[PATCH] erofs(shrinker): return SHRINK_EMPTY if no objects to free

[Gao Xiang]

Hi Linxuan,

On 2025/1/16 15:20, Chen Linxuan wrote:
> Comments in file include/linux/shrinker.h says that
> `count_objects` of `struct shrinker` should return SHRINK_EMPTY
> when there are no objects to free.
> 
>> If there are no objects to free, it should return SHRINK_EMPTY,
>> while 0 is returned in cases of the number of freeable items cannot
>> be determined or shrinker should skip this cache for this time
>> (e.g., their number is below shrinkable limit).

Thanks for the patch!

Yeah, it seems that is the case.  Yet it'd better to document
what the impact if 0 is returned here if you know more..

> 
> Signed-off-by: Chen Linxuan <chenlinxuan at uniontech.com>
> ---
>   fs/erofs/zutil.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/erofs/zutil.c b/fs/erofs/zutil.c
> index 0dd65cefce33..682863fa9e1c 100644
> --- a/fs/erofs/zutil.c
> +++ b/fs/erofs/zutil.c
> @@ -243,7 +243,9 @@ void erofs_shrinker_unregister(struct super_block *sb)
>   static unsigned long erofs_shrink_count(struct shrinker *shrink,
>   					struct shrink_control *sc)
>   {
> -	return atomic_long_read(&erofs_global_shrink_cnt);
> +	unsigned long count = atomic_long_read(&erofs_global_shrink_cnt);
> +
> +	return count ? count : SHRINK_EMPTY;

I guess you could just use

	return atomic_long_read(&erofs_global_shrink_cnt) ?: SHRINK_EMPTY;

Thanks,
Gao Xiang

>   }
>   
>   static unsigned long erofs_shrink_scan(struct shrinker *shrink,