[PATCH 1/8] xfs: don't try to write a start record into every iclog

[Christoph Hellwig <hch@lst.de>]

From: Dave Chinner <dchinner@redhat.com>

The xlog_write() function iterates over iclogs until it completes
writing all the log vectors passed in. The ticket tracks whether
a start record has been written or not, so only the first iclog gets
a start record. We only ever pass single use tickets to
xlog_write() so we only ever need to write a start record once per
xlog_write() call.

Hence we don't need to store whether we should write a start record
in the ticket as the callers provide all the information we need to
determine if a start record should be written. For the moment, we
have to ensure that we clear the XLOG_TIC_INITED appropriately so
the code in xfs_log_done() still works correctly for committing
transactions.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
[hch: use an need_start_rec bool]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_log.c | 63 ++++++++++++++++++++++++------------------------
 1 file changed, 32 insertions(+), 31 deletions(-)

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 2a90a483c2d6..bf071552094a 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -2112,23 +2112,21 @@ xlog_print_trans(
 }
 
 /*
- * Calculate the potential space needed by the log vector.  Each region gets
- * its own xlog_op_header_t and may need to be double word aligned.
+ * Calculate the potential space needed by the log vector.  We may need a start
+ * record, and each region gets its own struct xlog_op_header and may need to be
+ * double word aligned.
  */
 static int
 xlog_write_calc_vec_length(
 	struct xlog_ticket	*ticket,
-	struct xfs_log_vec	*log_vector)
+	struct xfs_log_vec	*log_vector,
+	bool			need_start_rec)
 {
 	struct xfs_log_vec	*lv;
-	int			headers = 0;
+	int			headers = need_start_rec ? 1 : 0;
 	int			len = 0;
 	int			i;
 
-	/* acct for start rec of xact */
-	if (ticket->t_flags & XLOG_TIC_INITED)
-		headers++;
-
 	for (lv = log_vector; lv; lv = lv->lv_next) {
 		/* we don't write ordered log vectors */
 		if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED)
@@ -2150,27 +2148,16 @@ xlog_write_calc_vec_length(
 	return len;
 }
 
-/*
- * If first write for transaction, insert start record  We can't be trying to
- * commit if we are inited.  We can't have any "partial_copy" if we are inited.
- */
-static int
+static void
 xlog_write_start_rec(
 	struct xlog_op_header	*ophdr,
 	struct xlog_ticket	*ticket)
 {
-	if (!(ticket->t_flags & XLOG_TIC_INITED))
-		return 0;
-
 	ophdr->oh_tid	= cpu_to_be32(ticket->t_tid);
 	ophdr->oh_clientid = ticket->t_clientid;
 	ophdr->oh_len = 0;
 	ophdr->oh_flags = XLOG_START_TRANS;
 	ophdr->oh_res2 = 0;
-
-	ticket->t_flags &= ~XLOG_TIC_INITED;
-
-	return sizeof(struct xlog_op_header);
 }
 
 static xlog_op_header_t *
@@ -2372,25 +2359,29 @@ xlog_write(
 	int			record_cnt = 0;
 	int			data_cnt = 0;
 	int			error = 0;
+	bool			need_start_rec = true;
 
 	*start_lsn = 0;
 
-	len = xlog_write_calc_vec_length(ticket, log_vector);
 
 	/*
 	 * Region headers and bytes are already accounted for.
 	 * We only need to take into account start records and
 	 * split regions in this function.
 	 */
-	if (ticket->t_flags & XLOG_TIC_INITED)
-		ticket->t_curr_res -= sizeof(xlog_op_header_t);
+	if (ticket->t_flags & XLOG_TIC_INITED) {
+		ticket->t_curr_res -= sizeof(struct xlog_op_header);
+		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)) {
+		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,
@@ -2399,6 +2390,8 @@ xlog_write(
 		xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
 	}
 
+	len = xlog_write_calc_vec_length(ticket, log_vector, need_start_rec);
+
 	index = 0;
 	lv = log_vector;
 	vecp = lv->lv_iovecp;
@@ -2425,7 +2418,6 @@ xlog_write(
 		while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
 			struct xfs_log_iovec	*reg;
 			struct xlog_op_header	*ophdr;
-			int			start_rec_copy;
 			int			copy_len;
 			int			copy_off;
 			bool			ordered = false;
@@ -2441,11 +2433,15 @@ xlog_write(
 			ASSERT(reg->i_len % sizeof(int32_t) == 0);
 			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
 
-			start_rec_copy = xlog_write_start_rec(ptr, ticket);
-			if (start_rec_copy) {
-				record_cnt++;
+			/*
+			 * Before we start formatting log vectors, we need to
+			 * write a start record. Only do this for the first
+			 * iclog we write to.
+			 */
+			if (need_start_rec) {
+				xlog_write_start_rec(ptr, ticket);
 				xlog_write_adv_cnt(&ptr, &len, &log_offset,
-						   start_rec_copy);
+						sizeof(struct xlog_op_header));
 			}
 
 			ophdr = xlog_write_setup_ophdr(log, ptr, ticket, flags);
@@ -2477,8 +2473,13 @@ xlog_write(
 				xlog_write_adv_cnt(&ptr, &len, &log_offset,
 						   copy_len);
 			}
-			copy_len += start_rec_copy + sizeof(xlog_op_header_t);
+			copy_len += sizeof(struct xlog_op_header);
 			record_cnt++;
+			if (need_start_rec) {
+				copy_len += sizeof(struct xlog_op_header);
+				record_cnt++;
+				need_start_rec = false;
+			}
 			data_cnt += contwr ? copy_len : 0;
 
 			error = xlog_write_copy_finish(log, iclog, flags,
-- 
2.25.1