5 files changed, 142 insertions, 360 deletions

diff --git a/block/as-iosched.c b/block/as-iosched.c
index ad1cc4077819..6db494333c3a 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -14,7 +14,6 @@
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <linux/compiler.h>
-#include <linux/hash.h>
 #include <linux/rbtree.h>
 #include <linux/interrupt.h>
 
@@ -95,7 +94,6 @@ struct as_data {
 
         struct as_rq *next_arq[2];      /* next in sort order */
         sector_t last_sector[2];        /* last REQ_SYNC & REQ_ASYNC sectors */
-        struct hlist_head *hash;        /* request hash */
 
         unsigned long exit_prob;        /* probability a task will exit while
                                            being waited on */
@@ -162,11 +160,6 @@ struct as_rq {
         struct io_context *io_context;  /* The submitting task */
 
         /*
-         * request hash, key is the ending offset (for back merge lookup)
-         */
-        struct hlist_node hash;
-
-        /*
          * expire fifo
          */
         struct list_head fifo;
@@ -273,77 +266,6 @@ static void as_put_io_context(struct as_rq *arq)
 }
 
 /*
- * the back merge hash support functions
- */
-static const int as_hash_shift = 6;
-#define AS_HASH_BLOCK(sec)      ((sec) >> 3)
-#define AS_HASH_FN(sec)         (hash_long(AS_HASH_BLOCK((sec)), as_hash_shift))
-#define AS_HASH_ENTRIES         (1 << as_hash_shift)
-#define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
-
-static inline void __as_del_arq_hash(struct as_rq *arq)
-{
-        hlist_del_init(&arq->hash);
-}
-
-static inline void as_del_arq_hash(struct as_rq *arq)
-{
-        if (!hlist_unhashed(&arq->hash))
-                __as_del_arq_hash(arq);
-}
-
-static void as_add_arq_hash(struct as_data *ad, struct as_rq *arq)
-{
-        struct request *rq = arq->request;
-
-        BUG_ON(!hlist_unhashed(&arq->hash));
-
-        hlist_add_head(&arq->hash, &ad->hash[AS_HASH_FN(rq_hash_key(rq))]);
-}
-
-/*
- * move hot entry to front of chain
- */
-static inline void as_hot_arq_hash(struct as_data *ad, struct as_rq *arq)
-{
-        struct request *rq = arq->request;
-        struct hlist_head *head = &ad->hash[AS_HASH_FN(rq_hash_key(rq))];
-
-        if (hlist_unhashed(&arq->hash)) {
-                WARN_ON(1);
-                return;
-        }
-
-        if (&arq->hash != head->first) {
-                hlist_del(&arq->hash);
-                hlist_add_head(&arq->hash, head);
-        }
-}
-
-static struct request *as_find_arq_hash(struct as_data *ad, sector_t offset)
-{
-        struct hlist_head *hash_list = &ad->hash[AS_HASH_FN(offset)];
-        struct hlist_node *entry, *next;
-        struct as_rq *arq;
-
-        hlist_for_each_entry_safe(arq, entry, next, hash_list, hash) {
-                struct request *__rq = arq->request;
-
-                BUG_ON(hlist_unhashed(&arq->hash));
-
-                if (!rq_mergeable(__rq)) {
-                        as_del_arq_hash(arq);
-                        continue;
-                }
-
-                if (rq_hash_key(__rq) == offset)
-                        return __rq;
-        }
-
-        return NULL;
-}
-
-/*
  * rb tree support functions
  */
 #define rb_entry_arq(node)      rb_entry((node), struct as_rq, rb_node)
@@ -1060,7 +982,6 @@ static void as_remove_queued_request(request_queue_t *q, struct request *rq)
                 ad->next_arq[data_dir] = as_find_next_arq(ad, arq);
 
         list_del_init(&arq->fifo);
-        as_del_arq_hash(arq);
         as_del_arq_rb(ad, arq);
 }
 
@@ -1349,8 +1270,6 @@ static void as_add_request(request_queue_t *q, struct request *rq)
         }
 
         as_add_arq_rb(ad, arq);
-        if (rq_mergeable(arq->request))
-                as_add_arq_hash(ad, arq);
 
