[PATCH] misc elevator/block updates

I've got a new i/o scheduler in testing, some changes where needed in
the block layer to accomodate it. Basically because right now
assumptions are made about q->queue_head being the sort list. The
changes in detail:

o elevator_merge_requests_fn takes queue argument as well

o __make_request() inits insert_here to NULL instead of
  q->queue_head.prev, which means that the i/o schedulers must
  explicitly check for this condition now.

o incorporate elv_queue_empty(), it was just a place holder before

o add elv_get_sort_head(). it returns the sort head of the elevator for
  a given request. attempt_{back,front}_merge uses it to determine
  whether a request is valid or not. Maybe attempt_{back,front}_merge
  should just be killed, I doubt they have much relevance with the wake
  up batching.

o call the merge_cleanup functions of the elevator _after_ the merge has
  been done, not before. This way the elevator functions get the new
  state of the request, which is the most interesting.

o Kill extra nr_sectors check in ll_merge_requests_fn()

o bi->bi_bdev is always set in __make_request(), so kill check.

drivers/block/elevator.c

@@ -220,7 +220,8 @@ void elevator_linus_merge_cleanup(request_queue_t *q, struct request *req, int c
 	}
 }
 
-void elevator_linus_merge_req(struct request *req, struct request *next)
+void elevator_linus_merge_req(request_queue_t *q, struct request *req,
+			      struct request *next)
 {
 	if (elv_linus_sequence(next) < elv_linus_sequence(req))
 		elv_linus_sequence(req) = elv_linus_sequence(next);
@@ -232,6 +233,9 @@ void elevator_linus_add_request(request_queue_t *q, struct request *rq,
 	elevator_t *e = &q->elevator;
 	int lat = 0, *latency = e->elevator_data;
 
+	if (!insert_here)
+		insert_here = q->queue_head.prev;
+
 	if (!(rq->flags & REQ_BARRIER))
 		lat = latency[rq_data_dir(rq)];
 
@@ -318,7 +322,7 @@ void elevator_noop_add_request(request_queue_t *q, struct request *rq,
 
 struct request *elevator_noop_next_request(request_queue_t *q)
 {
-	if (!blk_queue_empty(q))
+	if (!list_empty(&q->queue_head))
 		return list_entry_rq(q->queue_head.next);
 
 	return NULL;
@@ -376,7 +380,7 @@ void elv_merge_requests(request_queue_t *q, struct request *rq,
 	elevator_t *e = &q->elevator;
 
 	if (e->elevator_merge_req_fn)
-		e->elevator_merge_req_fn(rq, next);
+		e->elevator_merge_req_fn(q, rq, next);
 }
 
 /*
@@ -433,6 +437,27 @@ void elv_remove_request(request_queue_t *q, struct request *rq)
 		e->elevator_remove_req_fn(q, rq);
 }
 
+int elv_queue_empty(request_queue_t *q)
+{
+	elevator_t *e = &q->elevator;
+
+	if (e->elevator_queue_empty_fn)
+		return e->elevator_queue_empty_fn(q);
+
+	return list_empty(&q->queue_head);
+}
+
+inline struct list_head *elv_get_sort_head(request_queue_t *q,
+					   struct request *rq)
+{
+	elevator_t *e = &q->elevator;
+
+	if (e->elevator_get_sort_head_fn)
+		return e->elevator_get_sort_head_fn(q, rq);
+
+	return &q->queue_head;
+}
+
 elevator_t elevator_linus = {
 	elevator_merge_fn:		elevator_linus_merge,
 	elevator_merge_cleanup_fn:	elevator_linus_merge_cleanup,

drivers/block/ll_rw_blk.c

@@ -1391,7 +1391,6 @@ static void attempt_merge(request_queue_t *q, struct request *req,
 
 	if (rq_data_dir(req) != rq_data_dir(next)
 	    || !kdev_same(req->rq_dev, next->rq_dev)
-	    || req->nr_sectors + next->nr_sectors > q->max_sectors
 	    || next->waiting || next->special)
 		return;
 
@@ -1402,15 +1401,14 @@ static void attempt_merge(request_queue_t *q, struct request *req,
 	 * counts here.
 	 */
 	if (q->merge_requests_fn(q, req, next)) {
-		elv_merge_requests(q, req, next);
-
-		blkdev_dequeue_request(next);
-
 		req->biotail->bi_next = next->bio;
 		req->biotail = next->biotail;
 
 		req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
 
+		elv_merge_requests(q, req, next);
+
+		blkdev_dequeue_request(next);
 		blk_put_request(next);
 	}
 }
@@ -1418,16 +1416,18 @@ static void attempt_merge(request_queue_t *q, struct request *req,
 static inline void attempt_back_merge(request_queue_t *q, struct request *rq)
 {
 	struct list_head *next = rq->queuelist.next;
+	struct list_head *sort_head = elv_get_sort_head(q, rq);
 
