drivers/block/cfq-iosched.c

/*
 *  linux/drivers/block/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@suse.de>
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/config.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/hash.h>
#include <linux/rbtree.h>
#include <linux/mempool.h>
#include <linux/ioprio.h>
#include <linux/writeback.h>

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

static int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static int cfq_slice_async_rq = 2;
static int cfq_slice_idle = HZ / 100;

#define CFQ_IDLE_GRACE		(HZ / 10)
#define CFQ_SLICE_SCALE		(5)

#define CFQ_KEY_ASYNC		(0)
#define CFQ_KEY_ANY		(0xffff)

/*
 * disable queueing at the driver/hardware level
 */
static int cfq_max_depth = 2;

/*
 * for the hash of cfqq inside the cfqd
 */
#define CFQ_QHASH_SHIFT		6
#define CFQ_QHASH_ENTRIES	(1 << CFQ_QHASH_SHIFT)
#define list_entry_qhash(entry)	hlist_entry((entry), struct cfq_queue, cfq_hash)

/*
 * for the hash of crq inside the cfqq
 */
#define CFQ_MHASH_SHIFT		6
#define CFQ_MHASH_BLOCK(sec)	((sec) >> 3)
#define CFQ_MHASH_ENTRIES	(1 << CFQ_MHASH_SHIFT)
#define CFQ_MHASH_FN(sec)	hash_long(CFQ_MHASH_BLOCK(sec), CFQ_MHASH_SHIFT)
#define rq_hash_key(rq)		((rq)->sector + (rq)->nr_sectors)
#define list_entry_hash(ptr)	hlist_entry((ptr), struct cfq_rq, hash)

#define list_entry_cfqq(ptr)	list_entry((ptr), struct cfq_queue, cfq_list)
#define list_entry_fifo(ptr)	list_entry((ptr), struct request, queuelist)

#define RQ_DATA(rq)		(rq)->elevator_private

/*
 * rb-tree defines
 */
#define RB_NONE			(2)
#define RB_EMPTY(node)		((node)->rb_node == NULL)
#define RB_CLEAR_COLOR(node)	(node)->rb_color = RB_NONE
#define RB_CLEAR(node)		do {	\
	(node)->rb_parent = NULL;	\
	RB_CLEAR_COLOR((node));		\
	(node)->rb_right = NULL;	\
	(node)->rb_left = NULL;		\
} while (0)
#define RB_CLEAR_ROOT(root)	((root)->rb_node = NULL)
#define rb_entry_crq(node)	rb_entry((node), struct cfq_rq, rb_node)
#define rq_rb_key(rq)		(rq)->sector

static kmem_cache_t *crq_pool;
static kmem_cache_t *cfq_pool;
static kmem_cache_t *cfq_ioc_pool;

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

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

#define cfq_cfqq_dispatched(cfqq)	\
	((cfqq)->on_dispatch[ASYNC] + (cfqq)->on_dispatch[SYNC])

#define cfq_cfqq_class_sync(cfqq)	((cfqq)->key != CFQ_KEY_ASYNC)

#define cfq_cfqq_sync(cfqq)		\
	(cfq_cfqq_class_sync(cfqq) || (cfqq)->on_dispatch[SYNC])

/*
 * Per block device queue structure
 */
struct cfq_data {
	atomic_t ref;
	request_queue_t *queue;

	/*
	 * rr list of queues with requests and the count of them
	 */
	struct list_head rr_list[CFQ_PRIO_LISTS];
	struct list_head busy_rr;
	struct list_head cur_rr;
	struct list_head idle_rr;
	unsigned int busy_queues;

	/*
	 * non-ordered list of empty cfqq's
	 */
	struct list_head empty_list;

	/*
	 * cfqq lookup hash
	 */
	struct hlist_head *cfq_hash;

	/*
	 * global crq hash for all queues
	 */
	struct hlist_head *crq_hash;

	unsigned int max_queued;

	mempool_t *crq_pool;

	int rq_in_driver;

	/*
	 * schedule slice state info
	 */
	/*
	 * 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;
	int cur_prio, cur_end_prio;
	unsigned int dispatch_slice;

	struct timer_list idle_class_timer;

	sector_t last_sector;
	unsigned long last_end_request;

	unsigned int rq_starved;

	/*
	 * tunables, see top of file
	 */
	unsigned int cfq_quantum;
	unsigned int cfq_queued;
	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;
	unsigned int cfq_max_depth;
};

/*
 * Per process-grouping structure
 */
struct cfq_queue {
	/* reference count */
	atomic_t ref;
	/* parent cfq_data */
	struct cfq_data *cfqd;
	/* cfqq lookup hash */
	struct hlist_node cfq_hash;
	/* hash key */
	unsigned int key;
	/* on either rr or empty list of cfqd */
	struct list_head cfq_list;
	/* sorted list of pending requests */
	struct rb_root sort_list;
	/* if fifo isn't expired, next request to serve */
	struct cfq_rq *next_crq;
	/* requests queued in sort_list */
	int queued[2];
	/* currently allocated requests */
	int allocated[2];
	/* fifo list of requests in sort_list */
	struct list_head fifo;

	unsigned long slice_start;
	unsigned long slice_end;
	unsigned long slice_left;
	unsigned long service_last;

	/* number of requests that are on the dispatch list */
	int on_dispatch[2];

	/* 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;
};

struct cfq_rq {
	struct rb_node rb_node;
	sector_t rb_key;
	struct request *request;
	struct hlist_node hash;

	struct cfq_queue *cfq_queue;
	struct cfq_io_context *io_context;

	unsigned int crq_flags;
};

enum cfqq_state_flags {
	CFQ_CFQQ_FLAG_on_rr = 0,
	CFQ_CFQQ_FLAG_wait_request,
	CFQ_CFQQ_FLAG_must_alloc,
	CFQ_CFQQ_FLAG_must_alloc_slice,
	CFQ_CFQQ_FLAG_must_dispatch,
	CFQ_CFQQ_FLAG_fifo_expire,
	CFQ_CFQQ_FLAG_idle_window,
	CFQ_CFQQ_FLAG_prio_changed,
	CFQ_CFQQ_FLAG_expired,
};

#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(expired);
#undef CFQ_CFQQ_FNS

enum cfq_rq_state_flags {
	CFQ_CRQ_FLAG_is_sync = 0,
};

#define CFQ_CRQ_FNS(name)						\
static inline void cfq_mark_crq_##name(struct cfq_rq *crq)		\
{									\
	crq->crq_flags |= (1 << CFQ_CRQ_FLAG_##name);			\
}									\
static inline void cfq_clear_crq_##name(struct cfq_rq *crq)		\
{									\
	crq->crq_flags &= ~(1 << CFQ_CRQ_FLAG_##name);			\
}									\
static inline int cfq_crq_##name(const struct cfq_rq *crq)		\
{									\
	return (crq->crq_flags & (1 << CFQ_CRQ_FLAG_##name)) != 0;	\
}

