drbd: improve throttling decisions of background resynchronisation
Background resynchronisation does some "side-stepping", or throttles
itself, if it detects application IO activity, and the current resync
rate estimate is above the configured "cmin-rate".
What was not detected: if there is no application IO,
because it blocks on activity log transactions.
Introduce a new atomic_t ap_actlog_cnt, tracking such blocked requests,
and count non-zero as application IO activity.
This counter is exposed at proc_details level 2 and above.
Also make sure to release the currently locked resync extent
if we side-step due to such voluntary throttling.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 7a1078d..0d3cbd8 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -2417,13 +2417,14 @@
* 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.
*/
-bool 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,
+ bool throttle_if_app_is_waiting)
{
struct lc_element *tmp;
- bool throttle = true;
+ bool throttle = drbd_rs_c_min_rate_throttle(device);
- if (!drbd_rs_c_min_rate_throttle(device))
- return false;
+ if (!throttle || throttle_if_app_is_waiting)
+ return throttle;
spin_lock_irq(&device->al_lock);
tmp = lc_find(device->resync, BM_SECT_TO_EXT(sector));
@@ -2431,7 +2432,8 @@
struct bm_extent *bm_ext = lc_entry(tmp, struct bm_extent, lce);
if (test_bit(BME_PRIORITY, &bm_ext->flags))
throttle = false;
- /* Do not slow down if app IO is already waiting for this extent */
+ /* Do not slow down if app IO is already waiting for this extent,
+ * and our progress is necessary for application IO to complete. */
}
spin_unlock_irq(&device->al_lock);
@@ -2456,7 +2458,9 @@
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) {
+
+ if (atomic_read(&device->ap_actlog_cnt)
+ || !device->rs_last_events || curr_events - device->rs_last_events > 64) {
unsigned long rs_left;
int i;
@@ -2646,7 +2650,8 @@
* we would also throttle its application reads.
* In that case, throttling is done on the SyncTarget only.
*/
- if (device->state.peer != R_PRIMARY && drbd_rs_should_slow_down(device, sector))
+ if (device->state.peer != R_PRIMARY
+ && drbd_rs_should_slow_down(device, sector, false))
schedule_timeout_uninterruptible(HZ/10);
if (drbd_rs_begin_io(device, sector))
goto out_free_e;