Re: [PATCH] f2fs: support to disable linear lookup fallback

[Daniel Lee]

On Sun, Mar 30, 2025 at 7:54 PM Chao Yu <chao@xxxxxxxxxx> wrote:
>
> After commit 91b587ba79e1 ("f2fs: Introduce linear search for
> dentries"), f2fs forced to use linear lookup whenever a hash-based
> lookup fails on casefolded directory, it may affect performance
> for scenarios: a) create a new file w/ filename it doesn't exist
> in directory, b) lookup a file which may be removed.
>
> This patch supports to disable linear lookup fallback, so, once there
> is a solution for commit 5c26d2f1d3f5 ("unicode: Don't special case
> ignorable code points") to fix red heart unicode issue, then we can
> set an encodeing flag to disable the fallback for performance recovery.
>
> The way is kept in line w/ ext4, refer to commit 9e28059d5664 ("ext4:
> introduce linear search for dentries").
>
> Cc: Daniel Lee <chullee@xxxxxxxxxx>
> Cc: Gabriel Krisman Bertazi <krisman@xxxxxxx>
> Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
> ---
>  fs/f2fs/dir.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> index 5a63ff0df03b..e12445afb95a 100644
> --- a/fs/f2fs/dir.c
> +++ b/fs/f2fs/dir.c
> @@ -366,7 +366,8 @@ struct f2fs_dir_entry *__f2fs_find_entry(struct inode *dir,
>
>  out:
>  #if IS_ENABLED(CONFIG_UNICODE)
> -       if (IS_CASEFOLDED(dir) && !de && use_hash) {
> +       if (IS_CASEFOLDED(dir) && !de && use_hash &&
> +               !sb_no_casefold_compat_fallback(dir->i_sb)) {


Would it be beneficial to evaluate
!sb_no_casefold_compat_fallback(dir->i_sb) first for short-circuiting?


>
>                 use_hash = false;
>                 goto start_find_entry;
>         }
> --
> 2.49.0
>