Re: [PATCH] exfat: enable request merging for dir readahead

[Namjae Jeon]

On Mon, Apr 7, 2025 at 7:23 PM Anthony Iliopoulos <ailiop@xxxxxxxx> wrote:
>
> Directory listings that need to access the inode metadata (e.g. via
> statx to obtain the file types) of large filesystems with lots of
> metadata that aren't yet in dcache, will take a long time due to the
> directory readahead submitting one io request at a time which although
> targeting sequential disk sectors (up to EXFAT_MAX_RA_SIZE) are not
> merged at the block layer.
>
> Add plugging around sb_breadahead so that the requests can be batched
> and submitted jointly to the block layer where they can be merged by the
> io schedulers, instead of having each request individually submitted to
> the hardware queues.
>
> This significantly improves the throughput of directory listings as it
> also minimizes the number of io completions and related handling from
> the device driver side.
>
> Signed-off-by: Anthony Iliopoulos <ailiop@xxxxxxxx>
> ---
>  fs/exfat/dir.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
> index 3103b932b674..a46ab2690b4d 100644
> --- a/fs/exfat/dir.c
> +++ b/fs/exfat/dir.c

Hi Anthony,
> @@ -621,6 +621,7 @@ static int exfat_dir_readahead(struct super_block *sb, sector_t sec)
>  {
>         struct exfat_sb_info *sbi = EXFAT_SB(sb);
>         struct buffer_head *bh;
> +       struct blk_plug plug;
>         unsigned int max_ra_count = EXFAT_MAX_RA_SIZE >> sb->s_blocksize_bits;
>         unsigned int page_ra_count = PAGE_SIZE >> sb->s_blocksize_bits;
>         unsigned int adj_ra_count = max(sbi->sect_per_clus, page_ra_count);
> @@ -644,8 +645,10 @@ static int exfat_dir_readahead(struct super_block *sb, sector_t sec)
>         if (!bh || !buffer_uptodate(bh)) {
>                 unsigned int i;
It is better to move plug declaration here.
Thanks!
>
> +               blk_start_plug(&plug);
>                 for (i = 0; i < ra_count; i++)
>                         sb_breadahead(sb, (sector_t)(sec + i));
> +               blk_finish_plug(&plug);
>         }
>         brelse(bh);
>         return 0;
> --
> 2.49.0
>