CFQ_CRQ_FNS(is_sync);
#undef CFQ_CRQ_FNS

static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned int, unsigned short);
static void cfq_dispatch_insert(request_queue_t *, struct cfq_rq *);
static void cfq_put_cfqd(struct cfq_data *cfqd);

#define process_sync(tsk)	((tsk)->flags & PF_SYNCWRITE)

/*
 * lots of deadline iosched dupes, can be abstracted later...
 */
static inline void cfq_del_crq_hash(struct cfq_rq *crq)
{
	hlist_del_init(&crq->hash);
}

static inline void cfq_add_crq_hash(struct cfq_data *cfqd, struct cfq_rq *crq)
{
	const int hash_idx = CFQ_MHASH_FN(rq_hash_key(crq->request));

	hlist_add_head(&crq->hash, &cfqd->crq_hash[hash_idx]);
}

static struct request *cfq_find_rq_hash(struct cfq_data *cfqd, sector_t offset)
{
	struct hlist_head *hash_list = &cfqd->crq_hash[CFQ_MHASH_FN(offset)];
	struct hlist_node *entry, *next;

	hlist_for_each_safe(entry, next, hash_list) {
		struct cfq_rq *crq = list_entry_hash(entry);
		struct request *__rq = crq->request;

		if (!rq_mergeable(__rq)) {
			cfq_del_crq_hash(crq);
			continue;
		}

		if (rq_hash_key(__rq) == offset)
			return __rq;
	}

	return NULL;
}

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

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

	return !cfqd->busy_queues;
}

/*
 * Lifted from AS - choose which of crq1 and crq2 that is best served now.
 * We choose the request that is closest to the head right now. Distance
 * behind the head are penalized and only allowed to a certain extent.
 */
static struct cfq_rq *
cfq_choose_req(struct cfq_data *cfqd, struct cfq_rq *crq1, struct cfq_rq *crq2)
{
	sector_t last, s1, s2, d1 = 0, d2 = 0;
	int r1_wrap = 0, r2_wrap = 0;	/* requests are behind the disk head */
	unsigned long back_max;

	if (crq1 == NULL || crq1 == crq2)
		return crq2;
	if (crq2 == NULL)
		return crq1;

	if (cfq_crq_is_sync(crq1) && !cfq_crq_is_sync(crq2))
		return crq1;
	else if (cfq_crq_is_sync(crq2) && !cfq_crq_is_sync(crq1))
		return crq2;

	s1 = crq1->request->sector;
	s2 = crq2->request->sector;

	last = cfqd->last_sector;

	/*
	 * 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
		r1_wrap = 1;

	if (s2 >= last)
		d2 = s2 - last;
	else if (s2 + back_max >= last)
		d2 = (last - s2) * cfqd->cfq_back_penalty;
	else
		r2_wrap = 1;

	/* Found required data */
	if (!r1_wrap && r2_wrap)
		return crq1;
	else if (!r2_wrap && r1_wrap)
		return crq2;
	else if (r1_wrap && r2_wrap) {
		/* both behind the head */
		if (s1 <= s2)
			return crq1;
		else
			return crq2;
	}

	/* Both requests in front of the head */
	if (d1 < d2)
		return crq1;
	else if (d2 < d1)
		return crq2;
	else {
		if (s1 >= s2)
			return crq1;
		else
			return crq2;
	}
}

/*
 * would be nice to take fifo expire time into account as well
 */
static struct cfq_rq *
cfq_find_next_crq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
		  struct cfq_rq *last)
{
	struct cfq_rq *crq_next = NULL, *crq_prev = NULL;
	struct rb_node *rbnext, *rbprev;

	if (!(rbnext = rb_next(&last->rb_node))) {
		rbnext = rb_first(&cfqq->sort_list);
		if (rbnext == &last->rb_node)
			rbnext = NULL;
	}

	rbprev = rb_prev(&last->rb_node);

	if (rbprev)
		crq_prev = rb_entry_crq(rbprev);
	if (rbnext)
		crq_next = rb_entry_crq(rbnext);

	return cfq_choose_req(cfqd, crq_next, crq_prev);
}

static void cfq_update_next_crq(struct cfq_rq *crq)
{
	struct cfq_queue *cfqq = crq->cfq_queue;

	if (cfqq->next_crq == crq)
		cfqq->next_crq = cfq_find_next_crq(cfqq->cfqd, cfqq, crq);
}

static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
{
	struct cfq_data *cfqd = cfqq->cfqd;
	struct list_head *list, *entry;

	BUG_ON(!cfq_cfqq_on_rr(cfqq));

	list_del(&cfqq->cfq_list);

	if (cfq_class_rt(cfqq))
		list = &cfqd->cur_rr;
	else if (cfq_class_idle(cfqq))
		list = &cfqd->idle_rr;
	else {
		/*
		 * if cfqq has requests in flight, don't allow it to be
		 * found in cfq_set_active_queue before it has finished them.
		 * this is done to increase fairness between a process that
		 * has lots of io pending vs one that only generates one
		 * sporadically or synchronously
		 */
		if (cfq_cfqq_dispatched(cfqq))
			list = &cfqd->busy_rr;
		else
			list = &cfqd->rr_list[cfqq->ioprio];
	}

	/*
	 * if queue was preempted, just add to front to be fair. busy_rr
	 * isn't sorted.
	 */
	if (preempted || list == &cfqd->busy_rr) {
		list_add(&cfqq->cfq_list, list);
		return;
	}

	/*
	 * sort by when queue was last serviced
	 */
	entry = list;
	while ((entry = entry->prev) != list) {
		struct cfq_queue *__cfqq = list_entry_cfqq(entry);

		if (!__cfqq->service_last)
			break;
		if (time_before(__cfqq->service_last, cfqq->service_last))
			break;
	}

	list_add(&cfqq->cfq_list, entry);
}

/*
 * 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(cfqq, 0);
}

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);
	list_move(&cfqq->cfq_list, &cfqd->empty_list);

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

/*
 * rb tree support functions
 */
static inline void cfq_del_crq_rb(struct cfq_rq *crq)
{
	struct cfq_queue *cfqq = crq->cfq_queue;
	struct cfq_data *cfqd = cfqq->cfqd;
	const int sync = cfq_crq_is_sync(crq);

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

	cfq_update_next_crq(crq);

	rb_erase(&crq->rb_node, &cfqq->sort_list);
	RB_CLEAR_COLOR(&crq->rb_node);

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

static struct cfq_rq *
__cfq_add_crq_rb(struct cfq_rq *crq)
{
	struct rb_node **p = &crq->cfq_queue->sort_list.rb_node;
	struct rb_node *parent = NULL;
	struct cfq_rq *__crq;

	while (*p) {
		parent = *p;
		__crq = rb_entry_crq(parent);

		if (crq->rb_key < __crq->rb_key)
			p = &(*p)->rb_left;
		else if (crq->rb_key > __crq->rb_key)
			p = &(*p)->rb_right;
		else
			return __crq;
	}

	rb_link_node(&crq->rb_node, parent, p);
	return NULL;
}

static void cfq_add_crq_rb(struct cfq_rq *crq)
{
	struct cfq_queue *cfqq = crq->cfq_queue;
	struct cfq_data *cfqd = cfqq->cfqd;
	struct request *rq = crq->request;
	struct cfq_rq *__alias;

	crq->rb_key = rq_rb_key(rq);
	cfqq->queued[cfq_crq_is_sync(crq)]++;

