Re: [PATCH v2] mm/shrinker: simplify shrinker_memcg_alloc() using guard()

[SeongJae Park]

On Wed, 13 May 2026 15:52:14 +0800 wangxuewen <18810879172@xxxxxxx> wrote:

> Use guard(mutex) to automatically handle shrinker_mutex locking and
> unlocking in shrinker_memcg_alloc(). This removes the explicit
> mutex_unlock() call, the goto-based error path, and the redundant
> ret variable, resulting in cleaner and more concise code.
> 
> v2:
> - Drop unused 'ret' variable to avoid compiler warning (Muchun Song).

Patch changelog should go to commentary area [1].  Also adding links to
previous versions would be helpful.

> 
> Signed-off-by: wangxuewen <wangxuewen@xxxxxxxxxx>
> ---
>  mm/shrinker.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/shrinker.c b/mm/shrinker.c
> index 76b3f750cf65..cb03fbecc75d 100644
> --- a/mm/shrinker.c
> +++ b/mm/shrinker.c
> @@ -215,29 +215,26 @@ static DEFINE_IDR(shrinker_idr);
>  
>  static int shrinker_memcg_alloc(struct shrinker *shrinker)
>  {
> -	int id, ret = -ENOMEM;
> +	int id;
>  
>  	if (mem_cgroup_disabled())
>  		return -ENOSYS;
>  	if (mem_cgroup_kmem_disabled() && !(shrinker->flags & SHRINKER_NONSLAB))
>  		return -ENOSYS;
>  
> -	mutex_lock(&shrinker_mutex);
> +	guard(mutex)(&shrinker_mutex);
>  	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
>  	if (id < 0)
> -		goto unlock;
> +		return id;

Could this change the return value?  This code was always returning -ENOMEM
before, but seems it can now return -ENOSPC?  Seems that doesn't matter,
though.

>  
>  	if (id >= shrinker_nr_max) {
>  		if (expand_shrinker_info(id)) {
>  			idr_remove(&shrinker_idr, id);
> -			goto unlock;
> +			return -ENOMEM;
>  		}
>  	}
>  	shrinker->id = id;
> -	ret = 0;
> -unlock:
> -	mutex_unlock(&shrinker_mutex);
> -	return ret;
> +	return 0;
>  }

[1] https://docs.kernel.org/process/submitting-patches.html#commentary


Thanks,
SJ

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