Merge branch 'block-dir' of git://brick.kernel.dk/data/git/linux-2.6-block

1 files changed, 2005 insertions, 0 deletions

diff --git a/block/as-iosched.c b/block/as-iosched.c
new file mode 100644
index 000000000000..a78e160b59a3
--- /dev/null
+++ b/block/as-iosched.c
@@ -0,0 +1,2005 @@
+/*
+ *  linux/drivers/block/as-iosched.c
+ *
+ *  Anticipatory & deadline i/o scheduler.
+ *
+ *  Copyright (C) 2002 Jens Axboe <axboe@suse.de>
+ *                     Nick Piggin <nickpiggin@yahoo.com.au>
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/blkdev.h>
+#include <linux/elevator.h>
+#include <linux/bio.h>
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/compiler.h>
+#include <linux/hash.h>
+#include <linux/rbtree.h>
+#include <linux/interrupt.h>
+
+#define REQ_SYNC        1
+#define REQ_ASYNC       0
+
+/*
+ * See Documentation/block/as-iosched.txt
+ */
+
+/*
+ * max time before a read is submitted.
+ */
+#define default_read_expire (HZ / 8)
+
+/*
+ * ditto for writes, these limits are not hard, even
+ * if the disk is capable of satisfying them.
+ */
+#define default_write_expire (HZ / 4)
+
+/*
+ * read_batch_expire describes how long we will allow a stream of reads to
+ * persist before looking to see whether it is time to switch over to writes.
+ */
+#define default_read_batch_expire (HZ / 2)
+
+/*
+ * write_batch_expire describes how long we want a stream of writes to run for.
+ * This is not a hard limit, but a target we set for the auto-tuning thingy.
+ * See, the problem is: we can send a lot of writes to disk cache / TCQ in
+ * a short amount of time...
+ */
+#define default_write_batch_expire (HZ / 8)
+
+/*
+ * max time we may wait to anticipate a read (default around 6ms)
+ */
+#define default_antic_expire ((HZ / 150) ? HZ / 150 : 1)
+
+/*
+ * Keep track of up to 20ms thinktimes. We can go as big as we like here,
+ * however huge values tend to interfere and not decay fast enough. A program
+ * might be in a non-io phase of operation. Waiting on user input for example,
+ * or doing a lengthy computation. A small penalty can be justified there, and
+ * will still catch out those processes that constantly have large thinktimes.
+ */
+#define MAX_THINKTIME (HZ/50UL)
+
+/* Bits in as_io_context.state */
+enum as_io_states {
+        AS_TASK_RUNNING=0,      /* Process has not exited */
+        AS_TASK_IOSTARTED,      /* Process has started some IO */
+        AS_TASK_IORUNNING,      /* Process has completed some IO */
+};
+
+enum anticipation_status {
+        ANTIC_OFF=0,            /* Not anticipating (normal operation)  */
+        ANTIC_WAIT_REQ,         /* The last read has not yet completed  */
+        ANTIC_WAIT_NEXT,        /* Currently anticipating a request vs
+                                   last read (which has completed) */
+        ANTIC_FINISHED,         /* Anticipating but have found a candidate
+                                 * or timed out */
+};
+
+struct as_data {
+        /*
+         * run time data
+         */
+
+        struct request_queue *q;        /* the "owner" queue */
+
+        /*
+         * requests (as_rq s) are present on both sort_list and fifo_list
+         */
+        struct rb_root sort_list[2];
+        struct list_head fifo_list[2];
+
+        struct as_rq *next_arq[2];      /* next in sort order */
+        sector_t last_sector[2];        /* last REQ_SYNC & REQ_ASYNC sectors */
+        struct list_head *hash;         /* request hash */
+
+        unsigned long exit_prob;        /* probability a task will exit while
+                                           being waited on */
+        unsigned long exit_no_coop;     /* probablility an exited task will
+                                           not be part of a later cooperating
+                                           request */
+        unsigned long new_ttime_total;  /* mean thinktime on new proc */
+        unsigned long new_ttime_mean;
+        u64 new_seek_total;             /* mean seek on new proc */
+        sector_t new_seek_mean;
+
+        unsigned long current_batch_expires;
+        unsigned long last_check_fifo[2];
+        int changed_batch;              /* 1: waiting for old batch to end */
+        int new_batch;                  /* 1: waiting on first read complete */
+        int batch_data_dir;             /* current batch REQ_SYNC / REQ_ASYNC */
+        int write_batch_count;          /* max # of reqs in a write batch */
+        int current_write_count;        /* how many requests left this batch */
+        int write_batch_idled;          /* has the write batch gone idle? */
+        mempool_t *arq_pool;
+
+        enum anticipation_status antic_status;
+        unsigned long antic_start;      /* jiffies: when it started */
+        struct timer_list antic_timer;  /* anticipatory scheduling timer */
+        struct work_struct antic_work;  /* Deferred unplugging */
+        struct io_context *io_context;  /* Identify the expected process */
+        int ioc_finished; /* IO associated with io_context is finished */
+        int nr_dispatched;
+
+        /*
+         * settings that change how the i/o scheduler behaves
+         */
+        unsigned long fifo_expire[2];
+        unsigned long batch_expire[2];
+        unsigned long antic_expire;
+};
+
+#define list_entry_fifo(ptr)    list_entry((ptr), struct as_rq, fifo)
+
+/*
+ * per-request data.
+ */
+enum arq_state {
+        AS_RQ_NEW=0,            /* New - not referenced and not on any lists */
+        AS_RQ_QUEUED,           /* In the request queue. It belongs to the
+                                   scheduler */
+        AS_RQ_DISPATCHED,       /* On the dispatch list. It belongs to the
+                                   driver now */
+        AS_RQ_PRESCHED,         /* Debug poisoning for requests being used */
+        AS_RQ_REMOVED,
+        AS_RQ_MERGED,
+        AS_RQ_POSTSCHED,        /* when they shouldn't be */
+};
+
+struct as_rq {
+        /*
+         * rbtree index, key is the starting offset
+         */
+        struct rb_node rb_node;
+        sector_t rb_key;
+
+        struct request *request;
+
+        struct io_context *io_context;  /* The submitting task */
+
+        /*
+         * request hash, key is the ending offset (for back merge lookup)
+         */
+        struct list_head hash;
+        unsigned int on_hash;
+
+        /*
+         * expire fifo
+         */
+        struct list_head fifo;
+        unsigned long expires;
+
+        unsigned int is_sync;
+        enum arq_state state;
+};
+
+#define RQ_DATA(rq)     ((struct as_rq *) (rq)->elevator_private)
+
+static kmem_cache_t *arq_pool;
+
+/*
+ * IO Context helper functions
+ */
+
+/* Called to deallocate the as_io_context */
+static void free_as_io_context(struct as_io_context *aic)
+{
+        kfree(aic);
+}
+
+/* Called when the task exits */
+static void exit_as_io_context(struct as_io_context *aic)
+{
+        WARN_ON(!test_bit(AS_TASK_RUNNING, &aic->state));
+        clear_bit(AS_TASK_RUNNING, &aic->state);
+}
+
+static struct as_io_context *alloc_as_io_context(void)
+{
+        struct as_io_context *ret;
+
+        ret = kmalloc(sizeof(*ret), GFP_ATOMIC);
+        if (ret) {
+                ret->dtor = free_as_io_context;
+                ret->exit = exit_as_io_context;
+                ret->state = 1 << AS_TASK_RUNNING;
+                atomic_set(&ret->nr_queued, 0);
+                atomic_set(&ret->nr_dispatched, 0);
+                spin_lock_init(&ret->lock);
+                ret->ttime_total = 0;
+                ret->ttime_samples = 0;
+                ret->ttime_mean = 0;
+                ret->seek_total = 0;
+                ret->seek_samples = 0;
+                ret->seek_mean = 0;
+        }
+
+        return ret;
+}
+
+/*
+ * If the current task has no AS IO context then create one and initialise it.
+ * Then take a ref on the task's io context and return it.
