Initial import

1 files changed, 1491 insertions, 0 deletions

diff --git a/drivers/md/dm-cache-policy-mq.c b/drivers/md/dm-cache-policy-mq.c
new file mode 100644
index 000000000..515d44bf2
--- /dev/null
+++ b/drivers/md/dm-cache-policy-mq.c
@@ -0,0 +1,1491 @@
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#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/slab.h>
+#include <linux/vmalloc.h>
+
+#define DM_MSG_PREFIX "cache-policy-mq"
+
+static struct kmem_cache *mq_entry_cache;
+
+/*----------------------------------------------------------------*/
+
+static unsigned next_power(unsigned n, unsigned min)
+{
+	return roundup_pow_of_two(max(n, min));
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Large, sequential ios are probably better left on the origin device since
+ * spindles tend to have good bandwidth.
+ *
+ * The io_tracker tries to spot when the io is in one of these sequential
+ * modes.
+ *
+ * Two thresholds to switch between random and sequential io mode are defaulting
+ * as follows and can be adjusted via the constructor and message interfaces.
+ */
+#define RANDOM_THRESHOLD_DEFAULT 4
+#define SEQUENTIAL_THRESHOLD_DEFAULT 512
+
+enum io_pattern {
+	PATTERN_SEQUENTIAL,
+	PATTERN_RANDOM
+};
+
+struct io_tracker {
+	enum io_pattern pattern;
+
+	unsigned nr_seq_samples;
+	unsigned nr_rand_samples;
+	unsigned thresholds[2];
+
+	dm_oblock_t last_end_oblock;
+};
+
+static void iot_init(struct io_tracker *t,
+		     int sequential_threshold, int random_threshold)
+{
+	t->pattern = PATTERN_RANDOM;
+	t->nr_seq_samples = 0;
+	t->nr_rand_samples = 0;
+	t->last_end_oblock = 0;
+	t->thresholds[PATTERN_RANDOM] = random_threshold;
+	t->thresholds[PATTERN_SEQUENTIAL] = sequential_threshold;
+}
+
+static enum io_pattern iot_pattern(struct io_tracker *t)
+{
+	return t->pattern;
+}
+
+static void iot_update_stats(struct io_tracker *t, struct bio *bio)
+{
+	if (bio->bi_iter.bi_sector == from_oblock(t->last_end_oblock) + 1)
+		t->nr_seq_samples++;
+	else {
+		/*
+		 * Just one non-sequential IO is enough to reset the
+		 * counters.
+		 */
+		if (t->nr_seq_samples) {
+			t->nr_seq_samples = 0;
+			t->nr_rand_samples = 0;
+		}
+
+		t->nr_rand_samples++;
+	}
+
+	t->last_end_oblock = to_oblock(bio_end_sector(bio) - 1);
+}
+
+static void iot_check_for_pattern_switch(struct io_tracker *t)
+{
+	switch (t->pattern) {
+	case PATTERN_SEQUENTIAL:
+		if (t->nr_rand_samples >= t->thresholds[PATTERN_RANDOM]) {
+			t->pattern = PATTERN_RANDOM;
+			t->nr_seq_samples = t->nr_rand_samples = 0;
+		}
+		break;
+
+	case PATTERN_RANDOM:
+		if (t->nr_seq_samples >= t->thresholds[PATTERN_SEQUENTIAL]) {
+			t->pattern = PATTERN_SEQUENTIAL;
+			t->nr_seq_samples = t->nr_rand_samples = 0;
+		}
+		break;
+	}
+}
+
+static void iot_examine_bio(struct io_tracker *t, struct bio *bio)
+{
+	iot_update_stats(t, bio);
+	iot_check_for_pattern_switch(t);
+}
+
+/*----------------------------------------------------------------*/
+
+
+/*
+ * This queue is divided up into different levels.  Allowing us to push
+ * entries to the back of any of the levels.  Think of it as a partially
+ * sorted queue.
+ */
+#define NR_QUEUE_LEVELS 16u
+#define NR_SENTINELS NR_QUEUE_LEVELS * 3
+
+#define WRITEBACK_PERIOD HZ
+
+struct queue {
+	unsigned nr_elts;
+	bool current_writeback_sentinels;
+	unsigned long next_writeback;
+	struct list_head qs[NR_QUEUE_LEVELS];
+	struct list_head sentinels[NR_SENTINELS];
+};
+
+static void queue_init(struct queue *q)
+{
+	unsigned i;
+
+	q->nr_elts = 0;
+	q->current_writeback_sentinels = false;
+	q->next_writeback = 0;
+	for (i = 0; i < NR_QUEUE_LEVELS; i++) {
+		INIT_LIST_HEAD(q->qs + i);
+		INIT_LIST_HEAD(q->sentinels + i);
+		INIT_LIST_HEAD(q->sentinels + NR_QUEUE_LEVELS + i);
+		INIT_LIST_HEAD(q->sentinels + (2 * NR_QUEUE_LEVELS) + i);
+	}
+}
+
+static unsigned queue_size(struct queue *q)
+{
+	return q->nr_elts;
+}
+
+static bool queue_empty(struct queue *q)
+{
+	return q->nr_elts == 0;
+}
+
+/*
+ * Insert an entry to the back of the given level.
