diff --git a/block/blk-core.c b/block/blk-core.c
index c66333d..b2d0ac8 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2100,6 +2100,34 @@
 		rq->rq_disk = bio->bi_bdev->bd_disk;
 }
 
+/**
+ * blk_lld_busy - Check if underlying low-level drivers of a device are busy
+ * @q : the queue of the device being checked
+ *
+ * Description:
+ *    Check if underlying low-level drivers of a device are busy.
+ *    If the drivers want to export their busy state, they must set own
+ *    exporting function using blk_queue_lld_busy() first.
+ *
+ *    Basically, this function is used only by request stacking drivers
+ *    to stop dispatching requests to underlying devices when underlying
+ *    devices are busy.  This behavior helps more I/O merging on the queue
+ *    of the request stacking driver and prevents I/O throughput regression
+ *    on burst I/O load.
+ *
+ * Return:
+ *    0 - Not busy (The request stacking driver should dispatch request)
+ *    1 - Busy (The request stacking driver should stop dispatching request)
+ */
+int blk_lld_busy(struct request_queue *q)
+{
+	if (q->lld_busy_fn)
+		return q->lld_busy_fn(q);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(blk_lld_busy);
+
 int kblockd_schedule_work(struct request_queue *q, struct work_struct *work)
 {
 	return queue_work(kblockd_workqueue, work);
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 1d0330d..b21dcdb 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -89,6 +89,12 @@
 }
 EXPORT_SYMBOL_GPL(blk_queue_rq_timed_out);
 
+void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn)
+{
+	q->lld_busy_fn = fn;
+}
+EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
+
 /**
  * blk_queue_make_request - define an alternate make_request function for a device
  * @q:  the request queue for the device to be affected
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 0cf3e61..9e0ee1a 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -269,6 +269,7 @@
 typedef void (prepare_flush_fn) (struct request_queue *, struct request *);
 typedef void (softirq_done_fn)(struct request *);
 typedef int (dma_drain_needed_fn)(struct request *);
+typedef int (lld_busy_fn) (struct request_queue *q);
 
 enum blk_eh_timer_return {
 	BLK_EH_NOT_HANDLED,
@@ -325,6 +326,7 @@
 	softirq_done_fn		*softirq_done_fn;
 	rq_timed_out_fn		*rq_timed_out_fn;
 	dma_drain_needed_fn	*dma_drain_needed;
+	lld_busy_fn		*lld_busy_fn;
 
 	/*
 	 * Dispatch queue sorting
@@ -699,6 +701,7 @@
 extern void blk_insert_request(struct request_queue *, struct request *, int, void *);
 extern void blk_requeue_request(struct request_queue *, struct request *);
 extern int blk_rq_check_limits(struct request_queue *q, struct request *rq);
+extern int blk_lld_busy(struct request_queue *q);
 extern int blk_insert_cloned_request(struct request_queue *q,
 				     struct request *rq);
 extern void blk_plug_device(struct request_queue *);
@@ -835,6 +838,7 @@
 extern int blk_queue_dma_drain(struct request_queue *q,
 			       dma_drain_needed_fn *dma_drain_needed,
 			       void *buf, unsigned int size);
+extern void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn);
 extern void blk_queue_segment_boundary(struct request_queue *, unsigned long);
 extern void blk_queue_prep_rq(struct request_queue *, prep_rq_fn *pfn);
 extern void blk_queue_merge_bvec(struct request_queue *, merge_bvec_fn *);