Merge tag 'trace-printf-v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/trace...

[drm/drm-misc.git] / drivers / md / dm-cache-policy-smq.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2015 Red Hat. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include "dm-cache-background-tracker.h"
#include "dm-cache-policy-internal.h"
#include "dm-cache-policy.h"
#include "dm.h"

#include <linux/hash.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/vmalloc.h>
#include <linux/math64.h>

#define DM_MSG_PREFIX "cache-policy-smq"

/*----------------------------------------------------------------*/

/*
 * Safe division functions that return zero on divide by zero.
 */
static unsigned int safe_div(unsigned int n, unsigned int d)
{
        return d ? n / d : 0u;
}

static unsigned int safe_mod(unsigned int n, unsigned int d)
{
        return d ? n % d : 0u;
}

/*----------------------------------------------------------------*/

struct entry {
        unsigned int hash_next:28;
        unsigned int prev:28;
        unsigned int next:28;
        unsigned int level:6;
        bool dirty:1;
        bool allocated:1;
        bool sentinel:1;
        bool pending_work:1;

        dm_oblock_t oblock;
};

/*----------------------------------------------------------------*/

#define INDEXER_NULL ((1u << 28u) - 1u)

/*
 * An entry_space manages a set of entries that we use for the queues.
 * The clean and dirty queues share entries, so this object is separate
 * from the queue itself.
 */
struct entry_space {
        struct entry *begin;
        struct entry *end;
};

static int space_init(struct entry_space *es, unsigned int nr_entries)
{
        if (!nr_entries) {
                es->begin = es->end = NULL;
                return 0;
        }

        es->begin = vzalloc(array_size(nr_entries, sizeof(struct entry)));
        if (!es->begin)
                return -ENOMEM;

        es->end = es->begin + nr_entries;
        return 0;
}

static void space_exit(struct entry_space *es)
{
        vfree(es->begin);
}

static struct entry *__get_entry(struct entry_space *es, unsigned int block)
{
        struct entry *e;

        e = es->begin + block;
        BUG_ON(e >= es->end);

        return e;
}

static unsigned int to_index(struct entry_space *es, struct entry *e)
{
        BUG_ON(e < es->begin || e >= es->end);
        return e - es->begin;
}

static struct entry *to_entry(struct entry_space *es, unsigned int block)
{
        if (block == INDEXER_NULL)
                return NULL;

        return __get_entry(es, block);
}

/*----------------------------------------------------------------*/

struct ilist {
        unsigned int nr_elts;   /* excluding sentinel entries */
        unsigned int head, tail;
};

static void l_init(struct ilist *l)
{
        l->nr_elts = 0;
        l->head = l->tail = INDEXER_NULL;
}

static struct entry *l_head(struct entry_space *es, struct ilist *l)
{
        return to_entry(es, l->head);
}

static struct entry *l_tail(struct entry_space *es, struct ilist *l)
{
        return to_entry(es, l->tail);
}

static struct entry *l_next(struct entry_space *es, struct entry *e)
{
        return to_entry(es, e->next);
}

static struct entry *l_prev(struct entry_space *es, struct entry *e)
{
        return to_entry(es, e->prev);
}

static bool l_empty(struct ilist *l)
{
        return l->head == INDEXER_NULL;
}

static void l_add_head(struct entry_space *es, struct ilist *l, struct entry *e)
{
        struct entry *head = l_head(es, l);

        e->next = l->head;
        e->prev = INDEXER_NULL;

        if (head)
                head->prev = l->head = to_index(es, e);
        else
                l->head = l->tail = to_index(es, e);

        if (!e->sentinel)
                l->nr_elts++;
}

static void l_add_tail(struct entry_space *es, struct ilist *l, struct entry *e)
{
        struct entry *tail = l_tail(es, l);

        e->next = INDEXER_NULL;
        e->prev = l->tail;

        if (tail)
                tail->next = l->tail = to_index(es, e);
        else
                l->head = l->tail = to_index(es, e);

        if (!e->sentinel)
                l->nr_elts++;
}

static void l_add_before(struct entry_space *es, struct ilist *l,
                         struct entry *old, struct entry *e)
{
        struct entry *prev = l_prev(es, old);

        if (!prev)
                l_add_head(es, l, e);

        else {
                e->prev = old->prev;
                e->next = to_index(es, old);
                prev->next = old->prev = to_index(es, e);

                if (!e->sentinel)
                        l->nr_elts++;
        }
}

static void l_del(struct entry_space *es, struct ilist *l, struct entry *e)
{
        struct entry *prev = l_prev(es, e);
        struct entry *next = l_next(es, e);

        if (prev)
                prev->next = e->next;
        else
                l->head = e->next;

        if (next)
                next->prev = e->prev;
        else
                l->tail = e->prev;

        if (!e->sentinel)
                l->nr_elts--;
}

static struct entry *l_pop_head(struct entry_space *es, struct ilist *l)
{
        struct entry *e;

        for (e = l_head(es, l); e; e = l_next(es, e))
                if (!e->sentinel) {
                        l_del(es, l, e);
                        return e;
                }

        return NULL;
}

static struct entry *l_pop_tail(struct entry_space *es, struct ilist *l)
{
        struct entry *e;

        for (e = l_tail(es, l); e; e = l_prev(es, e))
                if (!e->sentinel) {
                        l_del(es, l, e);
                        return e;
                }

        return NULL;
}

/*----------------------------------------------------------------*/

/*
 * The stochastic-multi-queue is a set of lru lists stacked into levels.
 * Entries are moved up levels when they are used, which loosely orders the
 * most accessed entries in the top levels and least in the bottom.  This
 * structure is *much* better than a single lru list.
 */
#define MAX_LEVELS 64u

struct queue {
        struct entry_space *es;

        unsigned int nr_elts;
        unsigned int nr_levels;
        struct ilist qs[MAX_LEVELS];

        /*
         * We maintain a count of the number of entries we would like in each
         * level.
         */
        unsigned int last_target_nr_elts;
        unsigned int nr_top_levels;
        unsigned int nr_in_top_levels;
        unsigned int target_count[MAX_LEVELS];
};

static void q_init(struct queue *q, struct entry_space *es, unsigned int nr_levels)
{
        unsigned int i;

        q->es = es;
        q->nr_elts = 0;
        q->nr_levels = nr_levels;

        for (i = 0; i < q->nr_levels; i++) {
                l_init(q->qs + i);
                q->target_count[i] = 0u;
        }

        q->last_target_nr_elts = 0u;
        q->nr_top_levels = 0u;
        q->nr_in_top_levels = 0u;
}

static unsigned int q_size(struct queue *q)
{
        return q->nr_elts;
}

/*
 * Insert an entry to the back of the given level.
 */
static void q_push(struct queue *q, struct entry *e)
{
        BUG_ON(e->pending_work);

        if (!e->sentinel)
                q->nr_elts++;

        l_add_tail(q->es, q->qs + e->level, e);
}

static void q_push_front(struct queue *q, struct entry *e)
{
        BUG_ON(e->pending_work);

        if (!e->sentinel)
                q->nr_elts++;

        l_add_head(q->es, q->qs + e->level, e);
}

static void q_push_before(struct queue *q, struct entry *old, struct entry *e)
{
        BUG_ON(e->pending_work);

        if (!e->sentinel)
                q->nr_elts++;

        l_add_before(q->es, q->qs + e->level, old, e);
}

static void q_del(struct queue *q, struct entry *e)
{
        l_del(q->es, q->qs + e->level, e);
        if (!e->sentinel)
                q->nr_elts--;
}