-	if (next != &q->queue_head)
+	if (next != sort_head)
 		attempt_merge(q, rq, list_entry_rq(next));
 }
 
 static inline void attempt_front_merge(request_queue_t *q, struct request *rq)
 {
 	struct list_head *prev = rq->queuelist.prev;
+	struct list_head *sort_head = elv_get_sort_head(q, rq);
 
-	if (prev != &q->queue_head)
+	if (prev != sort_head)
 		attempt_merge(q, list_entry_rq(prev), rq);
 }
 
@@ -1487,7 +1487,7 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 	spin_lock_irq(q->queue_lock);
 again:
 	req = NULL;
-	insert_here = q->queue_head.prev;
+	insert_here = NULL;
 
 	if (blk_queue_empty(q)) {
 		blk_plug_device(q);
@@ -1505,11 +1505,10 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 				break;
 			}
 
-			elv_merge_cleanup(q, req, nr_sectors);
-
 			req->biotail->bi_next = bio;
 			req->biotail = bio;
 			req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+			elv_merge_cleanup(q, req, nr_sectors);
 			drive_stat_acct(req, nr_sectors, 0);
 			attempt_back_merge(q, req);
 			goto out;
@@ -1521,8 +1520,6 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 				break;
 			}
 
-			elv_merge_cleanup(q, req, nr_sectors);
-
 			bio->bi_next = req->bio;
 			req->bio = bio;
 			/*
@@ -1535,6 +1532,7 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 			req->hard_cur_sectors = cur_nr_sectors;
 			req->sector = req->hard_sector = sector;
 			req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+			elv_merge_cleanup(q, req, nr_sectors);
 			drive_stat_acct(req, nr_sectors, 0);
 			attempt_front_merge(q, req);
 			goto out;
@@ -1603,9 +1601,7 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 	req->buffer = bio_data(bio);	/* see ->buffer comment above */
 	req->waiting = NULL;
 	req->bio = req->biotail = bio;
-	if (bio->bi_bdev)
-		req->rq_dev = to_kdev_t(bio->bi_bdev->bd_dev);
-	else	req->rq_dev = NODEV;
+	req->rq_dev = to_kdev_t(bio->bi_bdev->bd_dev);
 	add_request(q, req, insert_here);
 out:
 	if (freereq)

include/linux/elevator.h

@@ -6,13 +6,14 @@ typedef int (elevator_merge_fn) (request_queue_t *, struct request **,
 
 typedef void (elevator_merge_cleanup_fn) (request_queue_t *, struct request *, int);
 
-typedef void (elevator_merge_req_fn) (struct request *, struct request *);
+typedef void (elevator_merge_req_fn) (request_queue_t *, struct request *, struct request *);
 
 typedef struct request *(elevator_next_req_fn) (request_queue_t *);
 
 typedef void (elevator_add_req_fn) (request_queue_t *, struct request *, struct list_head *);
 typedef int (elevator_queue_empty_fn) (request_queue_t *);
 typedef void (elevator_remove_req_fn) (request_queue_t *, struct request *);
+typedef struct list_head *(elevator_get_sort_head_fn) (request_queue_t *, struct request *);
 
 typedef int (elevator_init_fn) (request_queue_t *, elevator_t *);
 typedef void (elevator_exit_fn) (request_queue_t *, elevator_t *);
@@ -28,6 +29,7 @@ struct elevator_s
 	elevator_remove_req_fn *elevator_remove_req_fn;
 
 	elevator_queue_empty_fn *elevator_queue_empty_fn;
+	elevator_get_sort_head_fn *elevator_get_sort_head_fn;
 
 	elevator_init_fn *elevator_init_fn;
 	elevator_exit_fn *elevator_exit_fn;
@@ -45,6 +47,8 @@ extern int elv_merge(request_queue_t *, struct request **, struct bio *);
 extern void elv_merge_requests(request_queue_t *, struct request *,
 			       struct request *);
 extern void elv_remove_request(request_queue_t *, struct request *);
+extern int elv_queue_empty(request_queue_t *);
+extern inline struct list_head *elv_get_sort_head(request_queue_t *, struct request *);
 
 /*
  * noop I/O scheduler. always merges, always inserts new request at tail
@@ -72,6 +76,10 @@ typedef struct blkelv_ioctl_arg_s {
 
 extern int elevator_init(request_queue_t *, elevator_t *, elevator_t);
 extern void elevator_exit(request_queue_t *, elevator_t *);
+extern inline int bio_rq_in_between(struct bio *, struct request *, struct list_head *);
+extern inline int elv_rq_merge_ok(struct request *, struct bio *);
+extern inline int elv_try_merge(struct request *, struct bio *);
+extern inline int elv_try_last_merge(request_queue_t *, struct request **, struct bio *);
 
 /*
  * Return values from elevator merger
@@ -80,10 +88,4 @@ extern void elevator_exit(request_queue_t *, elevator_t *);
 #define ELEVATOR_FRONT_MERGE	1
 #define ELEVATOR_BACK_MERGE	2
 
-/*
- * will change once we move to a more complex data structure than a simple
- * list for pending requests
- */
-#define elv_queue_empty(q)	list_empty(&(q)->queue_head)
-
 #endif