/*

   *  Anticipatory & deadline i/o scheduler.
   *

   *  Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>

   *                     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/module.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/compiler.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 request *next_rq[2];	/* next in sort order */

  	sector_t last_sector[2];	/* last REQ_SYNC & REQ_ASYNC sectors */

  
  	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? */

  
  	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;
  };

  /*
   * 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 */
  };

  #define RQ_IOC(rq)	((struct io_context *) (rq)->elevator_private)
  #define RQ_STATE(rq)	((enum arq_state)(rq)->elevator_private2)
  #define RQ_SET_STATE(rq, state)	((rq)->elevator_private2 = (void *) state)

  static DEFINE_PER_CPU(unsigned long, ioc_count);

  static struct completion *ioc_gone;

  static void as_move_to_dispatch(struct as_data *ad, struct request *rq);

  static void as_antic_stop(struct as_data *ad);

  /*
   * IO Context helper functions
   */
  
  /* Called to deallocate the as_io_context */
  static void free_as_io_context(struct as_io_context *aic)
  {
  	kfree(aic);

  	elv_ioc_count_dec(ioc_count);
  	if (ioc_gone && !elv_ioc_count_read(ioc_count))

  		complete(ioc_gone);

  }

  static void as_trim(struct io_context *ioc)
  {

  	if (ioc->aic)
  		free_as_io_context(ioc->aic);

  	ioc->aic = NULL;
  }

  /* 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;

  		elv_ioc_count_inc(ioc_count);

  	}
  
  	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(int node)

  {

  	struct io_context *ioc = get_io_context(GFP_ATOMIC, node);

  	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 request *rq)

  {
  	struct as_io_context *aic;

  	if (unlikely(!RQ_IOC(rq)))

  		return;

  	aic = RQ_IOC(rq)->aic;

  	if (rq_is_sync(rq) && aic) {

  		spin_lock(&aic->lock);
  		set_bit(AS_TASK_IORUNNING, &aic->state);
  		aic->last_end_request = jiffies;
  		spin_unlock(&aic->lock);
  	}

  	put_io_context(RQ_IOC(rq));

  }

  /*

   * rb tree support functions
   */

  #define RQ_RB_ROOT(ad, rq)	(&(ad)->sort_list[rq_is_sync((rq))])

  static void as_add_rq_rb(struct as_data *ad, struct request *rq)

  {

  	struct request *alias;

  	while ((unlikely(alias = elv_rb_add(RQ_RB_ROOT(ad, rq), rq)))) {

  		as_move_to_dispatch(ad, alias);

  		as_antic_stop(ad);
  	}
  }

  static inline void as_del_rq_rb(struct as_data *ad, struct request *rq)

  {

  	elv_rb_del(RQ_RB_ROOT(ad, rq), rq);

  }
  
  /*
   * 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 request *
  as_choose_req(struct as_data *ad, struct request *rq1, struct request *rq2)

  {
  	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 (rq1 == NULL || rq1 == rq2)
  		return rq2;
  	if (rq2 == NULL)
  		return rq1;

  	data_dir = rq_is_sync(rq1);

  
  	last = ad->last_sector[data_dir];

  	s1 = rq1->sector;
  	s2 = rq2->sector;

  	BUG_ON(data_dir != rq_is_sync(rq2));

  
  	/*
  	 * 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 rq1;

  	else if (!r2_wrap && r1_wrap)

  		return rq2;

  	else if (r1_wrap && r2_wrap) {
  		/* both behind the head */
  		if (s1 <= s2)

  			return rq1;

  		else

  			return rq2;

  	}
  
  	/* Both requests in front of the head */
  	if (d1 < d2)

  		return rq1;

  	else if (d2 < d1)

  		return rq2;

  	else {
  		if (s1 >= s2)

  			return rq1;

  		else

  			return rq2;

  	}
  }
  
  /*

   * as_find_next_rq 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 request *
  as_find_next_rq(struct as_data *ad, struct request *last)

  {

  	struct rb_node *rbnext = rb_next(&last->rb_node);
  	struct rb_node *rbprev = rb_prev(&last->rb_node);

  	struct request *next = NULL, *prev = NULL;

  	BUG_ON(RB_EMPTY_NODE(&last->rb_node));

  
  	if (rbprev)

  		prev = rb_entry_rq(rbprev);

  
  	if (rbnext)

  		next = rb_entry_rq(rbnext);

  	else {

  		const int data_dir = rq_is_sync(last);

  		rbnext = rb_first(&ad->sort_list[data_dir]);
  		if (rbnext && rbnext != &last->rb_node)

  			next = rb_entry_rq(rbnext);

  	}

  	return as_choose_req(ad, next, prev);