         /*
          * set expire time (only used for reads) and add to fifo list
@@ -1428,42 +1347,17 @@ 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);
         struct request *__rq;
-        int ret;
-
-        /*
-         * see if the merge hash can satisfy a back merge
-         */
-        __rq = as_find_arq_hash(ad, bio->bi_sector);
-        if (__rq) {
-                BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector);
-
-                if (elv_rq_merge_ok(__rq, bio)) {
-                        ret = ELEVATOR_BACK_MERGE;
-                        goto out;
-                }
-        }
 
         /*
          * check for front merge
          */
         __rq = as_find_arq_rb(ad, rb_key, bio_data_dir(bio));
-        if (__rq) {
-                BUG_ON(rb_key != rq_rb_key(__rq));
-
-                if (elv_rq_merge_ok(__rq, bio)) {
-                        ret = ELEVATOR_FRONT_MERGE;
-                        goto out;
-                }
+        if (__rq && elv_rq_merge_ok(__rq, bio)) {
+                *req = __rq;
+                return ELEVATOR_FRONT_MERGE;
         }
 
         return ELEVATOR_NO_MERGE;
-out:
-        if (ret) {
-                if (rq_mergeable(__rq))
-                        as_hot_arq_hash(ad, RQ_DATA(__rq));
-        }
-        *req = __rq;
-        return ret;
 }
 
 static void as_merged_request(request_queue_t *q, struct request *req)
@@ -1472,12 +1366,6 @@ static void as_merged_request(request_queue_t *q, struct request *req)
         struct as_rq *arq = RQ_DATA(req);
 
         /*
-         * hash always needs to be repositioned, key is end sector
-         */
-        as_del_arq_hash(arq);
-        as_add_arq_hash(ad, arq);
-
-        /*
          * if the merge was a front merge, we need to reposition request
          */
         if (rq_rb_key(req) != arq->rb_key) {
@@ -1501,13 +1389,6 @@ static void as_merged_requests(request_queue_t *q, struct request *req,
         BUG_ON(!arq);
         BUG_ON(!anext);
 
-        /*
-         * reposition arq (this is the merged request) in hash, and in rbtree
-         * in case of a front merge
-         */
-        as_del_arq_hash(arq);
-        as_add_arq_hash(ad, arq);
-
         if (rq_rb_key(req) != arq->rb_key) {
                 as_del_arq_rb(ad, arq);
                 as_add_arq_rb(ad, arq);
@@ -1591,7 +1472,6 @@ static int as_set_request(request_queue_t *q, struct request *rq,
                 arq->request = rq;
                 arq->state = AS_RQ_PRESCHED;
                 arq->io_context = NULL;
-                INIT_HLIST_NODE(&arq->hash);
                 INIT_LIST_HEAD(&arq->fifo);
                 rq->elevator_private = arq;
                 return 0;
@@ -1628,7 +1508,6 @@ static void as_exit_queue(elevator_t *e)
 
         mempool_destroy(ad->arq_pool);
         put_io_context(ad->io_context);
-        kfree(ad->hash);
         kfree(ad);
 }
 
@@ -1639,7 +1518,6 @@ static void as_exit_queue(elevator_t *e)
 static void *as_init_queue(request_queue_t *q, elevator_t *e)
 {
         struct as_data *ad;
-        int i;
 
         if (!arq_pool)
                 return NULL;
@@ -1651,17 +1529,9 @@ static void *as_init_queue(request_queue_t *q, elevator_t *e)
 
         ad->q = q; /* Identify what queue the data belongs to */
 
-        ad->hash = kmalloc_node(sizeof(struct hlist_head)*AS_HASH_ENTRIES,
-                                GFP_KERNEL, q->node);
-        if (!ad->hash) {
-                kfree(ad);
-                return NULL;
-        }
-
         ad->arq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
                                 mempool_free_slab, arq_pool, q->node);
         if (!ad->arq_pool) {
-                kfree(ad->hash);
                 kfree(ad);
                 return NULL;
         }
@@ -1672,9 +1542,6 @@ static void *as_init_queue(request_queue_t *q, elevator_t *e)
         init_timer(&ad->antic_timer);
         INIT_WORK(&ad->antic_work, as_work_handler, q);
 
