[PATCH] fix IO hangs

The "insert_here" list pointer logic was broken, and unnecessary. 

Kill it and its associated logic off completely - just tell the IO
scheduler what kind of insert it is.

This also makes the *_insert_request strategies much easier to follow,
imo.

drivers/block/as-iosched.c

@@ -255,7 +255,7 @@ static void as_remove_merge_hints(request_queue_t *q, struct as_rq *arq)
 {
 	as_del_arq_hash(arq);
 
-	if (q->last_merge == &arq->request->queuelist)
+	if (q->last_merge == arq->request)
 		q->last_merge = NULL;
 }
 
@@ -1347,39 +1347,30 @@ static void as_requeue_request(request_queue_t *q, struct request *rq)
 }
 
 static void
-as_insert_request(request_queue_t *q, struct request *rq,
-			struct list_head *insert_here)
+as_insert_request(request_queue_t *q, struct request *rq, int where)
 {
 	struct as_data *ad = q->elevator.elevator_data;
 	struct as_rq *arq = RQ_DATA(rq);
 
-	if (unlikely(rq->flags & (REQ_HARDBARRIER|REQ_SOFTBARRIER))) {
-		q->last_merge = NULL;
-
-		if (insert_here != ad->dispatch) {
+	switch (where) {
+		case ELEVATOR_INSERT_BACK:
 			while (ad->next_arq[REQ_SYNC])
 				as_move_to_dispatch(ad, ad->next_arq[REQ_SYNC]);
 
 			while (ad->next_arq[REQ_ASYNC])
 				as_move_to_dispatch(ad, ad->next_arq[REQ_ASYNC]);
-		}
-
-		if (!insert_here)
-			insert_here = ad->dispatch->prev;
-	}
-
-	if (unlikely(!blk_fs_request(rq))) {
-		if (!insert_here)
-			insert_here = ad->dispatch;
-	}
-
-	if (insert_here) {
-		list_add(&rq->queuelist, insert_here);
-
-		/* Stop anticipating - let this request get through */
-		if (list_empty(ad->dispatch))
+			list_add_tail(&rq->queuelist, ad->dispatch);
+			break;
+		case ELEVATOR_INSERT_FRONT:
+			list_add(&rq->queuelist, ad->dispatch);
 			as_antic_stop(ad);
-
+			break;
+		case ELEVATOR_INSERT_SORT:
+			BUG_ON(!blk_fs_request(rq));
+			as_add_request(ad, arq);
+			break;
+		default:
+			printk("%s: bad insert point %d\n", __FUNCTION__,where);
 			return;
 	}
 
@@ -1387,10 +1378,8 @@ as_insert_request(request_queue_t *q, struct request *rq,
 		as_add_arq_hash(ad, arq);
 
 		if (!q->last_merge)
-			q->last_merge = &rq->queuelist;
+			q->last_merge = rq;
 	}
-
-	as_add_request(ad, arq);
 }
 
 /*
@@ -1438,7 +1427,7 @@ as_latter_request(request_queue_t *q, struct request *rq)
 }
 
 static int
-as_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
+as_merge(request_queue_t *q, struct request **req, struct bio *bio)
 {
 	struct as_data *ad = q->elevator.elevator_data;
 	sector_t rb_key = bio->bi_sector + bio_sectors(bio);
@@ -1450,7 +1439,7 @@ as_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
 	 */
 	ret = elv_try_last_merge(q, bio);
 	if (ret != ELEVATOR_NO_MERGE) {
-		__rq = list_entry_rq(q->last_merge);
+		__rq = q->last_merge;
 		goto out_insert;
 	}
 
@@ -1482,11 +1471,11 @@ as_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
 
 	return ELEVATOR_NO_MERGE;
 out:
-	q->last_merge = &__rq->queuelist;
+	q->last_merge = __rq;
 out_insert:
 	if (ret)
 		as_hot_arq_hash(ad, RQ_DATA(__rq));
-	*insert = &__rq->queuelist;
+	*req = __rq;
 	return ret;
 }
 
@@ -1514,7 +1503,7 @@ static void as_merged_request(request_queue_t *q, struct request *req)
 		 */
 	}
 