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

	rb_insert_color(&crq->rb_node, &cfqq->sort_list);

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

	/*
	 * check if this request is a better next-serve candidate
	 */
	cfqq->next_crq = cfq_choose_req(cfqd, cfqq->next_crq, crq);
}

static inline void
cfq_reposition_crq_rb(struct cfq_queue *cfqq, struct cfq_rq *crq)
{
	rb_erase(&crq->rb_node, &cfqq->sort_list);
	cfqq->queued[cfq_crq_is_sync(crq)]--;

	cfq_add_crq_rb(crq);
}

static struct request *cfq_find_rq_rb(struct cfq_data *cfqd, sector_t sector)

{
	struct cfq_queue *cfqq = cfq_find_cfq_hash(cfqd, current->pid, CFQ_KEY_ANY);
	struct rb_node *n;

	if (!cfqq)
		goto out;

	n = cfqq->sort_list.rb_node;
	while (n) {
		struct cfq_rq *crq = rb_entry_crq(n);

		if (sector < crq->rb_key)
			n = n->rb_left;
		else if (sector > crq->rb_key)
			n = n->rb_right;
		else
			return crq->request;
	}

out:
	return NULL;
}

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

	cfqd->rq_in_driver++;
}

static void cfq_deactivate_request(request_queue_t *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_rq *crq = RQ_DATA(rq);

	list_del_init(&rq->queuelist);
	cfq_del_crq_rb(crq);
	cfq_del_crq_hash(crq);
}

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

	__rq = cfq_find_rq_hash(cfqd, bio->bi_sector);
	if (__rq && elv_rq_merge_ok(__rq, bio)) {
		ret = ELEVATOR_BACK_MERGE;
		goto out;
	}

	__rq = cfq_find_rq_rb(cfqd, bio->bi_sector + bio_sectors(bio));
	if (__rq && elv_rq_merge_ok(__rq, bio)) {
		ret = ELEVATOR_FRONT_MERGE;
		goto out;
	}

	return ELEVATOR_NO_MERGE;
out:
	*req = __rq;
	return ret;
}

static void cfq_merged_request(request_queue_t *q, struct request *req)
{
	struct cfq_data *cfqd = q->elevator->elevator_data;
	struct cfq_rq *crq = RQ_DATA(req);

	cfq_del_crq_hash(crq);
	cfq_add_crq_hash(cfqd, crq);

	if (rq_rb_key(req) != crq->rb_key) {
		struct cfq_queue *cfqq = crq->cfq_queue;

		cfq_update_next_crq(crq);
		cfq_reposition_crq_rb(cfqq, crq);
	}
}

static void
cfq_merged_requests(request_queue_t *q, struct request *rq,
		    struct request *next)
{
	cfq_merged_request(q, rq);

	/*
	 * 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 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_start = jiffies;
		cfqq->slice_end = 0;
		cfqq->slice_left = 0;
		cfq_clear_cfqq_must_alloc_slice(cfqq);
		cfq_clear_cfqq_fifo_expire(cfqq);
		cfq_clear_cfqq_expired(cfqq);
	}

	cfqd->active_queue = cfqq;
}

/*
 * 0
 * 0,1
 * 0,1,2
 * 0,1,2,3
 * 0,1,2,3,4
 * 0,1,2,3,4,5
 * 0,1,2,3,4,5,6
 * 0,1,2,3,4,5,6,7
 */
static int cfq_get_next_prio_level(struct cfq_data *cfqd)
{
	int prio, wrap;

	prio = -1;
	wrap = 0;
	do {
		int p;

		for (p = cfqd->cur_prio; p <= cfqd->cur_end_prio; p++) {
			if (!list_empty(&cfqd->rr_list[p])) {
				prio = p;
				break;
			}
		}

		if (prio != -1)
			break;
		cfqd->cur_prio = 0;
		if (++cfqd->cur_end_prio == CFQ_PRIO_LISTS) {
			cfqd->cur_end_prio = 0;
			if (wrap)
				break;
			wrap = 1;
		}
	} while (1);

	if (unlikely(prio == -1))
		return -1;

	BUG_ON(prio >= CFQ_PRIO_LISTS);

	list_splice_init(&cfqd->rr_list[prio], &cfqd->cur_rr);

	cfqd->cur_prio = prio + 1;
	if (cfqd->cur_prio > cfqd->cur_end_prio) {
		cfqd->cur_end_prio = cfqd->cur_prio;
		cfqd->cur_prio = 0;
	}
	if (cfqd->cur_end_prio == CFQ_PRIO_LISTS) {
		cfqd->cur_prio = 0;
		cfqd->cur_end_prio = 0;
	}

	return prio;
}

static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
{
	struct cfq_queue *cfqq;

	/*
	 * if current queue is expired but not done with its requests yet,
	 * wait for that to happen
	 */
	if ((cfqq = cfqd->active_queue) != NULL) {
		if (cfq_cfqq_expired(cfqq) && cfq_cfqq_dispatched(cfqq))
			return NULL;
	}

	/*
	 * if current list is non-empty, grab first entry. if it is empty,
	 * get next prio level and grab first entry then if any are spliced
	 */
	if (!list_empty(&cfqd->cur_rr) || cfq_get_next_prio_level(cfqd) != -1)
		cfqq = list_entry_cfqq(cfqd->cur_rr.next);

	/*
	 * 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 (!cfqq && !list_empty(&cfqd->idle_rr)) {
		unsigned long end = cfqd->last_end_request + CFQ_IDLE_GRACE;

		if (time_after_eq(jiffies, end))
			cfqq = list_entry_cfqq(cfqd->idle_rr.next);
		else
			mod_timer(&cfqd->idle_class_timer, end);
	}

	__cfq_set_active_queue(cfqd, cfqq);
	return 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 preempted)
{
	unsigned long now = jiffies;

	if (cfq_cfqq_wait_request(cfqq))
		del_timer(&cfqd->idle_slice_timer);

	if (!preempted && !cfq_cfqq_dispatched(cfqq))
		cfqq->service_last = now;

	cfq_clear_cfqq_must_dispatch(cfqq);
	cfq_clear_cfqq_wait_request(cfqq);

	/*
	 * store what was left of this slice, if the queue idled out
	 * or was preempted
	 */
	if (time_after(now, cfqq->slice_end))
		cfqq->slice_left = now - cfqq->slice_end;
	else
		cfqq->slice_left = 0;

	if (cfq_cfqq_on_rr(cfqq))
		cfq_resort_rr_list(cfqq, preempted);