+ */
+static void queue_push(struct queue *q, unsigned level, struct list_head *elt)
+{
+	q->nr_elts++;
+	list_add_tail(elt, q->qs + level);
+}
+
+static void queue_remove(struct queue *q, struct list_head *elt)
+{
+	q->nr_elts--;
+	list_del(elt);
+}
+
+static bool is_sentinel(struct queue *q, struct list_head *h)
+{
+	return (h >= q->sentinels) && (h < (q->sentinels + NR_SENTINELS));
+}
+
+/*
+ * Gives us the oldest entry of the lowest popoulated level.  If the first
+ * level is emptied then we shift down one level.
+ */
+static struct list_head *queue_peek(struct queue *q)
+{
+	unsigned level;
+	struct list_head *h;
+
+	for (level = 0; level < NR_QUEUE_LEVELS; level++)
+		list_for_each(h, q->qs + level)
+			if (!is_sentinel(q, h))
+				return h;
+
+	return NULL;
+}
+
+static struct list_head *queue_pop(struct queue *q)
+{
+	struct list_head *r = queue_peek(q);
+
+	if (r) {
+		q->nr_elts--;
+		list_del(r);
+	}
+
+	return r;
+}
+
+/*
+ * Pops an entry from a level that is not past a sentinel.
+ */
+static struct list_head *queue_pop_old(struct queue *q)
+{
+	unsigned level;
+	struct list_head *h;
+
+	for (level = 0; level < NR_QUEUE_LEVELS; level++)
+		list_for_each(h, q->qs + level) {
+			if (is_sentinel(q, h))
+				break;
+
+			q->nr_elts--;
+			list_del(h);
+			return h;
+		}
+
+	return NULL;
+}
+
+static struct list_head *list_pop(struct list_head *lh)
+{
+	struct list_head *r = lh->next;
+
+	BUG_ON(!r);
+	list_del_init(r);
+
+	return r;
+}
+
+static struct list_head *writeback_sentinel(struct queue *q, unsigned level)
+{
+	if (q->current_writeback_sentinels)
+		return q->sentinels + NR_QUEUE_LEVELS + level;
+	else
+		return q->sentinels + 2 * NR_QUEUE_LEVELS + level;
+}
+
+static void queue_update_writeback_sentinels(struct queue *q)
+{
+	unsigned i;
+	struct list_head *h;
+
+	if (time_after(jiffies, q->next_writeback)) {
+		for (i = 0; i < NR_QUEUE_LEVELS; i++) {
+			h = writeback_sentinel(q, i);
+			list_del(h);
+			list_add_tail(h, q->qs + i);
+		}
+
+		q->next_writeback = jiffies + WRITEBACK_PERIOD;
+		q->current_writeback_sentinels = !q->current_writeback_sentinels;
+	}
+}
+
+/*
+ * Sometimes we want to iterate through entries that have been pushed since
+ * a certain event.  We use sentinel entries on the queues to delimit these
+ * 'tick' events.
+ */
+static void queue_tick(struct queue *q)
+{
+	unsigned i;
+
+	for (i = 0; i < NR_QUEUE_LEVELS; i++) {
+		list_del(q->sentinels + i);
+		list_add_tail(q->sentinels + i, q->qs + i);
+	}
+}
+
+typedef void (*iter_fn)(struct list_head *, void *);
+static void queue_iterate_tick(struct queue *q, iter_fn fn, void *context)
+{
+	unsigned i;
+	struct list_head *h;
+
+	for (i = 0; i < NR_QUEUE_LEVELS; i++) {
+		list_for_each_prev(h, q->qs + i) {
+			if (is_sentinel(q, h))
+				break;
+
+			fn(h, context);
+		}
+	}
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Describes a cache entry.  Used in both the cache and the pre_cache.
+ */
+struct entry {
+	struct hlist_node hlist;
+	struct list_head list;
+	dm_oblock_t oblock;
+
+	/*
+	 * FIXME: pack these better
+	 */
+	bool dirty:1;
+	unsigned hit_count;
+};
+
+/*
+ * Rather than storing the cblock in an entry, we allocate all entries in
+ * an array, and infer the cblock from the entry position.