-	q->last_merge = &req->queuelist;
+	q->last_merge = req;
 }
 
 static void

drivers/block/deadline-iosched.c

@@ -33,13 +33,7 @@ static const int deadline_hash_shift = 5;
 #define DL_HASH_ENTRIES		(1 << deadline_hash_shift)
 #define rq_hash_key(rq)		((rq)->sector + (rq)->nr_sectors)
 #define list_entry_hash(ptr)	list_entry((ptr), struct deadline_rq, hash)
-#define ON_HASH(drq)		(drq)->hash_valid_count
-
-#define DL_INVALIDATE_HASH(dd)				\
-	do {						\
-		if (!++(dd)->hash_valid_count)		\
-			(dd)->hash_valid_count = 1;	\
-	} while (0)
+#define ON_HASH(drq)		(drq)->on_hash
 
 struct deadline_data {
 	/*
@@ -58,7 +52,6 @@ struct deadline_data {
 	struct deadline_rq *next_drq[2];
 	struct list_head *dispatch;	/* driver dispatch queue */
 	struct list_head *hash;		/* request hash */
-	unsigned long hash_valid_count;	/* barrier hash count */
 	unsigned int batching;		/* number of sequential requests made */
 	sector_t last_sector;		/* head position */
 	unsigned int starved;		/* times reads have starved writes */
@@ -90,7 +83,7 @@ struct deadline_rq {
 	 * request hash, key is the ending offset (for back merge lookup)
 	 */
 	struct list_head hash;
-	unsigned long hash_valid_count;
+	char on_hash;
 
 	/*
 	 * expire fifo
@@ -110,7 +103,7 @@ static kmem_cache_t *drq_pool;
  */
 static inline void __deadline_del_drq_hash(struct deadline_rq *drq)
 {
-	drq->hash_valid_count = 0;
+	drq->on_hash = 0;
 	list_del_init(&drq->hash);
 }
 
@@ -125,7 +118,7 @@ deadline_remove_merge_hints(request_queue_t *q, struct deadline_rq *drq)
 {
 	deadline_del_drq_hash(drq);
 
-	if (q->last_merge == &drq->request->queuelist)
+	if (q->last_merge == drq->request)
 		q->last_merge = NULL;
 }
 
@@ -136,7 +129,7 @@ deadline_add_drq_hash(struct deadline_data *dd, struct deadline_rq *drq)
 
 	BUG_ON(ON_HASH(drq));
 
-	drq->hash_valid_count = dd->hash_valid_count;
+	drq->on_hash = 1;
 	list_add(&drq->hash, &dd->hash[DL_HASH_FN(rq_hash_key(rq))]);
 }
 
@@ -169,8 +162,7 @@ deadline_find_drq_hash(struct deadline_data *dd, sector_t offset)
 		
 		BUG_ON(!ON_HASH(drq));
 
-		if (!rq_mergeable(__rq)
-		    || drq->hash_valid_count != dd->hash_valid_count) {
+		if (!rq_mergeable(__rq)) {
 			__deadline_del_drq_hash(drq);
 			continue;
 		}
@@ -324,7 +316,7 @@ static void deadline_remove_request(request_queue_t *q, struct request *rq)
 }
 
 static int
-deadline_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
+deadline_merge(request_queue_t *q, struct request **req, struct bio *bio)
 {
 	struct deadline_data *dd = q->elevator.elevator_data;
 	struct request *__rq;
@@ -335,7 +327,7 @@ deadline_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
 	 */
 	ret = elv_try_last_merge(q, bio);
 	if (ret != ELEVATOR_NO_MERGE) {
-		__rq = list_entry_rq(q->last_merge);
+		__rq = q->last_merge;
 		goto out_insert;
 	}
 
@@ -371,11 +363,11 @@ deadline_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
 
 	return ELEVATOR_NO_MERGE;
 out:
-	q->last_merge = &__rq->queuelist;
+	q->last_merge = __rq;
 out_insert:
 	if (ret)
 		deadline_hot_drq_hash(dd, RQ_DATA(__rq));
-	*insert = &__rq->queuelist;
+	*req = __rq;
 	return ret;
 }
 