+ */
+static struct io_context *as_get_io_context(void)
+{
+        struct io_context *ioc = get_io_context(GFP_ATOMIC);
+        if (ioc && !ioc->aic) {
+                ioc->aic = alloc_as_io_context();
+                if (!ioc->aic) {
+                        put_io_context(ioc);
+                        ioc = NULL;
+                }
+        }
+        return ioc;
+}
+
+static void as_put_io_context(struct as_rq *arq)
+{
+        struct as_io_context *aic;
+
+        if (unlikely(!arq->io_context))
+                return;
+
+        aic = arq->io_context->aic;
+
+        if (arq->is_sync == REQ_SYNC && aic) {
+                spin_lock(&aic->lock);
+                set_bit(AS_TASK_IORUNNING, &aic->state);
+                aic->last_end_request = jiffies;
+                spin_unlock(&aic->lock);
+        }
+
+        put_io_context(arq->io_context);
+}
+
+/*
+ * 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)
+#define list_entry_hash(ptr)    list_entry((ptr), struct as_rq, hash)
+
+static inline void __as_del_arq_hash(struct as_rq *arq)
+{
+        arq->on_hash = 0;
+        list_del_init(&arq->hash);
+}
+
+static inline void as_del_arq_hash(struct as_rq *arq)
+{
+        if (arq->on_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(arq->on_hash);
+
+        arq->on_hash = 1;
+        list_add(&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 list_head *head = &ad->hash[AS_HASH_FN(rq_hash_key(rq))];
+
+        if (!arq->on_hash) {
+                WARN_ON(1);
+                return;
+        }
+
+        if (arq->hash.prev != head) {
+                list_del(&arq->hash);
+                list_add(&arq->hash, head);
+        }
+}
+
+static struct request *as_find_arq_hash(struct as_data *ad, sector_t offset)
+{
+        struct list_head *hash_list = &ad->hash[AS_HASH_FN(offset)];
+        struct list_head *entry, *next = hash_list->next;
+
+        while ((entry = next) != hash_list) {
+                struct as_rq *arq = list_entry_hash(entry);
+                struct request *__rq = arq->request;
+
+                next = entry->next;
+
+                BUG_ON(!arq->on_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_NONE         (2)
+#define RB_EMPTY(root)  ((root)->rb_node == NULL)
+#define ON_RB(node)     ((node)->rb_color != RB_NONE)
+#define RB_CLEAR(node)  ((node)->rb_color = RB_NONE)
+#define rb_entry_arq(node)      rb_entry((node), struct as_rq, rb_node)
+#define ARQ_RB_ROOT(ad, arq)    (&(ad)->sort_list[(arq)->is_sync])
+#define rq_rb_key(rq)           (rq)->sector
+
+/*
+ * as_find_first_arq finds the first (lowest sector numbered) request
+ * for the specified data_dir. Used to sweep back to the start of the disk
+ * (1-way elevator) after we process the last (highest sector) request.
+ */
+static struct as_rq *as_find_first_arq(struct as_data *ad, int data_dir)
+{
+        struct rb_node *n = ad->sort_list[data_dir].rb_node;
+
+        if (n == NULL)
+                return NULL;
+
+        for (;;) {
+                if (n->rb_left == NULL)
+                        return rb_entry_arq(n);
+
+                n = n->rb_left;
+        }
+}
+
+/*
+ * Add the request to the rb tree if it is unique.  If there is an alias (an
+ * existing request against the same sector), which can happen when using
+ * direct IO, then return the alias.
+ */
+static struct as_rq *as_add_arq_rb(struct as_data *ad, struct as_rq *arq)
+{
+        struct rb_node **p = &ARQ_RB_ROOT(ad, arq)->rb_node;
+        struct rb_node *parent = NULL;
+        struct as_rq *__arq;
+        struct request *rq = arq->request;
+
+        arq->rb_key = rq_rb_key(rq);
+
+        while (*p) {
+                parent = *p;
+                __arq = rb_entry_arq(parent);
+
+                if (arq->rb_key < __arq->rb_key)
+                        p = &(*p)->rb_left;
+                else if (arq->rb_key > __arq->rb_key)
+                        p = &(*p)->rb_right;
+                else
+                        return __arq;
+        }
+
+        rb_link_node(&arq->rb_node, parent, p);
+        rb_insert_color(&arq->rb_node, ARQ_RB_ROOT(ad, arq));
+
+        return NULL;
+}
+
+static inline void as_del_arq_rb(struct as_data *ad, struct as_rq *arq)
+{
+        if (!ON_RB(&arq->rb_node)) {
+                WARN_ON(1);
+                return;
+        }
+
+        rb_erase(&arq->rb_node, ARQ_RB_ROOT(ad, arq));
+        RB_CLEAR(&arq->rb_node);
+}
+
+static struct request *
+as_find_arq_rb(struct as_data *ad, sector_t sector, int data_dir)
+{
+        struct rb_node *n = ad->sort_list[data_dir].rb_node;
+        struct as_rq *arq;
+
+        while (n) {
+                arq = rb_entry_arq(n);
+
+                if (sector < arq->rb_key)
+                        n = n->rb_left;
+                else if (sector > arq->rb_key)
+                        n = n->rb_right;
+                else
+                        return arq->request;
+        }
+
+        return NULL;
+}
+
+/*
+ * IO Scheduler proper
+ */
+
+#define MAXBACK (1024 * 1024)   /*
+                                 * Maximum distance the disk will go backward
+                                 * for a request.
+                                 */
+
+#define BACK_PENALTY    2
+
+/*
+ * as_choose_req selects the preferred one of two requests of the same data_dir
+ * ignoring time - eg. timeouts, which is the job of as_dispatch_request
+ */
+static struct as_rq *
+as_choose_req(struct as_data *ad, struct as_rq *arq1, struct as_rq *arq2)
+{
+        int data_dir;
+        sector_t last, s1, s2, d1, d2;
+        int r1_wrap=0, r2_wrap=0;       /* requests are behind the disk head */
+        const sector_t maxback = MAXBACK;
+
+        if (arq1 == NULL || arq1 == arq2)
+                return arq2;
+        if (arq2 == NULL)
+                return arq1;
+
+        data_dir = arq1->is_sync;
+
+        last = ad->last_sector[data_dir];
+        s1 = arq1->request->sector;
+        s2 = arq2->request->sector;
+
+        BUG_ON(data_dir != arq2->is_sync);
+
+        /*
+         * Strict one way elevator _except_ in the case where we allow
+         * short backward seeks which are biased as twice the cost of a
+         * similar forward seek.
+         */
+        if (s1 >= last)
+                d1 = s1 - last;
+        else if (s1+maxback >= last)
+                d1 = (last - s1)*BACK_PENALTY;
+        else {
+                r1_wrap = 1;
+                d1 = 0; /* shut up, gcc */
+        }
+
+        if (s2 >= last)
+                d2 = s2 - last;
+        else if (s2+maxback >= last)
+                d2 = (last - s2)*BACK_PENALTY;
+        else {
+                r2_wrap = 1;
+                d2 = 0;
+        }
+
+        /* Found required data */
+        if (!r1_wrap && r2_wrap)
+                return arq1;
+        else if (!r2_wrap && r1_wrap)
+                return arq2;
+        else if (r1_wrap && r2_wrap) {
+                /* both behind the head */
+                if (s1 <= s2)
+                        return arq1;
+                else
+                        return arq2;
+        }
+
+        /* Both requests in front of the head */
+        if (d1 < d2)
+                return arq1;
+        else if (d2 < d1)
+                return arq2;
+        else {
+                if (s1 >= s2)
+                        return arq1;
+                else
+                        return arq2;
+        }
+}
+
+/*
+ * as_find_next_arq finds the next request after @prev in elevator order.
+ * this with as_choose_req form the basis for how the scheduler chooses
+ * what request to process next. Anticipation works on top of this.
