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cfq-iosched.c

/*
 *  CFQ, or complete fairness queueing, disk scheduler.
 *
 *  Based on ideas from a previously unfinished io
 *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
 *
 *  Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
 */
#include <linux/module.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/rbtree.h>
#include <linux/ioprio.h>

/*
 * tunables
 */
static const int cfq_quantum = 4;         /* max queue in one round of service */
static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
static const int cfq_back_max = 16 * 1024;      /* maximum backwards seek, in KiB */
static const int cfq_back_penalty = 2;          /* penalty of a backwards seek */

static const int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static const int cfq_slice_async_rq = 2;
static int cfq_slice_idle = HZ / 125;

/*
 * grace period before allowing idle class to get disk access
 */
#define CFQ_IDLE_GRACE        (HZ / 10)

/*
 * below this threshold, we consider thinktime immediate
 */
#define CFQ_MIN_TT            (2)

#define CFQ_SLICE_SCALE       (5)

#define RQ_CIC(rq)            ((struct cfq_io_context*)(rq)->elevator_private)
#define RQ_CFQQ(rq)           ((rq)->elevator_private2)

static struct kmem_cache *cfq_pool;
static struct kmem_cache *cfq_ioc_pool;

static DEFINE_PER_CPU(unsigned long, ioc_count);
static struct completion *ioc_gone;

#define CFQ_PRIO_LISTS        IOPRIO_BE_NR
#define cfq_class_idle(cfqq)  ((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
#define cfq_class_rt(cfqq)    ((cfqq)->ioprio_class == IOPRIO_CLASS_RT)

#define ASYNC                 (0)
#define SYNC                  (1)

#define sample_valid(samples) ((samples) > 80)

/*
 * Most of our rbtree usage is for sorting with min extraction, so
 * if we cache the leftmost node we don't have to walk down the tree
 * to find it. Idea borrowed from Ingo Molnars CFS scheduler. We should
 * move this into the elevator for the rq sorting as well.
 */
struct cfq_rb_root {
      struct rb_root rb;
      struct rb_node *left;
};
#define CFQ_RB_ROOT     (struct cfq_rb_root) { RB_ROOT, NULL, }

/*
 * Per block device queue structure
 */
struct cfq_data {
      struct request_queue *queue;

      /*
       * rr list of queues with requests and the count of them
       */
      struct cfq_rb_root service_tree;
      unsigned int busy_queues;

      int rq_in_driver;
      int sync_flight;
      int hw_tag;

      /*
       * idle window management
       */
      struct timer_list idle_slice_timer;
      struct work_struct unplug_work;

      struct cfq_queue *active_queue;
      struct cfq_io_context *active_cic;

      /*
       * async queue for each priority case
       */
      struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
      struct cfq_queue *async_idle_cfqq;

      struct timer_list idle_class_timer;

      sector_t last_position;
      unsigned long last_end_request;

      /*
       * tunables, see top of file
       */
      unsigned int cfq_quantum;
      unsigned int cfq_fifo_expire[2];
      unsigned int cfq_back_penalty;
      unsigned int cfq_back_max;
      unsigned int cfq_slice[2];
      unsigned int cfq_slice_async_rq;
      unsigned int cfq_slice_idle;

      struct list_head cic_list;
};

/*
 * Per process-grouping structure
 */
struct cfq_queue {
      /* reference count */
      atomic_t ref;
      /* parent cfq_data */
      struct cfq_data *cfqd;
      /* service_tree member */
      struct rb_node rb_node;
      /* service_tree key */
      unsigned long rb_key;
      /* sorted list of pending requests */
      struct rb_root sort_list;
      /* if fifo isn't expired, next request to serve */
      struct request *next_rq;
      /* requests queued in sort_list */
      int queued[2];
      /* currently allocated requests */
      int allocated[2];
      /* pending metadata requests */
      int meta_pending;
      /* fifo list of requests in sort_list */
      struct list_head fifo;

      unsigned long slice_end;
      long slice_resid;

      /* number of requests that are on the dispatch list or inside driver */
      int dispatched;

      /* io prio of this group */
      unsigned short ioprio, org_ioprio;
      unsigned short ioprio_class, org_ioprio_class;

      /* various state flags, see below */
      unsigned int flags;
};

enum cfqq_state_flags {
      CFQ_CFQQ_FLAG_on_rr = 0,      /* on round-robin busy list */
      CFQ_CFQQ_FLAG_wait_request,   /* waiting for a request */
      CFQ_CFQQ_FLAG_must_alloc,     /* must be allowed rq alloc */
      CFQ_CFQQ_FLAG_must_alloc_slice,     /* per-slice must_alloc flag */
      CFQ_CFQQ_FLAG_must_dispatch,  /* must dispatch, even if expired */
      CFQ_CFQQ_FLAG_fifo_expire,    /* FIFO checked in this slice */
      CFQ_CFQQ_FLAG_idle_window,    /* slice idling enabled */
      CFQ_CFQQ_FLAG_prio_changed,   /* task priority has changed */
      CFQ_CFQQ_FLAG_queue_new,      /* queue never been serviced */
      CFQ_CFQQ_FLAG_slice_new,      /* no requests dispatched in slice */
      CFQ_CFQQ_FLAG_sync,           /* synchronous queue */
};

#define CFQ_CFQQ_FNS(name)                                  \
static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq)         \
{                                                     \
      cfqq->flags |= (1 << CFQ_CFQQ_FLAG_##name);                 \
}                                                     \
static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq)  \
{                                                     \
      cfqq->flags &= ~(1 << CFQ_CFQQ_FLAG_##name);                \
}                                                     \
static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)         \
{                                                     \
      return (cfqq->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0;    \
}

CFQ_CFQQ_FNS(on_rr);
CFQ_CFQQ_FNS(wait_request);
CFQ_CFQQ_FNS(must_alloc);
CFQ_CFQQ_FNS(must_alloc_slice);
CFQ_CFQQ_FNS(must_dispatch);
CFQ_CFQQ_FNS(fifo_expire);
CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(queue_new);
CFQ_CFQQ_FNS(slice_new);
CFQ_CFQQ_FNS(sync);
#undef CFQ_CFQQ_FNS

static void cfq_dispatch_insert(struct request_queue *, struct request *);
static struct cfq_queue *cfq_get_queue(struct cfq_data *, int,
                               struct task_struct *, gfp_t);
static struct cfq_io_context *cfq_cic_rb_lookup(struct cfq_data *,
                                    struct io_context *);

static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_context *cic,
                                  int is_sync)
{
      return cic->cfqq[!!is_sync];
}

static inline void cic_set_cfqq(struct cfq_io_context *cic,
                        struct cfq_queue *cfqq, int is_sync)
{
      cic->cfqq[!!is_sync] = cfqq;
}

/*
 * We regard a request as SYNC, if it's either a read or has the SYNC bit
 * set (in which case it could also be direct WRITE).
 */
static inline int cfq_bio_sync(struct bio *bio)
{
      if (bio_data_dir(bio) == READ || bio_sync(bio))
            return 1;

      return 0;
}

/*
 * scheduler run of queue, if there are requests pending and no one in the
 * driver that will restart queueing
 */
static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
{
      if (cfqd->busy_queues)
            kblockd_schedule_work(&cfqd->unplug_work);
}

static int cfq_queue_empty(struct request_queue *q)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;

      return !cfqd->busy_queues;
}

/*
 * Scale schedule slice based on io priority. Use the sync time slice only
 * if a queue is marked sync and has sync io queued. A sync queue with async
 * io only, should not get full sync slice length.
 */
static inline int cfq_prio_slice(struct cfq_data *cfqd, int sync,
                         unsigned short prio)
{
      const int base_slice = cfqd->cfq_slice[sync];

      WARN_ON(prio >= IOPRIO_BE_NR);

      return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - prio));
}

static inline int
cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
      return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);
}

static inline void
cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
      cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;
}