+ *
+ * Free entries are linked together into a list.
+ */
+struct entry_pool {
+	struct entry *entries, *entries_end;
+	struct list_head free;
+	unsigned nr_allocated;
+};
+
+static int epool_init(struct entry_pool *ep, unsigned nr_entries)
+{
+	unsigned i;
+
+	ep->entries = vzalloc(sizeof(struct entry) * nr_entries);
+	if (!ep->entries)
+		return -ENOMEM;
+
+	ep->entries_end = ep->entries + nr_entries;
+
+	INIT_LIST_HEAD(&ep->free);
+	for (i = 0; i < nr_entries; i++)
+		list_add(&ep->entries[i].list, &ep->free);
+
+	ep->nr_allocated = 0;
+
+	return 0;
+}
+
+static void epool_exit(struct entry_pool *ep)
+{
+	vfree(ep->entries);
+}
+
+static struct entry *alloc_entry(struct entry_pool *ep)
+{
+	struct entry *e;
+
+	if (list_empty(&ep->free))
+		return NULL;
+
+	e = list_entry(list_pop(&ep->free), struct entry, list);
+	INIT_LIST_HEAD(&e->list);
+	INIT_HLIST_NODE(&e->hlist);
+	ep->nr_allocated++;
+
+	return e;
+}
+
+/*
+ * This assumes the cblock hasn't already been allocated.
+ */
+static struct entry *alloc_particular_entry(struct entry_pool *ep, dm_cblock_t cblock)
+{
+	struct entry *e = ep->entries + from_cblock(cblock);
+
+	list_del_init(&e->list);
+	INIT_HLIST_NODE(&e->hlist);
+	ep->nr_allocated++;
+
+	return e;
+}
+
+static void free_entry(struct entry_pool *ep, struct entry *e)
+{
+	BUG_ON(!ep->nr_allocated);
+	ep->nr_allocated--;
+	INIT_HLIST_NODE(&e->hlist);
+	list_add(&e->list, &ep->free);
+}
+
+/*
+ * Returns NULL if the entry is free.
+ */
+static struct entry *epool_find(struct entry_pool *ep, dm_cblock_t cblock)
+{
+	struct entry *e = ep->entries + from_cblock(cblock);
+	return !hlist_unhashed(&e->hlist) ? e : NULL;
+}
+
+static bool epool_empty(struct entry_pool *ep)
+{
+	return list_empty(&ep->free);
+}
+
+static bool in_pool(struct entry_pool *ep, struct entry *e)
+{
+	return e >= ep->entries && e < ep->entries_end;
+}
+
+static dm_cblock_t infer_cblock(struct entry_pool *ep, struct entry *e)
+{
+	return to_cblock(e - ep->entries);
+}
+
+/*----------------------------------------------------------------*/
+
+struct mq_policy {
+	struct dm_cache_policy policy;
+
+	/* protects everything */
+	struct mutex lock;
+	dm_cblock_t cache_size;
+	struct io_tracker tracker;
+
+	/*
+	 * Entries come from two pools, one of pre-cache entries, and one
+	 * for the cache proper.
+	 */
+	struct entry_pool pre_cache_pool;
+	struct entry_pool cache_pool;
+
+	/*
+	 * We maintain three queues of entries.  The cache proper,
+	 * consisting of a clean and dirty queue, contains the currently
+	 * active mappings.  Whereas the pre_cache tracks blocks that
+	 * are being hit frequently and potential candidates for promotion
+	 * to the cache.
+	 */
+	struct queue pre_cache;
+	struct queue cache_clean;
+	struct queue cache_dirty;
+
+	/*
+	 * Keeps track of time, incremented by the core.  We use this to
+	 * avoid attributing multiple hits within the same tick.
+	 *
+	 * Access to tick_protected should be done with the spin lock held.
+	 * It's copied to tick at the start of the map function (within the
+	 * mutex).
+	 */
+	spinlock_t tick_lock;
+	unsigned tick_protected;
+	unsigned tick;
+
+	/*
+	 * A count of the number of times the map function has been called
+	 * and found an entry in the pre_cache or cache.  Currently used to
+	 * calculate the generation.
+	 */
+	unsigned hit_count;
+
+	/*
+	 * A generation is a longish period that is used to trigger some
+	 * book keeping effects.  eg, decrementing hit counts on entries.
+	 * This is needed to allow the cache to evolve as io patterns
+	 * change.