-        for (i = 0; i < AS_HASH_ENTRIES; i++)
-                INIT_HLIST_HEAD(&ad->hash[i]);
-
         INIT_LIST_HEAD(&ad->fifo_list[REQ_SYNC]);
         INIT_LIST_HEAD(&ad->fifo_list[REQ_ASYNC]);
         ad->sort_list[REQ_SYNC] = RB_ROOT;
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 3a3aee08ec5f..1b803c0c90f1 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -41,16 +41,6 @@ static DEFINE_SPINLOCK(cfq_exit_lock);
 #define CFQ_QHASH_ENTRIES       (1 << CFQ_QHASH_SHIFT)
 #define list_entry_qhash(entry) hlist_entry((entry), struct cfq_queue, cfq_hash)
 
-/*
- * for the hash of crq inside the cfqq
- */
-#define CFQ_MHASH_SHIFT         6
-#define CFQ_MHASH_BLOCK(sec)    ((sec) >> 3)
-#define CFQ_MHASH_ENTRIES       (1 << CFQ_MHASH_SHIFT)
-#define CFQ_MHASH_FN(sec)       hash_long(CFQ_MHASH_BLOCK(sec), CFQ_MHASH_SHIFT)
-#define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
-#define list_entry_hash(ptr)    hlist_entry((ptr), struct cfq_rq, hash)
-
 #define list_entry_cfqq(ptr)    list_entry((ptr), struct cfq_queue, cfq_list)
 #define list_entry_fifo(ptr)    list_entry((ptr), struct request, queuelist)
 
@@ -112,11 +102,6 @@ struct cfq_data {
          */
         struct hlist_head *cfq_hash;
 
-        /*
-         * global crq hash for all queues
-         */
-        struct hlist_head *crq_hash;
-
         mempool_t *crq_pool;
 
         int rq_in_driver;
@@ -203,7 +188,6 @@ struct cfq_rq {
         struct rb_node rb_node;
         sector_t rb_key;
         struct request *request;
-        struct hlist_node hash;
 
         struct cfq_queue *cfq_queue;
         struct cfq_io_context *io_context;
@@ -272,42 +256,6 @@ static void cfq_dispatch_insert(request_queue_t *, struct cfq_rq *);
 static struct cfq_queue *cfq_get_queue(struct cfq_data *cfqd, unsigned int key, struct task_struct *tsk, gfp_t gfp_mask);
 
 /*
- * lots of deadline iosched dupes, can be abstracted later...
- */
-static inline void cfq_del_crq_hash(struct cfq_rq *crq)
-{
-        hlist_del_init(&crq->hash);
-}
-
-static inline void cfq_add_crq_hash(struct cfq_data *cfqd, struct cfq_rq *crq)
-{
-        const int hash_idx = CFQ_MHASH_FN(rq_hash_key(crq->request));
-
-        hlist_add_head(&crq->hash, &cfqd->crq_hash[hash_idx]);
-}
-
-static struct request *cfq_find_rq_hash(struct cfq_data *cfqd, sector_t offset)
-{
-        struct hlist_head *hash_list = &cfqd->crq_hash[CFQ_MHASH_FN(offset)];
-        struct hlist_node *entry, *next;
-
-        hlist_for_each_safe(entry, next, hash_list) {
-                struct cfq_rq *crq = list_entry_hash(entry);
-                struct request *__rq = crq->request;
-
-                if (!rq_mergeable(__rq)) {
-                        cfq_del_crq_hash(crq);
-                        continue;
-                }
-
-                if (rq_hash_key(__rq) == offset)
-                        return __rq;
-        }
-
-        return NULL;
-}
-
-/*
  * scheduler run of queue, if there are requests pending and no one in the
  * driver that will restart queueing
  */
@@ -677,7 +625,6 @@ static void cfq_remove_request(struct request *rq)
 
         list_del_init(&rq->queuelist);
         cfq_del_crq_rb(crq);
-        cfq_del_crq_hash(crq);
 }
 
 static int
@@ -685,34 +632,20 @@ cfq_merge(request_queue_t *q, struct request **req, struct bio *bio)
 {
         struct cfq_data *cfqd = q->elevator->elevator_data;
         struct request *__rq;
-        int ret;
-
-        __rq = cfq_find_rq_hash(cfqd, bio->bi_sector);
-        if (__rq && elv_rq_merge_ok(__rq, bio)) {
-                ret = ELEVATOR_BACK_MERGE;
-                goto out;
-        }
 