/*
 * Return the oldest entry of the lowest populated level.
 */
static struct entry *q_peek(struct queue *q, unsigned int max_level, bool can_cross_sentinel)
{
        unsigned int level;
        struct entry *e;

        max_level = min(max_level, q->nr_levels);

        for (level = 0; level < max_level; level++)
                for (e = l_head(q->es, q->qs + level); e; e = l_next(q->es, e)) {
                        if (e->sentinel) {
                                if (can_cross_sentinel)
                                        continue;
                                else
                                        break;
                        }

                        return e;
                }

        return NULL;
}

static struct entry *q_pop(struct queue *q)
{
        struct entry *e = q_peek(q, q->nr_levels, true);

        if (e)
                q_del(q, e);

        return e;
}

/*
 * This function assumes there is a non-sentinel entry to pop.  It's only
 * used by redistribute, so we know this is true.  It also doesn't adjust
 * the q->nr_elts count.
 */
static struct entry *__redist_pop_from(struct queue *q, unsigned int level)
{
        struct entry *e;

        for (; level < q->nr_levels; level++)
                for (e = l_head(q->es, q->qs + level); e; e = l_next(q->es, e))
                        if (!e->sentinel) {
                                l_del(q->es, q->qs + e->level, e);
                                return e;
                        }

        return NULL;
}

static void q_set_targets_subrange_(struct queue *q, unsigned int nr_elts,
                                    unsigned int lbegin, unsigned int lend)
{
        unsigned int level, nr_levels, entries_per_level, remainder;

        BUG_ON(lbegin > lend);
        BUG_ON(lend > q->nr_levels);
        nr_levels = lend - lbegin;
        entries_per_level = safe_div(nr_elts, nr_levels);
        remainder = safe_mod(nr_elts, nr_levels);

        for (level = lbegin; level < lend; level++)
                q->target_count[level] =
                        (level < (lbegin + remainder)) ? entries_per_level + 1u : entries_per_level;
}

/*
 * Typically we have fewer elements in the top few levels which allows us
 * to adjust the promote threshold nicely.
 */
static void q_set_targets(struct queue *q)
{
        if (q->last_target_nr_elts == q->nr_elts)
                return;

        q->last_target_nr_elts = q->nr_elts;

        if (q->nr_top_levels > q->nr_levels)
                q_set_targets_subrange_(q, q->nr_elts, 0, q->nr_levels);

        else {
                q_set_targets_subrange_(q, q->nr_in_top_levels,
                                        q->nr_levels - q->nr_top_levels, q->nr_levels);

                if (q->nr_in_top_levels < q->nr_elts)
                        q_set_targets_subrange_(q, q->nr_elts - q->nr_in_top_levels,
                                                0, q->nr_levels - q->nr_top_levels);
                else
                        q_set_targets_subrange_(q, 0, 0, q->nr_levels - q->nr_top_levels);
        }
}

static void q_redistribute(struct queue *q)
{
        unsigned int target, level;
        struct ilist *l, *l_above;
        struct entry *e;

        q_set_targets(q);

        for (level = 0u; level < q->nr_levels - 1u; level++) {
                l = q->qs + level;
                target = q->target_count[level];

                /*
                 * Pull down some entries from the level above.
                 */
                while (l->nr_elts < target) {
                        e = __redist_pop_from(q, level + 1u);
                        if (!e) {
                                /* bug in nr_elts */
                                break;
                        }

                        e->level = level;
                        l_add_tail(q->es, l, e);
                }

                /*
                 * Push some entries up.
                 */
                l_above = q->qs + level + 1u;
                while (l->nr_elts > target) {
                        e = l_pop_tail(q->es, l);

                        if (!e)
                                /* bug in nr_elts */
                                break;

                        e->level = level + 1u;
                        l_add_tail(q->es, l_above, e);
                }
        }
}

static void q_requeue(struct queue *q, struct entry *e, unsigned int extra_levels,
                      struct entry *s1, struct entry *s2)
{
        struct entry *de;
        unsigned int sentinels_passed = 0;
        unsigned int new_level = min(q->nr_levels - 1u, e->level + extra_levels);

        /* try and find an entry to swap with */
        if (extra_levels && (e->level < q->nr_levels - 1u)) {
                for (de = l_head(q->es, q->qs + new_level); de && de->sentinel; de = l_next(q->es, de))
                        sentinels_passed++;

                if (de) {
                        q_del(q, de);
                        de->level = e->level;
                        if (s1) {
                                switch (sentinels_passed) {
                                case 0:
                                        q_push_before(q, s1, de);
                                        break;

                                case 1:
                                        q_push_before(q, s2, de);
                                        break;

                                default:
                                        q_push(q, de);
                                }
                        } else
                                q_push(q, de);
                }
        }

        q_del(q, e);
        e->level = new_level;
        q_push(q, e);
}

/*----------------------------------------------------------------*/

#define FP_SHIFT 8
#define SIXTEENTH (1u << (FP_SHIFT - 4u))
#define EIGHTH (1u << (FP_SHIFT - 3u))

struct stats {
        unsigned int hit_threshold;
        unsigned int hits;
        unsigned int misses;
};

enum performance {
        Q_POOR,
        Q_FAIR,
        Q_WELL
};

static void stats_init(struct stats *s, unsigned int nr_levels)
{
        s->hit_threshold = (nr_levels * 3u) / 4u;
        s->hits = 0u;
        s->misses = 0u;
}

static void stats_reset(struct stats *s)
{
        s->hits = s->misses = 0u;
}

static void stats_level_accessed(struct stats *s, unsigned int level)
{
        if (level >= s->hit_threshold)
                s->hits++;
        else
                s->misses++;
}

static void stats_miss(struct stats *s)
{
        s->misses++;
}

/*
 * There are times when we don't have any confidence in the hotspot queue.
 * Such as when a fresh cache is created and the blocks have been spread
 * out across the levels, or if an io load changes.  We detect this by
 * seeing how often a lookup is in the top levels of the hotspot queue.
 */
static enum performance stats_assess(struct stats *s)
{
        unsigned int confidence = safe_div(s->hits << FP_SHIFT, s->hits + s->misses);

        if (confidence < SIXTEENTH)
                return Q_POOR;

        else if (confidence < EIGHTH)
                return Q_FAIR;

        else
                return Q_WELL;
}

/*----------------------------------------------------------------*/

struct smq_hash_table {
        struct entry_space *es;
        unsigned long long hash_bits;
        unsigned int *buckets;
};