/*
 * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
 * isn't valid until the first request from the dispatch is activated
 * and the slice time set.
 */
static inline int cfq_slice_used(struct cfq_queue *cfqq)
{
      if (cfq_cfqq_slice_new(cfqq))
            return 0;
      if (time_before(jiffies, cfqq->slice_end))
            return 0;

      return 1;
}

/*
 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
 * We choose the request that is closest to the head right now. Distance
 * behind the head is penalized and only allowed to a certain extent.
 */
static struct request *
cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2)
{
      sector_t last, s1, s2, d1 = 0, d2 = 0;
      unsigned long back_max;
#define CFQ_RQ1_WRAP    0x01 /* request 1 wraps */
#define CFQ_RQ2_WRAP    0x02 /* request 2 wraps */
      unsigned wrap = 0; /* bit mask: requests behind the disk head? */

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

      if (rq_is_sync(rq1) && !rq_is_sync(rq2))
            return rq1;
      else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
            return rq2;
      if (rq_is_meta(rq1) && !rq_is_meta(rq2))
            return rq1;
      else if (rq_is_meta(rq2) && !rq_is_meta(rq1))
            return rq2;

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

      last = cfqd->last_position;

      /*
       * by definition, 1KiB is 2 sectors
       */
      back_max = cfqd->cfq_back_max * 2;

      /*
       * 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 + back_max >= last)
            d1 = (last - s1) * cfqd->cfq_back_penalty;
      else
            wrap |= CFQ_RQ1_WRAP;

      if (s2 >= last)
            d2 = s2 - last;
      else if (s2 + back_max >= last)
            d2 = (last - s2) * cfqd->cfq_back_penalty;
      else
            wrap |= CFQ_RQ2_WRAP;

      /* Found required data */

      /*
       * By doing switch() on the bit mask "wrap" we avoid having to
       * check two variables for all permutations: --> faster!
       */
      switch (wrap) {
      case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
            if (d1 < d2)
                  return rq1;
            else if (d2 < d1)
                  return rq2;
            else {
                  if (s1 >= s2)
                        return rq1;
                  else
                        return rq2;
            }

      case CFQ_RQ2_WRAP:
            return rq1;
      case CFQ_RQ1_WRAP:
            return rq2;
      case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both rqs wrapped */
      default:
            /*
             * Since both rqs are wrapped,
             * start with the one that's further behind head
             * (--> only *one* back seek required),
             * since back seek takes more time than forward.
             */
            if (s1 <= s2)
                  return rq1;
            else
                  return rq2;
      }
}

/*
 * The below is leftmost cache rbtree addon
 */
static struct rb_node *cfq_rb_first(struct cfq_rb_root *root)
{
      if (!root->left)
            root->left = rb_first(&root->rb);

      return root->left;
}

static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
{
      if (root->left == n)
            root->left = NULL;

      rb_erase(n, &root->rb);
      RB_CLEAR_NODE(n);
}

/*
 * would be nice to take fifo expire time into account as well
 */
static struct request *
cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
              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 {
            rbnext = rb_first(&cfqq->sort_list);
            if (rbnext && rbnext != &last->rb_node)
                  next = rb_entry_rq(rbnext);
      }

      return cfq_choose_req(cfqd, next, prev);
}

static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
                              struct cfq_queue *cfqq)
{
      /*
       * just an approximation, should be ok.
       */
      return (cfqd->busy_queues - 1) * (cfq_prio_slice(cfqd, 1, 0) -
                   cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));
}

/*
 * The cfqd->service_tree holds all pending cfq_queue's that have
 * requests waiting to be processed. It is sorted in the order that
 * we will service the queues.
 */
static void cfq_service_tree_add(struct cfq_data *cfqd,
                            struct cfq_queue *cfqq, int add_front)
{
      struct rb_node **p = &cfqd->service_tree.rb.rb_node;
      struct rb_node *parent = NULL;
      unsigned long rb_key;
      int left;

      if (!add_front) {
            rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
            rb_key += cfqq->slice_resid;
            cfqq->slice_resid = 0;
      } else
            rb_key = 0;

      if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
            /*
             * same position, nothing more to do
             */
            if (rb_key == cfqq->rb_key)
                  return;

            cfq_rb_erase(&cfqq->rb_node, &cfqd->service_tree);
      }

      left = 1;
      while (*p) {
            struct cfq_queue *__cfqq;
            struct rb_node **n;

            parent = *p;
            __cfqq = rb_entry(parent, struct cfq_queue, rb_node);

            /*
             * sort RT queues first, we always want to give
             * preference to them. IDLE queues goes to the back.
             * after that, sort on the next service time.
             */
            if (cfq_class_rt(cfqq) > cfq_class_rt(__cfqq))
                  n = &(*p)->rb_left;
            else if (cfq_class_rt(cfqq) < cfq_class_rt(__cfqq))
                  n = &(*p)->rb_right;
            else if (cfq_class_idle(cfqq) < cfq_class_idle(__cfqq))
                  n = &(*p)->rb_left;
            else if (cfq_class_idle(cfqq) > cfq_class_idle(__cfqq))
                  n = &(*p)->rb_right;
            else if (rb_key < __cfqq->rb_key)
                  n = &(*p)->rb_left;
            else
                  n = &(*p)->rb_right;

            if (n == &(*p)->rb_right)
                  left = 0;

            p = n;
      }

      if (left)
            cfqd->service_tree.left = &cfqq->rb_node;

      cfqq->rb_key = rb_key;
      rb_link_node(&cfqq->rb_node, parent, p);
      rb_insert_color(&cfqq->rb_node, &cfqd->service_tree.rb);
}

/*
 * Update cfqq's position in the service tree.
 */
static void cfq_resort_rr_list(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
      /*
       * Resorting requires the cfqq to be on the RR list already.
       */
      if (cfq_cfqq_on_rr(cfqq))
            cfq_service_tree_add(cfqd, cfqq, 0);
}

/*
 * add to busy list of queues for service, trying to be fair in ordering
 * the pending list according to last request service
 */
static inline void
cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
      BUG_ON(cfq_cfqq_on_rr(cfqq));
      cfq_mark_cfqq_on_rr(cfqq);
      cfqd->busy_queues++;

      cfq_resort_rr_list(cfqd, cfqq);
}

/*
 * Called when the cfqq no longer has requests pending, remove it from
 * the service tree.
 */
static inline void
cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
      BUG_ON(!cfq_cfqq_on_rr(cfqq));
      cfq_clear_cfqq_on_rr(cfqq);

      if (!RB_EMPTY_NODE(&cfqq->rb_node))
            cfq_rb_erase(&cfqq->rb_node, &cfqd->service_tree);

      BUG_ON(!cfqd->busy_queues);
      cfqd->busy_queues--;
}

/*
 * rb tree support functions
 */
static inline void cfq_del_rq_rb(struct request *rq)
{
      struct cfq_queue *cfqq = RQ_CFQQ(rq);
      struct cfq_data *cfqd = cfqq->cfqd;
      const int sync = rq_is_sync(rq);

      BUG_ON(!cfqq->queued[sync]);
      cfqq->queued[sync]--;

      elv_rb_del(&cfqq->sort_list, rq);

      if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
            cfq_del_cfqq_rr(cfqd, cfqq);
}

static void cfq_add_rq_rb(struct request *rq)
{
      struct cfq_queue *cfqq = RQ_CFQQ(rq);
      struct cfq_data *cfqd = cfqq->cfqd;
      struct request *__alias;

      cfqq->queued[rq_is_sync(rq)]++;

      /*
       * looks a little odd, but the first insert might return an alias.
       * if that happens, put the alias on the dispatch list
       */
      while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL)
            cfq_dispatch_insert(cfqd->queue, __alias);

      if (!cfq_cfqq_on_rr(cfqq))
            cfq_add_cfqq_rr(cfqd, cfqq);

      /*
       * check if this request is a better next-serve candidate
       */
      cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq);
      BUG_ON(!cfqq->next_rq);
}

static inline void
cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)
{
      elv_rb_del(&cfqq->sort_list, rq);
      cfqq->queued[rq_is_sync(rq)]--;
      cfq_add_rq_rb(rq);
}

static struct request *
cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)
{
      struct task_struct *tsk = current;
      struct cfq_io_context *cic;
      struct cfq_queue *cfqq;

      cic = cfq_cic_rb_lookup(cfqd, tsk->io_context);
      if (!cic)
            return NULL;

      cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
      if (cfqq) {
            sector_t sector = bio->bi_sector + bio_sectors(bio);

            return elv_rb_find(&cfqq->sort_list, sector);
      }

      return NULL;
}

static void cfq_activate_request(struct request_queue *q, struct request *rq)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;

      cfqd->rq_in_driver++;