@@ -398,7 +390,7 @@ static void deadline_merged_request(request_queue_t *q, struct request *req)
 		deadline_add_drq_rb(dd, drq);
 	}
 
-	q->last_merge = &req->queuelist;
+	q->last_merge = req;
 }
 
 static void
@@ -621,32 +613,26 @@ static struct request *deadline_next_request(request_queue_t *q)
 }
 
 static void
-deadline_insert_request(request_queue_t *q, struct request *rq,
-			struct list_head *insert_here)
+deadline_insert_request(request_queue_t *q, struct request *rq, int where)
 {
 	struct deadline_data *dd = q->elevator.elevator_data;
 	struct deadline_rq *drq = RQ_DATA(rq);
 
-	if (unlikely(rq->flags & (REQ_HARDBARRIER|REQ_SOFTBARRIER))) {
-		DL_INVALIDATE_HASH(dd);
-		q->last_merge = NULL;
-
-		if (insert_here != dd->dispatch) {
+	switch (where) {
+		case ELEVATOR_INSERT_BACK:
 			while (deadline_dispatch_requests(dd))
 				;
-		}
-
-		if (!insert_here)
-			insert_here = dd->dispatch->prev;
-	}
-
-	if (unlikely(!blk_fs_request(rq))) {
-		if (!insert_here)
-			insert_here = dd->dispatch;
-	}
-
-	if (insert_here) {
-		list_add(&rq->queuelist, insert_here);
+			list_add_tail(&rq->queuelist, dd->dispatch);
+			break;
+		case ELEVATOR_INSERT_FRONT:
+			list_add(&rq->queuelist, dd->dispatch);
+			break;
+		case ELEVATOR_INSERT_SORT:
+			BUG_ON(!blk_fs_request(rq));
+			deadline_add_request(dd, drq);
+			break;
+		default:
+			printk("%s: bad insert point %d\n", __FUNCTION__,where);
 			return;
 	}
 
@@ -654,10 +640,8 @@ deadline_insert_request(request_queue_t *q, struct request *rq,
 		deadline_add_drq_hash(dd, drq);
 
 		if (!q->last_merge)
-			q->last_merge = &rq->queuelist;
+			q->last_merge = rq;
 	}
-
-	deadline_add_request(dd, drq);
 }
 
 static int deadline_queue_empty(request_queue_t *q)
@@ -748,7 +732,6 @@ static int deadline_init(request_queue_t *q, elevator_t *e)
 	dd->dispatch = &q->queue_head;
 	dd->fifo_expire[READ] = read_expire;
 	dd->fifo_expire[WRITE] = write_expire;
-	dd->hash_valid_count = 1;
 	dd->writes_starved = writes_starved;
 	dd->front_merges = 1;
 	dd->fifo_batch = fifo_batch;
@@ -779,7 +762,7 @@ deadline_set_request(request_queue_t *q, struct request *rq, int gfp_mask)
 		drq->request = rq;
 
 		INIT_LIST_HEAD(&drq->hash);
-		drq->hash_valid_count = 0;
+		drq->on_hash = 0;
 
 		INIT_LIST_HEAD(&drq->fifo);
 

drivers/block/elevator.c

@@ -81,7 +81,7 @@ inline int elv_try_merge(struct request *__rq, struct bio *bio)
 inline int elv_try_last_merge(request_queue_t *q, struct bio *bio)
 {
 	if (q->last_merge)
-		return elv_try_merge(list_entry_rq(q->last_merge), bio);
+		return elv_try_merge(q->last_merge, bio);
 
 	return ELEVATOR_NO_MERGE;
 }
@@ -117,12 +117,12 @@ int elevator_global_init(void)
 	return 0;
 }
 
-int elv_merge(request_queue_t *q, struct list_head **entry, struct bio *bio)
+int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 {
 	elevator_t *e = &q->elevator;
 
 	if (e->elevator_merge_fn)
-		return e->elevator_merge_fn(q, entry, bio);
+		return e->elevator_merge_fn(q, req, bio);
 
 	return ELEVATOR_NO_MERGE;
 }
@@ -140,7 +140,7 @@ void elv_merge_requests(request_queue_t *q, struct request *rq,
 {
 	elevator_t *e = &q->elevator;
 