/*
 * All cache entries are stored in a chained hash table.  To save space we
 * use indexing again, and only store indexes to the next entry.
 */
static int h_init(struct smq_hash_table *ht, struct entry_space *es, unsigned int nr_entries)
{
        unsigned int i, nr_buckets;

        ht->es = es;
        nr_buckets = roundup_pow_of_two(max(nr_entries / 4u, 16u));
        ht->hash_bits = __ffs(nr_buckets);

        ht->buckets = vmalloc(array_size(nr_buckets, sizeof(*ht->buckets)));
        if (!ht->buckets)
                return -ENOMEM;

        for (i = 0; i < nr_buckets; i++)
                ht->buckets[i] = INDEXER_NULL;

        return 0;
}

static void h_exit(struct smq_hash_table *ht)
{
        vfree(ht->buckets);
}

static struct entry *h_head(struct smq_hash_table *ht, unsigned int bucket)
{
        return to_entry(ht->es, ht->buckets[bucket]);
}

static struct entry *h_next(struct smq_hash_table *ht, struct entry *e)
{
        return to_entry(ht->es, e->hash_next);
}

static void __h_insert(struct smq_hash_table *ht, unsigned int bucket, struct entry *e)
{
        e->hash_next = ht->buckets[bucket];
        ht->buckets[bucket] = to_index(ht->es, e);
}

static void h_insert(struct smq_hash_table *ht, struct entry *e)
{
        unsigned int h = hash_64(from_oblock(e->oblock), ht->hash_bits);

        __h_insert(ht, h, e);
}

static struct entry *__h_lookup(struct smq_hash_table *ht, unsigned int h, dm_oblock_t oblock,
                                struct entry **prev)
{
        struct entry *e;

        *prev = NULL;
        for (e = h_head(ht, h); e; e = h_next(ht, e)) {
                if (e->oblock == oblock)
                        return e;

                *prev = e;
        }

        return NULL;
}

static void __h_unlink(struct smq_hash_table *ht, unsigned int h,
                       struct entry *e, struct entry *prev)
{
        if (prev)
                prev->hash_next = e->hash_next;
        else
                ht->buckets[h] = e->hash_next;
}

/*
 * Also moves each entry to the front of the bucket.
 */
static struct entry *h_lookup(struct smq_hash_table *ht, dm_oblock_t oblock)
{
        struct entry *e, *prev;
        unsigned int h = hash_64(from_oblock(oblock), ht->hash_bits);

        e = __h_lookup(ht, h, oblock, &prev);
        if (e && prev) {
                /*
                 * Move to the front because this entry is likely
                 * to be hit again.
                 */
                __h_unlink(ht, h, e, prev);
                __h_insert(ht, h, e);
        }

        return e;
}

static void h_remove(struct smq_hash_table *ht, struct entry *e)
{
        unsigned int h = hash_64(from_oblock(e->oblock), ht->hash_bits);
        struct entry *prev;

        /*
         * The down side of using a singly linked list is we have to
         * iterate the bucket to remove an item.
         */
        e = __h_lookup(ht, h, e->oblock, &prev);
        if (e)
                __h_unlink(ht, h, e, prev);
}

/*----------------------------------------------------------------*/

struct entry_alloc {
        struct entry_space *es;
        unsigned int begin;

        unsigned int nr_allocated;
        struct ilist free;
};

static void init_allocator(struct entry_alloc *ea, struct entry_space *es,
                           unsigned int begin, unsigned int end)
{
        unsigned int i;

        ea->es = es;
        ea->nr_allocated = 0u;
        ea->begin = begin;

        l_init(&ea->free);
        for (i = begin; i != end; i++)
                l_add_tail(ea->es, &ea->free, __get_entry(ea->es, i));
}

static void init_entry(struct entry *e)
{
        /*
         * We can't memset because that would clear the hotspot and
         * sentinel bits which remain constant.
         */
        e->hash_next = INDEXER_NULL;
        e->next = INDEXER_NULL;
        e->prev = INDEXER_NULL;
        e->level = 0u;
        e->dirty = true;        /* FIXME: audit */
        e->allocated = true;
        e->sentinel = false;
        e->pending_work = false;
}

static struct entry *alloc_entry(struct entry_alloc *ea)
{
        struct entry *e;

        if (l_empty(&ea->free))
                return NULL;

        e = l_pop_head(ea->es, &ea->free);
        init_entry(e);
        ea->nr_allocated++;

        return e;
}

/*
 * This assumes the cblock hasn't already been allocated.
 */
static struct entry *alloc_particular_entry(struct entry_alloc *ea, unsigned int i)
{
        struct entry *e = __get_entry(ea->es, ea->begin + i);

        BUG_ON(e->allocated);

        l_del(ea->es, &ea->free, e);
        init_entry(e);
        ea->nr_allocated++;

        return e;
}

static void free_entry(struct entry_alloc *ea, struct entry *e)
{
        BUG_ON(!ea->nr_allocated);
        BUG_ON(!e->allocated);

        ea->nr_allocated--;
        e->allocated = false;
        l_add_tail(ea->es, &ea->free, e);
}

static bool allocator_empty(struct entry_alloc *ea)
{
        return l_empty(&ea->free);
}

static unsigned int get_index(struct entry_alloc *ea, struct entry *e)
{
        return to_index(ea->es, e) - ea->begin;
}

static struct entry *get_entry(struct entry_alloc *ea, unsigned int index)
{
        return __get_entry(ea->es, ea->begin + index);
}

/*----------------------------------------------------------------*/

#define NR_HOTSPOT_LEVELS 64u
#define NR_CACHE_LEVELS 64u

#define WRITEBACK_PERIOD (10ul * HZ)
#define DEMOTE_PERIOD (60ul * HZ)

#define HOTSPOT_UPDATE_PERIOD (HZ)
#define CACHE_UPDATE_PERIOD (60ul * HZ)

struct smq_policy {
        struct dm_cache_policy policy;

        /* protects everything */
        spinlock_t lock;
        dm_cblock_t cache_size;
        sector_t cache_block_size;

        sector_t hotspot_block_size;
        unsigned int nr_hotspot_blocks;
        unsigned int cache_blocks_per_hotspot_block;
        unsigned int hotspot_level_jump;

        struct entry_space es;
        struct entry_alloc writeback_sentinel_alloc;
        struct entry_alloc demote_sentinel_alloc;
        struct entry_alloc hotspot_alloc;
        struct entry_alloc cache_alloc;

        unsigned long *hotspot_hit_bits;
        unsigned long *cache_hit_bits;

        /*
         * We maintain three queues of entries.  The cache proper,
         * consisting of a clean and dirty queue, containing the currently
         * active mappings.  The hotspot queue uses a larger block size to
         * track blocks that are being hit frequently and potential
         * candidates for promotion to the cache.
         */
        struct queue hotspot;
        struct queue clean;
        struct queue dirty;

        struct stats hotspot_stats;
        struct stats cache_stats;