      /*
       * If the depth is larger 1, it really could be queueing. But lets
       * make the mark a little higher - idling could still be good for
       * low queueing, and a low queueing number could also just indicate
       * a SCSI mid layer like behaviour where limit+1 is often seen.
       */
      if (!cfqd->hw_tag && cfqd->rq_in_driver > 4)
            cfqd->hw_tag = 1;

      cfqd->last_position = rq->hard_sector + rq->hard_nr_sectors;
}

static void cfq_deactivate_request(struct request_queue *q, struct request *rq)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;

      WARN_ON(!cfqd->rq_in_driver);
      cfqd->rq_in_driver--;
}

static void cfq_remove_request(struct request *rq)
{
      struct cfq_queue *cfqq = RQ_CFQQ(rq);

      if (cfqq->next_rq == rq)
            cfqq->next_rq = cfq_find_next_rq(cfqq->cfqd, cfqq, rq);

      list_del_init(&rq->queuelist);
      cfq_del_rq_rb(rq);

      if (rq_is_meta(rq)) {
            WARN_ON(!cfqq->meta_pending);
            cfqq->meta_pending--;
      }
}

static int cfq_merge(struct request_queue *q, struct request **req,
                 struct bio *bio)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;
      struct request *__rq;

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

      return ELEVATOR_NO_MERGE;
}

static void cfq_merged_request(struct request_queue *q, struct request *req,
                         int type)
{
      if (type == ELEVATOR_FRONT_MERGE) {
            struct cfq_queue *cfqq = RQ_CFQQ(req);

            cfq_reposition_rq_rb(cfqq, req);
      }
}

static void
cfq_merged_requests(struct request_queue *q, struct request *rq,
                struct request *next)
{
      /*
       * reposition in fifo if next is older than rq
       */
      if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
          time_before(next->start_time, rq->start_time))
            list_move(&rq->queuelist, &next->queuelist);

      cfq_remove_request(next);
}

static int cfq_allow_merge(struct request_queue *q, struct request *rq,
                     struct bio *bio)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;
      struct cfq_io_context *cic;
      struct cfq_queue *cfqq;

      /*
       * Disallow merge of a sync bio into an async request.
       */
      if (cfq_bio_sync(bio) && !rq_is_sync(rq))
            return 0;

      /*
       * Lookup the cfqq that this bio will be queued with. Allow
       * merge only if rq is queued there.
       */
      cic = cfq_cic_rb_lookup(cfqd, current->io_context);
      if (!cic)
            return 0;

      cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
      if (cfqq == RQ_CFQQ(rq))
            return 1;

      return 0;
}

static inline void
__cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
      if (cfqq) {
            /*
             * stop potential idle class queues waiting service
             */
            del_timer(&cfqd->idle_class_timer);

            cfqq->slice_end = 0;
            cfq_clear_cfqq_must_alloc_slice(cfqq);
            cfq_clear_cfqq_fifo_expire(cfqq);
            cfq_mark_cfqq_slice_new(cfqq);
            cfq_clear_cfqq_queue_new(cfqq);
      }

      cfqd->active_queue = cfqq;
}

/*
 * current cfqq expired its slice (or was too idle), select new one
 */
static void
__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                int timed_out)
{
      if (cfq_cfqq_wait_request(cfqq))
            del_timer(&cfqd->idle_slice_timer);

      cfq_clear_cfqq_must_dispatch(cfqq);
      cfq_clear_cfqq_wait_request(cfqq);

      /*
       * store what was left of this slice, if the queue idled/timed out
       */
      if (timed_out && !cfq_cfqq_slice_new(cfqq))
            cfqq->slice_resid = cfqq->slice_end - jiffies;

      cfq_resort_rr_list(cfqd, cfqq);

      if (cfqq == cfqd->active_queue)
            cfqd->active_queue = NULL;

      if (cfqd->active_cic) {
            put_io_context(cfqd->active_cic->ioc);
            cfqd->active_cic = NULL;
      }
}

static inline void cfq_slice_expired(struct cfq_data *cfqd, int timed_out)
{
      struct cfq_queue *cfqq = cfqd->active_queue;

      if (cfqq)
            __cfq_slice_expired(cfqd, cfqq, timed_out);
}

static int start_idle_class_timer(struct cfq_data *cfqd)
{
      unsigned long end = cfqd->last_end_request + CFQ_IDLE_GRACE;
      unsigned long now = jiffies;

      if (time_before(now, end) &&
          time_after_eq(now, cfqd->last_end_request)) {
            mod_timer(&cfqd->idle_class_timer, end);
            return 1;
      }

      return 0;
}

/*
 * Get next queue for service. Unless we have a queue preemption,
 * we'll simply select the first cfqq in the service tree.
 */
static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
{
      struct cfq_queue *cfqq;
      struct rb_node *n;

      if (RB_EMPTY_ROOT(&cfqd->service_tree.rb))
            return NULL;

      n = cfq_rb_first(&cfqd->service_tree);
      cfqq = rb_entry(n, struct cfq_queue, rb_node);

      if (cfq_class_idle(cfqq)) {
            /*
             * if we have idle queues and no rt or be queues had
             * pending requests, either allow immediate service if
             * the grace period has passed or arm the idle grace
             * timer
             */
            if (start_idle_class_timer(cfqd))
                  cfqq = NULL;
      }

      return cfqq;
}

/*
 * Get and set a new active queue for service.
 */
static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
{
      struct cfq_queue *cfqq;

      cfqq = cfq_get_next_queue(cfqd);
      __cfq_set_active_queue(cfqd, cfqq);
      return cfqq;
}

static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
                                struct request *rq)
{
      if (rq->sector >= cfqd->last_position)
            return rq->sector - cfqd->last_position;
      else
            return cfqd->last_position - rq->sector;
}

static inline int cfq_rq_close(struct cfq_data *cfqd, struct request *rq)
{
      struct cfq_io_context *cic = cfqd->active_cic;

      if (!sample_valid(cic->seek_samples))
            return 0;

      return cfq_dist_from_last(cfqd, rq) <= cic->seek_mean;
}

static int cfq_close_cooperator(struct cfq_data *cfq_data,
                        struct cfq_queue *cfqq)
{
      /*
       * We should notice if some of the queues are cooperating, eg
       * working closely on the same area of the disk. In that case,
       * we can group them together and don't waste time idling.
       */
      return 0;
}

#define CIC_SEEKY(cic) ((cic)->seek_mean > (8 * 1024))

static void cfq_arm_slice_timer(struct cfq_data *cfqd)
{
      struct cfq_queue *cfqq = cfqd->active_queue;
      struct cfq_io_context *cic;
      unsigned long sl;

      WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
      WARN_ON(cfq_cfqq_slice_new(cfqq));

      /*
       * idle is disabled, either manually or by past process history
       */
      if (!cfqd->cfq_slice_idle || !cfq_cfqq_idle_window(cfqq))
            return;

      /*
       * task has exited, don't wait
       */
      cic = cfqd->active_cic;
      if (!cic || !cic->ioc->task)
            return;

      /*
       * See if this prio level has a good candidate
       */
      if (cfq_close_cooperator(cfqd, cfqq) &&
          (sample_valid(cic->ttime_samples) && cic->ttime_mean > 2))
            return;

      cfq_mark_cfqq_must_dispatch(cfqq);
      cfq_mark_cfqq_wait_request(cfqq);

