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Date:   Tue, 12 Sep 2023 15:17:24 +0800
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Subject: Re: PATCH] xfs: use roundup_pow_of_two in xlog_write_log_records
From:   Wang Jianchao <jianchwa@outlook.com>
To:     djwong@kernel.org
Cc:     linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org
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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))) {