        /*
         * Keeps track of time, incremented by the core.  We use this to
         * avoid attributing multiple hits within the same tick.
         */
        unsigned int tick;

        /*
         * The hash tables allows us to quickly find an entry by origin
         * block.
         */
        struct smq_hash_table table;
        struct smq_hash_table hotspot_table;

        bool current_writeback_sentinels;
        unsigned long next_writeback_period;

        bool current_demote_sentinels;
        unsigned long next_demote_period;

        unsigned int write_promote_level;
        unsigned int read_promote_level;

        unsigned long next_hotspot_period;
        unsigned long next_cache_period;

        struct background_tracker *bg_work;

        bool migrations_allowed:1;

        /*
         * If this is set the policy will try and clean the whole cache
         * even if the device is not idle.
         */
        bool cleaner:1;
};

/*----------------------------------------------------------------*/

static struct entry *get_sentinel(struct entry_alloc *ea, unsigned int level, bool which)
{
        return get_entry(ea, which ? level : NR_CACHE_LEVELS + level);
}

static struct entry *writeback_sentinel(struct smq_policy *mq, unsigned int level)
{
        return get_sentinel(&mq->writeback_sentinel_alloc, level, mq->current_writeback_sentinels);
}

static struct entry *demote_sentinel(struct smq_policy *mq, unsigned int level)
{
        return get_sentinel(&mq->demote_sentinel_alloc, level, mq->current_demote_sentinels);
}

static void __update_writeback_sentinels(struct smq_policy *mq)
{
        unsigned int level;
        struct queue *q = &mq->dirty;
        struct entry *sentinel;

        for (level = 0; level < q->nr_levels; level++) {
                sentinel = writeback_sentinel(mq, level);
                q_del(q, sentinel);
                q_push(q, sentinel);
        }
}

static void __update_demote_sentinels(struct smq_policy *mq)
{
        unsigned int level;
        struct queue *q = &mq->clean;
        struct entry *sentinel;

        for (level = 0; level < q->nr_levels; level++) {
                sentinel = demote_sentinel(mq, level);
                q_del(q, sentinel);
                q_push(q, sentinel);
        }
}

static void update_sentinels(struct smq_policy *mq)
{
        if (time_after(jiffies, mq->next_writeback_period)) {
                mq->next_writeback_period = jiffies + WRITEBACK_PERIOD;
                mq->current_writeback_sentinels = !mq->current_writeback_sentinels;
                __update_writeback_sentinels(mq);
        }

        if (time_after(jiffies, mq->next_demote_period)) {
                mq->next_demote_period = jiffies + DEMOTE_PERIOD;
                mq->current_demote_sentinels = !mq->current_demote_sentinels;
                __update_demote_sentinels(mq);
        }
}

static void __sentinels_init(struct smq_policy *mq)
{
        unsigned int level;
        struct entry *sentinel;

        for (level = 0; level < NR_CACHE_LEVELS; level++) {
                sentinel = writeback_sentinel(mq, level);
                sentinel->level = level;
                q_push(&mq->dirty, sentinel);

                sentinel = demote_sentinel(mq, level);
                sentinel->level = level;
                q_push(&mq->clean, sentinel);
        }
}

static void sentinels_init(struct smq_policy *mq)
{
        mq->next_writeback_period = jiffies + WRITEBACK_PERIOD;
        mq->next_demote_period = jiffies + DEMOTE_PERIOD;

        mq->current_writeback_sentinels = false;
        mq->current_demote_sentinels = false;
        __sentinels_init(mq);

        mq->current_writeback_sentinels = !mq->current_writeback_sentinels;
        mq->current_demote_sentinels = !mq->current_demote_sentinels;
        __sentinels_init(mq);
}

/*----------------------------------------------------------------*/

static void del_queue(struct smq_policy *mq, struct entry *e)
{
        q_del(e->dirty ? &mq->dirty : &mq->clean, e);
}

static void push_queue(struct smq_policy *mq, struct entry *e)
{
        if (e->dirty)
                q_push(&mq->dirty, e);
        else
                q_push(&mq->clean, e);
}

// !h, !q, a -> h, q, a
static void push(struct smq_policy *mq, struct entry *e)
{
        h_insert(&mq->table, e);
        if (!e->pending_work)
                push_queue(mq, e);
}

static void push_queue_front(struct smq_policy *mq, struct entry *e)
{
        if (e->dirty)
                q_push_front(&mq->dirty, e);
        else
                q_push_front(&mq->clean, e);
}

static void push_front(struct smq_policy *mq, struct entry *e)
{
        h_insert(&mq->table, e);
        if (!e->pending_work)
                push_queue_front(mq, e);
}

static dm_cblock_t infer_cblock(struct smq_policy *mq, struct entry *e)
{
        return to_cblock(get_index(&mq->cache_alloc, e));
}

static void requeue(struct smq_policy *mq, struct entry *e)
{
        /*
         * Pending work has temporarily been taken out of the queues.
         */
        if (e->pending_work)
                return;

        if (!test_and_set_bit(from_cblock(infer_cblock(mq, e)), mq->cache_hit_bits)) {
                if (!e->dirty) {
                        q_requeue(&mq->clean, e, 1u, NULL, NULL);
                        return;
                }

                q_requeue(&mq->dirty, e, 1u,
                          get_sentinel(&mq->writeback_sentinel_alloc, e->level, !mq->current_writeback_sentinels),
                          get_sentinel(&mq->writeback_sentinel_alloc, e->level, mq->current_writeback_sentinels));
        }
}

static unsigned int default_promote_level(struct smq_policy *mq)
{
        /*
         * The promote level depends on the current performance of the
         * cache.
         *
         * If the cache is performing badly, then we can't afford
         * to promote much without causing performance to drop below that
         * of the origin device.
         *
         * If the cache is performing well, then we don't need to promote
         * much.  If it isn't broken, don't fix it.
         *
         * If the cache is middling then we promote more.
         *
         * This scheme reminds me of a graph of entropy vs probability of a
         * binary variable.
         */
        static const unsigned int table[] = {
                1, 1, 1, 2, 4, 6, 7, 8, 7, 6, 4, 4, 3, 3, 2, 2, 1
        };

        unsigned int hits = mq->cache_stats.hits;
        unsigned int misses = mq->cache_stats.misses;
        unsigned int index = safe_div(hits << 4u, hits + misses);
        return table[index];
}

static void update_promote_levels(struct smq_policy *mq)
{
        /*
         * If there are unused cache entries then we want to be really
         * eager to promote.
         */
        unsigned int threshold_level = allocator_empty(&mq->cache_alloc) ?
                default_promote_level(mq) : (NR_HOTSPOT_LEVELS / 2u);

        threshold_level = max(threshold_level, NR_HOTSPOT_LEVELS);