      /*
       * we don't want to idle for seeks, but we do want to allow
       * fair distribution of slice time for a process doing back-to-back
       * seeks. so allow a little bit of time for him to submit a new rq
       */
      sl = cfqd->cfq_slice_idle;
      if (sample_valid(cic->seek_samples) && CIC_SEEKY(cic))
            sl = min(sl, msecs_to_jiffies(CFQ_MIN_TT));

      mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
}

/*
 * Move request from internal lists to the request queue dispatch list.
 */
static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;
      struct cfq_queue *cfqq = RQ_CFQQ(rq);

      cfq_remove_request(rq);
      cfqq->dispatched++;
      elv_dispatch_sort(q, rq);

      if (cfq_cfqq_sync(cfqq))
            cfqd->sync_flight++;
}

/*
 * return expired entry, or NULL to just start from scratch in rbtree
 */
static inline struct request *cfq_check_fifo(struct cfq_queue *cfqq)
{
      struct cfq_data *cfqd = cfqq->cfqd;
      struct request *rq;
      int fifo;

      if (cfq_cfqq_fifo_expire(cfqq))
            return NULL;

      cfq_mark_cfqq_fifo_expire(cfqq);

      if (list_empty(&cfqq->fifo))
            return NULL;

      fifo = cfq_cfqq_sync(cfqq);
      rq = rq_entry_fifo(cfqq->fifo.next);

      if (time_before(jiffies, rq->start_time + cfqd->cfq_fifo_expire[fifo]))
            return NULL;

      return rq;
}

static inline int
cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
      const int base_rq = cfqd->cfq_slice_async_rq;

      WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);

      return 2 * (base_rq + base_rq * (CFQ_PRIO_LISTS - 1 - cfqq->ioprio));
}

/*
 * Select a queue for service. If we have a current active queue,
 * check whether to continue servicing it, or retrieve and set a new one.
 */
static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
{
      struct cfq_queue *cfqq;

      cfqq = cfqd->active_queue;
      if (!cfqq)
            goto new_queue;

      /*
       * The active queue has run out of time, expire it and select new.
       */
      if (cfq_slice_used(cfqq))
            goto expire;

      /*
       * The active queue has requests and isn't expired, allow it to
       * dispatch.
       */
      if (!RB_EMPTY_ROOT(&cfqq->sort_list))
            goto keep_queue;

      /*
       * No requests pending. If the active queue still has requests in
       * flight or is idling for a new request, allow either of these
       * conditions to happen (or time out) before selecting a new queue.
       */
      if (timer_pending(&cfqd->idle_slice_timer) ||
          (cfqq->dispatched && cfq_cfqq_idle_window(cfqq))) {
            cfqq = NULL;
            goto keep_queue;
      }

expire:
      cfq_slice_expired(cfqd, 0);
new_queue:
      cfqq = cfq_set_active_queue(cfqd);
keep_queue:
      return cfqq;
}

/*
 * Dispatch some requests from cfqq, moving them to the request queue
 * dispatch list.
 */
static int
__cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                  int max_dispatch)
{
      int dispatched = 0;

      BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));

      do {
            struct request *rq;

            /*
             * follow expired path, else get first next available
             */
            if ((rq = cfq_check_fifo(cfqq)) == NULL)
                  rq = cfqq->next_rq;

            /*
             * finally, insert request into driver dispatch list
             */
            cfq_dispatch_insert(cfqd->queue, rq);

            dispatched++;

            if (!cfqd->active_cic) {
                  atomic_inc(&RQ_CIC(rq)->ioc->refcount);
                  cfqd->active_cic = RQ_CIC(rq);
            }

            if (RB_EMPTY_ROOT(&cfqq->sort_list))
                  break;

      } while (dispatched < max_dispatch);

      /*
       * expire an async queue immediately if it has used up its slice. idle
       * queue always expire after 1 dispatch round.
       */
      if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
          dispatched >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
          cfq_class_idle(cfqq))) {
            cfqq->slice_end = jiffies + 1;
            cfq_slice_expired(cfqd, 0);
      }

      return dispatched;
}

static inline int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)
{
      int dispatched = 0;

      while (cfqq->next_rq) {
            cfq_dispatch_insert(cfqq->cfqd->queue, cfqq->next_rq);
            dispatched++;
      }

      BUG_ON(!list_empty(&cfqq->fifo));
      return dispatched;
}

/*
 * Drain our current requests. Used for barriers and when switching
 * io schedulers on-the-fly.
 */
static int cfq_forced_dispatch(struct cfq_data *cfqd)
{
      int dispatched = 0;
      struct rb_node *n;

      while ((n = cfq_rb_first(&cfqd->service_tree)) != NULL) {
            struct cfq_queue *cfqq = rb_entry(n, struct cfq_queue, rb_node);

            dispatched += __cfq_forced_dispatch_cfqq(cfqq);
      }

      cfq_slice_expired(cfqd, 0);

      BUG_ON(cfqd->busy_queues);

      return dispatched;
}

static int cfq_dispatch_requests(struct request_queue *q, int force)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;
      struct cfq_queue *cfqq;
      int dispatched;

      if (!cfqd->busy_queues)
            return 0;

      if (unlikely(force))
            return cfq_forced_dispatch(cfqd);

      dispatched = 0;
      while ((cfqq = cfq_select_queue(cfqd)) != NULL) {
            int max_dispatch;

            max_dispatch = cfqd->cfq_quantum;
            if (cfq_class_idle(cfqq))
                  max_dispatch = 1;

            if (cfqq->dispatched >= max_dispatch) {
                  if (cfqd->busy_queues > 1)
                        break;
                  if (cfqq->dispatched >= 4 * max_dispatch)
                        break;
            }

            if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq))
                  break;

            cfq_clear_cfqq_must_dispatch(cfqq);
            cfq_clear_cfqq_wait_request(cfqq);
            del_timer(&cfqd->idle_slice_timer);

            dispatched += __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
      }

      return dispatched;
}

/*
 * task holds one reference to the queue, dropped when task exits. each rq
 * in-flight on this queue also holds a reference, dropped when rq is freed.
 *
 * queue lock must be held here.
 */
static void cfq_put_queue(struct cfq_queue *cfqq)
{
      struct cfq_data *cfqd = cfqq->cfqd;

      BUG_ON(atomic_read(&cfqq->ref) <= 0);

      if (!atomic_dec_and_test(&cfqq->ref))
            return;

      BUG_ON(rb_first(&cfqq->sort_list));
      BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
      BUG_ON(cfq_cfqq_on_rr(cfqq));

      if (unlikely(cfqd->active_queue == cfqq)) {
            __cfq_slice_expired(cfqd, cfqq, 0);
            cfq_schedule_dispatch(cfqd);
      }

      kmem_cache_free(cfq_pool, cfqq);
}

static void cfq_free_io_context(struct io_context *ioc)
{
      struct cfq_io_context *__cic;
      struct rb_node *n;
      int freed = 0;

      ioc->ioc_data = NULL;

      while ((n = rb_first(&ioc->cic_root)) != NULL) {
            __cic = rb_entry(n, struct cfq_io_context, rb_node);
            rb_erase(&__cic->rb_node, &ioc->cic_root);
            kmem_cache_free(cfq_ioc_pool, __cic);
            freed++;
      }

      elv_ioc_count_mod(ioc_count, -freed);

      if (ioc_gone && !elv_ioc_count_read(ioc_count))
            complete(ioc_gone);
}

static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
      if (unlikely(cfqq == cfqd->active_queue)) {
            __cfq_slice_expired(cfqd, cfqq, 0);
            cfq_schedule_dispatch(cfqd);
      }

      cfq_put_queue(cfqq);
}

static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
                               struct cfq_io_context *cic)
{
      list_del_init(&cic->queue_list);
      smp_wmb();
      cic->key = NULL;

      if (cic->cfqq[ASYNC]) {
            cfq_exit_cfqq(cfqd, cic->cfqq[ASYNC]);
            cic->cfqq[ASYNC] = NULL;
      }

      if (cic->cfqq[SYNC]) {
            cfq_exit_cfqq(cfqd, cic->cfqq[SYNC]);
            cic->cfqq[SYNC] = NULL;
      }
}

static void cfq_exit_single_io_context(struct cfq_io_context *cic)
{
      struct cfq_data *cfqd = cic->key;

      if (cfqd) {
            struct request_queue *q = cfqd->queue;

            spin_lock_irq(q->queue_lock);
            __cfq_exit_single_io_context(cfqd, cic);
            spin_unlock_irq(q->queue_lock);
      }
}

/*
 * The process that ioc belongs to has exited, we need to clean up
 * and put the internal structures we have that belongs to that process.
 */
static void cfq_exit_io_context(struct io_context *ioc)
{
      struct cfq_io_context *__cic;
      struct rb_node *n;

      ioc->ioc_data = NULL;

      /*
       * put the reference this task is holding to the various queues
       */
      n = rb_first(&ioc->cic_root);
      while (n != NULL) {
            __cic = rb_entry(n, struct cfq_io_context, rb_node);

            cfq_exit_single_io_context(__cic);
            n = rb_next(n);
      }
}

static struct cfq_io_context *
cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
{
      struct cfq_io_context *cic;

      cic = kmem_cache_alloc_node(cfq_ioc_pool, gfp_mask | __GFP_ZERO,
                                          cfqd->queue->node);
      if (cic) {
            cic->last_end_request = jiffies;
            INIT_LIST_HEAD(&cic->queue_list);
            cic->dtor = cfq_free_io_context;
            cic->exit = cfq_exit_io_context;
            elv_ioc_count_inc(ioc_count);
      }

      return cic;
}

static void cfq_init_prio_data(struct cfq_queue *cfqq)
{
      struct task_struct *tsk = current;
      int ioprio_class;

      if (!cfq_cfqq_prio_changed(cfqq))
            return;

      ioprio_class = IOPRIO_PRIO_CLASS(tsk->ioprio);
      switch (ioprio_class) {
            default:
                  printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
            case IOPRIO_CLASS_NONE:
                  /*
                   * no prio set, place us in the middle of the BE classes
                   */
                  cfqq->ioprio = task_nice_ioprio(tsk);
                  cfqq->ioprio_class = IOPRIO_CLASS_BE;
                  break;
            case IOPRIO_CLASS_RT:
                  cfqq->ioprio = task_ioprio(tsk);
                  cfqq->ioprio_class = IOPRIO_CLASS_RT;
                  break;
            case IOPRIO_CLASS_BE:
                  cfqq->ioprio = task_ioprio(tsk);
                  cfqq->ioprio_class = IOPRIO_CLASS_BE;
                  break;
            case IOPRIO_CLASS_IDLE:
                  cfqq->ioprio_class = IOPRIO_CLASS_IDLE;
                  cfqq->ioprio = 7;
                  cfq_clear_cfqq_idle_window(cfqq);
                  break;
      }

      /*
       * keep track of original prio settings in case we have to temporarily
       * elevate the priority of this queue
       */
      cfqq->org_ioprio = cfqq->ioprio;
      cfqq->org_ioprio_class = cfqq->ioprio_class;
      cfq_clear_cfqq_prio_changed(cfqq);
}

static inline void changed_ioprio(struct cfq_io_context *cic)
{
      struct cfq_data *cfqd = cic->key;
      struct cfq_queue *cfqq;
      unsigned long flags;

      if (unlikely(!cfqd))
            return;

      spin_lock_irqsave(cfqd->queue->queue_lock, flags);

      cfqq = cic->cfqq[ASYNC];
      if (cfqq) {
            struct cfq_queue *new_cfqq;
            new_cfqq = cfq_get_queue(cfqd, ASYNC, cic->ioc->task,
                               GFP_ATOMIC);
            if (new_cfqq) {
                  cic->cfqq[ASYNC] = new_cfqq;
                  cfq_put_queue(cfqq);
            }
      }

      cfqq = cic->cfqq[SYNC];
      if (cfqq)
            cfq_mark_cfqq_prio_changed(cfqq);

      spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

static void cfq_ioc_set_ioprio(struct io_context *ioc)
{
      struct cfq_io_context *cic;
      struct rb_node *n;

      ioc->ioprio_changed = 0;

      n = rb_first(&ioc->cic_root);
      while (n != NULL) {
            cic = rb_entry(n, struct cfq_io_context, rb_node);

            changed_ioprio(cic);
            n = rb_next(n);
      }
}

static struct cfq_queue *
cfq_find_alloc_queue(struct cfq_data *cfqd, int is_sync,
                 struct task_struct *tsk, gfp_t gfp_mask)
{
      struct cfq_queue *cfqq, *new_cfqq = NULL;
      struct cfq_io_context *cic;

retry:
      cic = cfq_cic_rb_lookup(cfqd, tsk->io_context);
      /* cic always exists here */
      cfqq = cic_to_cfqq(cic, is_sync);

      if (!cfqq) {
            if (new_cfqq) {
                  cfqq = new_cfqq;
                  new_cfqq = NULL;
            } else if (gfp_mask & __GFP_WAIT) {
                  /*
                   * Inform the allocator of the fact that we will
                   * just repeat this allocation if it fails, to allow
                   * the allocator to do whatever it needs to attempt to
                   * free memory.
                   */
                  spin_unlock_irq(cfqd->queue->queue_lock);
                  new_cfqq = kmem_cache_alloc_node(cfq_pool,
                              gfp_mask | __GFP_NOFAIL | __GFP_ZERO,
                              cfqd->queue->node);
                  spin_lock_irq(cfqd->queue->queue_lock);
                  goto retry;
            } else {
                  cfqq = kmem_cache_alloc_node(cfq_pool,
                              gfp_mask | __GFP_ZERO,
                              cfqd->queue->node);
                  if (!cfqq)
                        goto out;
            }

            RB_CLEAR_NODE(&cfqq->rb_node);
            INIT_LIST_HEAD(&cfqq->fifo);

            atomic_set(&cfqq->ref, 0);
            cfqq->cfqd = cfqd;

            if (is_sync) {
                  cfq_mark_cfqq_idle_window(cfqq);
                  cfq_mark_cfqq_sync(cfqq);
            }

            cfq_mark_cfqq_prio_changed(cfqq);
            cfq_mark_cfqq_queue_new(cfqq);

            cfq_init_prio_data(cfqq);
      }

      if (new_cfqq)
            kmem_cache_free(cfq_pool, new_cfqq);

out:
      WARN_ON((gfp_mask & __GFP_WAIT) && !cfqq);
      return cfqq;
}

static struct cfq_queue **
cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
{
      switch(ioprio_class) {
      case IOPRIO_CLASS_RT:
            return &cfqd->async_cfqq[0][ioprio];
      case IOPRIO_CLASS_BE:
            return &cfqd->async_cfqq[1][ioprio];
      case IOPRIO_CLASS_IDLE:
            return &cfqd->async_idle_cfqq;
      default:
            BUG();
      }
}

static struct cfq_queue *
cfq_get_queue(struct cfq_data *cfqd, int is_sync, struct task_struct *tsk,
            gfp_t gfp_mask)
{
      const int ioprio = task_ioprio(tsk);
      const int ioprio_class = task_ioprio_class(tsk);
      struct cfq_queue **async_cfqq = NULL;
      struct cfq_queue *cfqq = NULL;

      if (!is_sync) {
            async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
            cfqq = *async_cfqq;
      }

      if (!cfqq) {
            cfqq = cfq_find_alloc_queue(cfqd, is_sync, tsk, gfp_mask);
            if (!cfqq)
                  return NULL;
      }

      /*
       * pin the queue now that it's allocated, scheduler exit will prune it
       */
      if (!is_sync && !(*async_cfqq)) {
            atomic_inc(&cfqq->ref);
            *async_cfqq = cfqq;
      }

      atomic_inc(&cfqq->ref);
      return cfqq;
}

/*
 * We drop cfq io contexts lazily, so we may find a dead one.
 */
static void
cfq_drop_dead_cic(struct io_context *ioc, struct cfq_io_context *cic)
{
      WARN_ON(!list_empty(&cic->queue_list));

      if (ioc->ioc_data == cic)
            ioc->ioc_data = NULL;

      rb_erase(&cic->rb_node, &ioc->cic_root);
      kmem_cache_free(cfq_ioc_pool, cic);
      elv_ioc_count_dec(ioc_count);
}

static struct cfq_io_context *
cfq_cic_rb_lookup(struct cfq_data *cfqd, struct io_context *ioc)
{
      struct rb_node *n;
      struct cfq_io_context *cic;
      void *k, *key = cfqd;

      if (unlikely(!ioc))
            return NULL;

      /*
       * we maintain a last-hit cache, to avoid browsing over the tree
       */
      cic = ioc->ioc_data;
      if (cic && cic->key == cfqd)
            return cic;

restart:
      n = ioc->cic_root.rb_node;
      while (n) {
            cic = rb_entry(n, struct cfq_io_context, rb_node);
            /* ->key must be copied to avoid race with cfq_exit_queue() */
            k = cic->key;
            if (unlikely(!k)) {
                  cfq_drop_dead_cic(ioc, cic);
                  goto restart;
            }

            if (key < k)
                  n = n->rb_left;
            else if (key > k)
                  n = n->rb_right;
            else {
                  ioc->ioc_data = cic;
                  return cic;
            }
      }

      return NULL;
}

static inline void
cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
           struct cfq_io_context *cic)
{
      struct rb_node **p;
      struct rb_node *parent;
      struct cfq_io_context *__cic;
      unsigned long flags;
      void *k;

      cic->ioc = ioc;
      cic->key = cfqd;

restart:
      parent = NULL;
      p = &ioc->cic_root.rb_node;
      while (*p) {
            parent = *p;
            __cic = rb_entry(parent, struct cfq_io_context, rb_node);
            /* ->key must be copied to avoid race with cfq_exit_queue() */
            k = __cic->key;
            if (unlikely(!k)) {
                  cfq_drop_dead_cic(ioc, __cic);
                  goto restart;
            }

            if (cic->key < k)
                  p = &(*p)->rb_left;
            else if (cic->key > k)
                  p = &(*p)->rb_right;
            else
                  BUG();
      }

      rb_link_node(&cic->rb_node, parent, p);
      rb_insert_color(&cic->rb_node, &ioc->cic_root);

      spin_lock_irqsave(cfqd->queue->queue_lock, flags);
      list_add(&cic->queue_list, &cfqd->cic_list);
      spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

/*
 * Setup general io context and cfq io context. There can be several cfq
 * io contexts per general io context, if this process is doing io to more
 * than one device managed by cfq.
 */
static struct cfq_io_context *
cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
{
      struct io_context *ioc = NULL;
      struct cfq_io_context *cic;

      might_sleep_if(gfp_mask & __GFP_WAIT);

      ioc = get_io_context(gfp_mask, cfqd->queue->node);
      if (!ioc)
            return NULL;

      cic = cfq_cic_rb_lookup(cfqd, ioc);
      if (cic)
            goto out;

      cic = cfq_alloc_io_context(cfqd, gfp_mask);
      if (cic == NULL)
            goto err;

      cfq_cic_link(cfqd, ioc, cic);
out:
      smp_read_barrier_depends();
      if (unlikely(ioc->ioprio_changed))
            cfq_ioc_set_ioprio(ioc);

      return cic;
err:
      put_io_context(ioc);
      return NULL;
}

static void
cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic)
{
      unsigned long elapsed = jiffies - cic->last_end_request;
      unsigned long ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);

      cic->ttime_samples = (7*cic->ttime_samples + 256) / 8;
      cic->ttime_total = (7*cic->ttime_total + 256*ttime) / 8;
      cic->ttime_mean = (cic->ttime_total + 128) / cic->ttime_samples;
}

static void
cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_io_context *cic,
                   struct request *rq)
{
      sector_t sdist;
      u64 total;

      if (cic->last_request_pos < rq->sector)
            sdist = rq->sector - cic->last_request_pos;
      else
            sdist = cic->last_request_pos - rq->sector;

      /*
       * Don't allow the seek distance to get too large from the
       * odd fragment, pagein, etc
       */
      if (cic->seek_samples <= 60) /* second&third seek */
            sdist = min(sdist, (cic->seek_mean * 4) + 2*1024*1024);
      else
            sdist = min(sdist, (cic->seek_mean * 4)   + 2*1024*64);

      cic->seek_samples = (7*cic->seek_samples + 256) / 8;
      cic->seek_total = (7*cic->seek_total + (u64)256*sdist) / 8;
      total = cic->seek_total + (cic->seek_samples/2);
      do_div(total, cic->seek_samples);
      cic->seek_mean = (sector_t)total;
}

/*
 * Disable idle window if the process thinks too long or seeks so much that
 * it doesn't matter
 */
static void
cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                   struct cfq_io_context *cic)
{
      int enable_idle;

      if (!cfq_cfqq_sync(cfqq))
            return;

      enable_idle = cfq_cfqq_idle_window(cfqq);

      if (!cic->ioc->task || !cfqd->cfq_slice_idle ||
          (cfqd->hw_tag && CIC_SEEKY(cic)))
            enable_idle = 0;
      else if (sample_valid(cic->ttime_samples)) {
            if (cic->ttime_mean > cfqd->cfq_slice_idle)
                  enable_idle = 0;
            else
                  enable_idle = 1;
      }

      if (enable_idle)
            cfq_mark_cfqq_idle_window(cfqq);
      else
            cfq_clear_cfqq_idle_window(cfqq);
}

/*
 * Check if new_cfqq should preempt the currently active queue. Return 0 for
 * no or if we aren't sure, a 1 will cause a preempt.
 */
static int
cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
               struct request *rq)
{
      struct cfq_queue *cfqq;

      cfqq = cfqd->active_queue;
      if (!cfqq)
            return 0;

      if (cfq_slice_used(cfqq))
            return 1;

      if (cfq_class_idle(new_cfqq))
            return 0;

      if (cfq_class_idle(cfqq))
            return 1;

      /*
       * if the new request is sync, but the currently running queue is
       * not, let the sync request have priority.
       */
      if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
            return 1;

      /*
       * So both queues are sync. Let the new request get disk time if
       * it's a metadata request and the current queue is doing regular IO.
       */
      if (rq_is_meta(rq) && !cfqq->meta_pending)
            return 1;

      if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
            return 0;

      /*
       * if this request is as-good as one we would expect from the
       * current cfqq, let it preempt
       */
      if (cfq_rq_close(cfqd, rq))
            return 1;

      return 0;
}

/*
 * cfqq preempts the active queue. if we allowed preempt with no slice left,
 * let it have half of its nominal slice.
 */
static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
      cfq_slice_expired(cfqd, 1);

      /*
       * Put the new queue at the front of the of the current list,
       * so we know that it will be selected next.
       */
      BUG_ON(!cfq_cfqq_on_rr(cfqq));

      cfq_service_tree_add(cfqd, cfqq, 1);

      cfqq->slice_end = 0;
      cfq_mark_cfqq_slice_new(cfqq);
}

/*
 * Called when a new fs request (rq) is added (to cfqq). Check if there's
 * something we should do about it
 */
static void
cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
            struct request *rq)
{
      struct cfq_io_context *cic = RQ_CIC(rq);

      if (rq_is_meta(rq))
            cfqq->meta_pending++;

      cfq_update_io_thinktime(cfqd, cic);
      cfq_update_io_seektime(cfqd, cic, rq);
      cfq_update_idle_window(cfqd, cfqq, cic);

      cic->last_request_pos = rq->sector + rq->nr_sectors;

      if (cfqq == cfqd->active_queue) {
            /*
             * if we are waiting for a request for this queue, let it rip
             * immediately and flag that we must not expire this queue
             * just now
             */
            if (cfq_cfqq_wait_request(cfqq)) {
                  cfq_mark_cfqq_must_dispatch(cfqq);
                  del_timer(&cfqd->idle_slice_timer);
                  blk_start_queueing(cfqd->queue);
            }
      } else if (cfq_should_preempt(cfqd, cfqq, rq)) {
            /*
             * not the active queue - expire current slice if it is
             * idle and has expired it's mean thinktime or this new queue
             * has some old slice time left and is of higher priority
             */
            cfq_preempt_queue(cfqd, cfqq);
            cfq_mark_cfqq_must_dispatch(cfqq);
            blk_start_queueing(cfqd->queue);
      }
}

static void cfq_insert_request(struct request_queue *q, struct request *rq)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;
      struct cfq_queue *cfqq = RQ_CFQQ(rq);

      cfq_init_prio_data(cfqq);

      cfq_add_rq_rb(rq);

      list_add_tail(&rq->queuelist, &cfqq->fifo);

      cfq_rq_enqueued(cfqd, cfqq, rq);
}

static void cfq_completed_request(struct request_queue *q, struct request *rq)
{
      struct cfq_queue *cfqq = RQ_CFQQ(rq);
      struct cfq_data *cfqd = cfqq->cfqd;
      const int sync = rq_is_sync(rq);
      unsigned long now;

      now = jiffies;