+ */
+static struct as_rq *as_find_next_arq(struct as_data *ad, struct as_rq *last)
+{
+        const int data_dir = last->is_sync;
+        struct as_rq *ret;
+        struct rb_node *rbnext = rb_next(&last->rb_node);
+        struct rb_node *rbprev = rb_prev(&last->rb_node);
+        struct as_rq *arq_next, *arq_prev;
+
+        BUG_ON(!ON_RB(&last->rb_node));
+
+        if (rbprev)
+                arq_prev = rb_entry_arq(rbprev);
+        else
+                arq_prev = NULL;
+
+        if (rbnext)
+                arq_next = rb_entry_arq(rbnext);
+        else {
+                arq_next = as_find_first_arq(ad, data_dir);
+                if (arq_next == last)
+                        arq_next = NULL;
+        }
+
+        ret = as_choose_req(ad, arq_next, arq_prev);
+
+        return ret;
+}
+
+/*
+ * anticipatory scheduling functions follow
+ */
+
+/*
+ * as_antic_expired tells us when we have anticipated too long.
+ * The funny "absolute difference" math on the elapsed time is to handle
+ * jiffy wraps, and disks which have been idle for 0x80000000 jiffies.
+ */
+static int as_antic_expired(struct as_data *ad)
+{
+        long delta_jif;
+
+        delta_jif = jiffies - ad->antic_start;
+        if (unlikely(delta_jif < 0))
+                delta_jif = -delta_jif;
+        if (delta_jif < ad->antic_expire)
+                return 0;
+
+        return 1;
+}
+
+/*
+ * as_antic_waitnext starts anticipating that a nice request will soon be
+ * submitted. See also as_antic_waitreq
+ */
+static void as_antic_waitnext(struct as_data *ad)
+{
+        unsigned long timeout;
+
+        BUG_ON(ad->antic_status != ANTIC_OFF
+                        && ad->antic_status != ANTIC_WAIT_REQ);
+
+        timeout = ad->antic_start + ad->antic_expire;
+
+        mod_timer(&ad->antic_timer, timeout);
+
+        ad->antic_status = ANTIC_WAIT_NEXT;
+}
+
+/*
+ * as_antic_waitreq starts anticipating. We don't start timing the anticipation
+ * until the request that we're anticipating on has finished. This means we
+ * are timing from when the candidate process wakes up hopefully.
+ */
+static void as_antic_waitreq(struct as_data *ad)
+{
+        BUG_ON(ad->antic_status == ANTIC_FINISHED);
+        if (ad->antic_status == ANTIC_OFF) {
+                if (!ad->io_context || ad->ioc_finished)
+                        as_antic_waitnext(ad);
+                else
+                        ad->antic_status = ANTIC_WAIT_REQ;
+        }
+}
+
+/*
+ * This is called directly by the functions in this file to stop anticipation.
+ * We kill the timer and schedule a call to the request_fn asap.
+ */
+static void as_antic_stop(struct as_data *ad)
+{
+        int status = ad->antic_status;
+
+        if (status == ANTIC_WAIT_REQ || status == ANTIC_WAIT_NEXT) {
+                if (status == ANTIC_WAIT_NEXT)
+                        del_timer(&ad->antic_timer);
+                ad->antic_status = ANTIC_FINISHED;
+                /* see as_work_handler */
+                kblockd_schedule_work(&ad->antic_work);
+        }
+}
+
+/*
+ * as_antic_timeout is the timer function set by as_antic_waitnext.
+ */
+static void as_antic_timeout(unsigned long data)
+{
+        struct request_queue *q = (struct request_queue *)data;
+        struct as_data *ad = q->elevator->elevator_data;
+        unsigned long flags;
+
+        spin_lock_irqsave(q->queue_lock, flags);
+        if (ad->antic_status == ANTIC_WAIT_REQ
+                        || ad->antic_status == ANTIC_WAIT_NEXT) {
+                struct as_io_context *aic = ad->io_context->aic;
+
+                ad->antic_status = ANTIC_FINISHED;
+                kblockd_schedule_work(&ad->antic_work);
+
+                if (aic->ttime_samples == 0) {
+                        /* process anticipated on has exited or timed out*/
+                        ad->exit_prob = (7*ad->exit_prob + 256)/8;
+                }
+                if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
+                        /* process not "saved" by a cooperating request */
+                        ad->exit_no_coop = (7*ad->exit_no_coop + 256)/8;
+                }
+        }
+        spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
+static void as_update_thinktime(struct as_data *ad, struct as_io_context *aic,
+                                unsigned long ttime)
+{
+        /* fixed point: 1.0 == 1<<8 */
+        if (aic->ttime_samples == 0) {
+                ad->new_ttime_total = (7*ad->new_ttime_total + 256*ttime) / 8;
+                ad->new_ttime_mean = ad->new_ttime_total / 256;
+
+                ad->exit_prob = (7*ad->exit_prob)/8;
+        }
+        aic->ttime_samples = (7*aic->ttime_samples + 256) / 8;
+        aic->ttime_total = (7*aic->ttime_total + 256*ttime) / 8;
+        aic->ttime_mean = (aic->ttime_total + 128) / aic->ttime_samples;
+}
+
+static void as_update_seekdist(struct as_data *ad, struct as_io_context *aic,
+                                sector_t sdist)
+{
+        u64 total;
+
+        if (aic->seek_samples == 0) {
+                ad->new_seek_total = (7*ad->new_seek_total + 256*(u64)sdist)/8;
+                ad->new_seek_mean = ad->new_seek_total / 256;
+        }
+
+        /*
+         * Don't allow the seek distance to get too large from the
+         * odd fragment, pagein, etc
+         */
+        if (aic->seek_samples <= 60) /* second&third seek */
+                sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*1024);
+        else
+                sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*64);
+
+        aic->seek_samples = (7*aic->seek_samples + 256) / 8;
+        aic->seek_total = (7*aic->seek_total + (u64)256*sdist) / 8;
+        total = aic->seek_total + (aic->seek_samples/2);
+        do_div(total, aic->seek_samples);
+        aic->seek_mean = (sector_t)total;
+}
+
+/*
+ * as_update_iohist keeps a decaying histogram of IO thinktimes, and
+ * updates @aic->ttime_mean based on that. It is called when a new
+ * request is queued.
+ */
+static void as_update_iohist(struct as_data *ad, struct as_io_context *aic,
+                                struct request *rq)
+{
+        struct as_rq *arq = RQ_DATA(rq);
+        int data_dir = arq->is_sync;
+        unsigned long thinktime = 0;
+        sector_t seek_dist;
+
+        if (aic == NULL)
+                return;
+
+        if (data_dir == REQ_SYNC) {
+                unsigned long in_flight = atomic_read(&aic->nr_queued)
+                                        + atomic_read(&aic->nr_dispatched);
+                spin_lock(&aic->lock);
+                if (test_bit(AS_TASK_IORUNNING, &aic->state) ||
+                        test_bit(AS_TASK_IOSTARTED, &aic->state)) {
+                        /* Calculate read -> read thinktime */
+                        if (test_bit(AS_TASK_IORUNNING, &aic->state)
+                                                        && in_flight == 0) {
+                                thinktime = jiffies - aic->last_end_request;
+                                thinktime = min(thinktime, MAX_THINKTIME-1);
+                        }
+                        as_update_thinktime(ad, aic, thinktime);
+
+                        /* Calculate read -> read seek distance */
+                        if (aic->last_request_pos < rq->sector)
+                                seek_dist = rq->sector - aic->last_request_pos;
+                        else
+                                seek_dist = aic->last_request_pos - rq->sector;
+                        as_update_seekdist(ad, aic, seek_dist);
+                }
+                aic->last_request_pos = rq->sector + rq->nr_sectors;
+                set_bit(AS_TASK_IOSTARTED, &aic->state);
+                spin_unlock(&aic->lock);
+        }
+}
+
+/*
+ * as_close_req decides if one request is considered "close" to the
+ * previous one issued.