        /*
         * If the hotspot queue is performing badly then we have little
         * confidence that we know which blocks to promote.  So we cut down
         * the amount of promotions.
         */
        switch (stats_assess(&mq->hotspot_stats)) {
        case Q_POOR:
                threshold_level /= 4u;
                break;

        case Q_FAIR:
                threshold_level /= 2u;
                break;

        case Q_WELL:
                break;
        }

        mq->read_promote_level = NR_HOTSPOT_LEVELS - threshold_level;
        mq->write_promote_level = (NR_HOTSPOT_LEVELS - threshold_level);
}

/*
 * If the hotspot queue is performing badly, then we try and move entries
 * around more quickly.
 */
static void update_level_jump(struct smq_policy *mq)
{
        switch (stats_assess(&mq->hotspot_stats)) {
        case Q_POOR:
                mq->hotspot_level_jump = 4u;
                break;

        case Q_FAIR:
                mq->hotspot_level_jump = 2u;
                break;

        case Q_WELL:
                mq->hotspot_level_jump = 1u;
                break;
        }
}

static void end_hotspot_period(struct smq_policy *mq)
{
        clear_bitset(mq->hotspot_hit_bits, mq->nr_hotspot_blocks);
        update_promote_levels(mq);

        if (time_after(jiffies, mq->next_hotspot_period)) {
                update_level_jump(mq);
                q_redistribute(&mq->hotspot);
                stats_reset(&mq->hotspot_stats);
                mq->next_hotspot_period = jiffies + HOTSPOT_UPDATE_PERIOD;
        }
}

static void end_cache_period(struct smq_policy *mq)
{
        if (time_after(jiffies, mq->next_cache_period)) {
                clear_bitset(mq->cache_hit_bits, from_cblock(mq->cache_size));

                q_redistribute(&mq->dirty);
                q_redistribute(&mq->clean);
                stats_reset(&mq->cache_stats);

                mq->next_cache_period = jiffies + CACHE_UPDATE_PERIOD;
        }
}

/*----------------------------------------------------------------*/

/*
 * Targets are given as a percentage.
 */
#define CLEAN_TARGET 25u
#define FREE_TARGET 25u

static unsigned int percent_to_target(struct smq_policy *mq, unsigned int p)
{
        return from_cblock(mq->cache_size) * p / 100u;
}

static bool clean_target_met(struct smq_policy *mq, bool idle)
{
        /*
         * Cache entries may not be populated.  So we cannot rely on the
         * size of the clean queue.
         */
        if (idle || mq->cleaner) {
                /*
                 * We'd like to clean everything.
                 */
                return q_size(&mq->dirty) == 0u;
        }

        /*
         * If we're busy we don't worry about cleaning at all.
         */
        return true;
}

static bool free_target_met(struct smq_policy *mq)
{
        unsigned int nr_free;

        nr_free = from_cblock(mq->cache_size) - mq->cache_alloc.nr_allocated;
        return (nr_free + btracker_nr_demotions_queued(mq->bg_work)) >=
                percent_to_target(mq, FREE_TARGET);
}

/*----------------------------------------------------------------*/

static void mark_pending(struct smq_policy *mq, struct entry *e)
{
        BUG_ON(e->sentinel);
        BUG_ON(!e->allocated);
        BUG_ON(e->pending_work);
        e->pending_work = true;
}

static void clear_pending(struct smq_policy *mq, struct entry *e)
{
        BUG_ON(!e->pending_work);
        e->pending_work = false;
}

static void queue_writeback(struct smq_policy *mq, bool idle)
{
        int r;
        struct policy_work work;
        struct entry *e;

        e = q_peek(&mq->dirty, mq->dirty.nr_levels, idle);
        if (e) {
                mark_pending(mq, e);
                q_del(&mq->dirty, e);

                work.op = POLICY_WRITEBACK;
                work.oblock = e->oblock;
                work.cblock = infer_cblock(mq, e);

                r = btracker_queue(mq->bg_work, &work, NULL);
                if (r) {
                        clear_pending(mq, e);
                        q_push_front(&mq->dirty, e);
                }
        }
}

static void queue_demotion(struct smq_policy *mq)
{
        int r;
        struct policy_work work;
        struct entry *e;

        if (WARN_ON_ONCE(!mq->migrations_allowed))
                return;

        e = q_peek(&mq->clean, mq->clean.nr_levels / 2, true);
        if (!e) {
                if (!clean_target_met(mq, true))
                        queue_writeback(mq, false);
                return;
        }

        mark_pending(mq, e);
        q_del(&mq->clean, e);

        work.op = POLICY_DEMOTE;
        work.oblock = e->oblock;
        work.cblock = infer_cblock(mq, e);
        r = btracker_queue(mq->bg_work, &work, NULL);
        if (r) {
                clear_pending(mq, e);
                q_push_front(&mq->clean, e);
        }
}

static void queue_promotion(struct smq_policy *mq, dm_oblock_t oblock,
                            struct policy_work **workp)
{
        int r;
        struct entry *e;
        struct policy_work work;

        if (!mq->migrations_allowed)
                return;

        if (allocator_empty(&mq->cache_alloc)) {
                /*
                 * We always claim to be 'idle' to ensure some demotions happen
                 * with continuous loads.
                 */
                if (!free_target_met(mq))
                        queue_demotion(mq);
                return;
        }

        if (btracker_promotion_already_present(mq->bg_work, oblock))
                return;

        /*
         * We allocate the entry now to reserve the cblock.  If the
         * background work is aborted we must remember to free it.
         */
        e = alloc_entry(&mq->cache_alloc);
        BUG_ON(!e);
        e->pending_work = true;
        work.op = POLICY_PROMOTE;
        work.oblock = oblock;
        work.cblock = infer_cblock(mq, e);
        r = btracker_queue(mq->bg_work, &work, workp);
        if (r)
                free_entry(&mq->cache_alloc, e);
}

/*----------------------------------------------------------------*/

enum promote_result {
        PROMOTE_NOT,
        PROMOTE_TEMPORARY,
        PROMOTE_PERMANENT
};

/*
 * Converts a boolean into a promote result.
 */
static enum promote_result maybe_promote(bool promote)
{
        return promote ? PROMOTE_PERMANENT : PROMOTE_NOT;
}

static enum promote_result should_promote(struct smq_policy *mq, struct entry *hs_e,
                                          int data_dir, bool fast_promote)
{
        if (data_dir == WRITE) {
                if (!allocator_empty(&mq->cache_alloc) && fast_promote)
                        return PROMOTE_TEMPORARY;

                return maybe_promote(hs_e->level >= mq->write_promote_level);
        } else
                return maybe_promote(hs_e->level >= mq->read_promote_level);
}

static dm_oblock_t to_hblock(struct smq_policy *mq, dm_oblock_t b)
{
        sector_t r = from_oblock(b);
        (void) sector_div(r, mq->cache_blocks_per_hotspot_block);
        return to_oblock(r);
}

static struct entry *update_hotspot_queue(struct smq_policy *mq, dm_oblock_t b)
{
        unsigned int hi;
        dm_oblock_t hb = to_hblock(mq, b);
        struct entry *e = h_lookup(&mq->hotspot_table, hb);

        if (e) {
                stats_level_accessed(&mq->hotspot_stats, e->level);

                hi = get_index(&mq->hotspot_alloc, e);
                q_requeue(&mq->hotspot, e,
                          test_and_set_bit(hi, mq->hotspot_hit_bits) ?
                          0u : mq->hotspot_level_jump,
                          NULL, NULL);

