[Cluster-devel] [PATCH v2 16/20] gfs2: No revokes for transactions at the tail of the log

[Andreas Gruenbacher]

In gfs2_log_flush, we're going through all active transactions.  For
each of the buffers in those transactions that has completed, we either
add a revoke to the active transaction immediately, or we move the
buffer to the transaction's ail2 list, which may result in a revoke
later.

However, whenever a transaction at the tail of the log completes, the
current tail of the log advances.  gfs2_log_flush writes out the log
header for the system transaction, with lh_tail set to that current tail
(sd_log_flush_head).  This implicitly revokes all previous blocks in the
log, so the revokes we've just written immediately become obsolete.
(This is not the case for transactions that haven't completed or aren't
at the tail of the log.)

Fix this by skipping completed transactions at the tail of the log
instead of writing revokes for them.

Signed-off-by: Andreas Gruenbacher <agruenba at redhat.com>
---
 fs/gfs2/log.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index b771575bce11..14c5edf2bf51 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -287,15 +287,31 @@ static void gfs2_ail_empty_tr(struct gfs2_sbd *sdp, struct gfs2_trans *tr,
  * @tr: the transaction
  * @max_revokes: If nonzero, issue revokes for the bd items for written buffers
  *
- * returns: the transaction's count of remaining active items
+ * Returns: true if the transaction has completed
  */
 
-static int gfs2_ail1_empty_one(struct gfs2_sbd *sdp, struct gfs2_trans *tr,
+static bool gfs2_ail1_empty_one(struct gfs2_sbd *sdp, struct gfs2_trans *tr,
 				int *max_revokes)
 {
 	struct gfs2_bufdata *bd, *s;
 	struct buffer_head *bh;
-	int active_count = 0;
+	bool empty = true;
+
+	if (!sdp->sd_log_error) {
+		list_for_each_entry_reverse(bd, &tr->tr_ail1_list, bd_ail_st_list) {
+			bh = bd->bd_bh;
+
+			if (buffer_busy(bh)) {
+				empty = false;
+				break;
+			}
+		}
+		if (empty) {
+			gfs2_ail_empty_tr(sdp, tr, &tr->tr_ail1_list);
+			gfs2_ail_empty_tr(sdp, tr, &tr->tr_ail2_list);
+			return empty;
+		}
+	}
 
 	list_for_each_entry_safe_reverse(bd, s, &tr->tr_ail1_list,
 					 bd_ail_st_list) {
@@ -311,7 +327,7 @@ static int gfs2_ail1_empty_one(struct gfs2_sbd *sdp, struct gfs2_trans *tr,
 		 * for others.
 		 */
 		if (!sdp->sd_log_error && buffer_busy(bh)) {
-			active_count++;
+			empty = false;
 			continue;
 		}
 		if (!buffer_uptodate(bh) &&
@@ -332,7 +348,7 @@ static int gfs2_ail1_empty_one(struct gfs2_sbd *sdp, struct gfs2_trans *tr,
 		}
 		list_move(&bd->bd_ail_st_list, &tr->tr_ail2_list);
 	}
-	return active_count;
+	return empty;
 }
 
 /**
@@ -351,7 +367,7 @@ static int gfs2_ail1_empty(struct gfs2_sbd *sdp, int max_revokes)
 
 	spin_lock(&sdp->sd_ail_lock);
 	list_for_each_entry_safe_reverse(tr, s, &sdp->sd_ail1_list, tr_list) {
-		if (!gfs2_ail1_empty_one(sdp, tr, &max_revokes) && oldest_tr)
+		if (gfs2_ail1_empty_one(sdp, tr, &max_revokes) && oldest_tr)
 			list_move(&tr->tr_list, &sdp->sd_ail2_list);
 		else
 			oldest_tr = 0;
-- 
2.26.2