xfs: re-order initial space accounting checks in xlog_write

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>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_log.c

@@ -2356,10 +2356,10 @@ xlog_write(
 	bool			need_start_rec)
 {
 	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;
@@ -2367,24 +2367,16 @@ xlog_write(
 	int			data_cnt = 0;
 	int			error = 0;
 
-	*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.
 	 */
-	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 and unmount records need to be accounted for.
-	 * These come in as separate writes so are easy to detect.
-	 */
-	if (!need_start_rec)
-		ticket->t_curr_res -= sizeof(struct xlog_op_header);
 	if (ticket->t_curr_res < 0) {
 		xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
 		     "ctx ticket reservation ran out. Need to up reservation");
@@ -2393,10 +2385,7 @@ xlog_write(
 	}
 
 	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;