-	if (q->last_merge == &next->queuelist)
+	if (q->last_merge == next)
 		q->last_merge = NULL;
 
 	if (e->elevator_merge_req_fn)
@@ -156,29 +156,25 @@ void elv_requeue_request(request_queue_t *q, struct request *rq)
 	if (q->elevator.elevator_requeue_req_fn)
 		q->elevator.elevator_requeue_req_fn(q, rq);
 	else
-		__elv_add_request(q, rq, 0, 0);
+		__elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
 }
 
-void __elv_add_request(request_queue_t *q, struct request *rq, int at_end,
+void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 		       int plug)
 {
-	struct list_head *insert = NULL;
-
-	if (!at_end)
-		insert = &q->queue_head;
 	if (plug)
 		blk_plug_device(q);
 
-	q->elevator.elevator_add_req_fn(q, rq, insert);
+	q->elevator.elevator_add_req_fn(q, rq, where);
 }
 
-void elv_add_request(request_queue_t *q, struct request *rq, int at_end,
+void elv_add_request(request_queue_t *q, struct request *rq, int where,
 		     int plug)
 {
 	unsigned long flags;
 
 	spin_lock_irqsave(q->queue_lock, flags);
-	__elv_add_request(q, rq, at_end, plug);
+	__elv_add_request(q, rq, where, plug);
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
@@ -200,7 +196,7 @@ struct request *elv_next_request(request_queue_t *q)
 		 */
 		rq->flags |= REQ_STARTED;
 
-		if (&rq->queuelist == q->last_merge)
+		if (rq == q->last_merge)
 			q->last_merge = NULL;
 
 		if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
@@ -238,7 +234,7 @@ void elv_remove_request(request_queue_t *q, struct request *rq)
 	 * deleted without ever being given to driver (merged with another
 	 * request).
 	 */
-	if (&rq->queuelist == q->last_merge)
+	if (rq == q->last_merge)
 		q->last_merge = NULL;
 
 	if (e->elevator_remove_req_fn)

drivers/block/ll_rw_blk.c

@@ -703,7 +703,7 @@ void blk_queue_invalidate_tags(request_queue_t *q)
 			blk_queue_end_tag(q, rq);
 
 		rq->flags &= ~REQ_STARTED;
-		__elv_add_request(q, rq, 0, 0);
+		__elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 0);
 	}
 }
 
@@ -1632,11 +1632,16 @@ void blk_insert_request(request_queue_t *q, struct request *rq,
 	if(reinsert) {
 		blk_requeue_request(q, rq);
 	} else {
+		int where = ELEVATOR_INSERT_BACK;
+
+		if (at_head)
+			where = ELEVATOR_INSERT_FRONT;
+
 		if (blk_rq_tagged(rq))
 			blk_queue_end_tag(q, rq);
 
 		drive_stat_acct(rq, rq->nr_sectors, 1);
-		__elv_add_request(q, rq, !at_head, 0);
+		__elv_add_request(q, rq, where, 0);
 	}
 	q->request_fn(q);
 	spin_unlock_irqrestore(q->queue_lock, flags);
@@ -1669,8 +1674,7 @@ void drive_stat_acct(struct request *rq, int nr_sectors, int new_io)
  * queue lock is held and interrupts disabled, as we muck with the
  * request queue list.
  */
-static inline void add_request(request_queue_t * q, struct request * req,
-			       struct list_head *insert_here)
+static inline void add_request(request_queue_t * q, struct request * req)
 {
 	drive_stat_acct(req, req->nr_sectors, 1);
 
@@ -1681,7 +1685,7 @@ static inline void add_request(request_queue_t * q, struct request * req,
 	 * elevator indicated where it wants this request to be
 	 * inserted at elevator_merge time
 	 */
-	__elv_add_request_pos(q, req, insert_here);
+	__elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
 }
  