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

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

	cfqd->dispatch_slice = 0;
}

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

	if (cfqq) {
		/*
		 * use deferred expiry, if there are requests in progress as
		 * not to disturb the slice of the next queue
		 */
		if (cfq_cfqq_dispatched(cfqq))
			cfq_mark_cfqq_expired(cfqq);
		else
			__cfq_slice_expired(cfqd, cfqq, preempted);
	}
}

static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)

{
	WARN_ON(!RB_EMPTY(&cfqq->sort_list));
	WARN_ON(cfqq != cfqd->active_queue);

	/*
	 * idle is disabled, either manually or by past process history
	 */
	if (!cfqd->cfq_slice_idle)
		return 0;
	if (!cfq_cfqq_idle_window(cfqq))
		return 0;
	/*
	 * task has exited, don't wait
	 */
	if (cfqd->active_cic && !cfqd->active_cic->ioc->task)
		return 0;

	cfq_mark_cfqq_must_dispatch(cfqq);
	cfq_mark_cfqq_wait_request(cfqq);

	if (!timer_pending(&cfqd->idle_slice_timer)) {
		unsigned long slice_left = min(cfqq->slice_end - 1, (unsigned long) cfqd->cfq_slice_idle);

		cfqd->idle_slice_timer.expires = jiffies + slice_left;
		add_timer(&cfqd->idle_slice_timer);
	}

	return 1;
}

static void cfq_dispatch_insert(request_queue_t *q, struct cfq_rq *crq)
{
	struct cfq_data *cfqd = q->elevator->elevator_data;
	struct cfq_queue *cfqq = crq->cfq_queue;

	cfqq->next_crq = cfq_find_next_crq(cfqd, cfqq, crq);
	cfq_remove_request(crq->request);
	cfqq->on_dispatch[cfq_crq_is_sync(crq)]++;
	elv_dispatch_sort(q, crq->request);
}

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

	if (cfq_cfqq_fifo_expire(cfqq))
		return NULL;

	if (!list_empty(&cfqq->fifo)) {
		int fifo = cfq_cfqq_class_sync(cfqq);

		crq = RQ_DATA(list_entry_fifo(cfqq->fifo.next));
		rq = crq->request;
		if (time_after(jiffies, rq->start_time + cfqd->cfq_fifo_expire[fifo])) {
			cfq_mark_cfqq_fifo_expire(cfqq);
			return crq;
		}
	}

	return NULL;
}

/*
 * 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_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
	const int base_slice = cfqd->cfq_slice[cfq_cfqq_sync(cfqq)];

	WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);

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

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));
}

/*
 * get next queue for service
 */
static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd, int force)
{
	unsigned long now = jiffies;
	struct cfq_queue *cfqq;

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

	if (cfq_cfqq_expired(cfqq))
		goto new_queue;

	/*
	 * slice has expired
	 */
	if (!cfq_cfqq_must_dispatch(cfqq) && time_after(now, cfqq->slice_end))
		goto expire;

	/*
	 * if queue has requests, dispatch one. if not, check if
	 * enough slice is left to wait for one
	 */
	if (!RB_EMPTY(&cfqq->sort_list))
		goto keep_queue;
	else if (!force && cfq_cfqq_class_sync(cfqq) &&
		 time_before(now, cfqq->slice_end)) {
		if (cfq_arm_slice_timer(cfqd, cfqq))
			return NULL;
	}

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

static int
__cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
			int max_dispatch)
{
	int dispatched = 0;

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

	do {
		struct cfq_rq *crq;

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

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

		cfqd->dispatch_slice++;
		dispatched++;

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

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

	} while (dispatched < max_dispatch);

	/*
	 * if slice end isn't set yet, set it. if at least one request was
	 * sync, use the sync time slice value
	 */
	if (!cfqq->slice_end)
		cfq_set_prio_slice(cfqd, cfqq);

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

	return dispatched;
}

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

	if (!cfqd->busy_queues)
		return 0;

	cfqq = cfq_select_queue(cfqd, force);
	if (cfqq) {
		int max_dispatch;

		/*
		 * if idle window is disabled, allow queue buildup
		 */
		if (!cfq_cfqq_idle_window(cfqq) &&
		    cfqd->rq_in_driver >= cfqd->cfq_max_depth)
			return 0;

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

		if (!force) {
			max_dispatch = cfqd->cfq_quantum;
			if (cfq_class_idle(cfqq))
				max_dispatch = 1;
		} else
			max_dispatch = INT_MAX;

		return __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
	}

	return 0;
}

/*
 * task holds one reference to the queue, dropped when task exits. each crq
 * in-flight on this queue also holds a reference, dropped when crq 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);
	}

	cfq_put_cfqd(cfqq->cfqd);

	/*
	 * it's on the empty list and still hashed
	 */
	list_del(&cfqq->cfq_list);
	hlist_del(&cfqq->cfq_hash);
	kmem_cache_free(cfq_pool, cfqq);
}

static inline struct cfq_queue *
__cfq_find_cfq_hash(struct cfq_data *cfqd, unsigned int key, unsigned int prio,
		    const int hashval)
{
	struct hlist_head *hash_list = &cfqd->cfq_hash[hashval];
	struct hlist_node *entry, *next;

	hlist_for_each_safe(entry, next, hash_list) {
		struct cfq_queue *__cfqq = list_entry_qhash(entry);
		const unsigned short __p = IOPRIO_PRIO_VALUE(__cfqq->ioprio_class, __cfqq->ioprio);

		if (__cfqq->key == key && (__p == prio || prio == CFQ_KEY_ANY))
			return __cfqq;
	}

	return NULL;
}

static struct cfq_queue *
cfq_find_cfq_hash(struct cfq_data *cfqd, unsigned int key, unsigned short prio)
{
	return __cfq_find_cfq_hash(cfqd, key, prio, hash_long(key, CFQ_QHASH_SHIFT));
}

static void cfq_free_io_context(struct cfq_io_context *cic)
{
	struct cfq_io_context *__cic;
	struct list_head *entry, *next;

	list_for_each_safe(entry, next, &cic->list) {
		__cic = list_entry(entry, struct cfq_io_context, list);
		kmem_cache_free(cfq_ioc_pool, __cic);
	}

	kmem_cache_free(cfq_ioc_pool, cic);
}

/*
 * Called with interrupts disabled
 */
static void cfq_exit_single_io_context(struct cfq_io_context *cic)
{
	struct cfq_data *cfqd = cic->cfqq->cfqd;
	request_queue_t *q = cfqd->queue;

	WARN_ON(!irqs_disabled());

	spin_lock(q->queue_lock);

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

	cfq_put_queue(cic->cfqq);
	cic->cfqq = NULL;
	spin_unlock(q->queue_lock);
}

/*
 * Another task may update the task cic list, if it is doing a queue lookup
 * on its behalf. cfq_cic_lock excludes such concurrent updates
 */
static void cfq_exit_io_context(struct cfq_io_context *cic)
{
	struct cfq_io_context *__cic;
	struct list_head *entry;
	unsigned long flags;

	local_irq_save(flags);