  }
  
  /*
   * 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)
  {

  	int data_dir = rq_is_sync(rq);

  	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 request *rq)

  {

  	unsigned long delay;	/* jiffies */

  	sector_t last = ad->last_sector[ad->batch_data_dir];

  	sector_t next = rq->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;

  	if (delay == 0)
  		delta = 8192;

  	else if (delay <= (20 * HZ / 1000) && 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 request *rq)

  {
  	struct io_context *ioc;
  	struct as_io_context *aic;

  
  	ioc = ad->io_context;
  	BUG_ON(!ioc);

  	if (rq && ioc == RQ_IOC(rq)) {

  		/* 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 (rq && rq_is_sync(rq) && as_close_req(ad, aic, rq)) {

  		/*
  		 * 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, rq);

  		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 whether we should either run rq

   * or keep anticipating a better request.
   */

  static int as_can_anticipate(struct as_data *ad, struct request *rq)

  {
  	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, rq))

  		/*
  		 * 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_rq must be called whenever a request (rq) 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_rq(struct as_data *ad, struct request *rq)

  {

  	const int data_dir = rq_is_sync(rq);

  	/* keep the next_rq cache up to date */
  	ad->next_rq[data_dir] = as_choose_req(ad, rq, ad->next_rq[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, rq))

  			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;

  
  	WARN_ON(!list_empty(&rq->queuelist));

  	if (RQ_STATE(rq) != AS_RQ_REMOVED) {
  		printk("rq->state %d
  ", RQ_STATE(rq));

  		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 == rq_is_sync(rq)) {

  		update_write_batch(ad);
  		ad->current_batch_expires = jiffies +
  				ad->batch_expire[REQ_SYNC];
  		ad->new_batch = 0;
  	}

  	if (ad->io_context == RQ_IOC(rq) && 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(rq);

  out:

  	RQ_SET_STATE(rq, 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)
  {

  	const int data_dir = rq_is_sync(rq);

  	struct as_data *ad = q->elevator->elevator_data;

  	struct io_context *ioc;

  	WARN_ON(RQ_STATE(rq) != AS_RQ_QUEUED);

  	ioc = RQ_IOC(rq);
  	if (ioc && ioc->aic) {
  		BUG_ON(!atomic_read(&ioc->aic->nr_queued));
  		atomic_dec(&ioc->aic->nr_queued);

  	}
  
  	/*

  	 * Update the "next_rq" cache if we are about to remove its

  	 * entry
  	 */

  	if (ad->next_rq[data_dir] == rq)
  		ad->next_rq[data_dir] = as_find_next_rq(ad, rq);

  	rq_fifo_clear(rq);

  	as_del_rq_rb(ad, rq);

  }
  
  /*

   * 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 request *rq;

  	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;

  	rq = rq_entry_fifo(ad->fifo_list[adir].next);

  	return time_after(jiffies, rq_fifo_time(rq));

  }
  
  /*
   * 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 request *rq)

  {

  	const int data_dir = rq_is_sync(rq);

  	BUG_ON(RB_EMPTY_NODE(&rq->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_rq

  	 */
  	ad->last_sector[data_dir] = rq->sector + rq->nr_sectors;
  
  	if (data_dir == REQ_SYNC) {

  		struct io_context *ioc = RQ_IOC(rq);

  		/* In case we have to anticipate after this */

  		copy_io_context(&ad->io_context, &ioc);

  	} 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_rq[data_dir] = as_find_next_rq(ad, rq);

  
  	/*
  	 * take it off the sort and fifo list, add to dispatch queue
  	 */

  	as_remove_queued_request(ad->q, rq);

  	WARN_ON(RQ_STATE(rq) != AS_RQ_QUEUED);

  	elv_dispatch_sort(ad->q, rq);

  	RQ_SET_STATE(rq, AS_RQ_DISPATCHED);
  	if (RQ_IOC(rq) && RQ_IOC(rq)->aic)
  		atomic_inc(&RQ_IOC(rq)->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;

  	const int reads = !list_empty(&ad->fifo_list[REQ_SYNC]);
  	const int writes = !list_empty(&ad->fifo_list[REQ_ASYNC]);

  	struct request *rq;

  	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_rq[REQ_SYNC]) {
  			as_move_to_dispatch(ad, ad->next_rq[REQ_SYNC]);

  			dispatched++;
  		}
  		ad->last_check_fifo[REQ_SYNC] = jiffies;

  		while (ad->next_rq[REQ_ASYNC]) {
  			as_move_to_dispatch(ad, ad->next_rq[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
  		 */

  		rq = ad->next_rq[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, rq)) {

  				as_antic_waitreq(ad);
  				return 0;
  			}
  		}

  		if (rq) {

  			/* 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_ROOT(&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;

  		rq = rq_entry_fifo(ad->fifo_list[REQ_SYNC].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_ROOT(&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;

  		rq = ad->next_rq[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:

  		rq = rq_entry_fifo(ad->fifo_list[ad->batch_data_dir].next);

  	}
  
  	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;
  	}
  
  	/*

  	 * rq is the selected appropriate request.

