
> +static inline struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
> +{
> +	return NULL;
> +}
> +#endif
> +
>  static inline struct mem_cgroup *mem_cgroup_from_seq(struct seq_file *m)
>  {
>  	return NULL;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 04cea4fa362a..e6472728fa66 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5018,6 +5018,29 @@ struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
>  	return idr_find(&mem_cgroup_idr, id);
>  }
>  
> +#ifdef CONFIG_SHRINKER_DEBUG
> +struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
> +{
> +	struct cgroup *cgrp;
> +	struct cgroup_subsys_state *css;
> +	struct mem_cgroup *memcg;
> +
> +	cgrp = cgroup_get_from_id(ino);
> +	if (!cgrp)
> +		return ERR_PTR(-ENOENT);
> +
> +	css = cgroup_get_e_css(cgrp, &memory_cgrp_subsys);
> +	if (css)
> +		memcg = container_of(css, struct mem_cgroup, css);
> +	else
> +		memcg = ERR_PTR(-ENOENT);
> +
> +	cgroup_put(cgrp);

I think it's better to use css_put() here since the refcount is get
via cgroup_get_e_css() which returns a css struct.

Thanks.

> +
> +	return memcg;
> +}
> +#endif
> +
>  static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
>  {
>  	struct mem_cgroup_per_node *pn;
> -- 
> 2.35.3
> 
>