	/*
	 * put the reference this task is holding to the various queues
	 */
	list_for_each(entry, &cic->list) {
		__cic = list_entry(entry, struct cfq_io_context, list);
		cfq_exit_single_io_context(__cic);
	}

	cfq_exit_single_io_context(cic);
	local_irq_restore(flags);
}

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

	if (cic) {
		INIT_LIST_HEAD(&cic->list);
		cic->cfqq = NULL;
		cic->key = NULL;
		cic->last_end_request = jiffies;
		cic->ttime_total = 0;
		cic->ttime_samples = 0;
		cic->ttime_mean = 0;
		cic->dtor = cfq_free_io_context;
		cic->exit = cfq_exit_io_context;
	}

	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;

	if (cfq_cfqq_on_rr(cfqq))
		cfq_resort_rr_list(cfqq, 0);

	cfq_clear_cfqq_prio_changed(cfqq);
}

static inline void changed_ioprio(struct cfq_queue *cfqq)
{
	if (cfqq) {
		struct cfq_data *cfqd = cfqq->cfqd;

		spin_lock(cfqd->queue->queue_lock);
		cfq_mark_cfqq_prio_changed(cfqq);
		cfq_init_prio_data(cfqq);
		spin_unlock(cfqd->queue->queue_lock);
	}
}

/*
 * callback from sys_ioprio_set, irqs are disabled
 */
static int cfq_ioc_set_ioprio(struct io_context *ioc, unsigned int ioprio)
{
	struct cfq_io_context *cic = ioc->cic;

	changed_ioprio(cic->cfqq);

	list_for_each_entry(cic, &cic->list, list)
		changed_ioprio(cic->cfqq);

	return 0;
}

static struct cfq_queue *
cfq_get_queue(struct cfq_data *cfqd, unsigned int key, unsigned short ioprio,
	      gfp_t gfp_mask)
{
	const int hashval = hash_long(key, CFQ_QHASH_SHIFT);
	struct cfq_queue *cfqq, *new_cfqq = NULL;

retry:
	cfqq = __cfq_find_cfq_hash(cfqd, key, ioprio, hashval);

	if (!cfqq) {
		if (new_cfqq) {
			cfqq = new_cfqq;
			new_cfqq = NULL;
		} else if (gfp_mask & __GFP_WAIT) {
			spin_unlock_irq(cfqd->queue->queue_lock);
			new_cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
			spin_lock_irq(cfqd->queue->queue_lock);
			goto retry;
		} else {
			cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
			if (!cfqq)
				goto out;
		}

		memset(cfqq, 0, sizeof(*cfqq));

		INIT_HLIST_NODE(&cfqq->cfq_hash);
		INIT_LIST_HEAD(&cfqq->cfq_list);
		RB_CLEAR_ROOT(&cfqq->sort_list);
		INIT_LIST_HEAD(&cfqq->fifo);

		cfqq->key = key;
		hlist_add_head(&cfqq->cfq_hash, &cfqd->cfq_hash[hashval]);
		atomic_set(&cfqq->ref, 0);
		cfqq->cfqd = cfqd;
		atomic_inc(&cfqd->ref);
		cfqq->service_last = 0;
		/*
		 * set ->slice_left to allow preemption for a new process
		 */
		cfqq->slice_left = 2 * cfqd->cfq_slice_idle;
		cfq_mark_cfqq_idle_window(cfqq);
		cfq_mark_cfqq_prio_changed(cfqq);
		cfq_init_prio_data(cfqq);
	}

	if (new_cfqq)
		kmem_cache_free(cfq_pool, new_cfqq);

	atomic_inc(&cfqq->ref);
out:
	WARN_ON((gfp_mask & __GFP_WAIT) && !cfqq);
	return cfqq;
}

/*
 * 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. Note that caller is holding a reference to
 * cfqq, so we don't need to worry about it disappearing
 */
static struct cfq_io_context *
cfq_get_io_context(struct cfq_data *cfqd, pid_t pid, 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);
	if (!ioc)
		return NULL;

	if ((cic = ioc->cic) == NULL) {
		cic = cfq_alloc_io_context(cfqd, gfp_mask);

		if (cic == NULL)
			goto err;

		/*
		 * manually increment generic io_context usage count, it
		 * cannot go away since we are already holding one ref to it
		 */
		ioc->cic = cic;
		ioc->set_ioprio = cfq_ioc_set_ioprio;
		cic->ioc = ioc;
		cic->key = cfqd;
		atomic_inc(&cfqd->ref);
	} else {
		struct cfq_io_context *__cic;

		/*
		 * the first cic on the list is actually the head itself
		 */
		if (cic->key == cfqd)
			goto out;

		/*
		 * cic exists, check if we already are there. linear search
		 * should be ok here, the list will usually not be more than
		 * 1 or a few entries long
		 */
		list_for_each_entry(__cic, &cic->list, list) {
			/*
			 * this process is already holding a reference to
			 * this queue, so no need to get one more
			 */
			if (__cic->key == cfqd) {
				cic = __cic;
				goto out;
			}
		}

		/*
		 * nope, process doesn't have a cic assoicated with this
		 * cfqq yet. get a new one and add to list
		 */
		__cic = cfq_alloc_io_context(cfqd, gfp_mask);
		if (__cic == NULL)
			goto err;

		__cic->ioc = ioc;
		__cic->key = cfqd;
		atomic_inc(&cfqd->ref);
		list_add(&__cic->list, &cic->list);
		cic = __cic;
	}

out:
	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, ttime;

	/*
	 * if this context already has stuff queued, thinktime is from
	 * last queue not last end
	 */
#if 0
	if (time_after(cic->last_end_request, cic->last_queue))
		elapsed = jiffies - cic->last_end_request;
	else
		elapsed = jiffies - cic->last_queue;
#else
		elapsed = jiffies - cic->last_end_request;
#endif

	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;
}

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

/*
 * 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 = cfq_cfqq_idle_window(cfqq);

	if (!cic->ioc->task || !cfqd->cfq_slice_idle)
		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 cfq_rq *crq)
{
	struct cfq_queue *cfqq = cfqd->active_queue;

	if (cfq_class_idle(new_cfqq))
		return 0;

	if (!cfqq)
		return 1;

	if (cfq_class_idle(cfqq))
		return 1;
	if (!cfq_cfqq_wait_request(new_cfqq))
		return 0;
	/*
	 * if it doesn't have slice left, forget it
	 */
	if (new_cfqq->slice_left < cfqd->cfq_slice_idle)
		return 0;
	if (cfq_crq_is_sync(crq) && !cfq_cfqq_sync(cfqq))
		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)
{
	struct cfq_queue *__cfqq, *next;

	list_for_each_entry_safe(__cfqq, next, &cfqd->cur_rr, cfq_list)
		cfq_resort_rr_list(__cfqq, 1);

	if (!cfqq->slice_left)
		cfqq->slice_left = cfq_prio_to_slice(cfqd, cfqq) / 2;

	cfqq->slice_end = cfqq->slice_left + jiffies;
	__cfq_slice_expired(cfqd, cfqq, 1);
	__cfq_set_active_queue(cfqd, cfqq);
}