  	 */

  	as_move_to_dispatch(ad, rq);

  
  	return 1;
  }

  /*

   * add rq to rbtree and fifo

   */

  static void as_add_request(request_queue_t *q, struct request *rq)

  {

  	struct as_data *ad = q->elevator->elevator_data;

  	int data_dir;

  	RQ_SET_STATE(rq, AS_RQ_NEW);

  	data_dir = rq_is_sync(rq);

  	rq->elevator_private = as_get_io_context(q->node);

  	if (RQ_IOC(rq)) {
  		as_update_iohist(ad, RQ_IOC(rq)->aic, rq);
  		atomic_inc(&RQ_IOC(rq)->aic->nr_queued);

  	}

  	as_add_rq_rb(ad, rq);

  	/*
  	 * set expire time (only used for reads) and add to fifo list
  	 */

  	rq_set_fifo_time(rq, jiffies + ad->fifo_expire[data_dir]);
  	list_add_tail(&rq->queuelist, &ad->fifo_list[data_dir]);

  	as_update_rq(ad, rq); /* keep state machine up to date */
  	RQ_SET_STATE(rq, AS_RQ_QUEUED);

  }

  static void as_activate_request(request_queue_t *q, struct request *rq)

  {

  	WARN_ON(RQ_STATE(rq) != AS_RQ_DISPATCHED);
  	RQ_SET_STATE(rq, AS_RQ_REMOVED);
  	if (RQ_IOC(rq) && RQ_IOC(rq)->aic)
  		atomic_dec(&RQ_IOC(rq)->aic->nr_dispatched);

  }

  static void as_deactivate_request(request_queue_t *q, struct request *rq)

  {

  	WARN_ON(RQ_STATE(rq) != AS_RQ_REMOVED);
  	RQ_SET_STATE(rq, AS_RQ_DISPATCHED);
  	if (RQ_IOC(rq) && RQ_IOC(rq)->aic)
  		atomic_inc(&RQ_IOC(rq)->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 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;

  
  	/*
  	 * check for front merge
  	 */

  	__rq = elv_rb_find(&ad->sort_list[bio_data_dir(bio)], rb_key);

  	if (__rq && elv_rq_merge_ok(__rq, bio)) {
  		*req = __rq;
  		return ELEVATOR_FRONT_MERGE;

  	}
  
  	return ELEVATOR_NO_MERGE;

  }

  static void as_merged_request(request_queue_t *q, struct request *req, int type)

  {
  	struct as_data *ad = q->elevator->elevator_data;

  
  	/*

  	 * if the merge was a front merge, we need to reposition request
  	 */

  	if (type == ELEVATOR_FRONT_MERGE) {

  		as_del_rq_rb(ad, req);
  		as_add_rq_rb(ad, req);

  		/*
  		 * 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)

  {

  	/*

  	 * if next expires before rq, assign its expire time to arq
  	 * and move into next position (next will be deleted) in fifo

  	 */

  	if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
  		if (time_before(rq_fifo_time(next), rq_fifo_time(req))) {

  			struct io_context *rioc = RQ_IOC(req);
  			struct io_context *nioc = RQ_IOC(next);

  			list_move(&req->queuelist, &next->queuelist);
  			rq_set_fifo_time(req, rq_fifo_time(next));

  			/*
  			 * Don't copy here but swap, because when anext is
  			 * removed below, it must contain the unused context
  			 */

  			swap_io_context(&rioc, &nioc);

  		}
  	}
  
  	/*

  	 * kill knowledge of next, this one is a goner
  	 */
  	as_remove_queued_request(q, next);

  	as_put_io_context(next);

  	RQ_SET_STATE(next, 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(struct work_struct *work)

  {

  	struct as_data *ad = container_of(work, struct as_data, antic_work);
  	struct request_queue *q = ad->q;

  	unsigned long flags;
  
  	spin_lock_irqsave(q->queue_lock, flags);

  	blk_start_queueing(q);

  	spin_unlock_irqrestore(q->queue_lock, flags);
  }

  static int as_may_queue(request_queue_t *q, int rw)

  {
  	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(q->node);

  		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_work(&ad->antic_work);

  
  	BUG_ON(!list_empty(&ad->fifo_list[REQ_SYNC]));
  	BUG_ON(!list_empty(&ad->fifo_list[REQ_ASYNC]));

  	put_io_context(ad->io_context);

  	kfree(ad);
  }
  
  /*

   * initialize elevator private data (as_data).

