linux-kernel - Re: [PATCH V3] xfs: use roundup_pow_of_two instead of ffs during xlog_find

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Date:   Tue, 19 Sep 2023 10:06:56 +0800
From:   Wang Jianchao <jianchwa@...look.com>
To:     djwong@...nel.org
Cc:     linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] xfs: use roundup_pow_of_two instead of ffs during
 xlog_find_tail

Ping ? Do I need other update on this patch ?

Thanks
Jianchao

On 2023/9/13 09:38, Wang Jianchao wrote:
> 
> In our production environment, we find that mounting a 500M /boot
> which is umount cleanly needs ~6s. One cause is that ffs() is
> used by xlog_write_log_records() 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. Things are similar in xlog_find_verify_cycle().
> 
> The code is able to handed bigger buffer very well, we can use
> roundup_pow_of_two() to replace ffs() directly to avoid small
> and sychronous IOs.
> 
> Reviewed-by: Dave Chinner <dchinner@...hat.com>
> Signed-off-by: Wang Jianchao <wangjc136@...ea.com>
> ---
> 
> Changes in V2:
>  - Move change log below "---"
>  - Add reviewed-by Dave Chinner tag
> 
> Changes in V1:
>  - Also replace the ffs in xlog_find_verify_cycle()
> 
>  fs/xfs/xfs_log_recover.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index 82c81d20459d..13b94d2e605b 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -329,7 +329,7 @@ xlog_find_verify_cycle(
>  	 * try a smaller size.  We need to be able to read at least
>  	 * a log sector, or we're out of luck.
>  	 */
> -	bufblks = 1 << ffs(nbblks);
> +	bufblks = roundup_pow_of_two(nbblks);
>  	while (bufblks > log->l_logBBsize)
>  		bufblks >>= 1;
>  	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {
> @@ -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))) {