        } else {
                stats_miss(&mq->hotspot_stats);

                e = alloc_entry(&mq->hotspot_alloc);
                if (!e) {
                        e = q_pop(&mq->hotspot);
                        if (e) {
                                h_remove(&mq->hotspot_table, e);
                                hi = get_index(&mq->hotspot_alloc, e);
                                clear_bit(hi, mq->hotspot_hit_bits);
                        }

                }

                if (e) {
                        e->oblock = hb;
                        q_push(&mq->hotspot, e);
                        h_insert(&mq->hotspot_table, e);
                }
        }

        return e;
}

/*----------------------------------------------------------------*/

/*
 * Public interface, via the policy struct.  See dm-cache-policy.h for a
 * description of these.
 */

static struct smq_policy *to_smq_policy(struct dm_cache_policy *p)
{
        return container_of(p, struct smq_policy, policy);
}

static void smq_destroy(struct dm_cache_policy *p)
{
        struct smq_policy *mq = to_smq_policy(p);

        btracker_destroy(mq->bg_work);
        h_exit(&mq->hotspot_table);
        h_exit(&mq->table);
        free_bitset(mq->hotspot_hit_bits);
        free_bitset(mq->cache_hit_bits);
        space_exit(&mq->es);
        kfree(mq);
}

/*----------------------------------------------------------------*/

static int __lookup(struct smq_policy *mq, dm_oblock_t oblock, dm_cblock_t *cblock,
                    int data_dir, bool fast_copy,
                    struct policy_work **work, bool *background_work)
{
        struct entry *e, *hs_e;
        enum promote_result pr;

        *background_work = false;

        e = h_lookup(&mq->table, oblock);
        if (e) {
                stats_level_accessed(&mq->cache_stats, e->level);

                requeue(mq, e);
                *cblock = infer_cblock(mq, e);
                return 0;

        } else {
                stats_miss(&mq->cache_stats);

                /*
                 * The hotspot queue only gets updated with misses.
                 */
                hs_e = update_hotspot_queue(mq, oblock);

                pr = should_promote(mq, hs_e, data_dir, fast_copy);
                if (pr != PROMOTE_NOT) {
                        queue_promotion(mq, oblock, work);
                        *background_work = true;
                }

                return -ENOENT;
        }
}

static int smq_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock,
                      int data_dir, bool fast_copy,
                      bool *background_work)
{
        int r;
        unsigned long flags;
        struct smq_policy *mq = to_smq_policy(p);

        spin_lock_irqsave(&mq->lock, flags);
        r = __lookup(mq, oblock, cblock,
                     data_dir, fast_copy,
                     NULL, background_work);
        spin_unlock_irqrestore(&mq->lock, flags);

        return r;
}

static int smq_lookup_with_work(struct dm_cache_policy *p,
                                dm_oblock_t oblock, dm_cblock_t *cblock,
                                int data_dir, bool fast_copy,
                                struct policy_work **work)
{
        int r;
        bool background_queued;
        unsigned long flags;
        struct smq_policy *mq = to_smq_policy(p);

        spin_lock_irqsave(&mq->lock, flags);
        r = __lookup(mq, oblock, cblock, data_dir, fast_copy, work, &background_queued);
        spin_unlock_irqrestore(&mq->lock, flags);

        return r;
}

static int smq_get_background_work(struct dm_cache_policy *p, bool idle,
                                   struct policy_work **result)
{
        int r;
        unsigned long flags;
        struct smq_policy *mq = to_smq_policy(p);

        spin_lock_irqsave(&mq->lock, flags);
        r = btracker_issue(mq->bg_work, result);
        if (r == -ENODATA) {
                if (!clean_target_met(mq, idle)) {
                        queue_writeback(mq, idle);
                        r = btracker_issue(mq->bg_work, result);
                }
        }
        spin_unlock_irqrestore(&mq->lock, flags);

        return r;
}

/*
 * We need to clear any pending work flags that have been set, and in the
 * case of promotion free the entry for the destination cblock.
 */
static void __complete_background_work(struct smq_policy *mq,
                                       struct policy_work *work,
                                       bool success)
{
        struct entry *e = get_entry(&mq->cache_alloc,
                                    from_cblock(work->cblock));

        switch (work->op) {
        case POLICY_PROMOTE:
                // !h, !q, a
                clear_pending(mq, e);
                if (success) {
                        e->oblock = work->oblock;
                        e->level = NR_CACHE_LEVELS - 1;
                        push(mq, e);
                        // h, q, a
                } else {
                        free_entry(&mq->cache_alloc, e);
                        // !h, !q, !a
                }
                break;

        case POLICY_DEMOTE:
                // h, !q, a
                if (success) {
                        h_remove(&mq->table, e);
                        free_entry(&mq->cache_alloc, e);
                        // !h, !q, !a
                } else {
                        clear_pending(mq, e);
                        push_queue(mq, e);
                        // h, q, a
                }
                break;

        case POLICY_WRITEBACK:
                // h, !q, a
                clear_pending(mq, e);
                push_queue(mq, e);
                // h, q, a
                break;
        }

        btracker_complete(mq->bg_work, work);
}

static void smq_complete_background_work(struct dm_cache_policy *p,
                                         struct policy_work *work,
                                         bool success)
{
        unsigned long flags;
        struct smq_policy *mq = to_smq_policy(p);

        spin_lock_irqsave(&mq->lock, flags);
        __complete_background_work(mq, work, success);
        spin_unlock_irqrestore(&mq->lock, flags);
}

// in_hash(oblock) -> in_hash(oblock)
static void __smq_set_clear_dirty(struct smq_policy *mq, dm_cblock_t cblock, bool set)
{
        struct entry *e = get_entry(&mq->cache_alloc, from_cblock(cblock));

        if (e->pending_work)
                e->dirty = set;
        else {
                del_queue(mq, e);
                e->dirty = set;
                push_queue(mq, e);
        }
}

static void smq_set_dirty(struct dm_cache_policy *p, dm_cblock_t cblock)
{
        unsigned long flags;
        struct smq_policy *mq = to_smq_policy(p);

        spin_lock_irqsave(&mq->lock, flags);
        __smq_set_clear_dirty(mq, cblock, true);
        spin_unlock_irqrestore(&mq->lock, flags);
}

static void smq_clear_dirty(struct dm_cache_policy *p, dm_cblock_t cblock)
{
        struct smq_policy *mq = to_smq_policy(p);
        unsigned long flags;

        spin_lock_irqsave(&mq->lock, flags);
        __smq_set_clear_dirty(mq, cblock, false);
        spin_unlock_irqrestore(&mq->lock, flags);
}

static unsigned int random_level(dm_cblock_t cblock)
{
        return hash_32(from_cblock(cblock), 9) & (NR_CACHE_LEVELS - 1);
}

static int smq_load_mapping(struct dm_cache_policy *p,
                            dm_oblock_t oblock, dm_cblock_t cblock,
                            bool dirty, uint32_t hint, bool hint_valid)
{
        struct smq_policy *mq = to_smq_policy(p);
        struct entry *e;

        e = alloc_particular_entry(&mq->cache_alloc, from_cblock(cblock));
        e->oblock = oblock;
        e->dirty = dirty;
        e->level = hint_valid ? min(hint, NR_CACHE_LEVELS - 1) : random_level(cblock);
        e->pending_work = false;

