blk-fair-batches vs 2.4.20-rc6

@@ -118,13 +118,21 @@ struct request_queue
 	/*
 	 * Boolean that indicates whether this queue is plugged or not.
 	 */
-	char			plugged;
+	int			plugged:1;
 
 	/*
 	 * Boolean that indicates whether current_request is active or
 	 * not.
 	 */
-	char			head_active;
+	int			head_active:1;
+
+	/*
+	 * Booleans that indicate whether the queue's free requests have
+	 * been exhausted and is waiting to drop below the batch_requests
+	 * threshold
+	 */
+	int			read_full:1;
+	int			write_full:1;
 
 	unsigned long		bounce_pfn;
 

@@ -140,6 +148,30 @@ struct request_queue
 	wait_queue_head_t	wait_for_requests[2];
 };
 
+static inline void set_queue_full(request_queue_t *q, int rw)
+{
+	if (rw == READ)
+		q->read_full = 1;
+	else
+		q->write_full = 1;
+}
+
+static inline void clear_queue_full(request_queue_t *q, int rw)
+{
+	if (rw == READ)
+		q->read_full = 0;
+	else
+		q->write_full = 0;
+}
+
+static inline int queue_full(request_queue_t *q, int rw)
+{
+	if (rw == READ)
+		return q->read_full;
+	else
+		return q->write_full;
+}
+
 extern unsigned long blk_max_low_pfn, blk_max_pfn;
 
 #define BLK_BOUNCE_HIGH		(blk_max_low_pfn << PAGE_SHIFT)

@@ -513,7 +513,10 @@ static struct request *get_request(reque
 	struct request *rq = NULL;
 	struct request_list *rl = q->rq + rw;
 
-	if (!list_empty(&rl->free)) {
+	if (list_empty(&rl->free))
+		set_queue_full(q, rw);
+	
+	if (!queue_full(q, rw)) {
 		rq = blkdev_free_rq(&rl->free);
 		list_del(&rq->queue);
 		rl->count--;

@@ -594,7 +597,7 @@ static struct request *__get_request_wai
 	add_wait_queue_exclusive(&q->wait_for_requests[rw], &wait);
 	do {
 		set_current_state(TASK_UNINTERRUPTIBLE);
-		if (q->rq[rw].count == 0)
+		if (queue_full(q, rw))
 			schedule();
 		spin_lock_irq(&io_request_lock);
 		rq = get_request(q, rw);

@@ -829,9 +832,14 @@ void blkdev_release_request(struct reque
 	 */
 	if (q) {
 		list_add(&req->queue, &q->rq[rw].free);
-		if (++q->rq[rw].count >= q->batch_requests &&
-				waitqueue_active(&q->wait_for_requests[rw]))
-			wake_up(&q->wait_for_requests[rw]);
+		q->rq[rw].count++;
+		if (q->rq[rw].count >= q->batch_requests) {
+			if (q->rq[rw].count == q->batch_requests) 
+				clear_queue_full(q, rw);
+
+			if (waitqueue_active(&q->wait_for_requests[rw]))
+				wake_up(&q->wait_for_requests[rw]);
+		}
 	}
 }