+ */
+static int as_close_req(struct as_data *ad, struct as_io_context *aic,
+                                struct as_rq *arq)
+{
+        unsigned long delay;    /* milliseconds */
+        sector_t last = ad->last_sector[ad->batch_data_dir];
+        sector_t next = arq->request->sector;
+        sector_t delta; /* acceptable close offset (in sectors) */
+        sector_t s;
+
+        if (ad->antic_status == ANTIC_OFF || !ad->ioc_finished)
+                delay = 0;
+        else
+                delay = ((jiffies - ad->antic_start) * 1000) / HZ;
+
+        if (delay == 0)
+                delta = 8192;
+        else if (delay <= 20 && delay <= ad->antic_expire)
+                delta = 8192 << delay;
+        else
+                return 1;
+
+        if ((last <= next + (delta>>1)) && (next <= last + delta))
+                return 1;
+
+        if (last < next)
+                s = next - last;
+        else
+                s = last - next;
+
+        if (aic->seek_samples == 0) {
+                /*
+                 * Process has just started IO. Use past statistics to
+                 * gauge success possibility
+                 */
+                if (ad->new_seek_mean > s) {
+                        /* this request is better than what we're expecting */
+                        return 1;
+                }
+
+        } else {
+                if (aic->seek_mean > s) {
+                        /* this request is better than what we're expecting */
+                        return 1;
+                }
+        }
+
+        return 0;
+}
+
+/*
+ * as_can_break_anticipation returns true if we have been anticipating this
+ * request.
+ *
+ * It also returns true if the process against which we are anticipating
+ * submits a write - that's presumably an fsync, O_SYNC write, etc. We want to
+ * dispatch it ASAP, because we know that application will not be submitting
+ * any new reads.
+ *
+ * If the task which has submitted the request has exited, break anticipation.
+ *
+ * If this task has queued some other IO, do not enter enticipation.
+ */
+static int as_can_break_anticipation(struct as_data *ad, struct as_rq *arq)
+{
+        struct io_context *ioc;
+        struct as_io_context *aic;
+
+        ioc = ad->io_context;
+        BUG_ON(!ioc);
+
+        if (arq && ioc == arq->io_context) {
+                /* request from same process */
+                return 1;
+        }
+
+        if (ad->ioc_finished && as_antic_expired(ad)) {
+                /*
+                 * In this situation status should really be FINISHED,
+                 * however the timer hasn't had the chance to run yet.
+                 */
+                return 1;
+        }
+
+        aic = ioc->aic;
+        if (!aic)
+                return 0;
+
+        if (atomic_read(&aic->nr_queued) > 0) {
+                /* process has more requests queued */
+                return 1;
+        }
+
+        if (atomic_read(&aic->nr_dispatched) > 0) {
+                /* process has more requests dispatched */
+                return 1;
+        }
+
+        if (arq && arq->is_sync == REQ_SYNC && as_close_req(ad, aic, arq)) {
+                /*
+                 * Found a close request that is not one of ours.
+                 *
+                 * This makes close requests from another process update
+                 * our IO history. Is generally useful when there are
+                 * two or more cooperating processes working in the same
+                 * area.
+                 */
+                if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
+                        if (aic->ttime_samples == 0)
+                                ad->exit_prob = (7*ad->exit_prob + 256)/8;
+
+                        ad->exit_no_coop = (7*ad->exit_no_coop)/8;
+                }
+
+                as_update_iohist(ad, aic, arq->request);
+                return 1;
+        }
+
+        if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
+                /* process anticipated on has exited */
+                if (aic->ttime_samples == 0)
+                        ad->exit_prob = (7*ad->exit_prob + 256)/8;
+
+                if (ad->exit_no_coop > 128)
+                        return 1;
+        }
+
+        if (aic->ttime_samples == 0) {
+                if (ad->new_ttime_mean > ad->antic_expire)
+                        return 1;
+                if (ad->exit_prob * ad->exit_no_coop > 128*256)
+                        return 1;
+        } else if (aic->ttime_mean > ad->antic_expire) {
+                /* the process thinks too much between requests */
+                return 1;
+        }
+
+        return 0;
+}
+
+/*
+ * as_can_anticipate indicates weather we should either run arq
+ * or keep anticipating a better request.
+ */
+static int as_can_anticipate(struct as_data *ad, struct as_rq *arq)
+{
+        if (!ad->io_context)
+                /*
+                 * Last request submitted was a write
+                 */
+                return 0;
+
+        if (ad->antic_status == ANTIC_FINISHED)
+                /*
+                 * Don't restart if we have just finished. Run the next request
+                 */
+                return 0;
+
+        if (as_can_break_anticipation(ad, arq))
+                /*
+                 * This request is a good candidate. Don't keep anticipating,
+                 * run it.
+                 */
+                return 0;
+
+        /*
+         * OK from here, we haven't finished, and don't have a decent request!
+         * Status is either ANTIC_OFF so start waiting,
+         * ANTIC_WAIT_REQ so continue waiting for request to finish
+         * or ANTIC_WAIT_NEXT so continue waiting for an acceptable request.
+         */
+
+        return 1;
+}
+
+/*
+ * as_update_arq must be called whenever a request (arq) is added to
+ * the sort_list. This function keeps caches up to date, and checks if the
+ * request might be one we are "anticipating"
+ */
+static void as_update_arq(struct as_data *ad, struct as_rq *arq)
+{
+        const int data_dir = arq->is_sync;
+
+        /* keep the next_arq cache up to date */
+        ad->next_arq[data_dir] = as_choose_req(ad, arq, ad->next_arq[data_dir]);
+
+        /*
+         * have we been anticipating this request?
+         * or does it come from the same process as the one we are anticipating
+         * for?
+         */
+        if (ad->antic_status == ANTIC_WAIT_REQ
+                        || ad->antic_status == ANTIC_WAIT_NEXT) {
+                if (as_can_break_anticipation(ad, arq))
+                        as_antic_stop(ad);
+        }
+}
+
+/*
+ * Gathers timings and resizes the write batch automatically
+ */
+static void update_write_batch(struct as_data *ad)
+{
+        unsigned long batch = ad->batch_expire[REQ_ASYNC];
+        long write_time;
+
+        write_time = (jiffies - ad->current_batch_expires) + batch;
+        if (write_time < 0)
+                write_time = 0;
+
+        if (write_time > batch && !ad->write_batch_idled) {
+                if (write_time > batch * 3)
+                        ad->write_batch_count /= 2;
+                else
+                        ad->write_batch_count--;
+        } else if (write_time < batch && ad->current_write_count == 0) {
+                if (batch > write_time * 3)
+                        ad->write_batch_count *= 2;
+                else
+                        ad->write_batch_count++;
+        }
+
+        if (ad->write_batch_count < 1)
+                ad->write_batch_count = 1;
+}
+
+/*
+ * as_completed_request is to be called when a request has completed and
+ * returned something to the requesting process, be it an error or data.