        /*
         * When we load mappings we push ahead of both sentinels in order to
         * allow demotions and cleaning to occur immediately.
         */
        push_front(mq, e);

        return 0;
}

static int smq_invalidate_mapping(struct dm_cache_policy *p, dm_cblock_t cblock)
{
        struct smq_policy *mq = to_smq_policy(p);
        struct entry *e = get_entry(&mq->cache_alloc, from_cblock(cblock));

        if (!e->allocated)
                return -ENODATA;

        // FIXME: what if this block has pending background work?
        del_queue(mq, e);
        h_remove(&mq->table, e);
        free_entry(&mq->cache_alloc, e);
        return 0;
}

static uint32_t smq_get_hint(struct dm_cache_policy *p, dm_cblock_t cblock)
{
        struct smq_policy *mq = to_smq_policy(p);
        struct entry *e = get_entry(&mq->cache_alloc, from_cblock(cblock));

        if (!e->allocated)
                return 0;

        return e->level;
}

static dm_cblock_t smq_residency(struct dm_cache_policy *p)
{
        dm_cblock_t r;
        unsigned long flags;
        struct smq_policy *mq = to_smq_policy(p);

        spin_lock_irqsave(&mq->lock, flags);
        r = to_cblock(mq->cache_alloc.nr_allocated);
        spin_unlock_irqrestore(&mq->lock, flags);

        return r;
}

static void smq_tick(struct dm_cache_policy *p, bool can_block)
{
        struct smq_policy *mq = to_smq_policy(p);
        unsigned long flags;

        spin_lock_irqsave(&mq->lock, flags);
        mq->tick++;
        update_sentinels(mq);
        end_hotspot_period(mq);
        end_cache_period(mq);
        spin_unlock_irqrestore(&mq->lock, flags);
}

static void smq_allow_migrations(struct dm_cache_policy *p, bool allow)
{
        struct smq_policy *mq = to_smq_policy(p);

        mq->migrations_allowed = allow;
}

/*
 * smq has no config values, but the old mq policy did.  To avoid breaking
 * software we continue to accept these configurables for the mq policy,
 * but they have no effect.
 */
static int mq_set_config_value(struct dm_cache_policy *p,
                               const char *key, const char *value)
{
        unsigned long tmp;

        if (kstrtoul(value, 10, &tmp))
                return -EINVAL;

        if (!strcasecmp(key, "random_threshold") ||
            !strcasecmp(key, "sequential_threshold") ||
            !strcasecmp(key, "discard_promote_adjustment") ||
            !strcasecmp(key, "read_promote_adjustment") ||
            !strcasecmp(key, "write_promote_adjustment")) {
                DMWARN("tunable '%s' no longer has any effect, mq policy is now an alias for smq", key);
                return 0;
        }

        return -EINVAL;
}

static int mq_emit_config_values(struct dm_cache_policy *p, char *result,
                                 unsigned int maxlen, ssize_t *sz_ptr)
{
        ssize_t sz = *sz_ptr;

        DMEMIT("10 random_threshold 0 "
               "sequential_threshold 0 "
               "discard_promote_adjustment 0 "
               "read_promote_adjustment 0 "
               "write_promote_adjustment 0 ");

        *sz_ptr = sz;
        return 0;
}

/* Init the policy plugin interface function pointers. */
static void init_policy_functions(struct smq_policy *mq, bool mimic_mq)
{
        mq->policy.destroy = smq_destroy;
        mq->policy.lookup = smq_lookup;
        mq->policy.lookup_with_work = smq_lookup_with_work;
        mq->policy.get_background_work = smq_get_background_work;
        mq->policy.complete_background_work = smq_complete_background_work;
        mq->policy.set_dirty = smq_set_dirty;
        mq->policy.clear_dirty = smq_clear_dirty;
        mq->policy.load_mapping = smq_load_mapping;
        mq->policy.invalidate_mapping = smq_invalidate_mapping;
        mq->policy.get_hint = smq_get_hint;
        mq->policy.residency = smq_residency;
        mq->policy.tick = smq_tick;
        mq->policy.allow_migrations = smq_allow_migrations;

        if (mimic_mq) {
                mq->policy.set_config_value = mq_set_config_value;
                mq->policy.emit_config_values = mq_emit_config_values;
        }
}

static bool too_many_hotspot_blocks(sector_t origin_size,
                                    sector_t hotspot_block_size,
                                    unsigned int nr_hotspot_blocks)
{
        return (hotspot_block_size * nr_hotspot_blocks) > origin_size;
}

static void calc_hotspot_params(sector_t origin_size,
                                sector_t cache_block_size,
                                unsigned int nr_cache_blocks,
                                sector_t *hotspot_block_size,
                                unsigned int *nr_hotspot_blocks)
{
        *hotspot_block_size = cache_block_size * 16u;
        *nr_hotspot_blocks = max(nr_cache_blocks / 4u, 1024u);

        while ((*hotspot_block_size > cache_block_size) &&
               too_many_hotspot_blocks(origin_size, *hotspot_block_size, *nr_hotspot_blocks))
                *hotspot_block_size /= 2u;
}

static struct dm_cache_policy *
__smq_create(dm_cblock_t cache_size, sector_t origin_size, sector_t cache_block_size,
             bool mimic_mq, bool migrations_allowed, bool cleaner)
{
        unsigned int i;
        unsigned int nr_sentinels_per_queue = 2u * NR_CACHE_LEVELS;
        unsigned int total_sentinels = 2u * nr_sentinels_per_queue;
        struct smq_policy *mq = kzalloc(sizeof(*mq), GFP_KERNEL);

        if (!mq)
                return NULL;

        init_policy_functions(mq, mimic_mq);
        mq->cache_size = cache_size;
        mq->cache_block_size = cache_block_size;

        calc_hotspot_params(origin_size, cache_block_size, from_cblock(cache_size),
                            &mq->hotspot_block_size, &mq->nr_hotspot_blocks);