/*
 * should really be a ll_rw_blk.c helper
 */
static void cfq_start_queueing(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
	request_queue_t *q = cfqd->queue;

	if (!blk_queue_plugged(q))
		q->request_fn(q);
	else
		__generic_unplug_device(q);
}

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

	cfqq->next_crq = cfq_choose_req(cfqd, cfqq->next_crq, crq);

	/*
	 * we never wait for an async request and we don't allow preemption
	 * of an async request. so just return early
	 */
	if (!cfq_crq_is_sync(crq))
		return;

	cic = crq->io_context;

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

	cic->last_queue = jiffies;

	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);
			cfq_start_queueing(cfqd, cfqq);
		}
	} else if (cfq_should_preempt(cfqd, cfqq, crq)) {
		/*
		 * 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);
		cfq_start_queueing(cfqd, cfqq);
	}
}

static void cfq_insert_request(request_queue_t *q, struct request *rq)
{
	struct cfq_data *cfqd = q->elevator->elevator_data;
	struct cfq_rq *crq = RQ_DATA(rq);
	struct cfq_queue *cfqq = crq->cfq_queue;

	cfq_init_prio_data(cfqq);

	cfq_add_crq_rb(crq);

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

	if (rq_mergeable(rq))
		cfq_add_crq_hash(cfqd, crq);

	cfq_crq_enqueued(cfqd, cfqq, crq);
}

static void cfq_completed_request(request_queue_t *q, struct request *rq)
{
	struct cfq_rq *crq = RQ_DATA(rq);
	struct cfq_queue *cfqq = crq->cfq_queue;
	struct cfq_data *cfqd = cfqq->cfqd;
	const int sync = cfq_crq_is_sync(crq);
	unsigned long now;

	now = jiffies;

	WARN_ON(!cfqd->rq_in_driver);
	WARN_ON(!cfqq->on_dispatch[sync]);
	cfqd->rq_in_driver--;
	cfqq->on_dispatch[sync]--;

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

	if (!cfq_cfqq_dispatched(cfqq)) {
		if (cfq_cfqq_on_rr(cfqq)) {
			cfqq->service_last = now;
			cfq_resort_rr_list(cfqq, 0);
		}
		if (cfq_cfqq_expired(cfqq)) {
			__cfq_slice_expired(cfqd, cfqq, 0);
			cfq_schedule_dispatch(cfqd);
		}
	}

	if (cfq_crq_is_sync(crq))
		crq->io_context->last_end_request = now;
}

static struct request *
cfq_former_request(request_queue_t *q, struct request *rq)
{
	struct cfq_rq *crq = RQ_DATA(rq);
	struct rb_node *rbprev = rb_prev(&crq->rb_node);

	if (rbprev)
		return rb_entry_crq(rbprev)->request;

	return NULL;
}

static struct request *
cfq_latter_request(request_queue_t *q, struct request *rq)
{
	struct cfq_rq *crq = RQ_DATA(rq);
	struct rb_node *rbnext = rb_next(&crq->rb_node);

	if (rbnext)
		return rb_entry_crq(rbnext)->request;

	return NULL;
}

/*
 * 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)
{
	const int ioprio_class = cfqq->ioprio_class;
	const int ioprio = cfqq->ioprio;

	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;
	}

	/*
	 * refile between round-robin lists if we moved the priority class
	 */
	if ((ioprio_class != cfqq->ioprio_class || ioprio != cfqq->ioprio) &&
	    cfq_cfqq_on_rr(cfqq))
		cfq_resort_rr_list(cfqq, 0);
}

static inline pid_t cfq_queue_pid(struct task_struct *task, int rw)
{
	if (rw == READ || process_sync(task))
		return task->pid;

	return CFQ_KEY_ASYNC;
}

static inline int
__cfq_may_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq,
		struct task_struct *task, int rw)
{
#if 1
	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;
#else
	if (!cfqq || task->flags & PF_MEMALLOC)
		return ELV_MQUEUE_MAY;
	if (!cfqq->allocated[rw] || cfq_cfqq_must_alloc(cfqq)) {
		if (cfq_cfqq_wait_request(cfqq))
			return ELV_MQUEUE_MUST;

		/*
		 * only allow 1 ELV_MQUEUE_MUST per slice, otherwise we
		 * can quickly flood the queue with writes from a single task
		 */
		if (rw == READ || !cfq_cfqq_must_alloc_slice(cfqq)) {
			cfq_mark_cfqq_must_alloc_slice(cfqq);
			return ELV_MQUEUE_MUST;
		}

		return ELV_MQUEUE_MAY;
	}
	if (cfq_class_idle(cfqq))
		return ELV_MQUEUE_NO;
	if (cfqq->allocated[rw] >= cfqd->max_queued) {
		struct io_context *ioc = get_io_context(GFP_ATOMIC);
		int ret = ELV_MQUEUE_NO;

		if (ioc && ioc->nr_batch_requests)
			ret = ELV_MQUEUE_MAY;

		put_io_context(ioc);
		return ret;
	}

	return ELV_MQUEUE_MAY;
#endif
}

static int cfq_may_queue(request_queue_t *q, int rw, struct bio *bio)
{
	struct cfq_data *cfqd = q->elevator->elevator_data;
	struct task_struct *tsk = current;
	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
	 */
	cfqq = cfq_find_cfq_hash(cfqd, cfq_queue_pid(tsk, rw), tsk->ioprio);
	if (cfqq) {
		cfq_init_prio_data(cfqq);
		cfq_prio_boost(cfqq);

		return __cfq_may_queue(cfqd, cfqq, tsk, rw);
	}

	return ELV_MQUEUE_MAY;
}

static void cfq_check_waiters(request_queue_t *q, struct cfq_queue *cfqq)
{
	struct cfq_data *cfqd = q->elevator->elevator_data;
	struct request_list *rl = &q->rq;

	if (cfqq->allocated[READ] <= cfqd->max_queued || cfqd->rq_starved) {
		smp_mb();
		if (waitqueue_active(&rl->wait[READ]))
			wake_up(&rl->wait[READ]);
	}

	if (cfqq->allocated[WRITE] <= cfqd->max_queued || cfqd->rq_starved) {
		smp_mb();
		if (waitqueue_active(&rl->wait[WRITE]))
			wake_up(&rl->wait[WRITE]);
	}
}

/*
 * queue lock held here
 */
static void cfq_put_request(request_queue_t *q, struct request *rq)
{
	struct cfq_data *cfqd = q->elevator->elevator_data;
	struct cfq_rq *crq = RQ_DATA(rq);

	if (crq) {
		struct cfq_queue *cfqq = crq->cfq_queue;
		const int rw = rq_data_dir(rq);