         __rq = cfq_find_rq_fmerge(cfqd, bio);
         if (__rq && elv_rq_merge_ok(__rq, bio)) {
-                ret = ELEVATOR_FRONT_MERGE;
-                goto out;
+                *req = __rq;
+                return ELEVATOR_FRONT_MERGE;
         }
 
         return ELEVATOR_NO_MERGE;
-out:
-        *req = __rq;
-        return ret;
 }
 
 static void cfq_merged_request(request_queue_t *q, struct request *req)
 {
-        struct cfq_data *cfqd = q->elevator->elevator_data;
         struct cfq_rq *crq = RQ_DATA(req);
 
-        cfq_del_crq_hash(crq);
-        cfq_add_crq_hash(cfqd, crq);
-
         if (rq_rb_key(req) != crq->rb_key) {
                 struct cfq_queue *cfqq = crq->cfq_queue;
 
@@ -1825,9 +1758,6 @@ static void cfq_insert_request(request_queue_t *q, struct request *rq)
 
         list_add_tail(&rq->queuelist, &cfqq->fifo);
 
-        if (rq_mergeable(rq))
-                cfq_add_crq_hash(cfqd, crq);
-
         cfq_crq_enqueued(cfqd, cfqq, crq);
 }
 
@@ -2055,7 +1985,6 @@ cfq_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
                 RB_CLEAR_NODE(&crq->rb_node);
                 crq->rb_key = 0;
                 crq->request = rq;
-                INIT_HLIST_NODE(&crq->hash);
                 crq->cfq_queue = cfqq;
                 crq->io_context = cic;
 
@@ -2221,7 +2150,6 @@ static void cfq_exit_queue(elevator_t *e)
         cfq_shutdown_timer_wq(cfqd);
 
         mempool_destroy(cfqd->crq_pool);
-        kfree(cfqd->crq_hash);
         kfree(cfqd->cfq_hash);
         kfree(cfqd);
 }
@@ -2246,20 +2174,14 @@ static void *cfq_init_queue(request_queue_t *q, elevator_t *e)
         INIT_LIST_HEAD(&cfqd->empty_list);
         INIT_LIST_HEAD(&cfqd->cic_list);
 
-        cfqd->crq_hash = kmalloc(sizeof(struct hlist_head) * CFQ_MHASH_ENTRIES, GFP_KERNEL);
-        if (!cfqd->crq_hash)
-                goto out_crqhash;
-
         cfqd->cfq_hash = kmalloc(sizeof(struct hlist_head) * CFQ_QHASH_ENTRIES, GFP_KERNEL);
         if (!cfqd->cfq_hash)
-                goto out_cfqhash;
+                goto out_crqhash;
 
         cfqd->crq_pool = mempool_create_slab_pool(BLKDEV_MIN_RQ, crq_pool);
         if (!cfqd->crq_pool)
                 goto out_crqpool;
 
-        for (i = 0; i < CFQ_MHASH_ENTRIES; i++)
-                INIT_HLIST_HEAD(&cfqd->crq_hash[i]);
         for (i = 0; i < CFQ_QHASH_ENTRIES; i++)
                 INIT_HLIST_HEAD(&cfqd->cfq_hash[i]);
 
@@ -2289,8 +2211,6 @@ static void *cfq_init_queue(request_queue_t *q, elevator_t *e)
         return cfqd;
 out_crqpool:
         kfree(cfqd->cfq_hash);
-out_cfqhash:
-        kfree(cfqd->crq_hash);
 out_crqhash:
         kfree(cfqd);
         return NULL;
diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index c7ca9f0b6498..b66e820f544d 100644
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -12,7 +12,6 @@
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <linux/compiler.h>
-#include <linux/hash.h>
 #include <linux/rbtree.h>
 
