drbd: only start a new epoch, if the current epoch contains writes

Almost all code paths calling start_new_tl_epoch() guarded it with
	if (... current_tle_writes > 0 ... ).
Just move that inside start_new_tl_epoch().

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

1 files changed, 12 insertions, 7 deletions

diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 6e8d09763510..0c1b6327e207 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -162,6 +162,10 @@ static void wake_all_senders(struct drbd_tconn *tconn) {
 /* must hold resource->req_lock */
 static void start_new_tl_epoch(struct drbd_tconn *tconn)
 {
+        /* no point closing an epoch, if it is empty, anyways. */
+        if (tconn->current_tle_writes == 0)
+                return;
+
         tconn->current_tle_writes = 0;
         atomic_inc(&tconn->current_tle_nr);
         wake_all_senders(tconn);
@@ -861,9 +865,8 @@ static void maybe_pull_ahead(struct drbd_conf *mdev)
         }
 
         if (congested) {
-                if (mdev->tconn->current_tle_writes)
-                        /* start a new epoch for non-mirrored writes */
-                        start_new_tl_epoch(mdev->tconn);
+                /* start a new epoch for non-mirrored writes */
+                start_new_tl_epoch(mdev->tconn);
 
                 if (on_congestion == OC_PULL_AHEAD)
                         _drbd_set_state(_NS(mdev, conn, C_AHEAD), 0, NULL);
@@ -950,7 +953,7 @@ static int drbd_process_write_request(struct drbd_request *req)
         if (unlikely(req->i.size == 0)) {
                 /* The only size==0 bios we expect are empty flushes. */
                 D_ASSERT(req->master_bio->bi_rw & REQ_FLUSH);
-                if (remote && mdev->tconn->current_tle_writes)
+                if (remote)
                         start_new_tl_epoch(mdev->tconn);
                 return 0;
         }
@@ -1066,13 +1069,15 @@ void __drbd_make_request(struct drbd_conf *mdev, struct bio *bio, unsigned long
 
         /* which transfer log epoch does this belong to? */
         req->epoch = atomic_read(&mdev->tconn->current_tle_nr);
-        if (rw == WRITE)
-                mdev->tconn->current_tle_writes++;
 
         /* no point in adding empty flushes to the transfer log,
          * they are mapped to drbd barriers already. */
-        if (likely(req->i.size!=0))
+        if (likely(req->i.size!=0)) {
+                if (rw == WRITE)
+                        mdev->tconn->current_tle_writes++;
+
                 list_add_tail(&req->tl_requests, &mdev->tconn->transfer_log);
+        }
 
         if (rw == WRITE) {
                 if (!drbd_process_write_request(req))