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

		put_io_context(crq->io_context->ioc);

		mempool_free(crq, cfqd->crq_pool);
		rq->elevator_private = NULL;

		cfq_check_waiters(q, cfqq);
		cfq_put_queue(cfqq);
	}
}

/*
 * Allocate cfq data structures associated with this request.
 */
static int
cfq_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
		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);
	pid_t key = cfq_queue_pid(tsk, rw);
	struct cfq_queue *cfqq;
	struct cfq_rq *crq;
	unsigned long flags;

	might_sleep_if(gfp_mask & __GFP_WAIT);

	cic = cfq_get_io_context(cfqd, key, gfp_mask);

	spin_lock_irqsave(q->queue_lock, flags);

	if (!cic)
		goto queue_fail;

	if (!cic->cfqq) {
		cfqq = cfq_get_queue(cfqd, key, tsk->ioprio, gfp_mask);
		if (!cfqq)
			goto queue_fail;

		cic->cfqq = cfqq;
	} else
		cfqq = cic->cfqq;

	cfqq->allocated[rw]++;
	cfq_clear_cfqq_must_alloc(cfqq);
	cfqd->rq_starved = 0;
	atomic_inc(&cfqq->ref);
	spin_unlock_irqrestore(q->queue_lock, flags);

	crq = mempool_alloc(cfqd->crq_pool, gfp_mask);
	if (crq) {
		RB_CLEAR(&crq->rb_node);
		crq->rb_key = 0;
		crq->request = rq;
		INIT_HLIST_NODE(&crq->hash);
		crq->cfq_queue = cfqq;
		crq->io_context = cic;

		if (rw == READ || process_sync(tsk))
			cfq_mark_crq_is_sync(crq);
		else
			cfq_clear_crq_is_sync(crq);

		rq->elevator_private = crq;
		return 0;
	}

	spin_lock_irqsave(q->queue_lock, flags);
	cfqq->allocated[rw]--;
	if (!(cfqq->allocated[0] + cfqq->allocated[1]))
		cfq_mark_cfqq_must_alloc(cfqq);
	cfq_put_queue(cfqq);
queue_fail:
	if (cic)
		put_io_context(cic->ioc);
	/*
	 * mark us rq allocation starved. we need to kickstart the process
	 * ourselves if there are no pending requests that can do it for us.
	 * that would be an extremely rare OOM situation
	 */
	cfqd->rq_starved = 1;
	cfq_schedule_dispatch(cfqd);
	spin_unlock_irqrestore(q->queue_lock, flags);
	return 1;
}

static void cfq_kick_queue(void *data)
{
	request_queue_t *q = data;
	struct cfq_data *cfqd = q->elevator->elevator_data;
	unsigned long flags;

	spin_lock_irqsave(q->queue_lock, flags);

	if (cfqd->rq_starved) {
		struct request_list *rl = &q->rq;

		/*
		 * we aren't guaranteed to get a request after this, but we
		 * have to be opportunistic
		 */
		smp_mb();
		if (waitqueue_active(&rl->wait[READ]))
			wake_up(&rl->wait[READ]);
		if (waitqueue_active(&rl->wait[WRITE]))
			wake_up(&rl->wait[WRITE]);
	}

	blk_remove_plug(q);
	q->request_fn(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;

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

	if ((cfqq = cfqd->active_queue) != NULL) {
		unsigned long now = jiffies;

		/*
		 * expired
		 */
		if (time_after(now, cfqq->slice_end))
			goto expire;

		/*
		 * only expire and reinvoke request handler, if there are
		 * other queues with pending requests
		 */
		if (!cfqd->busy_queues) {
			cfqd->idle_slice_timer.expires = min(now + cfqd->cfq_slice_idle, cfqq->slice_end);
			add_timer(&cfqd->idle_slice_timer);
			goto out_cont;
		}

		/*
		 * not expired and it has a request pending, let it dispatch
		 */
		if (!RB_EMPTY(&cfqq->sort_list)) {
			cfq_mark_cfqq_must_dispatch(cfqq);
			goto out_kick;
		}
	}
expire:
	cfq_slice_expired(cfqd, 0);
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, end;

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

	/*
	 * race with a non-idle queue, reset timer
	 */
	end = cfqd->last_end_request + CFQ_IDLE_GRACE;
	if (!time_after_eq(jiffies, end)) {
		cfqd->idle_class_timer.expires = end;
		add_timer(&cfqd->idle_class_timer);
	} else
		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);
	blk_sync_queue(cfqd->queue);
}

static void cfq_put_cfqd(struct cfq_data *cfqd)
{
	request_queue_t *q = cfqd->queue;

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

	blk_put_queue(q);

	cfq_shutdown_timer_wq(cfqd);
	q->elevator->elevator_data = NULL;

	mempool_destroy(cfqd->crq_pool);
	kfree(cfqd->crq_hash);
	kfree(cfqd->cfq_hash);
	kfree(cfqd);
}

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

	cfq_shutdown_timer_wq(cfqd);
	cfq_put_cfqd(cfqd);
}

static int cfq_init_queue(request_queue_t *q, elevator_t *e)
{
	struct cfq_data *cfqd;
	int i;

	cfqd = kmalloc(sizeof(*cfqd), GFP_KERNEL);
	if (!cfqd)
		return -ENOMEM;

	memset(cfqd, 0, sizeof(*cfqd));

	for (i = 0; i < CFQ_PRIO_LISTS; i++)
		INIT_LIST_HEAD(&cfqd->rr_list[i]);

	INIT_LIST_HEAD(&cfqd->busy_rr);
	INIT_LIST_HEAD(&cfqd->cur_rr);
	INIT_LIST_HEAD(&cfqd->idle_rr);
	INIT_LIST_HEAD(&cfqd->empty_list);

	cfqd->crq_hash = kmalloc(sizeof(struct hlist_head) * CFQ_MHASH_ENTRIES, GFP_KERNEL);
	if (!cfqd->crq_hash)
		goto out_crqhash;

	cfqd->cfq_hash = kmalloc(sizeof(struct hlist_head) * CFQ_QHASH_ENTRIES, GFP_KERNEL);
	if (!cfqd->cfq_hash)
		goto out_cfqhash;

	cfqd->crq_pool = mempool_create(BLKDEV_MIN_RQ, mempool_alloc_slab, mempool_free_slab, crq_pool);
	if (!cfqd->crq_pool)
		goto out_crqpool;

	for (i = 0; i < CFQ_MHASH_ENTRIES; i++)
		INIT_HLIST_HEAD(&cfqd->crq_hash[i]);
	for (i = 0; i < CFQ_QHASH_ENTRIES; i++)
		INIT_HLIST_HEAD(&cfqd->cfq_hash[i]);

	e->elevator_data = cfqd;

	cfqd->queue = q;
	atomic_inc(&q->refcnt);

	cfqd->max_queued = q->nr_requests / 4;
	q->nr_batching = cfq_queued;