   */

  static void *as_init_queue(request_queue_t *q)

  {
  	struct as_data *ad;

  	ad = kmalloc_node(sizeof(*ad), GFP_KERNEL | __GFP_ZERO, q->node);

  	if (!ad)

  		return NULL;

  
  	ad->q = q; /* Identify what queue the data belongs to */

  	/* 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);

  	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;

  
  	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 ad;

  }
  
  /*
   * sysfs parts below
   */

  
  static ssize_t
  as_var_show(unsigned int var, char *page)
  {

  	return sprintf(page, "%d
  ", 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 est_time_show(elevator_t *e, char *page)

  {

  	struct as_data *ad = e->elevator_data;

  	int pos = 0;

  	pos += sprintf(page+pos, "%lu %% exit probability
  ",
  				100*ad->exit_prob/256);
  	pos += sprintf(page+pos, "%lu %% probability of exiting without a "
  				"cooperating process submitting IO
  ",
  				100*ad->exit_no_coop/256);

  	pos += sprintf(page+pos, "%lu ms new thinktime
  ", ad->new_ttime_mean);

  	pos += sprintf(page+pos, "%llu sectors new seek distance
  ",
  				(unsigned long long)ad->new_seek_mean);

  
  	return pos;
  }
  
  #define SHOW_FUNCTION(__FUNC, __VAR)				\

  static ssize_t __FUNC(elevator_t *e, char *page)		\

  {								\

  	struct as_data *ad = e->elevator_data;			\

  	return as_var_show(jiffies_to_msecs((__VAR)), (page));	\
  }

  SHOW_FUNCTION(as_read_expire_show, ad->fifo_expire[REQ_SYNC]);
  SHOW_FUNCTION(as_write_expire_show, ad->fifo_expire[REQ_ASYNC]);
  SHOW_FUNCTION(as_antic_expire_show, ad->antic_expire);
  SHOW_FUNCTION(as_read_batch_expire_show, ad->batch_expire[REQ_SYNC]);
  SHOW_FUNCTION(as_write_batch_expire_show, ad->batch_expire[REQ_ASYNC]);

  #undef SHOW_FUNCTION
  
  #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX)				\

  static ssize_t __FUNC(elevator_t *e, const char *page, size_t count)	\

  {									\

  	struct as_data *ad = e->elevator_data;				\
  	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_read_expire_store, &ad->fifo_expire[REQ_SYNC], 0, INT_MAX);
  STORE_FUNCTION(as_write_expire_store, &ad->fifo_expire[REQ_ASYNC], 0, INT_MAX);
  STORE_FUNCTION(as_antic_expire_store, &ad->antic_expire, 0, INT_MAX);
  STORE_FUNCTION(as_read_batch_expire_store,

  			&ad->batch_expire[REQ_SYNC], 0, INT_MAX);

  STORE_FUNCTION(as_write_batch_expire_store,

  			&ad->batch_expire[REQ_ASYNC], 0, INT_MAX);
  #undef STORE_FUNCTION

  #define AS_ATTR(name) \
  	__ATTR(name, S_IRUGO|S_IWUSR, as_##name##_show, as_##name##_store)
  
  static struct elv_fs_entry as_attrs[] = {
  	__ATTR_RO(est_time),
  	AS_ATTR(read_expire),
  	AS_ATTR(write_expire),
  	AS_ATTR(antic_expire),
  	AS_ATTR(read_batch_expire),
  	AS_ATTR(write_batch_expire),
  	__ATTR_NULL

  };

  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 =	elv_rb_former_request,
  		.elevator_latter_req_fn =	elv_rb_latter_request,

  		.elevator_may_queue_fn =	as_may_queue,
  		.elevator_init_fn =		as_init_queue,
  		.elevator_exit_fn =		as_exit_queue,

  		.trim =				as_trim,

  	},

  	.elevator_attrs = as_attrs,

  	.elevator_name = "anticipatory",
  	.elevator_owner = THIS_MODULE,
  };
  
  static int __init as_init(void)
  {

  	return elv_register(&iosched_as);

  }
  
  static void __exit as_exit(void)
  {

  	DECLARE_COMPLETION_ONSTACK(all_gone);

  	elv_unregister(&iosched_as);

  	ioc_gone = &all_gone;

  	/* ioc_gone's update must be visible before reading ioc_count */
  	smp_wmb();

  	if (elv_ioc_count_read(ioc_count))

  		wait_for_completion(ioc_gone);

  	synchronize_rcu();

  }
  
  module_init(as_init);
  module_exit(as_exit);
  
  MODULE_AUTHOR("Nick Piggin");
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("anticipatory IO scheduler");