+ */
+static void as_completed_request(request_queue_t *q, struct request *rq)
+{
+        struct as_data *ad = q->elevator->elevator_data;
+        struct as_rq *arq = RQ_DATA(rq);
+
+        WARN_ON(!list_empty(&rq->queuelist));
+
+        if (arq->state != AS_RQ_REMOVED) {
+                printk("arq->state %d\n", arq->state);
+                WARN_ON(1);
+                goto out;
+        }
+
+        if (ad->changed_batch && ad->nr_dispatched == 1) {
+                kblockd_schedule_work(&ad->antic_work);
+                ad->changed_batch = 0;
+
+                if (ad->batch_data_dir == REQ_SYNC)
+                        ad->new_batch = 1;
+        }
+        WARN_ON(ad->nr_dispatched == 0);
+        ad->nr_dispatched--;
+
+        /*
+         * Start counting the batch from when a request of that direction is
+         * actually serviced. This should help devices with big TCQ windows
+         * and writeback caches
+         */
+        if (ad->new_batch && ad->batch_data_dir == arq->is_sync) {
+                update_write_batch(ad);
+                ad->current_batch_expires = jiffies +
+                                ad->batch_expire[REQ_SYNC];
+                ad->new_batch = 0;
+        }
+
+        if (ad->io_context == arq->io_context && ad->io_context) {
+                ad->antic_start = jiffies;
+                ad->ioc_finished = 1;
+                if (ad->antic_status == ANTIC_WAIT_REQ) {
+                        /*
+                         * We were waiting on this request, now anticipate
+                         * the next one
+                         */
+                        as_antic_waitnext(ad);
+                }
+        }
+
+        as_put_io_context(arq);
+out:
+        arq->state = AS_RQ_POSTSCHED;
+}
+
+/*
+ * as_remove_queued_request removes a request from the pre dispatch queue
+ * without updating refcounts. It is expected the caller will drop the
+ * reference unless it replaces the request at somepart of the elevator
+ * (ie. the dispatch queue)
+ */
+static void as_remove_queued_request(request_queue_t *q, struct request *rq)
+{
+        struct as_rq *arq = RQ_DATA(rq);
+        const int data_dir = arq->is_sync;
+        struct as_data *ad = q->elevator->elevator_data;
+
+        WARN_ON(arq->state != AS_RQ_QUEUED);
+
+        if (arq->io_context && arq->io_context->aic) {
+                BUG_ON(!atomic_read(&arq->io_context->aic->nr_queued));
+                atomic_dec(&arq->io_context->aic->nr_queued);
+        }
+
+        /*
+         * Update the "next_arq" cache if we are about to remove its
+         * entry
+         */
+        if (ad->next_arq[data_dir] == arq)
+                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);
+}
+
+/*
+ * as_fifo_expired returns 0 if there are no expired reads on the fifo,
+ * 1 otherwise.  It is ratelimited so that we only perform the check once per
+ * `fifo_expire' interval.  Otherwise a large number of expired requests
+ * would create a hopeless seekstorm.
+ *
+ * See as_antic_expired comment.
+ */
+static int as_fifo_expired(struct as_data *ad, int adir)
+{
+        struct as_rq *arq;
+        long delta_jif;
+
+        delta_jif = jiffies - ad->last_check_fifo[adir];
+        if (unlikely(delta_jif < 0))
+                delta_jif = -delta_jif;
+        if (delta_jif < ad->fifo_expire[adir])
+                return 0;
+
+        ad->last_check_fifo[adir] = jiffies;
+
+        if (list_empty(&ad->fifo_list[adir]))
+                return 0;
+
+        arq = list_entry_fifo(ad->fifo_list[adir].next);
+
+        return time_after(jiffies, arq->expires);
+}
+
+/*
+ * as_batch_expired returns true if the current batch has expired. A batch
+ * is a set of reads or a set of writes.
+ */
+static inline int as_batch_expired(struct as_data *ad)
+{
+        if (ad->changed_batch || ad->new_batch)
+                return 0;
+
+        if (ad->batch_data_dir == REQ_SYNC)
+                /* TODO! add a check so a complete fifo gets written? */
+                return time_after(jiffies, ad->current_batch_expires);
+
+        return time_after(jiffies, ad->current_batch_expires)
+                || ad->current_write_count == 0;
+}
+
+/*
+ * move an entry to dispatch queue
+ */
+static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq)
+{
+        struct request *rq = arq->request;
+        const int data_dir = arq->is_sync;
+
+        BUG_ON(!ON_RB(&arq->rb_node));
+
+        as_antic_stop(ad);
+        ad->antic_status = ANTIC_OFF;
+
+        /*
+         * This has to be set in order to be correctly updated by
+         * as_find_next_arq
+         */
+        ad->last_sector[data_dir] = rq->sector + rq->nr_sectors;
+
+        if (data_dir == REQ_SYNC) {
+                /* In case we have to anticipate after this */
+                copy_io_context(&ad->io_context, &arq->io_context);
+        } else {
+                if (ad->io_context) {
+                        put_io_context(ad->io_context);
+                        ad->io_context = NULL;
+                }
+
+                if (ad->current_write_count != 0)
+                        ad->current_write_count--;
+        }
+        ad->ioc_finished = 0;
+
+        ad->next_arq[data_dir] = as_find_next_arq(ad, arq);
+
+        /*
+         * take it off the sort and fifo list, add to dispatch queue
+         */
+        while (!list_empty(&rq->queuelist)) {
+                struct request *__rq = list_entry_rq(rq->queuelist.next);
+                struct as_rq *__arq = RQ_DATA(__rq);
+
+                list_del(&__rq->queuelist);
+
+                elv_dispatch_add_tail(ad->q, __rq);
+
+                if (__arq->io_context && __arq->io_context->aic)
+                        atomic_inc(&__arq->io_context->aic->nr_dispatched);
+
+                WARN_ON(__arq->state != AS_RQ_QUEUED);
+                __arq->state = AS_RQ_DISPATCHED;
+
+                ad->nr_dispatched++;
+        }
+
+        as_remove_queued_request(ad->q, rq);
+        WARN_ON(arq->state != AS_RQ_QUEUED);
+
+        elv_dispatch_sort(ad->q, rq);
+
+        arq->state = AS_RQ_DISPATCHED;
+        if (arq->io_context && arq->io_context->aic)
+                atomic_inc(&arq->io_context->aic->nr_dispatched);
+        ad->nr_dispatched++;
+}
+
+/*
+ * as_dispatch_request selects the best request according to
+ * read/write expire, batch expire, etc, and moves it to the dispatch
+ * queue. Returns 1 if a request was found, 0 otherwise.
+ */
+static int as_dispatch_request(request_queue_t *q, int force)
+{
+        struct as_data *ad = q->elevator->elevator_data;
+        struct as_rq *arq;
+        const int reads = !list_empty(&ad->fifo_list[REQ_SYNC]);
+        const int writes = !list_empty(&ad->fifo_list[REQ_ASYNC]);
+
+        if (unlikely(force)) {
+                /*
+                 * Forced dispatch, accounting is useless.  Reset
+                 * accounting states and dump fifo_lists.  Note that
+                 * batch_data_dir is reset to REQ_SYNC to avoid
+                 * screwing write batch accounting as write batch
+                 * accounting occurs on W->R transition.
+                 */
+                int dispatched = 0;
+
+                ad->batch_data_dir = REQ_SYNC;
+                ad->changed_batch = 0;
+                ad->new_batch = 0;
+
+                while (ad->next_arq[REQ_SYNC]) {
+                        as_move_to_dispatch(ad, ad->next_arq[REQ_SYNC]);
+                        dispatched++;
+                }
+                ad->last_check_fifo[REQ_SYNC] = jiffies;
+
+                while (ad->next_arq[REQ_ASYNC]) {
+                        as_move_to_dispatch(ad, ad->next_arq[REQ_ASYNC]);
+                        dispatched++;
+                }
+                ad->last_check_fifo[REQ_ASYNC] = jiffies;
+
+                return dispatched;
+        }
+
+        /* Signal that the write batch was uncontended, so we can't time it */
+        if (ad->batch_data_dir == REQ_ASYNC && !reads) {
+                if (ad->current_write_count == 0 || !writes)
+                        ad->write_batch_idled = 1;
+        }
+
+        if (!(reads || writes)
+                || ad->antic_status == ANTIC_WAIT_REQ
+                || ad->antic_status == ANTIC_WAIT_NEXT
+                || ad->changed_batch)
+                return 0;
+
+        if (!(reads && writes && as_batch_expired(ad))) {
+                /*
+                 * batch is still running or no reads or no writes
+                 */
+                arq = ad->next_arq[ad->batch_data_dir];
+
+                if (ad->batch_data_dir == REQ_SYNC && ad->antic_expire) {
+                        if (as_fifo_expired(ad, REQ_SYNC))
+                                goto fifo_expired;
+
+                        if (as_can_anticipate(ad, arq)) {
+                                as_antic_waitreq(ad);
+                                return 0;
+                        }
+                }
+
+                if (arq) {
+                        /* we have a "next request" */
+                        if (reads && !writes)
+                                ad->current_batch_expires =
+                                        jiffies + ad->batch_expire[REQ_SYNC];
+                        goto dispatch_request;
+                }
+        }
+
+        /*
+         * at this point we are not running a batch. select the appropriate
+         * data direction (read / write)
+         */
+
+        if (reads) {
+                BUG_ON(RB_EMPTY(&ad->sort_list[REQ_SYNC]));
+
+                if (writes && ad->batch_data_dir == REQ_SYNC)
+                        /*
+                         * Last batch was a read, switch to writes
+                         */
+                        goto dispatch_writes;
+
+                if (ad->batch_data_dir == REQ_ASYNC) {
+                        WARN_ON(ad->new_batch);
+                        ad->changed_batch = 1;
+                }
+                ad->batch_data_dir = REQ_SYNC;
+                arq = list_entry_fifo(ad->fifo_list[ad->batch_data_dir].next);
+                ad->last_check_fifo[ad->batch_data_dir] = jiffies;
+                goto dispatch_request;
+        }
+
+        /*
+         * the last batch was a read
+         */
+
+        if (writes) {
+dispatch_writes:
+                BUG_ON(RB_EMPTY(&ad->sort_list[REQ_ASYNC]));
+
+                if (ad->batch_data_dir == REQ_SYNC) {
+                        ad->changed_batch = 1;
+
+                        /*
+                         * new_batch might be 1 when the queue runs out of
+                         * reads. A subsequent submission of a write might
+                         * cause a change of batch before the read is finished.