      WARN_ON(!cfqd->rq_in_driver);
      WARN_ON(!cfqq->dispatched);
      cfqd->rq_in_driver--;
      cfqq->dispatched--;

      if (cfq_cfqq_sync(cfqq))
            cfqd->sync_flight--;

      if (!cfq_class_idle(cfqq))
            cfqd->last_end_request = now;

      if (sync)
            RQ_CIC(rq)->last_end_request = now;

      /*
       * If this is the active queue, check if it needs to be expired,
       * or if we want to idle in case it has no pending requests.
       */
      if (cfqd->active_queue == cfqq) {
            if (cfq_cfqq_slice_new(cfqq)) {
                  cfq_set_prio_slice(cfqd, cfqq);
                  cfq_clear_cfqq_slice_new(cfqq);
            }
            if (cfq_slice_used(cfqq))
                  cfq_slice_expired(cfqd, 1);
            else if (sync && RB_EMPTY_ROOT(&cfqq->sort_list))
                  cfq_arm_slice_timer(cfqd);
      }

      if (!cfqd->rq_in_driver)
            cfq_schedule_dispatch(cfqd);
}

/*
 * we temporarily boost lower priority queues if they are holding fs exclusive
 * resources. they are boosted to normal prio (CLASS_BE/4)
 */
static void cfq_prio_boost(struct cfq_queue *cfqq)
{
      if (has_fs_excl()) {
            /*
             * boost idle prio on transactions that would lock out other
             * users of the filesystem
             */
            if (cfq_class_idle(cfqq))
                  cfqq->ioprio_class = IOPRIO_CLASS_BE;
            if (cfqq->ioprio > IOPRIO_NORM)
                  cfqq->ioprio = IOPRIO_NORM;
      } else {
            /*
             * check if we need to unboost the queue
             */
            if (cfqq->ioprio_class != cfqq->org_ioprio_class)
                  cfqq->ioprio_class = cfqq->org_ioprio_class;
            if (cfqq->ioprio != cfqq->org_ioprio)
                  cfqq->ioprio = cfqq->org_ioprio;
      }
}

static inline int __cfq_may_queue(struct cfq_queue *cfqq)
{
      if ((cfq_cfqq_wait_request(cfqq) || cfq_cfqq_must_alloc(cfqq)) &&
          !cfq_cfqq_must_alloc_slice(cfqq)) {
            cfq_mark_cfqq_must_alloc_slice(cfqq);
            return ELV_MQUEUE_MUST;
      }

      return ELV_MQUEUE_MAY;
}

static int cfq_may_queue(struct request_queue *q, int rw)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;
      struct task_struct *tsk = current;
      struct cfq_io_context *cic;
      struct cfq_queue *cfqq;

      /*
       * don't force setup of a queue from here, as a call to may_queue
       * does not necessarily imply that a request actually will be queued.
       * so just lookup a possibly existing queue, or return 'may queue'
       * if that fails
       */
      cic = cfq_cic_rb_lookup(cfqd, tsk->io_context);
      if (!cic)
            return ELV_MQUEUE_MAY;

      cfqq = cic_to_cfqq(cic, rw & REQ_RW_SYNC);
      if (cfqq) {
            cfq_init_prio_data(cfqq);
            cfq_prio_boost(cfqq);

            return __cfq_may_queue(cfqq);
      }

      return ELV_MQUEUE_MAY;
}

/*
 * queue lock held here
 */
static void cfq_put_request(struct request *rq)
{
      struct cfq_queue *cfqq = RQ_CFQQ(rq);

      if (cfqq) {
            const int rw = rq_data_dir(rq);

            BUG_ON(!cfqq->allocated[rw]);
            cfqq->allocated[rw]--;

            put_io_context(RQ_CIC(rq)->ioc);

            rq->elevator_private = NULL;
            rq->elevator_private2 = NULL;

            cfq_put_queue(cfqq);
      }
}

/*
 * Allocate cfq data structures associated with this request.
 */
static int
cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
{
      struct cfq_data *cfqd = q->elevator->elevator_data;
      struct task_struct *tsk = current;
      struct cfq_io_context *cic;
      const int rw = rq_data_dir(rq);
      const int is_sync = rq_is_sync(rq);
      struct cfq_queue *cfqq;
      unsigned long flags;

      might_sleep_if(gfp_mask & __GFP_WAIT);

      cic = cfq_get_io_context(cfqd, gfp_mask);

      spin_lock_irqsave(q->queue_lock, flags);

      if (!cic)
            goto queue_fail;

      cfqq = cic_to_cfqq(cic, is_sync);
      if (!cfqq) {
            cfqq = cfq_get_queue(cfqd, is_sync, tsk, gfp_mask);

            if (!cfqq)
                  goto queue_fail;

            cic_set_cfqq(cic, cfqq, is_sync);
      }

      cfqq->allocated[rw]++;
      cfq_clear_cfqq_must_alloc(cfqq);
      atomic_inc(&cfqq->ref);

      spin_unlock_irqrestore(q->queue_lock, flags);

      rq->elevator_private = cic;
      rq->elevator_private2 = cfqq;
      return 0;

queue_fail:
      if (cic)
            put_io_context(cic->ioc);

      cfq_schedule_dispatch(cfqd);
      spin_unlock_irqrestore(q->queue_lock, flags);
      return 1;
}

static void cfq_kick_queue(struct work_struct *work)
{
      struct cfq_data *cfqd =
            container_of(work, struct cfq_data, unplug_work);
      struct request_queue *q = cfqd->queue;
      unsigned long flags;

      spin_lock_irqsave(q->queue_lock, flags);
      blk_start_queueing(q);
      spin_unlock_irqrestore(q->queue_lock, flags);
}

/*
 * Timer running if the active_queue is currently idling inside its time slice
 */
static void cfq_idle_slice_timer(unsigned long data)
{
      struct cfq_data *cfqd = (struct cfq_data *) data;
      struct cfq_queue *cfqq;
      unsigned long flags;
      int timed_out = 1;

      spin_lock_irqsave(cfqd->queue->queue_lock, flags);

      if ((cfqq = cfqd->active_queue) != NULL) {
            timed_out = 0;

            /*
             * expired
             */
            if (cfq_slice_used(cfqq))
                  goto expire;

            /*
             * only expire and reinvoke request handler, if there are
             * other queues with pending requests
             */
            if (!cfqd->busy_queues)
                  goto out_cont;

            /*
             * not expired and it has a request pending, let it dispatch
             */
            if (!RB_EMPTY_ROOT(&cfqq->sort_list)) {
                  cfq_mark_cfqq_must_dispatch(cfqq);
                  goto out_kick;
            }
      }
expire:
      cfq_slice_expired(cfqd, timed_out);
out_kick:
      cfq_schedule_dispatch(cfqd);
out_cont:
      spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

/*
 * Timer running if an idle class queue is waiting for service
 */
static void cfq_idle_class_timer(unsigned long data)
{
      struct cfq_data *cfqd = (struct cfq_data *) data;
      unsigned long flags;

      spin_lock_irqsave(cfqd->queue->queue_lock, flags);

      /*
       * race with a non-idle queue, reset timer
       */
      if (!start_idle_class_timer(cfqd))
            cfq_schedule_dispatch(cfqd);

      spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

static void cfq_shutdown_timer_wq(struct cfq_data *cfqd)
{
      del_timer_sync(&cfqd->idle_slice_timer);
      del_timer_sync(&cfqd->idle_class_timer);
      kblockd_flush_work(&cfqd->unplug_work);
}

static void cfq_put_async_queues(struct cfq_data *cfqd)
{
      int i;

      for (i = 0; i < IOPRIO_BE_NR; i++) {
            if (cfqd->async_cfqq[0][i])
                  cfq_put_queue(cfqd->async_cfqq[0][i]);
            if (cfqd->async_cfqq[1][i])
                  cfq_put_queue(cfqd->async_cfqq[1][i]);
      }

      if (cfqd->async_idle_cfqq)
            cfq_put_queue(cfqd->async_idle_cfqq);
}

static void cfq_exit_queue(elevator_t *e)
{
      struct cfq_data *cfqd = e->elevator_data;
      struct request_queue *q = cfqd->queue;

      cfq_shutdown_timer_wq(cfqd);

      spin_lock_irq(q->queue_lock);

      if (cfqd->active_queue)
            __cfq_slice_expired(cfqd, cfqd->active_queue, 0);

      while (!list_empty(&cfqd->cic_list)) {
            struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,
                                          struct cfq_io_context,
                                          queue_list);