 /*
@@ -24,13 +23,6 @@ static const int writes_starved = 2;    /* max times reads can starve a write */
 static const int fifo_batch = 16;       /* # of sequential requests treated as one
                                      by the above parameters. For throughput. */
 
-static const int deadline_hash_shift = 5;
-#define DL_HASH_BLOCK(sec)      ((sec) >> 3)
-#define DL_HASH_FN(sec)         (hash_long(DL_HASH_BLOCK((sec)), deadline_hash_shift))
-#define DL_HASH_ENTRIES         (1 << deadline_hash_shift)
-#define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
-#define ON_HASH(drq)            (!hlist_unhashed(&(drq)->hash))
-
 struct deadline_data {
         /*
          * run time data
@@ -46,7 +38,6 @@ struct deadline_data {
          * next in sort order. read, write or both are NULL
          */
         struct deadline_rq *next_drq[2];
-        struct hlist_head *hash;        /* request hash */
         unsigned int batching;          /* number of sequential requests made */
         sector_t last_sector;           /* head position */
         unsigned int starved;           /* times reads have starved writes */
@@ -75,11 +66,6 @@ struct deadline_rq {
         struct request *request;
 
         /*
-         * request hash, key is the ending offset (for back merge lookup)
-         */
-        struct hlist_node hash;
-
-        /*
          * expire fifo
          */
         struct list_head fifo;
@@ -93,69 +79,6 @@ static kmem_cache_t *drq_pool;
 #define RQ_DATA(rq)     ((struct deadline_rq *) (rq)->elevator_private)
 
 /*
- * the back merge hash support functions
- */
-static inline void __deadline_del_drq_hash(struct deadline_rq *drq)
-{
-        hlist_del_init(&drq->hash);
-}
-
-static inline void deadline_del_drq_hash(struct deadline_rq *drq)
-{
-        if (ON_HASH(drq))
-                __deadline_del_drq_hash(drq);
-}
-
-static inline void
-deadline_add_drq_hash(struct deadline_data *dd, struct deadline_rq *drq)
-{
-        struct request *rq = drq->request;
-
-        BUG_ON(ON_HASH(drq));
-
-        hlist_add_head(&drq->hash, &dd->hash[DL_HASH_FN(rq_hash_key(rq))]);
-}
-
-/*
- * move hot entry to front of chain
- */
-static inline void
-deadline_hot_drq_hash(struct deadline_data *dd, struct deadline_rq *drq)
-{
-        struct request *rq = drq->request;
-        struct hlist_head *head = &dd->hash[DL_HASH_FN(rq_hash_key(rq))];
-
-        if (ON_HASH(drq) && &drq->hash != head->first) {
-                hlist_del(&drq->hash);
-                hlist_add_head(&drq->hash, head);
-        }
-}
-
-static struct request *
-deadline_find_drq_hash(struct deadline_data *dd, sector_t offset)
-{
-        struct hlist_head *hash_list = &dd->hash[DL_HASH_FN(offset)];
-        struct hlist_node *entry, *next;
-        struct deadline_rq *drq;
-
-        hlist_for_each_entry_safe(drq, entry, next, hash_list, hash) {
-                struct request *__rq = drq->request;
-
-                BUG_ON(!ON_HASH(drq));
-
-                if (!rq_mergeable(__rq)) {
-                        __deadline_del_drq_hash(drq);
-                        continue;
-                }
-
-                if (rq_hash_key(__rq) == offset)
-                        return __rq;
-        }
-
-        return NULL;
-}
-
-/*
  * rb tree support functions
  */
 #define rb_entry_drq(node)      rb_entry((node), struct deadline_rq, rb_node)
@@ -267,22 +190,19 @@ deadline_add_request(struct request_queue *q, struct request *rq)
 {
         struct deadline_data *dd = q->elevator->elevator_data;
         struct deadline_rq *drq = RQ_DATA(rq);
-
         const int data_dir = rq_data_dir(drq->request);
 
         deadline_add_drq_rb(dd, drq);
+
         /*
          * set expire time (only used for reads) and add to fifo list
          */
         drq->expires = jiffies + dd->fifo_expire[data_dir];
         list_add_tail(&drq->fifo, &dd->fifo_list[data_dir]);
-
-        if (rq_mergeable(rq))
-                deadline_add_drq_hash(dd, drq);
 }
 