+                         */
+                        ad->new_batch = 0;
+                }
+                ad->batch_data_dir = REQ_ASYNC;
+                ad->current_write_count = ad->write_batch_count;
+                ad->write_batch_idled = 0;
+                arq = ad->next_arq[ad->batch_data_dir];
+                goto dispatch_request;
+        }
+
+        BUG();
+        return 0;
+
+dispatch_request:
+        /*
+         * If a request has expired, service it.
+         */
+
+        if (as_fifo_expired(ad, ad->batch_data_dir)) {
+fifo_expired:
+                arq = list_entry_fifo(ad->fifo_list[ad->batch_data_dir].next);
+                BUG_ON(arq == NULL);
+        }
+
+        if (ad->changed_batch) {
+                WARN_ON(ad->new_batch);
+
+                if (ad->nr_dispatched)
+                        return 0;
+
+                if (ad->batch_data_dir == REQ_ASYNC)
+                        ad->current_batch_expires = jiffies +
+                                        ad->batch_expire[REQ_ASYNC];
+                else
+                        ad->new_batch = 1;
+
+                ad->changed_batch = 0;
+        }
+
+        /*
+         * arq is the selected appropriate request.
+         */
+        as_move_to_dispatch(ad, arq);
+
+        return 1;
+}
+
+/*
+ * Add arq to a list behind alias
+ */
+static inline void
+as_add_aliased_request(struct as_data *ad, struct as_rq *arq,
+                                struct as_rq *alias)
+{
+        struct request  *req = arq->request;
+        struct list_head *insert = alias->request->queuelist.prev;
+
+        /*
+         * Transfer list of aliases
+         */
+        while (!list_empty(&req->queuelist)) {
+                struct request *__rq = list_entry_rq(req->queuelist.next);
+                struct as_rq *__arq = RQ_DATA(__rq);
+
+                list_move_tail(&__rq->queuelist, &alias->request->queuelist);
+
+                WARN_ON(__arq->state != AS_RQ_QUEUED);
+        }
+
+        /*
+         * Another request with the same start sector on the rbtree.
+         * Link this request to that sector. They are untangled in
+         * as_move_to_dispatch
+         */
+        list_add(&arq->request->queuelist, insert);
+
+        /*
+         * Don't want to have to handle merges.
+         */
+        as_del_arq_hash(arq);
+        arq->request->flags |= REQ_NOMERGE;
+}
+
+/*
+ * add arq to rbtree and fifo
+ */
+static void as_add_request(request_queue_t *q, struct request *rq)
+{
+        struct as_data *ad = q->elevator->elevator_data;
+        struct as_rq *arq = RQ_DATA(rq);
+        struct as_rq *alias;
+        int data_dir;
+
+        if (arq->state != AS_RQ_PRESCHED) {
+                printk("arq->state: %d\n", arq->state);
+                WARN_ON(1);
+        }
+        arq->state = AS_RQ_NEW;
+
+        if (rq_data_dir(arq->request) == READ
+                        || current->flags&PF_SYNCWRITE)
+                arq->is_sync = 1;
+        else
+                arq->is_sync = 0;
+        data_dir = arq->is_sync;
+
+        arq->io_context = as_get_io_context();
+
+        if (arq->io_context) {
+                as_update_iohist(ad, arq->io_context->aic, arq->request);
+                atomic_inc(&arq->io_context->aic->nr_queued);
+        }
+
+        alias = as_add_arq_rb(ad, arq);
+        if (!alias) {
+                /*
+                 * set expire time (only used for reads) and add to fifo list
+                 */
+                arq->expires = jiffies + ad->fifo_expire[data_dir];
+                list_add_tail(&arq->fifo, &ad->fifo_list[data_dir]);
+
+                if (rq_mergeable(arq->request))
+                        as_add_arq_hash(ad, arq);
+                as_update_arq(ad, arq); /* keep state machine up to date */
+
+        } else {
+                as_add_aliased_request(ad, arq, alias);
+
+                /*
+                 * have we been anticipating this request?
+                 * or does it come from the same process as the one we are
+                 * anticipating for?
+                 */
+                if (ad->antic_status == ANTIC_WAIT_REQ
+                                || ad->antic_status == ANTIC_WAIT_NEXT) {
+                        if (as_can_break_anticipation(ad, arq))
+                                as_antic_stop(ad);
+                }
+        }
+
+        arq->state = AS_RQ_QUEUED;
+}
+
+static void as_activate_request(request_queue_t *q, struct request *rq)
+{
+        struct as_rq *arq = RQ_DATA(rq);
+
+        WARN_ON(arq->state != AS_RQ_DISPATCHED);
+        arq->state = AS_RQ_REMOVED;
+        if (arq->io_context && arq->io_context->aic)
+                atomic_dec(&arq->io_context->aic->nr_dispatched);
+}
+
+static void as_deactivate_request(request_queue_t *q, struct request *rq)
+{
+        struct as_rq *arq = RQ_DATA(rq);
+
+        WARN_ON(arq->state != AS_RQ_REMOVED);
+        arq->state = AS_RQ_DISPATCHED;
+        if (arq->io_context && arq->io_context->aic)
+                atomic_inc(&arq->io_context->aic->nr_dispatched);
+}
+
+/*
+ * as_queue_empty tells us if there are requests left in the device. It may
+ * not be the case that a driver can get the next request even if the queue
+ * is not empty - it is used in the block layer to check for plugging and
+ * merging opportunities
+ */
+static int as_queue_empty(request_queue_t *q)
+{
+        struct as_data *ad = q->elevator->elevator_data;
+
+        return list_empty(&ad->fifo_list[REQ_ASYNC])
+                && list_empty(&ad->fifo_list[REQ_SYNC]);
+}
+
+static struct request *as_former_request(request_queue_t *q,
+                                        struct request *rq)
+{
+        struct as_rq *arq = RQ_DATA(rq);
+        struct rb_node *rbprev = rb_prev(&arq->rb_node);
+        struct request *ret = NULL;
+
+        if (rbprev)
+                ret = rb_entry_arq(rbprev)->request;
+
+        return ret;
+}
+
+static struct request *as_latter_request(request_queue_t *q,
+                                        struct request *rq)
+{
+        struct as_rq *arq = RQ_DATA(rq);
+        struct rb_node *rbnext = rb_next(&arq->rb_node);
+        struct request *ret = NULL;
+
+        if (rbnext)
+                ret = rb_entry_arq(rbnext)->request;
+
+        return ret;
+}
+
+static int
+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;
+                }
+        }
+
+        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)
+{
+        struct as_data *ad = q->elevator->elevator_data;
+        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) {
+                struct as_rq *alias, *next_arq = NULL;
+
+                if (ad->next_arq[arq->is_sync] == arq)
+                        next_arq = as_find_next_arq(ad, arq);
+
+                /*
+                 * Note! We should really be moving any old aliased requests
+                 * off this request and try to insert them into the rbtree. We
+                 * currently don't bother. Ditto the next function.
