linux-kernel - Re: [PATCH v2 -next] mm: memcg: make alloc_mem_cgroup_per_node

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Message-ID: <ZjooSnQ_vS30EXCT@tiehlicka>
Date: Tue, 7 May 2024 15:10:34 +0200
From: Michal Hocko <mhocko@...e.com>
To: Xiu Jianfeng <xiujianfeng@...wei.com>
Cc: hannes@...xchg.org, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
	muchun.song@...ux.dev, akpm@...ux-foundation.org,
	cgroups@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 -next] mm: memcg: make
 alloc_mem_cgroup_per_node_info() return bool

On Tue 07-05-24 11:08:32, Xiu Jianfeng wrote:
> Currently alloc_mem_cgroup_per_node_info() returns 1 if failed,
> make it return bool, false for failure and true for success.

This describes what the patch does rather than why it is doing that.
The former is clear from the diff while the motivation for this change
is unclear. I would propose something like:

alloc_mem_cgroup_per_node_info() returns int that doesn't map to any
errno error code. The only existing caller doesn't really need an error
code so change the the function to return bool (true on success) because
this is slightly less confusing and more consistent with the other code.

> Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>

With changelog clarified feel free to add
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/memcontrol.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d11536ef59ef..69d70feb8e68 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5653,13 +5653,13 @@ struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
>  }
>  #endif
>  
> -static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
> +static bool alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
>  {
>  	struct mem_cgroup_per_node *pn;
>  
>  	pn = kzalloc_node(sizeof(*pn), GFP_KERNEL, node);
>  	if (!pn)
> -		return 1;
> +		return false;
>  
>  	pn->lruvec_stats = kzalloc_node(sizeof(struct lruvec_stats), GFP_KERNEL,
>  					node);
> @@ -5675,11 +5675,11 @@ static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
>  	pn->memcg = memcg;
>  
>  	memcg->nodeinfo[node] = pn;
> -	return 0;
> +	return true;
>  fail:
>  	kfree(pn->lruvec_stats);
>  	kfree(pn);
> -	return 1;
> +	return false;
>  }
>  
>  static void free_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
> @@ -5751,7 +5751,7 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
>  	}
>  
>  	for_each_node(node)
> -		if (alloc_mem_cgroup_per_node_info(memcg, node))
> +		if (!alloc_mem_cgroup_per_node_info(memcg, node))
>  			goto fail;
>  
>  	if (memcg_wb_domain_init(memcg, GFP_KERNEL))
> -- 
> 2.34.1
> 

-- 
Michal Hocko
SUSE Labs