drbd: don't let application IO pre-empt resync too often

Before, application IO could pre-empt resync activity
for up to hardcoded 20 seconds per resync request.
A very busy server could throttle the effective resync bandwidth
down to one request per 20 seconds.

Now, we only let application IO pre-empt resync traffic
while the current resync rate estimate is above c-min-rate.

If you disable the c-min-rate throttle feature (set c-min-rate = 0),
application IO will no longer pre-empt resync traffic at all.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 26 insertions, 21 deletions

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 6ffbc22..10d2dcb 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -2323,39 +2323,45 @@ out_interrupted:
  * The current sync rate used here uses only the most recent two step marks,
  * to have a short time average so we can react faster.
  */
-int drbd_rs_should_slow_down(struct drbd_device *device, sector_t sector)
+bool drbd_rs_should_slow_down(struct drbd_device *device, sector_t sector)
 {
-	struct gendisk *disk = device->ldev->backing_bdev->bd_contains->bd_disk;
-	unsigned long db, dt, dbdt;
 	struct lc_element *tmp;
-	int curr_events;
-	int throttle = 0;
-	unsigned int c_min_rate;
+	bool throttle = true;
 
-	rcu_read_lock();
-	c_min_rate = rcu_dereference(device->ldev->disk_conf)->c_min_rate;
-	rcu_read_unlock();
-
-	/* feature disabled? */
-	if (c_min_rate == 0)
-		return 0;
+	if (!drbd_rs_c_min_rate_throttle(device))
+		return false;
 
 	spin_lock_irq(&device->al_lock);
 	tmp = lc_find(device->resync, BM_SECT_TO_EXT(sector));
 	if (tmp) {
 		struct bm_extent *bm_ext = lc_entry(tmp, struct bm_extent, lce);
-		if (test_bit(BME_PRIORITY, &bm_ext->flags)) {
-			spin_unlock_irq(&device->al_lock);
-			return 0;
-		}
+		if (test_bit(BME_PRIORITY, &bm_ext->flags))
+			throttle = false;
 		/* Do not slow down if app IO is already waiting for this extent */
 	}
 	spin_unlock_irq(&device->al_lock);
 
+	return throttle;
+}
+
+bool drbd_rs_c_min_rate_throttle(struct drbd_device *device)
+{
+	struct gendisk *disk = device->ldev->backing_bdev->bd_contains->bd_disk;
+	unsigned long db, dt, dbdt;
+	unsigned int c_min_rate;
+	int curr_events;
+
+	rcu_read_lock();
+	c_min_rate = rcu_dereference(device->ldev->disk_conf)->c_min_rate;
+	rcu_read_unlock();
+
+	/* feature disabled? */
+	if (c_min_rate == 0)
+		return false;
+
 	curr_events = (int)part_stat_read(&disk->part0, sectors[0]) +
 		      (int)part_stat_read(&disk->part0, sectors[1]) -
 			atomic_read(&device->rs_sect_ev);
-
 	if (!device->rs_last_events || curr_events - device->rs_last_events > 64) {
 		unsigned long rs_left;
 		int i;
@@ -2378,12 +2384,11 @@ int drbd_rs_should_slow_down(struct drbd_device *device, sector_t sector)
 		dbdt = Bit2KB(db/dt);
 
 		if (dbdt > c_min_rate)
-			throttle = 1;
+			return true;
 	}
-	return throttle;
+	return false;
 }
 
-
 static int receive_DataRequest(struct drbd_connection *connection, struct packet_info *pi)
 {
 	struct drbd_peer_device *peer_device;