> Loading the allocation bitmap is very slow if user set the small cluster
> size on large partition.
>
> For optimizing it, This patch uses sb_breadahead() read the allocation
> bitmap. It will improve the mount time.
>
> The following is the result of about 4TB partition(2KB cluster size)
> on my target.
>
> without patch:
> real 0m41.746s
> user 0m0.011s
> sys 0m0.000s
>
> with patch:
> real 0m2.525s
> user 0m0.008s
> sys 0m0.008s
>
> Reviewed-by: Sungjong Seo <sj1557.seo@xxxxxxxxxxx>
> Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
> ---
> fs/exfat/balloc.c | 12 +++++++++++-
> fs/exfat/dir.c | 1 -
> fs/exfat/exfat_fs.h | 1 +
> 3 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
> index cc01556c9d9b..c40b73701941 100644
> --- a/fs/exfat/balloc.c
> +++ b/fs/exfat/balloc.c
> @@ -30,9 +30,11 @@ static int exfat_allocate_bitmap(struct super_block *sb,
> struct exfat_dentry *ep)
> {
> struct exfat_sb_info *sbi = EXFAT_SB(sb);
> + struct blk_plug plug;
> long long map_size;
> - unsigned int i, need_map_size;
> + unsigned int i, j, need_map_size;
> sector_t sector;
> + unsigned int max_ra_count = EXFAT_MAX_RA_SIZE >> sb->s_blocksize_bits;
>
> sbi->map_clu = le32_to_cpu(ep->dentry.bitmap.start_clu);
> map_size = le64_to_cpu(ep->dentry.bitmap.size);
> @@ -57,6 +59,14 @@ static int exfat_allocate_bitmap(struct super_block *sb,
>
> sector = exfat_cluster_to_sector(sbi, sbi->map_clu);
> for (i = 0; i < sbi->map_sectors; i++) {
> + /* Trigger the next readahead in advance. */
> + if (0 == (i % max_ra_count)) {
> + blk_start_plug(&plug);
> + for (j = i; j < min(max_ra_count, sbi->map_sectors - i) + i; j++)
> + sb_breadahead(sb, sector + j);
> + blk_finish_plug(&plug);
> + }
> +
> sbi->vol_amap[i] = sb_bread(sb, sector + i);
> if (!sbi->vol_amap[i]) {
> /* release all buffers and free vol_amap */
> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
> index ee060e26f51d..e7a8550c0346 100644
> --- a/fs/exfat/dir.c
> +++ b/fs/exfat/dir.c
> @@ -616,7 +616,6 @@ static int exfat_find_location(struct super_block *sb, struct exfat_chain *p_dir
> return 0;
> }
>
> -#define EXFAT_MAX_RA_SIZE (128*1024)
> static int exfat_dir_readahead(struct super_block *sb, sector_t sec)
> {
> struct exfat_sb_info *sbi = EXFAT_SB(sb);
> diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
> index f8ead4d47ef0..d1792d5c9eed 100644
> --- a/fs/exfat/exfat_fs.h
> +++ b/fs/exfat/exfat_fs.h
> @@ -13,6 +13,7 @@
> #include <uapi/linux/exfat.h>
>
> #define EXFAT_ROOT_INO 1
> +#define EXFAT_MAX_RA_SIZE (128*1024)
Why is the max readahead size 128KiB?
If the limit is changed to max_sectors_kb, so that a read request reads as much
data as possible, will the performance be better?