 /*
@@ -1880,7 +1884,6 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 {
 	struct request *req, *freereq = NULL;
 	int el_ret, rw, nr_sectors, cur_nr_sectors, barrier, ra;
-	struct list_head *insert_here;
 	sector_t sector;
 
 	sector = bio->bi_sector;
@@ -1903,7 +1906,6 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 	ra = bio->bi_rw & (1 << BIO_RW_AHEAD);
 
 again:
-	insert_here = NULL;
 	spin_lock_irq(q->queue_lock);
 
 	if (elv_queue_empty(q)) {
@@ -1913,17 +1915,13 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 	if (barrier)
 		goto get_rq;
 
-	el_ret = elv_merge(q, &insert_here, bio);
+	el_ret = elv_merge(q, &req, bio);
 	switch (el_ret) {
 		case ELEVATOR_BACK_MERGE:
-			req = list_entry_rq(insert_here);
-
 			BUG_ON(!rq_mergeable(req));
 
-			if (!q->back_merge_fn(q, req, bio)) {
-				insert_here = &req->queuelist;
+			if (!q->back_merge_fn(q, req, bio))
 				break;
-			}
 
 			req->biotail->bi_next = bio;
 			req->biotail = bio;
@@ -1934,14 +1932,10 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 			goto out;
 
 		case ELEVATOR_FRONT_MERGE:
-			req = list_entry_rq(insert_here);
-
 			BUG_ON(!rq_mergeable(req));
 
-			if (!q->front_merge_fn(q, req, bio)) {
-				insert_here = req->queuelist.prev;
+			if (!q->front_merge_fn(q, req, bio))
 				break;
-			}
 
 			bio->bi_next = req->bio;
 			req->cbio = req->bio = bio;
@@ -2029,7 +2023,7 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 	req->rq_disk = bio->bi_bdev->bd_disk;
 	req->start_time = jiffies;
 
-	add_request(q, req, insert_here);
+	add_request(q, req);
 out:
 	if (freereq)
 		__blk_put_request(q, freereq);

drivers/block/noop-iosched.c

@@ -17,17 +17,15 @@
 /*
  * See if we can find a request that this buffer can be coalesced with.
  */
-int elevator_noop_merge(request_queue_t *q, struct list_head **insert,
+int elevator_noop_merge(request_queue_t *q, struct request **req,
 			struct bio *bio)
 {
 	struct list_head *entry = &q->queue_head;
 	struct request *__rq;
 	int ret;
 
-	if ((ret = elv_try_last_merge(q, bio))) {
-		*insert = q->last_merge;
+	if ((ret = elv_try_last_merge(q, bio)))
 		return ret;
-	}
 
 	while ((entry = entry->prev) != &q->queue_head) {
 		__rq = list_entry_rq(entry);
@@ -41,8 +39,8 @@ int elevator_noop_merge(request_queue_t *q, struct list_head **insert,
 			continue;
 
 		if ((ret = elv_try_merge(__rq, bio))) {
-			*insert = &__rq->queuelist;
-			q->last_merge = &__rq->queuelist;
+			*req = __rq;
+			q->last_merge = __rq;
 			return ret;
 		}
 	}
@@ -57,8 +55,13 @@ void elevator_noop_merge_requests(request_queue_t *q, struct request *req,
 }
 
 void elevator_noop_add_request(request_queue_t *q, struct request *rq,
-			       struct list_head *insert_here)
+			       int where)
 {
+	struct list_head *insert = q->queue_head.prev;
+
+	if (where == ELEVATOR_INSERT_FRONT)
+		insert = &q->queue_head;
+
 	list_add_tail(&rq->queuelist, &q->queue_head);
 
