In our production environment, we find that mounting a 500M and
clean /boot needs ~6 seconds sometimes. The one cause is that
xlog_write_log_records() uses ffs to decide the buffer size. It
can cause a lot of small IO easily when xlog_clear_stale_blocks()
needs to wrap around the end of log area and log head block is
not power of two. As xlog_write_log_records() has handled bigger
buffer very well, we can use roundup_pow_of_two instead of ffs to
decide buffer size.

Signed-off-by: Wang Jianchao <jianchwa@outlook.com>
---
 fs/xfs/xfs_log_recover.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 82c81d20459d..9368fefe1d0a 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -1528,7 +1528,7 @@ xlog_write_log_records(
 	 * a smaller size.  We need to be able to write at least a
 	 * log sector, or we're out of luck.
 	 */
-	bufblks = 1 << ffs(blocks);
+	bufblks = roundup_pow_of_two(blocks);
 	while (bufblks > log->l_logBBsize)
 		bufblks >>= 1;
 	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {
-- 
2.34.1

xlog_find_verify_cycle() has similar issue.
It will be covered in new version patch.

On 2023/9/12 14:17, Wang Jianchao wrote:
> 
> In our production environment, we find that mounting a 500M and
> clean /boot needs ~6 seconds sometimes. The one cause is that
> xlog_write_log_records() uses ffs to decide the buffer size. It
> can cause a lot of small IO easily when xlog_clear_stale_blocks()
> needs to wrap around the end of log area and log head block is
> not power of two. As xlog_write_log_records() has handled bigger
> buffer very well, we can use roundup_pow_of_two instead of ffs to
> decide buffer size.
> 
> Signed-off-by: Wang Jianchao <jianchwa@outlook.com>
> ---
>  fs/xfs/xfs_log_recover.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index 82c81d20459d..9368fefe1d0a 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -1528,7 +1528,7 @@ xlog_write_log_records(
>  	 * a smaller size.  We need to be able to write at least a
>  	 * log sector, or we're out of luck.
>  	 */
> -	bufblks = 1 << ffs(blocks);
> +	bufblks = roundup_pow_of_two(blocks);
>  	while (bufblks > log->l_logBBsize)
>  		bufblks >>= 1;
>  	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {