Re: [PATCH 02/11] xfs: re-order initial space accounting checks in xlog_write

[Brian Foster <bfoster@redhat.com>]

On Wed, Mar 04, 2020 at 06:53:52PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Commit and unmount records records do not need start records to be
> written, so rearrange the logic in xlog_write() to remove the need
> to check for XLOG_TIC_INITED to determine if we should account for
> the space used by a start record.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_log.c | 35 +++++++++++------------------------
>  1 file changed, 11 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 5b0568a86c07..d6c42954b70c 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
...
> @@ -2393,27 +2393,17 @@ xlog_write(
>  	int			error = 0;
>  	int			start_rec_size = sizeof(struct xlog_op_header);
>  
> -	*start_lsn = 0;
> -
> -
>  	/*
> -	 * Region headers and bytes are already accounted for.
> -	 * We only need to take into account start records and
> -	 * split regions in this function.
> +	 * If this is a commit or unmount transaction, we don't need a start
> +	 * record to be written. We do, however, have to account for the
> +	 * commit or unmount header that gets written. Hence we always have
> +	 * to account for an extra xlog_op_header here.
>  	 */

This addresses my comment on the previous patch, thanks. ;)

> -	if (ticket->t_flags & XLOG_TIC_INITED) {
> -		ticket->t_curr_res -= sizeof(xlog_op_header_t);
> +	ticket->t_curr_res -= sizeof(xlog_op_header_t);

Ok, so we're combining the fact that either the ticket is inited (we
have a start rec) or otherwise this is an unmount or commit_trans write
with an associated header.

Reviewed-by: Brian Foster <bfoster@redhat.com>

> +	if (ticket->t_flags & XLOG_TIC_INITED)
>  		ticket->t_flags &= ~XLOG_TIC_INITED;
> -	}
> -
> -	/*
> -	 * Commit record headers need to be accounted for. These
> -	 * come in as separate writes so are easy to detect.
> -	 */
> -	if (flags & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)) {
> -		ticket->t_curr_res -= sizeof(xlog_op_header_t);
> +	if (flags & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS))
>  		start_rec_size = 0;
> -	}
>  
>  	if (ticket->t_curr_res < 0) {
>  		xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
> @@ -2423,10 +2413,7 @@ xlog_write(
>  	}
>  
>  	len = xlog_write_calc_vec_length(ticket, log_vector, start_rec_size);
> -
> -	index = 0;
> -	lv = log_vector;
> -	vecp = lv->lv_iovecp;
> +	*start_lsn = 0;
>  	while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
>  		void		*ptr;
>  		int		log_offset;
> -- 
> 2.24.0.rc0
>