drbd: Implemented priority inheritance for resync requests

We only issue resync requests if there is no significant application IO
going on. = Application IO has higher priority than resnyc IO.

If application IO can not be started because the resync process locked
an resync_lru entry, start the IO operations necessary to release the
lock ASAP.

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

4 files changed, 27 insertions, 20 deletions

diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index 33f6cc537d08..28f85d950781 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -182,6 +182,7 @@ static struct lc_element *_al_get(struct drbd_conf *mdev, unsigned int enr)
         if (unlikely(tmp != NULL)) {
                 struct bm_extent  *bm_ext = lc_entry(tmp, struct bm_extent, lce);
                 if (test_bit(BME_NO_WRITES, &bm_ext->flags)) {
+                        set_bit(BME_PRIORITY, &bm_ext->flags);
                         spin_unlock_irq(&mdev->al_lock);
                         return NULL;
                 }
@@ -1297,8 +1298,7 @@ void drbd_rs_complete_io(struct drbd_conf *mdev, sector_t sector)
         }
 
         if (lc_put(mdev->resync, &bm_ext->lce) == 0) {
-                clear_bit(BME_LOCKED, &bm_ext->flags);
-                clear_bit(BME_NO_WRITES, &bm_ext->flags);
+                bm_ext->flags = 0; /* clear BME_LOCKED, BME_NO_WRITES and BME_PRIORITY */
                 mdev->resync_locked--;
                 wake_up(&mdev->al_wait);
         }
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index da02cce374c9..366873d661b8 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -1326,6 +1326,7 @@ struct bm_extent {
 
 #define BME_NO_WRITES  0  /* bm_extent.flags: no more requests on this one! */
 #define BME_LOCKED     1  /* bm_extent.flags: syncer active on this one. */
+#define BME_PRIORITY   2  /* finish resync IO on this extent ASAP! App IO waiting! */
 
 /* drbd_bitmap.c */
 /*
@@ -1552,7 +1553,7 @@ extern int w_start_resync(struct drbd_conf *, struct drbd_work *, int);
 extern void resync_timer_fn(unsigned long data);
 
 /* drbd_receiver.c */
-extern int drbd_rs_should_slow_down(struct drbd_conf *mdev);
+extern int drbd_rs_should_slow_down(struct drbd_conf *mdev, sector_t sector);
 extern int drbd_submit_ee(struct drbd_conf *mdev, struct drbd_epoch_entry *e,
                 const unsigned rw, const int fault_type);
 extern int drbd_release_ee(struct drbd_conf *mdev, struct list_head *list);
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index ee9238e59327..0630a2e122d3 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -1862,10 +1862,11 @@ 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_conf *mdev)
+int drbd_rs_should_slow_down(struct drbd_conf *mdev, sector_t sector)
 {
         struct gendisk *disk = mdev->ldev->backing_bdev->bd_contains->bd_disk;
         unsigned long db, dt, dbdt;
+        struct lc_element *tmp;
         int curr_events;
         int throttle = 0;
 
@@ -1873,9 +1874,22 @@ int drbd_rs_should_slow_down(struct drbd_conf *mdev)
         if (mdev->sync_conf.c_min_rate == 0)
                 return 0;
 
+        spin_lock_irq(&mdev->al_lock);
+        tmp = lc_find(mdev->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(&mdev->al_lock);
+                        return 0;
+                }
+                /* Do not slow down if app IO is already waiting for this extent */
+        }
+        spin_unlock_irq(&mdev->al_lock);
+
         curr_events = (int)part_stat_read(&disk->part0, sectors[0]) +
                       (int)part_stat_read(&disk->part0, sectors[1]) -
                         atomic_read(&mdev->rs_sect_ev);
+
         if (!mdev->rs_last_events || curr_events - mdev->rs_last_events > 64) {
                 unsigned long rs_left;
                 int i;
@@ -2060,9 +2074,9 @@ static int receive_DataRequest(struct drbd_conf *mdev, enum drbd_packets cmd, un
          * we would also throttle its application reads.
          * In that case, throttling is done on the SyncTarget only.
          */
-        if (mdev->state.peer != R_PRIMARY && drbd_rs_should_slow_down(mdev))
-                msleep(100);
-        if (drbd_rs_begin_io(mdev, e->sector))
+        if (mdev->state.peer != R_PRIMARY && drbd_rs_should_slow_down(mdev, sector))
+                schedule_timeout_uninterruptible(HZ/10);
+        if (drbd_rs_begin_io(mdev, sector))
                 goto out_free_e;
 
 submit_for_resync:
diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 982d68432a0f..4008130f2b2c 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -355,7 +355,7 @@ static int read_for_csum(struct drbd_conf *mdev, sector_t sector, int size)
         if (!get_ldev(mdev))
                 return -EIO;
 
-        if (drbd_rs_should_slow_down(mdev))
+        if (drbd_rs_should_slow_down(mdev, sector))
                 goto defer;
 
         /* GFP_TRY, because if there is no memory available right now, this may
@@ -503,16 +503,6 @@ int drbd_rs_number_requests(struct drbd_conf *mdev)
                 number = SLEEP_TIME * mdev->c_sync_rate  / ((BM_BLOCK_SIZE / 1024) * HZ);
         }
 
-        /* Throttle resync on lower level disk activity, which may also be
-         * caused by application IO on Primary/SyncTarget.
-         * Keep this after the call to drbd_rs_controller, as that assumes
-         * to be called as precisely as possible every SLEEP_TIME,
-         * and would be confused otherwise. */
-        if (number && drbd_rs_should_slow_down(mdev)) {
-                mdev->c_sync_rate = 1;
-                number = 0;
-        }
-
         /* ignore the amount of pending requests, the resync controller should
          * throttle down to incoming reply rate soon enough anyways. */
         return number;
@@ -594,7 +584,8 @@ next_sector:
 
                 sector = BM_BIT_TO_SECT(bit);
 
-                if (drbd_try_rs_begin_io(mdev, sector)) {
+                if (drbd_rs_should_slow_down(mdev, sector) ||
+                    drbd_try_rs_begin_io(mdev, sector)) {
                         mdev->bm_resync_fo = bit;
                         goto requeue;
                 }
@@ -719,7 +710,8 @@ static int w_make_ov_request(struct drbd_conf *mdev, struct drbd_work *w, int ca
 
                 size = BM_BLOCK_SIZE;
 
-                if (drbd_try_rs_begin_io(mdev, sector)) {
+                if (drbd_rs_should_slow_down(mdev, sector) ||
+                    drbd_try_rs_begin_io(mdev, sector)) {
                         mdev->ov_position = sector;
                         goto requeue;
                 }