Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1942 insertions, 0 deletions

diff --git a/drivers/md/dm-cache-policy-smq.c b/drivers/md/dm-cache-policy-smq.c
new file mode 100644
index 000000000..1b5b9ad9e
--- /dev/null
+++ b/drivers/md/dm-cache-policy-smq.c
@@ -0,0 +1,1942 @@
+/*
+ * 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 safe_div(unsigned n, unsigned d)
+{
+	return d ? n / d : 0u;
+}
+
+static unsigned safe_mod(unsigned n, unsigned d)
+{
+	return d ? n % d : 0u;
+}
+
+/*----------------------------------------------------------------*/
+
+struct entry {
+	unsigned hash_next:28;
+	unsigned prev:28;
+	unsigned next:28;
+	unsigned 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 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 block)
+{
+	struct entry *e;
+
+	e = es->begin + block;
+	BUG_ON(e >= es->end);
+
+	return e;
+}
+
+static unsigned 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 block)
+{
+	if (block == INDEXER_NULL)
+		return NULL;
+
+	return __get_entry(es, block);
+}
+
+/*----------------------------------------------------------------*/
+
+struct ilist {
+	unsigned nr_elts;	/* excluding sentinel entries */
+	unsigned 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 nr_elts;
+	unsigned nr_levels;
+	struct ilist qs[MAX_LEVELS];
+
+	/*
+	 * We maintain a count of the number of entries we would like in each
+	 * level.
+	 */
+	unsigned last_target_nr_elts;
+	unsigned nr_top_levels;
+	unsigned nr_in_top_levels;
+	unsigned target_count[MAX_LEVELS];
+};
+
+static void q_init(struct queue *q, struct entry_space *es, unsigned nr_levels)
+{
+	unsigned 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 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 max_level, bool can_cross_sentinel)
+{
+	unsigned 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 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 nr_elts, unsigned lbegin, unsigned lend)
+{
+	unsigned 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 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 extra_levels,
+		      struct entry *s1, struct entry *s2)
+{
+	struct entry *de;
+	unsigned sentinels_passed = 0;
+	unsigned 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 hit_threshold;
+	unsigned hits;
+	unsigned misses;
+};
+
+enum performance {
+	Q_POOR,
+	Q_FAIR,
+	Q_WELL
+};
+
+static void stats_init(struct stats *s, unsigned 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 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 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 *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 nr_entries)
+{
+	unsigned 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 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 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 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 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 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 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 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 begin;
+
+	unsigned nr_allocated;
+	struct ilist free;
+};
+
+static void init_allocator(struct entry_alloc *ea, struct entry_space *es,
+			   unsigned begin, unsigned end)
+{
+	unsigned 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 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 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 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 nr_hotspot_blocks;
+	unsigned cache_blocks_per_hotspot_block;
+	unsigned 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 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 write_promote_level;
+	unsigned read_promote_level;
+
+	unsigned long next_hotspot_period;
+	unsigned long next_cache_period;
+
+	struct background_tracker *bg_work;
+
+	bool migrations_allowed;
+};
+
+/*----------------------------------------------------------------*/
+
+static struct entry *get_sentinel(struct entry_alloc *ea, unsigned level, bool which)
+{
+	return get_entry(ea, which ? level : NR_CACHE_LEVELS + level);
+}
+
+static struct entry *writeback_sentinel(struct smq_policy *mq, unsigned level)
+{
+	return get_sentinel(&mq->writeback_sentinel_alloc, level, mq->current_writeback_sentinels);
+}
+
+static struct entry *demote_sentinel(struct smq_policy *mq, unsigned level)
+{
+	return get_sentinel(&mq->demote_sentinel_alloc, level, mq->current_demote_sentinels);
+}
+
+static void __update_writeback_sentinels(struct smq_policy *mq)
+{
+	unsigned 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 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 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 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 unsigned table[] = {1, 1, 1, 2, 4, 6, 7, 8, 7, 6, 4, 4, 3, 3, 2, 2, 1};
+
+	unsigned hits = mq->cache_stats.hits;
+	unsigned misses = mq->cache_stats.misses;
+	unsigned 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 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 percent_to_target(struct smq_policy *mq, unsigned 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) {
+		/*
+		 * 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 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 (unlikely(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 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 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 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 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 nr_cache_blocks,
+				sector_t *hotspot_block_size,
+				unsigned *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)
+{
+	unsigned i;
+	unsigned nr_sentinels_per_queue = 2u * NR_CACHE_LEVELS;
+	unsigned 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;
+
+	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);
+}
+
+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);
+}
+
+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);
+}
+
+/*----------------------------------------------------------------*/
+
+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@redhat.com>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("smq cache policy");
+
+MODULE_ALIAS("dm-cache-default");
+MODULE_ALIAS("dm-cache-mq");
+MODULE_ALIAS("dm-cache-cleaner");