 	/*
@@ -67,7 +70,7 @@ void elevator_noop_add_request(request_queue_t *q, struct request *rq,
 	if (rq->flags & REQ_HARDBARRIER)
 		q->last_merge = NULL;
 	else if (!q->last_merge)
-		q->last_merge = &rq->queuelist;
+		q->last_merge = rq;
 }
 
 struct request *elevator_noop_next_request(request_queue_t *q)

drivers/block/scsi_ioctl.c

@@ -68,7 +68,7 @@ static int blk_do_rq(request_queue_t *q, struct block_device *bdev,
 
 	rq->flags |= REQ_NOMERGE;
 	rq->waiting = &wait;
-	elv_add_request(q, rq, 1, 1);
+	elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 1);
 	generic_unplug_device(q);
 	wait_for_completion(&wait);
 

drivers/ide/ide-io.c

@@ -1387,7 +1387,7 @@ int ide_do_drive_cmd (ide_drive_t *drive, struct request *rq, ide_action_t actio
 	unsigned long flags;
 	ide_hwgroup_t *hwgroup = HWGROUP(drive);
 	DECLARE_COMPLETION(wait);
-	int insert_end = 1, err;
+	int where = ELEVATOR_INSERT_BACK, err;
 	int must_wait = (action == ide_wait || action == ide_head_wait);
 
 #ifdef CONFIG_BLK_DEV_PDC4030
@@ -1419,10 +1419,10 @@ int ide_do_drive_cmd (ide_drive_t *drive, struct request *rq, ide_action_t actio
 	spin_lock_irqsave(&ide_lock, flags);
 	if (action == ide_preempt || action == ide_head_wait) {
 		hwgroup->rq = NULL;
-		insert_end = 0;
+		where = ELEVATOR_INSERT_FRONT;
 		rq->flags |= REQ_PREEMPT;
 	}
-	__elv_add_request(drive->queue, rq, insert_end, 0);
+	__elv_add_request(drive->queue, rq, where, 0);
 	ide_do_request(hwgroup, IDE_NO_IRQ);
 	spin_unlock_irqrestore(&ide_lock, flags);
 

include/linux/blkdev.h

@@ -270,7 +270,7 @@ struct request_queue
 	 * Together with queue_head for cacheline sharing
 	 */
 	struct list_head	queue_head;
-	struct list_head	*last_merge;
+	struct request		*last_merge;
 	elevator_t		elevator;
 
 	/*

include/linux/elevator.h

 #ifndef _LINUX_ELEVATOR_H
 #define _LINUX_ELEVATOR_H
 
-typedef int (elevator_merge_fn) (request_queue_t *, struct list_head **,
+typedef int (elevator_merge_fn) (request_queue_t *, struct request **,
 				 struct bio *);
 
 typedef void (elevator_merge_req_fn) (request_queue_t *, struct request *, struct request *);
@@ -10,7 +10,7 @@ typedef void (elevator_merged_fn) (request_queue_t *, 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 void (elevator_add_req_fn) (request_queue_t *, struct request *, int);
 typedef int (elevator_queue_empty_fn) (request_queue_t *);
 typedef void (elevator_remove_req_fn) (request_queue_t *, struct request *);
 typedef void (elevator_requeue_req_fn) (request_queue_t *, struct request *);
@@ -62,7 +62,7 @@ struct elevator_s
  */
 extern void elv_add_request(request_queue_t *, struct request *, int, int);
 extern void __elv_add_request(request_queue_t *, struct request *, int, int);
-extern int elv_merge(request_queue_t *, struct list_head **, struct bio *);
+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_merged_request(request_queue_t *, struct request *);
@@ -79,9 +79,6 @@ extern void elv_completed_request(request_queue_t *, struct request *);
 extern int elv_set_request(request_queue_t *, struct request *, int);
 extern void elv_put_request(request_queue_t *, struct request *);
 
-#define __elv_add_request_pos(q, rq, pos)	\
-	(q)->elevator.elevator_add_req_fn((q), (rq), (pos))
-
 /*
  * noop I/O scheduler. always merges, always inserts new request at tail
  */
@@ -111,4 +108,11 @@ extern inline int elv_try_last_merge(request_queue_t *, struct bio *);
 #define ELEVATOR_FRONT_MERGE	1
 #define ELEVATOR_BACK_MERGE	2
 
+/*
+ * Insertion selection
+ */
+#define ELEVATOR_INSERT_FRONT	1
+#define ELEVATOR_INSERT_BACK	2
+#define ELEVATOR_INSERT_SORT	3
+
 #endif