            __cfq_exit_single_io_context(cfqd, cic);
      }

      cfq_put_async_queues(cfqd);

      spin_unlock_irq(q->queue_lock);

      cfq_shutdown_timer_wq(cfqd);

      kfree(cfqd);
}

static void *cfq_init_queue(struct request_queue *q)
{
      struct cfq_data *cfqd;

      cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);
      if (!cfqd)
            return NULL;

      cfqd->service_tree = CFQ_RB_ROOT;
      INIT_LIST_HEAD(&cfqd->cic_list);

      cfqd->queue = q;

      init_timer(&cfqd->idle_slice_timer);
      cfqd->idle_slice_timer.function = cfq_idle_slice_timer;
      cfqd->idle_slice_timer.data = (unsigned long) cfqd;

      init_timer(&cfqd->idle_class_timer);
      cfqd->idle_class_timer.function = cfq_idle_class_timer;
      cfqd->idle_class_timer.data = (unsigned long) cfqd;

      INIT_WORK(&cfqd->unplug_work, cfq_kick_queue);

      cfqd->last_end_request = jiffies;
      cfqd->cfq_quantum = cfq_quantum;
      cfqd->cfq_fifo_expire[0] = cfq_fifo_expire[0];
      cfqd->cfq_fifo_expire[1] = cfq_fifo_expire[1];
      cfqd->cfq_back_max = cfq_back_max;
      cfqd->cfq_back_penalty = cfq_back_penalty;
      cfqd->cfq_slice[0] = cfq_slice_async;
      cfqd->cfq_slice[1] = cfq_slice_sync;
      cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
      cfqd->cfq_slice_idle = cfq_slice_idle;

      return cfqd;
}

static void cfq_slab_kill(void)
{
      if (cfq_pool)
            kmem_cache_destroy(cfq_pool);
      if (cfq_ioc_pool)
            kmem_cache_destroy(cfq_ioc_pool);
}

static int __init cfq_slab_setup(void)
{
      cfq_pool = KMEM_CACHE(cfq_queue, 0);
      if (!cfq_pool)
            goto fail;

      cfq_ioc_pool = KMEM_CACHE(cfq_io_context, 0);
      if (!cfq_ioc_pool)
            goto fail;

      return 0;
fail:
      cfq_slab_kill();
      return -ENOMEM;
}

/*
 * sysfs parts below -->
 */
static ssize_t
cfq_var_show(unsigned int var, char *page)
{
      return sprintf(page, "%d\n", var);
}

static ssize_t
cfq_var_store(unsigned int *var, const char *page, size_t count)
{
      char *p = (char *) page;

      *var = simple_strtoul(p, &p, 10);
      return count;
}

#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                      \
static ssize_t __FUNC(elevator_t *e, char *page)                  \
{                                                     \
      struct cfq_data *cfqd = e->elevator_data;             \
      unsigned int __data = __VAR;                          \
      if (__CONV)                                     \
            __data = jiffies_to_msecs(__data);              \
      return cfq_var_show(__data, (page));                        \
}
SHOW_FUNCTION(cfq_quantum_show, cfqd->cfq_quantum, 0);
SHOW_FUNCTION(cfq_fifo_expire_sync_show, cfqd->cfq_fifo_expire[1], 1);
SHOW_FUNCTION(cfq_fifo_expire_async_show, cfqd->cfq_fifo_expire[0], 1);
SHOW_FUNCTION(cfq_back_seek_max_show, cfqd->cfq_back_max, 0);
SHOW_FUNCTION(cfq_back_seek_penalty_show, cfqd->cfq_back_penalty, 0);
SHOW_FUNCTION(cfq_slice_idle_show, cfqd->cfq_slice_idle, 1);
SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
#undef SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
static ssize_t __FUNC(elevator_t *e, const char *page, size_t count)    \
{                                                     \
      struct cfq_data *cfqd = e->elevator_data;             \
      unsigned int __data;                                  \
      int ret = cfq_var_store(&__data, (page), count);            \
      if (__data < (MIN))                                   \
            __data = (MIN);                                 \
      else if (__data > (MAX))                              \
            __data = (MAX);                                 \
      if (__CONV)                                     \
            *(__PTR) = msecs_to_jiffies(__data);                  \
      else                                            \
            *(__PTR) = __data;                              \
      return ret;                                     \
}
STORE_FUNCTION(cfq_quantum_store, &cfqd->cfq_quantum, 1, UINT_MAX, 0);
STORE_FUNCTION(cfq_fifo_expire_sync_store, &cfqd->cfq_fifo_expire[1], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_fifo_expire_async_store, &cfqd->cfq_fifo_expire[0], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_back_seek_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
STORE_FUNCTION(cfq_back_seek_penalty_store, &cfqd->cfq_back_penalty, 1, UINT_MAX, 0);
STORE_FUNCTION(cfq_slice_idle_store, &cfqd->cfq_slice_idle, 0, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1, UINT_MAX, 0);
#undef STORE_FUNCTION

#define CFQ_ATTR(name) \
      __ATTR(name, S_IRUGO|S_IWUSR, cfq_##name##_show, cfq_##name##_store)

static struct elv_fs_entry cfq_attrs[] = {
      CFQ_ATTR(quantum),
      CFQ_ATTR(fifo_expire_sync),
      CFQ_ATTR(fifo_expire_async),
      CFQ_ATTR(back_seek_max),
      CFQ_ATTR(back_seek_penalty),
      CFQ_ATTR(slice_sync),
      CFQ_ATTR(slice_async),
      CFQ_ATTR(slice_async_rq),
      CFQ_ATTR(slice_idle),
      __ATTR_NULL
};

static struct elevator_type iosched_cfq = {
      .ops = {
            .elevator_merge_fn =          cfq_merge,
            .elevator_merged_fn =         cfq_merged_request,
            .elevator_merge_req_fn =      cfq_merged_requests,
            .elevator_allow_merge_fn =    cfq_allow_merge,
            .elevator_dispatch_fn =       cfq_dispatch_requests,
            .elevator_add_req_fn =        cfq_insert_request,
            .elevator_activate_req_fn =   cfq_activate_request,
            .elevator_deactivate_req_fn = cfq_deactivate_request,
            .elevator_queue_empty_fn =    cfq_queue_empty,
            .elevator_completed_req_fn =  cfq_completed_request,
            .elevator_former_req_fn =     elv_rb_former_request,
            .elevator_latter_req_fn =     elv_rb_latter_request,
            .elevator_set_req_fn =        cfq_set_request,
            .elevator_put_req_fn =        cfq_put_request,
            .elevator_may_queue_fn =      cfq_may_queue,
            .elevator_init_fn =           cfq_init_queue,
            .elevator_exit_fn =           cfq_exit_queue,
            .trim =                       cfq_free_io_context,
      },
      .elevator_attrs = cfq_attrs,
      .elevator_name =  "cfq",
      .elevator_owner = THIS_MODULE,
};

static int __init cfq_init(void)
{
      /*
       * could be 0 on HZ < 1000 setups
       */
      if (!cfq_slice_async)
            cfq_slice_async = 1;
      if (!cfq_slice_idle)
            cfq_slice_idle = 1;

      if (cfq_slab_setup())
            return -ENOMEM;

      elv_register(&iosched_cfq);

      return 0;
}

static void __exit cfq_exit(void)
{
      DECLARE_COMPLETION_ONSTACK(all_gone);
      elv_unregister(&iosched_cfq);
      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();
      cfq_slab_kill();
}

module_init(cfq_init);
module_exit(cfq_exit);

MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Completely Fair Queueing IO scheduler");

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