ocfs2: optimize the reading of heartbeat data

Reading heartbeat data from lowest node rather than from zero, in cases
where the node is not defined from zero, can reduce the number of sectors
read.

Here is a simple test data obtained with 'iostat -dmx dm-5 2', with
two nodes in the cluster, node number 10, 20, respectively.

Before optimization:
Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
dm-5              0.00     0.00    0.50    0.50     0.01     0.00    11.00     0.00    1.00    1.00    1.00   1.50   0.15

After the optimization:
Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
dm-5              0.00     0.00    0.50    0.50     0.00     0.00     6.00     0.00    0.50    1.00    0.00   0.50   0.05

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Jia Guo <[email protected]>
Reviewed-by: Jun Piao <[email protected]>
Reviewed-by: Yiwen Jiang <[email protected]>
Acked-by: Joseph Qi <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: Junxiao Bi <[email protected]>
Cc: Changwei Ge <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/ocfs2/cluster/heartbeat.c

@@ -582,9 +582,10 @@ static struct bio *o2hb_setup_one_bio(struct o2hb_region *reg,
 }
 
 static int o2hb_read_slots(struct o2hb_region *reg,
+			   unsigned int begin_slot,
 			   unsigned int max_slots)
 {
-	unsigned int current_slot=0;
+	unsigned int current_slot = begin_slot;
 	int status;
 	struct o2hb_bio_wait_ctxt wc;
 	struct bio *bio;
@@ -1093,9 +1094,14 @@ static int o2hb_highest_node(unsigned long *nodes, int numbits)
 	return find_last_bit(nodes, numbits);
 }
 
+static int o2hb_lowest_node(unsigned long *nodes, int numbits)
+{
+	return find_first_bit(nodes, numbits);
+}
+
 static int o2hb_do_disk_heartbeat(struct o2hb_region *reg)
 {
-	int i, ret, highest_node;
+	int i, ret, highest_node, lowest_node;
 	int membership_change = 0, own_slot_ok = 0;
 	unsigned long configured_nodes[BITS_TO_LONGS(O2NM_MAX_NODES)];
 	unsigned long live_node_bitmap[BITS_TO_LONGS(O2NM_MAX_NODES)];
@@ -1120,7 +1126,8 @@ static int o2hb_do_disk_heartbeat(struct o2hb_region *reg)
 	}
 
 	highest_node = o2hb_highest_node(configured_nodes, O2NM_MAX_NODES);
-	if (highest_node >= O2NM_MAX_NODES) {
+	lowest_node = o2hb_lowest_node(configured_nodes, O2NM_MAX_NODES);
+	if (highest_node >= O2NM_MAX_NODES || lowest_node >= O2NM_MAX_NODES) {
 		mlog(ML_NOTICE, "o2hb: No configured nodes found!\n");
 		ret = -EINVAL;
 		goto bail;
@@ -1130,7 +1137,7 @@ static int o2hb_do_disk_heartbeat(struct o2hb_region *reg)
 	 * yet. Of course, if the node definitions have holes in them
 	 * then we're reading an empty slot anyway... Consider this
 	 * best-effort. */
-	ret = o2hb_read_slots(reg, highest_node + 1);
+	ret = o2hb_read_slots(reg, lowest_node, highest_node + 1);
 	if (ret < 0) {
 		mlog_errno(ret);
 		goto bail;
@@ -1801,7 +1808,7 @@ static int o2hb_populate_slot_data(struct o2hb_region *reg)
 	struct o2hb_disk_slot *slot;
 	struct o2hb_disk_heartbeat_block *hb_block;
 
-	ret = o2hb_read_slots(reg, reg->hr_blocks);
+	ret = o2hb_read_slots(reg, 0, reg->hr_blocks);
 	if (ret)
 		goto out;