Re: [PATCH -v2] f2fs: Remove lock from check_valid_map

[Jaegeuk Kim <jaegeuk@kernel.org>]

Hi,

On Sun, Sep 07, 2014 at 11:38:30AM +0800, Huang Ying wrote:
> Only one bit is read in check_valid_map, holding a lock to do that
> doesn't help anything except decreasing performance.
> 
> Signed-off-by: Huang, Ying <ying.huang@intel.com>
> ---
> 
> v2: Fixed a build warning.
> 
> ---
>  fs/f2fs/gc.c |    3 ---
>  1 file changed, 3 deletions(-)
> 
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -378,14 +378,11 @@ static void put_gc_inode(struct list_hea
>  static int check_valid_map(struct f2fs_sb_info *sbi,
>  				unsigned int segno, int offset)
>  {
> -	struct sit_info *sit_i = SIT_I(sbi);
>  	struct seg_entry *sentry;
>  	int ret;
>  
> -	mutex_lock(&sit_i->sentry_lock);
>  	sentry = get_seg_entry(sbi, segno);
>  	ret = f2fs_test_bit(offset, sentry->cur_valid_map);
> -	mutex_unlock(&sit_i->sentry_lock);
>  	return ret;

The f2fs_test_bit is not atomic, so I'm not sure this is a good approach.
How about introducing rw_semaphore?

>  }
>