[PATCH] elevator: move the backmerging logic into the elevator core

Right now, every IO scheduler implements its own backmerging (except for
noop, which does no merging). That results in duplicated code for
essentially the same operation, which is never a good thing. This patch
moves the backmerging out of the io schedulers and into the elevator
core. We save 1.6kb of text and as a bonus get backmerging for noop as
well. Win-win!

Signed-off-by: Jens Axboe <axboe@suse.de>

2 files changed, 4 insertions, 15 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index b2a412cf468f..8f5486964671 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -229,6 +229,8 @@ struct request {
         struct bio *bio;
         struct bio *biotail;
 
+        struct hlist_node hash; /* merge hash */
+
         void *elevator_private;
         void *completion_data;
 
@@ -697,21 +699,6 @@ static inline void blkdev_dequeue_request(struct request *req)
 }
 
 /*
- * This should be in elevator.h, but that requires pulling in rq and q
- */
-static inline void elv_dispatch_add_tail(struct request_queue *q,
-                                         struct request *rq)
-{
-        if (q->last_merge == rq)
-                q->last_merge = NULL;
-        q->nr_sorted--;
-
-        q->end_sector = rq_end_sector(rq);
-        q->boundary_rq = rq;
-        list_add_tail(&rq->queuelist, &q->queue_head);
-}
-
-/*
  * Access functions for manipulating queue properties
  */
 extern request_queue_t *blk_init_queue_node(request_fn_proc *rfn,
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 1713ace808bf..2c270e90b33e 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -82,12 +82,14 @@ struct elevator_queue
         struct kobject kobj;
         struct elevator_type *elevator_type;
         struct mutex sysfs_lock;
+        struct hlist_head *hash;
 };
 
 /*
  * block elevator interface
  */
 extern void elv_dispatch_sort(request_queue_t *, struct request *);
+extern void elv_dispatch_add_tail(request_queue_t *, struct request *);
 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 void elv_insert(request_queue_t *, struct request *, int);