Re: [PATCH 2/8] xfs: re-order initial space accounting checks in xlog_write

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Mar 24, 2020 at 06:44:53PM +0100, Christoph Hellwig 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>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Brian Foster <bfoster@redhat.com>

Looks pretty straightforward,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/xfs_log.c | 38 ++++++++++++--------------------------
>  1 file changed, 12 insertions(+), 26 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index bf071552094a..116f59b16b04 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -2349,39 +2349,27 @@ xlog_write(
>  	uint			flags)
>  {
>  	struct xlog_in_core	*iclog = NULL;
> -	struct xfs_log_iovec	*vecp;
> -	struct xfs_log_vec	*lv;
> +	struct xfs_log_vec	*lv = log_vector;
> +	struct xfs_log_iovec	*vecp = lv->lv_iovecp;
> +	int			index = 0;
>  	int			len;
> -	int			index;
>  	int			partial_copy = 0;
>  	int			partial_copy_len = 0;
>  	int			contwr = 0;
>  	int			record_cnt = 0;
>  	int			data_cnt = 0;
>  	int			error = 0;
> -	bool			need_start_rec = true;
> -
> -	*start_lsn = 0;
> -
> +	bool			need_start_rec;
>  
>  	/*
> -	 * 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.
>  	 */
> -	if (ticket->t_flags & XLOG_TIC_INITED) {
> -		ticket->t_curr_res -= sizeof(struct xlog_op_header);
> +	ticket->t_curr_res -= sizeof(struct xlog_op_header);
> +	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(struct xlog_op_header);
> -		need_start_rec = false;
> -	}
>  
>  	if (ticket->t_curr_res < 0) {
>  		xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
> @@ -2390,11 +2378,9 @@ xlog_write(
>  		xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
>  	}
>  
> +	need_start_rec = !(flags & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS));
>  	len = xlog_write_calc_vec_length(ticket, log_vector, need_start_rec);
> -
> -	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;
> -- 
> 2.25.1
>