 /*
- * remove rq from rbtree, fifo, and hash
+ * remove rq from rbtree and fifo.
  */
 static void deadline_remove_request(request_queue_t *q, struct request *rq)
 {
@@ -291,7 +211,6 @@ static void deadline_remove_request(request_queue_t *q, struct request *rq)
 
         list_del_init(&drq->fifo);
         deadline_del_drq_rb(dd, drq);
-        deadline_del_drq_hash(drq);
 }
 
 static int
@@ -302,19 +221,6 @@ deadline_merge(request_queue_t *q, struct request **req, struct bio *bio)
         int ret;
 
         /*
-         * see if the merge hash can satisfy a back merge
-         */
-        __rq = deadline_find_drq_hash(dd, bio->bi_sector);
-        if (__rq) {
-                BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector);
-
-                if (elv_rq_merge_ok(__rq, bio)) {
-                        ret = ELEVATOR_BACK_MERGE;
-                        goto out;
-                }
-        }
-
-        /*
          * check for front merge
          */
         if (dd->front_merges) {
@@ -333,8 +239,6 @@ deadline_merge(request_queue_t *q, struct request **req, struct bio *bio)
 
         return ELEVATOR_NO_MERGE;
 out:
-        if (ret)
-                deadline_hot_drq_hash(dd, RQ_DATA(__rq));
         *req = __rq;
         return ret;
 }
@@ -345,12 +249,6 @@ static void deadline_merged_request(request_queue_t *q, struct request *req)
         struct deadline_rq *drq = RQ_DATA(req);
 
         /*
-         * hash always needs to be repositioned, key is end sector
-         */
-        deadline_del_drq_hash(drq);
-        deadline_add_drq_hash(dd, drq);
-
-        /*
          * if the merge was a front merge, we need to reposition request
          */
         if (rq_rb_key(req) != drq->rb_key) {
@@ -370,13 +268,6 @@ deadline_merged_requests(request_queue_t *q, struct request *req,
         BUG_ON(!drq);
         BUG_ON(!dnext);
 
-        /*
-         * reposition drq (this is the merged request) in hash, and in rbtree
-         * in case of a front merge
-         */
-        deadline_del_drq_hash(drq);
-        deadline_add_drq_hash(dd, drq);
-
         if (rq_rb_key(req) != drq->rb_key) {
                 deadline_del_drq_rb(dd, drq);
                 deadline_add_drq_rb(dd, drq);
@@ -594,7 +485,6 @@ static void deadline_exit_queue(elevator_t *e)
         BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
 
         mempool_destroy(dd->drq_pool);
-        kfree(dd->hash);
         kfree(dd);
 }
 
@@ -605,7 +495,6 @@ static void deadline_exit_queue(elevator_t *e)
 static void *deadline_init_queue(request_queue_t *q, elevator_t *e)
 {
         struct deadline_data *dd;
-        int i;
 
         if (!drq_pool)
                 return NULL;
@@ -615,24 +504,13 @@ static void *deadline_init_queue(request_queue_t *q, elevator_t *e)
                 return NULL;
         memset(dd, 0, sizeof(*dd));
 
-        dd->hash = kmalloc_node(sizeof(struct hlist_head)*DL_HASH_ENTRIES,
-                                GFP_KERNEL, q->node);
-        if (!dd->hash) {
-                kfree(dd);
-                return NULL;
-        }
-
         dd->drq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
                                         mempool_free_slab, drq_pool, q->node);
         if (!dd->drq_pool) {
-                kfree(dd->hash);
                 kfree(dd);
                 return NULL;
         }
 
-        for (i = 0; i < DL_HASH_ENTRIES; i++)
-                INIT_HLIST_HEAD(&dd->hash[i]);
-
         INIT_LIST_HEAD(&dd->fifo_list[READ]);
         INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
         dd->sort_list[READ] = RB_ROOT;
@@ -667,8 +545,6 @@ deadline_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
                 RB_CLEAR_NODE(&drq->rb_node);
                 drq->request = rq;
 
