[Drbd-dev] [PATCH] drbd: fix throttling on newly created DM backing devices

[Imre Palik <imrep.amz@gmail.com>]

From: "Palik, Imre" <imrep@amazon.de>

If the drbd backing device is a new device mapper device (e.g., a
dm-linear mapping of an existing block device that contains data), the
counters are initially 0 even though the device contains useful
data. This causes throttling until something accesses the drbd device
or the backing device.

The patch disables throttling, as long as only resync is responsible
for disk activity on a freshly created device.

Reported-by: Mikhail Sugakov <msugakov@amazon.de>
Cc: Matt Wilson <msw@amazon.com>
Signed-off-by: Imre Palik <imrep@amazon.de>
---
 drivers/block/drbd/drbd_receiver.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 9342b8d..511d2eb 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -2482,7 +2482,8 @@ bool drbd_rs_c_min_rate_throttle(struct drbd_device *device)
 			atomic_read(&device->rs_sect_ev);
 
 	if (atomic_read(&device->ap_actlog_cnt)
-	    || !device->rs_last_events || curr_events - device->rs_last_events > 64) {
+		|| (curr_events && (!device->rs_last_events
+					|| curr_events - device->rs_last_events > 64))) {
 		unsigned long rs_left;
 		int i;
 
-- 
1.7.9.5