+                 */
+                as_del_arq_rb(ad, arq);
+                if ((alias = as_add_arq_rb(ad, arq))) {
+                        list_del_init(&arq->fifo);
+                        as_add_aliased_request(ad, arq, alias);
+                        if (next_arq)
+                                ad->next_arq[arq->is_sync] = next_arq;
+                }
+                /*
+                 * Note! At this stage of this and the next function, our next
+                 * request may not be optimal - eg the request may have "grown"
+                 * behind the disk head. We currently don't bother adjusting.
+                 */
+        }
+}
+
+static void as_merged_requests(request_queue_t *q, struct request *req,
+                                struct request *next)
+{
+        struct as_data *ad = q->elevator->elevator_data;
+        struct as_rq *arq = RQ_DATA(req);
+        struct as_rq *anext = RQ_DATA(next);
+
+        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) {
+                struct as_rq *alias, *next_arq = NULL;
+
+                if (ad->next_arq[arq->is_sync] == arq)
+                        next_arq = as_find_next_arq(ad, arq);
+
+                as_del_arq_rb(ad, arq);
+                if ((alias = as_add_arq_rb(ad, arq))) {
+                        list_del_init(&arq->fifo);
+                        as_add_aliased_request(ad, arq, alias);
+                        if (next_arq)
+                                ad->next_arq[arq->is_sync] = next_arq;
+                }
+        }
+
+        /*
+         * if anext expires before arq, assign its expire time to arq
+         * and move into anext position (anext will be deleted) in fifo
+         */
+        if (!list_empty(&arq->fifo) && !list_empty(&anext->fifo)) {
+                if (time_before(anext->expires, arq->expires)) {
+                        list_move(&arq->fifo, &anext->fifo);
+                        arq->expires = anext->expires;
+                        /*
+                         * Don't copy here but swap, because when anext is
+                         * removed below, it must contain the unused context
+                         */
+                        swap_io_context(&arq->io_context, &anext->io_context);
+                }
+        }
+
+        /*
+         * Transfer list of aliases
+         */
+        while (!list_empty(&next->queuelist)) {
+                struct request *__rq = list_entry_rq(next->queuelist.next);
+                struct as_rq *__arq = RQ_DATA(__rq);
+
+                list_move_tail(&__rq->queuelist, &req->queuelist);
+
+                WARN_ON(__arq->state != AS_RQ_QUEUED);
+        }
+
+        /*
+         * kill knowledge of next, this one is a goner
+         */
+        as_remove_queued_request(q, next);
+        as_put_io_context(anext);
+
+        anext->state = AS_RQ_MERGED;
+}
+
+/*
+ * This is executed in a "deferred" process context, by kblockd. It calls the
+ * driver's request_fn so the driver can submit that request.
+ *
+ * IMPORTANT! This guy will reenter the elevator, so set up all queue global
+ * state before calling, and don't rely on any state over calls.
+ *
+ * FIXME! dispatch queue is not a queue at all!
+ */
+static void as_work_handler(void *data)
+{
+        struct request_queue *q = data;
+        unsigned long flags;
+
+        spin_lock_irqsave(q->queue_lock, flags);
+        if (!as_queue_empty(q))
+                q->request_fn(q);
+        spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
+static void as_put_request(request_queue_t *q, struct request *rq)
+{
+        struct as_data *ad = q->elevator->elevator_data;
+        struct as_rq *arq = RQ_DATA(rq);
+
+        if (!arq) {
+                WARN_ON(1);
+                return;
+        }
+
+        if (unlikely(arq->state != AS_RQ_POSTSCHED &&
+                     arq->state != AS_RQ_PRESCHED &&
+                     arq->state != AS_RQ_MERGED)) {
+                printk("arq->state %d\n", arq->state);
+                WARN_ON(1);
+        }
+
+        mempool_free(arq, ad->arq_pool);
+        rq->elevator_private = NULL;
+}
+
+static int as_set_request(request_queue_t *q, struct request *rq,
+                          struct bio *bio, gfp_t gfp_mask)
+{
+        struct as_data *ad = q->elevator->elevator_data;
+        struct as_rq *arq = mempool_alloc(ad->arq_pool, gfp_mask);
+
+        if (arq) {
+                memset(arq, 0, sizeof(*arq));
+                RB_CLEAR(&arq->rb_node);
+                arq->request = rq;
+                arq->state = AS_RQ_PRESCHED;
+                arq->io_context = NULL;
+                INIT_LIST_HEAD(&arq->hash);
+                arq->on_hash = 0;
+                INIT_LIST_HEAD(&arq->fifo);
+                rq->elevator_private = arq;
+                return 0;
+        }
+
+        return 1;
+}
+
+static int as_may_queue(request_queue_t *q, int rw, struct bio *bio)
+{
+        int ret = ELV_MQUEUE_MAY;
+        struct as_data *ad = q->elevator->elevator_data;
+        struct io_context *ioc;
+        if (ad->antic_status == ANTIC_WAIT_REQ ||
+                        ad->antic_status == ANTIC_WAIT_NEXT) {
+                ioc = as_get_io_context();
+                if (ad->io_context == ioc)
+                        ret = ELV_MQUEUE_MUST;
+                put_io_context(ioc);
+        }
+
+        return ret;
+}
+
+static void as_exit_queue(elevator_t *e)
+{
+        struct as_data *ad = e->elevator_data;
+
+        del_timer_sync(&ad->antic_timer);
+        kblockd_flush();
+
+        BUG_ON(!list_empty(&ad->fifo_list[REQ_SYNC]));
+        BUG_ON(!list_empty(&ad->fifo_list[REQ_ASYNC]));
+
+        mempool_destroy(ad->arq_pool);
+        put_io_context(ad->io_context);
+        kfree(ad->hash);
+        kfree(ad);
+}
+
+/*
+ * initialize elevator private data (as_data), and alloc a arq for
+ * each request on the free lists
+ */
+static int as_init_queue(request_queue_t *q, elevator_t *e)
+{
+        struct as_data *ad;
+        int i;
+
+        if (!arq_pool)
+                return -ENOMEM;
+
+        ad = kmalloc_node(sizeof(*ad), GFP_KERNEL, q->node);
+        if (!ad)
+                return -ENOMEM;
+        memset(ad, 0, sizeof(*ad));
+
+        ad->q = q; /* Identify what queue the data belongs to */
+
+        ad->hash = kmalloc_node(sizeof(struct list_head)*AS_HASH_ENTRIES,
+                                GFP_KERNEL, q->node);
+        if (!ad->hash) {
+                kfree(ad);
+                return -ENOMEM;
+        }
+
+        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 -ENOMEM;
+        }
+
+        /* anticipatory scheduling helpers */
+        ad->antic_timer.function = as_antic_timeout;
+        ad->antic_timer.data = (unsigned long)q;
+        init_timer(&ad->antic_timer);
+        INIT_WORK(&ad->antic_work, as_work_handler, q);
+
+        for (i = 0; i < AS_HASH_ENTRIES; i++)
+                INIT_LIST_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;
+        ad->sort_list[REQ_ASYNC] = RB_ROOT;
+        ad->fifo_expire[REQ_SYNC] = default_read_expire;
+        ad->fifo_expire[REQ_ASYNC] = default_write_expire;
+        ad->antic_expire = default_antic_expire;
+        ad->batch_expire[REQ_SYNC] = default_read_batch_expire;
+        ad->batch_expire[REQ_ASYNC] = default_write_batch_expire;
+        e->elevator_data = ad;
+
+        ad->current_batch_expires = jiffies + ad->batch_expire[REQ_SYNC];
+        ad->write_batch_count = ad->batch_expire[REQ_ASYNC] / 10;
+        if (ad->write_batch_count < 2)
+                ad->write_batch_count = 2;
+
+        return 0;
+}
+
+/*
+ * sysfs parts below
+ */
+struct as_fs_entry {
