linux-kernel - Re: [PATCH v2] mm/memcg: remove return value of mem_cgroup_scan

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Date:   Fri, 16 Jun 2023 20:47:07 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Peng Zhang <zhangpeng362@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     hannes@...xchg.org, mhocko@...nel.org, roman.gushchin@...ux.dev,
        shakeelb@...gle.com, muchun.song@...ux.dev,
        akpm@...ux-foundation.org, wangkefeng.wang@...wei.com,
        sunnanyong@...wei.com
Subject: Re: [PATCH v2] mm/memcg: remove return value of
 mem_cgroup_scan_tasks()

Le 16/06/2023 à 08:30, Peng Zhang a écrit :
> From: ZhangPeng <zhangpeng362@...wei.com>
> 
> No user checks the return value of mem_cgroup_scan_tasks(). Make the
> return value void.
> 
> Signed-off-by: ZhangPeng <zhangpeng362@...wei.com>
> ---
> v2:
> - drop redundant return 0 per kernel test robot
> 
>   include/linux/memcontrol.h | 7 +++----
>   mm/memcontrol.c            | 9 ++++-----
>   2 files changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index c3d3a0c09315..5818af8eca5a 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -820,8 +820,8 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *,
>   				   struct mem_cgroup *,
>   				   struct mem_cgroup_reclaim_cookie *);
>   void mem_cgroup_iter_break(struct mem_cgroup *, struct mem_cgroup *);
> -int mem_cgroup_scan_tasks(struct mem_cgroup *,
> -			  int (*)(struct task_struct *, void *), void *);
> +void mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
> +			   int (*)(struct task_struct *, void *), void *arg);
>   
>   static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
>   {
> @@ -1364,10 +1364,9 @@ static inline void mem_cgroup_iter_break(struct mem_cgroup *root,
>   {
>   }
>   
> -static inline int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
> +static inline void mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
>   		int (*fn)(struct task_struct *, void *), void *arg)
>   {
> -	return 0;
>   }
>   
>   static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index cf06b1c9b3bb..a834b1edcde9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1259,13 +1259,13 @@ static void invalidate_reclaim_iterators(struct mem_cgroup *dead_memcg)
>    *
>    * This function iterates over tasks attached to @memcg or to any of its
>    * descendants and calls @fn for each task. If @fn returns a non-zero
> - * value, the function breaks the iteration loop and returns the value.
> - * Otherwise, it will iterate over all tasks and return 0.
> + * value, the function breaks the iteration loop. Otherwise, it will iterate
> + * over all tasks and return 0.

It does not return 0 any more in such a case.

CJ

>    *
>    * This function must not be called for the root memory cgroup.
>    */
> -int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
> -			  int (*fn)(struct task_struct *, void *), void *arg)
> +void mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
> +			   int (*fn)(struct task_struct *, void *), void *arg)
>   {
>   	struct mem_cgroup *iter;
>   	int ret = 0;
> @@ -1285,7 +1285,6 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
>   			break;
>   		}
>   	}
> -	return ret;
>   }
>   
>   #ifdef CONFIG_DEBUG_VM