[PATCH] elevator: move the backmerging logic into the elevator core
[linux-2.6.git] / block / elevator.c
index 4ac97b6..cff1102 100644 (file)
@@ -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);