+        struct attribute attr;
+        ssize_t (*show)(struct as_data *, char *);
+        ssize_t (*store)(struct as_data *, const char *, size_t);
+};
+
+static ssize_t
+as_var_show(unsigned int var, char *page)
+{
+        return sprintf(page, "%d\n", var);
+}
+
+static ssize_t
+as_var_store(unsigned long *var, const char *page, size_t count)
+{
+        char *p = (char *) page;
+
+        *var = simple_strtoul(p, &p, 10);
+        return count;
+}
+
+static ssize_t as_est_show(struct as_data *ad, char *page)
+{
+        int pos = 0;
+
+        pos += sprintf(page+pos, "%lu %% exit probability\n",
+                                100*ad->exit_prob/256);
+        pos += sprintf(page+pos, "%lu %% probability of exiting without a "
+                                "cooperating process submitting IO\n",
+                                100*ad->exit_no_coop/256);
+        pos += sprintf(page+pos, "%lu ms new thinktime\n", ad->new_ttime_mean);
+        pos += sprintf(page+pos, "%llu sectors new seek distance\n",
+                                (unsigned long long)ad->new_seek_mean);
+
+        return pos;
+}
+
+#define SHOW_FUNCTION(__FUNC, __VAR)                            \
+static ssize_t __FUNC(struct as_data *ad, char *page)           \
+{                                                               \
+        return as_var_show(jiffies_to_msecs((__VAR)), (page));  \
+}
+SHOW_FUNCTION(as_readexpire_show, ad->fifo_expire[REQ_SYNC]);
+SHOW_FUNCTION(as_writeexpire_show, ad->fifo_expire[REQ_ASYNC]);
+SHOW_FUNCTION(as_anticexpire_show, ad->antic_expire);
+SHOW_FUNCTION(as_read_batchexpire_show, ad->batch_expire[REQ_SYNC]);
+SHOW_FUNCTION(as_write_batchexpire_show, ad->batch_expire[REQ_ASYNC]);
+#undef SHOW_FUNCTION
+
+#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX)                         \
+static ssize_t __FUNC(struct as_data *ad, const char *page, size_t count)       \
+{                                                                       \
+        int ret = as_var_store(__PTR, (page), count);           \
+        if (*(__PTR) < (MIN))                                           \
+                *(__PTR) = (MIN);                                       \
+        else if (*(__PTR) > (MAX))                                      \
+                *(__PTR) = (MAX);                                       \
+        *(__PTR) = msecs_to_jiffies(*(__PTR));                          \
+        return ret;                                                     \
+}
+STORE_FUNCTION(as_readexpire_store, &ad->fifo_expire[REQ_SYNC], 0, INT_MAX);
+STORE_FUNCTION(as_writeexpire_store, &ad->fifo_expire[REQ_ASYNC], 0, INT_MAX);
+STORE_FUNCTION(as_anticexpire_store, &ad->antic_expire, 0, INT_MAX);
+STORE_FUNCTION(as_read_batchexpire_store,
+                        &ad->batch_expire[REQ_SYNC], 0, INT_MAX);
+STORE_FUNCTION(as_write_batchexpire_store,
+                        &ad->batch_expire[REQ_ASYNC], 0, INT_MAX);
+#undef STORE_FUNCTION
+
+static struct as_fs_entry as_est_entry = {
+        .attr = {.name = "est_time", .mode = S_IRUGO },
+        .show = as_est_show,
+};
+static struct as_fs_entry as_readexpire_entry = {
+        .attr = {.name = "read_expire", .mode = S_IRUGO | S_IWUSR },
+        .show = as_readexpire_show,
+        .store = as_readexpire_store,
+};
+static struct as_fs_entry as_writeexpire_entry = {
+        .attr = {.name = "write_expire", .mode = S_IRUGO | S_IWUSR },
+        .show = as_writeexpire_show,
+        .store = as_writeexpire_store,
+};
+static struct as_fs_entry as_anticexpire_entry = {
+        .attr = {.name = "antic_expire", .mode = S_IRUGO | S_IWUSR },
+        .show = as_anticexpire_show,
+        .store = as_anticexpire_store,
+};
+static struct as_fs_entry as_read_batchexpire_entry = {
+        .attr = {.name = "read_batch_expire", .mode = S_IRUGO | S_IWUSR },
+        .show = as_read_batchexpire_show,
+        .store = as_read_batchexpire_store,
+};
+static struct as_fs_entry as_write_batchexpire_entry = {
+        .attr = {.name = "write_batch_expire", .mode = S_IRUGO | S_IWUSR },
+        .show = as_write_batchexpire_show,
+        .store = as_write_batchexpire_store,
+};
+
+static struct attribute *default_attrs[] = {
+        &as_est_entry.attr,
+        &as_readexpire_entry.attr,
+        &as_writeexpire_entry.attr,
+        &as_anticexpire_entry.attr,
+        &as_read_batchexpire_entry.attr,
+        &as_write_batchexpire_entry.attr,
+        NULL,
+};
+
+#define to_as(atr) container_of((atr), struct as_fs_entry, attr)
+
+static ssize_t
+as_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
+{
+        elevator_t *e = container_of(kobj, elevator_t, kobj);
+        struct as_fs_entry *entry = to_as(attr);
+
+        if (!entry->show)
+                return -EIO;
+
+        return entry->show(e->elevator_data, page);
+}
+
+static ssize_t
+as_attr_store(struct kobject *kobj, struct attribute *attr,
+                    const char *page, size_t length)
+{
+        elevator_t *e = container_of(kobj, elevator_t, kobj);
+        struct as_fs_entry *entry = to_as(attr);
+
+        if (!entry->store)
+                return -EIO;
+
+        return entry->store(e->elevator_data, page, length);
+}
+
+static struct sysfs_ops as_sysfs_ops = {
+        .show   = as_attr_show,
+        .store  = as_attr_store,
+};
+
+static struct kobj_type as_ktype = {
+        .sysfs_ops      = &as_sysfs_ops,
+        .default_attrs  = default_attrs,
+};
+
+static struct elevator_type iosched_as = {
+        .ops = {
+                .elevator_merge_fn =            as_merge,
+                .elevator_merged_fn =           as_merged_request,
+                .elevator_merge_req_fn =        as_merged_requests,
+                .elevator_dispatch_fn =         as_dispatch_request,
+                .elevator_add_req_fn =          as_add_request,
+                .elevator_activate_req_fn =     as_activate_request,
+                .elevator_deactivate_req_fn =   as_deactivate_request,
+                .elevator_queue_empty_fn =      as_queue_empty,
+                .elevator_completed_req_fn =    as_completed_request,
+                .elevator_former_req_fn =       as_former_request,
+                .elevator_latter_req_fn =       as_latter_request,
+                .elevator_set_req_fn =          as_set_request,
+                .elevator_put_req_fn =          as_put_request,
+                .elevator_may_queue_fn =        as_may_queue,
+                .elevator_init_fn =             as_init_queue,
+                .elevator_exit_fn =             as_exit_queue,
+        },
+
+        .elevator_ktype = &as_ktype,
+        .elevator_name = "anticipatory",
+        .elevator_owner = THIS_MODULE,
+};
+
+static int __init as_init(void)
+{
+        int ret;
+
+        arq_pool = kmem_cache_create("as_arq", sizeof(struct as_rq),
+                                     0, 0, NULL, NULL);
+        if (!arq_pool)
+                return -ENOMEM;
+
+        ret = elv_register(&iosched_as);
+        if (!ret) {
+                /*
+                 * don't allow AS to get unregistered, since we would have
+                 * to browse all tasks in the system and release their
+                 * as_io_context first
+                 */
+                __module_get(THIS_MODULE);
+                return 0;
+        }
+
+        kmem_cache_destroy(arq_pool);
+        return ret;
+}
+
+static void __exit as_exit(void)
+{
+        elv_unregister(&iosched_as);
+        kmem_cache_destroy(arq_pool);
+}
+
+module_init(as_init);
+module_exit(as_exit);
+
+MODULE_AUTHOR("Nick Piggin");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("anticipatory IO scheduler");