-                INIT_HLIST_NODE(&drq->hash);
-
                 INIT_LIST_HEAD(&drq->fifo);
 
                 rq->elevator_private = drq;
diff --git a/block/elevator.c b/block/elevator.c
index 4ac97b642042..cff1102dac9d 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -33,6 +33,7 @@
 #include <linux/compiler.h>
 #include <linux/delay.h>
 #include <linux/blktrace_api.h>
+#include <linux/hash.h>
 
 #include <asm/uaccess.h>
 
@@ -40,6 +41,16 @@ static DEFINE_SPINLOCK(elv_list_lock);
 static LIST_HEAD(elv_list);
 
 /*
+ * Merge hash stuff.
+ */
+static const int elv_hash_shift = 6;
+#define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
+#define ELV_HASH_FN(sec)        (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
+#define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
+#define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
+#define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
+
+/*
  * can we safely merge with this request?
  */
 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
@@ -153,25 +164,41 @@ static struct kobj_type elv_ktype;
 
 static elevator_t *elevator_alloc(struct elevator_type *e)
 {
-        elevator_t *eq = kmalloc(sizeof(elevator_t), GFP_KERNEL);
-        if (eq) {
-                memset(eq, 0, sizeof(*eq));
-                eq->ops = &e->ops;
-                eq->elevator_type = e;
-                kobject_init(&eq->kobj);
-                snprintf(eq->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
-                eq->kobj.ktype = &elv_ktype;
-                mutex_init(&eq->sysfs_lock);
-        } else {
-                elevator_put(e);
-        }
+        elevator_t *eq;
+        int i;
+
+        eq = kmalloc(sizeof(elevator_t), GFP_KERNEL);
+        if (unlikely(!eq))
+                goto err;
+
+        memset(eq, 0, sizeof(*eq));
+        eq->ops = &e->ops;
+        eq->elevator_type = e;
+        kobject_init(&eq->kobj);
+        snprintf(eq->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
+        eq->kobj.ktype = &elv_ktype;
+        mutex_init(&eq->sysfs_lock);
+
+        eq->hash = kmalloc(sizeof(struct hlist_head) * ELV_HASH_ENTRIES, GFP_KERNEL);
+        if (!eq->hash)
+                goto err;
+
+        for (i = 0; i < ELV_HASH_ENTRIES; i++)
+                INIT_HLIST_HEAD(&eq->hash[i]);
+
         return eq;
+err:
+        kfree(eq);
+        elevator_put(e);
+        return NULL;
 }
 
 static void elevator_release(struct kobject *kobj)
 {
         elevator_t *e = container_of(kobj, elevator_t, kobj);
+
         elevator_put(e->elevator_type);
+        kfree(e->hash);
         kfree(e);
 }
 
@@ -223,6 +250,53 @@ void elevator_exit(elevator_t *e)
         kobject_put(&e->kobj);
 }
 
+static inline void __elv_rqhash_del(struct request *rq)
+{
+        hlist_del_init(&rq->hash);
+}
+
+static void elv_rqhash_del(request_queue_t *q, struct request *rq)
+{
+        if (ELV_ON_HASH(rq))
+                __elv_rqhash_del(rq);
+}
+
+static void elv_rqhash_add(request_queue_t *q, struct request *rq)
+{
+        elevator_t *e = q->elevator;
+
+        BUG_ON(ELV_ON_HASH(rq));
+        hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
+}
+
+static void elv_rqhash_reposition(request_queue_t *q, struct request *rq)
+{
+        __elv_rqhash_del(rq);
+        elv_rqhash_add(q, rq);
+}
+
+static struct request *elv_rqhash_find(request_queue_t *q, sector_t offset)
+{
+        elevator_t *e = q->elevator;
+        struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
+        struct hlist_node *entry, *next;
+        struct request *rq;
+
+        hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
+                BUG_ON(!ELV_ON_HASH(rq));
+
+                if (unlikely(!rq_mergeable(rq))) {
+                        __elv_rqhash_del(rq);
+                        continue;
+                }
+
+                if (rq_hash_key(rq) == offset)
+                        return rq;
+        }
+
+        return NULL;
+}
+
 /*
  * Insert rq into dispatch queue of q.  Queue lock must be held on
  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
@@ -235,6 +309,9 @@ void elv_dispatch_sort(request_queue_t *q, struct request *rq)
 
         if (q->last_merge == rq)
                 q->last_merge = NULL;
+
+        elv_rqhash_del(q, rq);
+
         q->nr_sorted--;
 
         boundary = q->end_sector;
@@ -258,11 +335,32 @@ void elv_dispatch_sort(request_queue_t *q, struct request *rq)
         list_add(&rq->queuelist, entry);
 }
 