        mq->cache_blocks_per_hotspot_block = div64_u64(mq->hotspot_block_size, mq->cache_block_size);
        mq->hotspot_level_jump = 1u;
        if (space_init(&mq->es, total_sentinels + mq->nr_hotspot_blocks + from_cblock(cache_size))) {
                DMERR("couldn't initialize entry space");
                goto bad_pool_init;
        }

        init_allocator(&mq->writeback_sentinel_alloc, &mq->es, 0, nr_sentinels_per_queue);
        for (i = 0; i < nr_sentinels_per_queue; i++)
                get_entry(&mq->writeback_sentinel_alloc, i)->sentinel = true;

        init_allocator(&mq->demote_sentinel_alloc, &mq->es, nr_sentinels_per_queue, total_sentinels);
        for (i = 0; i < nr_sentinels_per_queue; i++)
                get_entry(&mq->demote_sentinel_alloc, i)->sentinel = true;

        init_allocator(&mq->hotspot_alloc, &mq->es, total_sentinels,
                       total_sentinels + mq->nr_hotspot_blocks);

        init_allocator(&mq->cache_alloc, &mq->es,
                       total_sentinels + mq->nr_hotspot_blocks,
                       total_sentinels + mq->nr_hotspot_blocks + from_cblock(cache_size));

        mq->hotspot_hit_bits = alloc_bitset(mq->nr_hotspot_blocks);
        if (!mq->hotspot_hit_bits) {
                DMERR("couldn't allocate hotspot hit bitset");
                goto bad_hotspot_hit_bits;
        }
        clear_bitset(mq->hotspot_hit_bits, mq->nr_hotspot_blocks);

        if (from_cblock(cache_size)) {
                mq->cache_hit_bits = alloc_bitset(from_cblock(cache_size));
                if (!mq->cache_hit_bits) {
                        DMERR("couldn't allocate cache hit bitset");
                        goto bad_cache_hit_bits;
                }
                clear_bitset(mq->cache_hit_bits, from_cblock(mq->cache_size));
        } else
                mq->cache_hit_bits = NULL;

        mq->tick = 0;
        spin_lock_init(&mq->lock);

        q_init(&mq->hotspot, &mq->es, NR_HOTSPOT_LEVELS);
        mq->hotspot.nr_top_levels = 8;
        mq->hotspot.nr_in_top_levels = min(mq->nr_hotspot_blocks / NR_HOTSPOT_LEVELS,
                                           from_cblock(mq->cache_size) / mq->cache_blocks_per_hotspot_block);

        q_init(&mq->clean, &mq->es, NR_CACHE_LEVELS);
        q_init(&mq->dirty, &mq->es, NR_CACHE_LEVELS);

        stats_init(&mq->hotspot_stats, NR_HOTSPOT_LEVELS);
        stats_init(&mq->cache_stats, NR_CACHE_LEVELS);

        if (h_init(&mq->table, &mq->es, from_cblock(cache_size)))
                goto bad_alloc_table;

        if (h_init(&mq->hotspot_table, &mq->es, mq->nr_hotspot_blocks))
                goto bad_alloc_hotspot_table;

        sentinels_init(mq);
        mq->write_promote_level = mq->read_promote_level = NR_HOTSPOT_LEVELS;

        mq->next_hotspot_period = jiffies;
        mq->next_cache_period = jiffies;

        mq->bg_work = btracker_create(4096); /* FIXME: hard coded value */
        if (!mq->bg_work)
                goto bad_btracker;

        mq->migrations_allowed = migrations_allowed;
        mq->cleaner = cleaner;

        return &mq->policy;

bad_btracker:
        h_exit(&mq->hotspot_table);
bad_alloc_hotspot_table:
        h_exit(&mq->table);
bad_alloc_table:
        free_bitset(mq->cache_hit_bits);
bad_cache_hit_bits:
        free_bitset(mq->hotspot_hit_bits);
bad_hotspot_hit_bits:
        space_exit(&mq->es);
bad_pool_init:
        kfree(mq);

        return NULL;
}

static struct dm_cache_policy *smq_create(dm_cblock_t cache_size,
                                          sector_t origin_size,
                                          sector_t cache_block_size)
{
        return __smq_create(cache_size, origin_size, cache_block_size,
                            false, true, false);
}

static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
                                         sector_t origin_size,
                                         sector_t cache_block_size)
{
        return __smq_create(cache_size, origin_size, cache_block_size,
                            true, true, false);
}

static struct dm_cache_policy *cleaner_create(dm_cblock_t cache_size,
                                              sector_t origin_size,
                                              sector_t cache_block_size)
{
        return __smq_create(cache_size, origin_size, cache_block_size,
                            false, false, true);
}

/*----------------------------------------------------------------*/

static struct dm_cache_policy_type smq_policy_type = {
        .name = "smq",
        .version = {2, 0, 0},
        .hint_size = 4,
        .owner = THIS_MODULE,
        .create = smq_create
};

static struct dm_cache_policy_type mq_policy_type = {
        .name = "mq",
        .version = {2, 0, 0},
        .hint_size = 4,
        .owner = THIS_MODULE,
        .create = mq_create,
};

static struct dm_cache_policy_type cleaner_policy_type = {
        .name = "cleaner",
        .version = {2, 0, 0},
        .hint_size = 4,
        .owner = THIS_MODULE,
        .create = cleaner_create,
};

static struct dm_cache_policy_type default_policy_type = {
        .name = "default",
        .version = {2, 0, 0},
        .hint_size = 4,
        .owner = THIS_MODULE,
        .create = smq_create,
        .real = &smq_policy_type
};

static int __init smq_init(void)
{
        int r;

        r = dm_cache_policy_register(&smq_policy_type);
        if (r) {
                DMERR("register failed %d", r);
                return -ENOMEM;
        }

        r = dm_cache_policy_register(&mq_policy_type);
        if (r) {
                DMERR("register failed (as mq) %d", r);
                goto out_mq;
        }

        r = dm_cache_policy_register(&cleaner_policy_type);
        if (r) {
                DMERR("register failed (as cleaner) %d", r);
                goto out_cleaner;
        }

        r = dm_cache_policy_register(&default_policy_type);
        if (r) {
                DMERR("register failed (as default) %d", r);
                goto out_default;
        }

        return 0;

out_default:
        dm_cache_policy_unregister(&cleaner_policy_type);
out_cleaner:
        dm_cache_policy_unregister(&mq_policy_type);
out_mq:
        dm_cache_policy_unregister(&smq_policy_type);

        return -ENOMEM;
}

static void __exit smq_exit(void)
{
        dm_cache_policy_unregister(&cleaner_policy_type);
        dm_cache_policy_unregister(&smq_policy_type);
        dm_cache_policy_unregister(&mq_policy_type);
        dm_cache_policy_unregister(&default_policy_type);
}

module_init(smq_init);
module_exit(smq_exit);

MODULE_AUTHOR("Joe Thornber <dm-devel@lists.linux.dev>");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("smq cache policy");

MODULE_ALIAS("dm-cache-default");
MODULE_ALIAS("dm-cache-mq");
MODULE_ALIAS("dm-cache-cleaner");