drbd: drbd_rs_number_requests: fix unit mismatch in comparison

We try to limit the number of "in-flight" resync requests.
One condition for that is the amount of requested data should not exceed
half of what can be covered by our "max-buffers" setting.

However we compared number of 4k pages with number of in-flight 512 Byte
sectors, and this extra throttle triggered much earlier than intended.

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

1 files changed, 9 insertions, 4 deletions

diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 0b5e4294acf9..9f0acb011f30 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -504,9 +504,9 @@ struct fifo_buffer *fifo_alloc(int fifo_size)
 static int drbd_rs_controller(struct drbd_device *device, unsigned int sect_in)
 {
         struct disk_conf *dc;
-        unsigned int want;     /* The number of sectors we want in the proxy */
+        unsigned int want;     /* The number of sectors we want in-flight */
         int req_sect; /* Number of sectors to request in this turn */
-        int correction; /* Number of sectors more we need in the proxy*/
+        int correction; /* Number of sectors more we need in-flight */
         int cps; /* correction per invocation of drbd_rs_controller() */
         int steps; /* Number of time steps to plan ahead */
         int curr_corr;
@@ -577,8 +577,13 @@ static int drbd_rs_number_requests(struct drbd_device *device)
          * potentially causing a distributed deadlock on congestion during
          * online-verify or (checksum-based) resync, if max-buffers,
          * socket buffer sizes and resync rate settings are mis-configured. */
-        if (mxb - device->rs_in_flight < number)
-                number = mxb - device->rs_in_flight;
+
+        /* note that "number" is in units of "BM_BLOCK_SIZE" (which is 4k),
+         * mxb (as used here, and in drbd_alloc_pages on the peer) is
+         * "number of pages" (typically also 4k),
+         * but "rs_in_flight" is in "sectors" (512 Byte). */
+        if (mxb - device->rs_in_flight/8 < number)
+                number = mxb - device->rs_in_flight/8;
 
         return number;
 }