+/*
+ * This should be in elevator.h, but that requires pulling in rq and q
+ */
+void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
+{
+        if (q->last_merge == rq)
+                q->last_merge = NULL;
+
+        elv_rqhash_del(q, rq);
+
+        q->nr_sorted--;
+
+        q->end_sector = rq_end_sector(rq);
+        q->boundary_rq = rq;
+        list_add_tail(&rq->queuelist, &q->queue_head);
+}
+
 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 {
         elevator_t *e = q->elevator;
+        struct request *__rq;
         int ret;
 
+        /*
+         * First try one-hit cache.
+         */
         if (q->last_merge) {
                 ret = elv_try_merge(q->last_merge, bio);
                 if (ret != ELEVATOR_NO_MERGE) {
@@ -271,6 +369,15 @@ int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
                 }
         }
 
+        /*
+         * See if our hash lookup can find a potential backmerge.
+         */
+        __rq = elv_rqhash_find(q, bio->bi_sector);
+        if (__rq && elv_rq_merge_ok(__rq, bio)) {
+                *req = __rq;
+                return ELEVATOR_BACK_MERGE;
+        }
+
         if (e->ops->elevator_merge_fn)
                 return e->ops->elevator_merge_fn(q, req, bio);
 
@@ -284,6 +391,8 @@ void elv_merged_request(request_queue_t *q, struct request *rq)
         if (e->ops->elevator_merged_fn)
                 e->ops->elevator_merged_fn(q, rq);
 
+        elv_rqhash_reposition(q, rq);
+
         q->last_merge = rq;
 }
 
@@ -294,8 +403,11 @@ void elv_merge_requests(request_queue_t *q, struct request *rq,
 
         if (e->ops->elevator_merge_req_fn)
                 e->ops->elevator_merge_req_fn(q, rq, next);
-        q->nr_sorted--;
 
+        elv_rqhash_reposition(q, rq);
+        elv_rqhash_del(q, next);
+
+        q->nr_sorted--;
         q->last_merge = rq;
 }
 
@@ -371,8 +483,12 @@ void elv_insert(request_queue_t *q, struct request *rq, int where)
                 BUG_ON(!blk_fs_request(rq));
                 rq->cmd_flags |= REQ_SORTED;
                 q->nr_sorted++;
-                if (q->last_merge == NULL && rq_mergeable(rq))
-                        q->last_merge = rq;
+                if (rq_mergeable(rq)) {
+                        elv_rqhash_add(q, rq);
+                        if (!q->last_merge)
+                                q->last_merge = rq;
+                }
+
                 /*
                  * Some ioscheds (cfq) run q->request_fn directly, so
                  * rq cannot be accessed after calling
@@ -557,6 +673,7 @@ struct request *elv_next_request(request_queue_t *q)
 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 {
         BUG_ON(list_empty(&rq->queuelist));
+        BUG_ON(ELV_ON_HASH(rq));
 
         list_del_init(&rq->queuelist);
 
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 9b91bb70c5ed..9cbf7b550c78 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -281,6 +281,7 @@ static inline void rq_init(request_queue_t *q, struct request *rq)
 {
         INIT_LIST_HEAD(&rq->queuelist);
         INIT_LIST_HEAD(&rq->donelist);
+        INIT_HLIST_NODE(&rq->hash);
 
         rq->errors = 0;
         rq->rq_status = RQ_ACTIVE;
@@ -2700,6 +2701,7 @@ void __blk_put_request(request_queue_t *q, struct request *req)
                 int priv = req->cmd_flags & REQ_ELVPRIV;
 
                 BUG_ON(!list_empty(&req->queuelist));
+                BUG_ON(!hlist_unhashed(&req->hash));
 
                 blk_free_request(q, req);
                 freed_request(q, rw, priv);