	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, q);

	atomic_set(&cfqd->ref, 1);

	cfqd->cfq_queued = cfq_queued;
	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;
	cfqd->cfq_max_depth = cfq_max_depth;

	return 0;
out_crqpool:
	kfree(cfqd->cfq_hash);
out_cfqhash:
	kfree(cfqd->crq_hash);
out_crqhash:
	kfree(cfqd);
	return -ENOMEM;
}

static void cfq_slab_kill(void)
{
	if (crq_pool)
		kmem_cache_destroy(crq_pool);
	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)
{
	crq_pool = kmem_cache_create("crq_pool", sizeof(struct cfq_rq), 0, 0,
					NULL, NULL);
	if (!crq_pool)
		goto fail;

	cfq_pool = kmem_cache_create("cfq_pool", sizeof(struct cfq_queue), 0, 0,
					NULL, NULL);
	if (!cfq_pool)
		goto fail;

	cfq_ioc_pool = kmem_cache_create("cfq_ioc_pool",
			sizeof(struct cfq_io_context), 0, 0, NULL, NULL);
	if (!cfq_ioc_pool)
		goto fail;

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

/*
 * sysfs parts below -->
 */
struct cfq_fs_entry {
	struct attribute attr;
	ssize_t (*show)(struct cfq_data *, char *);
	ssize_t (*store)(struct cfq_data *, const char *, size_t);
};

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(struct cfq_data *cfqd, char *page)		\
{									\
	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_queued_show, cfqd->cfq_queued, 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_max_show, cfqd->cfq_back_max, 0);
SHOW_FUNCTION(cfq_back_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);
SHOW_FUNCTION(cfq_max_depth_show, cfqd->cfq_max_depth, 0);
#undef SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)			\
static ssize_t __FUNC(struct cfq_data *cfqd, const char *page, size_t count)	\
{									\
	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_queued_store, &cfqd->cfq_queued, 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_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
STORE_FUNCTION(cfq_back_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);
STORE_FUNCTION(cfq_max_depth_store, &cfqd->cfq_max_depth, 1, UINT_MAX, 0);
#undef STORE_FUNCTION

static struct cfq_fs_entry cfq_quantum_entry = {
	.attr = {.name = "quantum", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_quantum_show,
	.store = cfq_quantum_store,
};
static struct cfq_fs_entry cfq_queued_entry = {
	.attr = {.name = "queued", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_queued_show,
	.store = cfq_queued_store,
};
static struct cfq_fs_entry cfq_fifo_expire_sync_entry = {
	.attr = {.name = "fifo_expire_sync", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_fifo_expire_sync_show,
	.store = cfq_fifo_expire_sync_store,
};
static struct cfq_fs_entry cfq_fifo_expire_async_entry = {
	.attr = {.name = "fifo_expire_async", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_fifo_expire_async_show,
	.store = cfq_fifo_expire_async_store,
};
static struct cfq_fs_entry cfq_back_max_entry = {
	.attr = {.name = "back_seek_max", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_back_max_show,
	.store = cfq_back_max_store,
};
static struct cfq_fs_entry cfq_back_penalty_entry = {
	.attr = {.name = "back_seek_penalty", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_back_penalty_show,
	.store = cfq_back_penalty_store,
};
static struct cfq_fs_entry cfq_slice_sync_entry = {
	.attr = {.name = "slice_sync", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_slice_sync_show,
	.store = cfq_slice_sync_store,
};
static struct cfq_fs_entry cfq_slice_async_entry = {
	.attr = {.name = "slice_async", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_slice_async_show,
	.store = cfq_slice_async_store,
};
static struct cfq_fs_entry cfq_slice_async_rq_entry = {
	.attr = {.name = "slice_async_rq", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_slice_async_rq_show,
	.store = cfq_slice_async_rq_store,
};
static struct cfq_fs_entry cfq_slice_idle_entry = {
	.attr = {.name = "slice_idle", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_slice_idle_show,
	.store = cfq_slice_idle_store,
};
static struct cfq_fs_entry cfq_max_depth_entry = {
	.attr = {.name = "max_depth", .mode = S_IRUGO | S_IWUSR },
	.show = cfq_max_depth_show,
	.store = cfq_max_depth_store,
};

static struct attribute *default_attrs[] = {
	&cfq_quantum_entry.attr,
	&cfq_queued_entry.attr,
	&cfq_fifo_expire_sync_entry.attr,
	&cfq_fifo_expire_async_entry.attr,
	&cfq_back_max_entry.attr,
	&cfq_back_penalty_entry.attr,
	&cfq_slice_sync_entry.attr,
	&cfq_slice_async_entry.attr,
	&cfq_slice_async_rq_entry.attr,
	&cfq_slice_idle_entry.attr,
	&cfq_max_depth_entry.attr,
	NULL,
};

#define to_cfq(atr) container_of((atr), struct cfq_fs_entry, attr)

static ssize_t
cfq_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
{
	elevator_t *e = container_of(kobj, elevator_t, kobj);
	struct cfq_fs_entry *entry = to_cfq(attr);

	if (!entry->show)
		return -EIO;

	return entry->show(e->elevator_data, page);
}

static ssize_t
cfq_attr_store(struct kobject *kobj, struct attribute *attr,
	       const char *page, size_t length)
{
	elevator_t *e = container_of(kobj, elevator_t, kobj);
	struct cfq_fs_entry *entry = to_cfq(attr);

	if (!entry->store)
		return -EIO;

	return entry->store(e->elevator_data, page, length);
}

static struct sysfs_ops cfq_sysfs_ops = {
	.show	= cfq_attr_show,
	.store	= cfq_attr_store,
};

static struct kobj_type cfq_ktype = {
	.sysfs_ops	= &cfq_sysfs_ops,
	.default_attrs	= default_attrs,
};

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_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 =	cfq_former_request,
		.elevator_latter_req_fn =	cfq_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,
	},
	.elevator_ktype =	&cfq_ktype,
	.elevator_name =	"cfq",
	.elevator_owner =	THIS_MODULE,
};

static int __init cfq_init(void)
{
	int ret;

	/*
	 * 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;

	ret = elv_register(&iosched_cfq);
	if (ret)
		cfq_slab_kill();

	return ret;
}

static void __exit cfq_exit(void)
{
	struct task_struct *g, *p;
	unsigned long flags;

	read_lock_irqsave(&tasklist_lock, flags);

	/*
	 * iterate each process in the system, removing our io_context
	 */
	do_each_thread(g, p) {
		struct io_context *ioc = p->io_context;

		if (ioc && ioc->cic) {
			ioc->cic->exit(ioc->cic);
			cfq_free_io_context(ioc->cic);
			ioc->cic = NULL;
		}
	} while_each_thread(g, p);

	read_unlock_irqrestore(&tasklist_lock, flags);

	cfq_slab_kill();
	elv_unregister(&iosched_cfq);
}

module_init(cfq_init);
module_exit(cfq_exit);

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