+	 */
+	unsigned generation;
+	unsigned generation_period; /* in lookups (will probably change) */
+
+	unsigned discard_promote_adjustment;
+	unsigned read_promote_adjustment;
+	unsigned write_promote_adjustment;
+
+	/*
+	 * The hash table allows us to quickly find an entry by origin
+	 * block.  Both pre_cache and cache entries are in here.
+	 */
+	unsigned nr_buckets;
+	dm_block_t hash_bits;
+	struct hlist_head *table;
+};
+
+#define DEFAULT_DISCARD_PROMOTE_ADJUSTMENT 1
+#define DEFAULT_READ_PROMOTE_ADJUSTMENT 4
+#define DEFAULT_WRITE_PROMOTE_ADJUSTMENT 8
+#define DISCOURAGE_DEMOTING_DIRTY_THRESHOLD 128
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Simple hash table implementation.  Should replace with the standard hash
+ * table that's making its way upstream.
+ */
+static void hash_insert(struct mq_policy *mq, struct entry *e)
+{
+	unsigned h = hash_64(from_oblock(e->oblock), mq->hash_bits);
+
+	hlist_add_head(&e->hlist, mq->table + h);
+}
+
+static struct entry *hash_lookup(struct mq_policy *mq, dm_oblock_t oblock)
+{
+	unsigned h = hash_64(from_oblock(oblock), mq->hash_bits);
+	struct hlist_head *bucket = mq->table + h;
+	struct entry *e;
+
+	hlist_for_each_entry(e, bucket, hlist)
+		if (e->oblock == oblock) {
+			hlist_del(&e->hlist);
+			hlist_add_head(&e->hlist, bucket);
+			return e;
+		}
+
+	return NULL;
+}
+
+static void hash_remove(struct entry *e)
+{
+	hlist_del(&e->hlist);
+}
+
+/*----------------------------------------------------------------*/
+
+static bool any_free_cblocks(struct mq_policy *mq)
+{
+	return !epool_empty(&mq->cache_pool);
+}
+
+static bool any_clean_cblocks(struct mq_policy *mq)
+{
+	return !queue_empty(&mq->cache_clean);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Now we get to the meat of the policy.  This section deals with deciding
+ * when to to add entries to the pre_cache and cache, and move between
+ * them.
+ */
+
+/*
+ * The queue level is based on the log2 of the hit count.
+ */
+static unsigned queue_level(struct entry *e)
+{
+	return min((unsigned) ilog2(e->hit_count), NR_QUEUE_LEVELS - 1u);
+}
+
+static bool in_cache(struct mq_policy *mq, struct entry *e)
+{
+	return in_pool(&mq->cache_pool, e);
+}
+
+/*
+ * Inserts the entry into the pre_cache or the cache.  Ensures the cache
+ * block is marked as allocated if necc.  Inserts into the hash table.
+ * Sets the tick which records when the entry was last moved about.
+ */
+static void push(struct mq_policy *mq, struct entry *e)
+{
+	hash_insert(mq, e);
+
+	if (in_cache(mq, e))
+		queue_push(e->dirty ? &mq->cache_dirty : &mq->cache_clean,
+			   queue_level(e), &e->list);
+	else
+		queue_push(&mq->pre_cache, queue_level(e), &e->list);
+}
+
+/*
+ * Removes an entry from pre_cache or cache.  Removes from the hash table.
+ */
+static void del(struct mq_policy *mq, struct entry *e)
+{
+	if (in_cache(mq, e))
+		queue_remove(e->dirty ? &mq->cache_dirty : &mq->cache_clean, &e->list);
+	else
+		queue_remove(&mq->pre_cache, &e->list);
+
+	hash_remove(e);
+}
+
+/*
+ * Like del, except it removes the first entry in the queue (ie. the least
+ * recently used).
+ */
+static struct entry *pop(struct mq_policy *mq, struct queue *q)
+{
+	struct entry *e;
+	struct list_head *h = queue_pop(q);
+
+	if (!h)
+		return NULL;
+
+	e = container_of(h, struct entry, list);
+	hash_remove(e);
+
+	return e;
+}
+
+static struct entry *pop_old(struct mq_policy *mq, struct queue *q)
+{
+	struct entry *e;
+	struct list_head *h = queue_pop_old(q);
+
+	if (!h)
+		return NULL;
+
+	e = container_of(h, struct entry, list);
+	hash_remove(e);
+
+	return e;
+}
+
+static struct entry *peek(struct queue *q)
+{
+	struct list_head *h = queue_peek(q);
+	return h ? container_of(h, struct entry, list) : NULL;
+}
+
+/*
+ * The promotion threshold is adjusted every generation.  As are the counts
+ * of the entries.
+ *
+ * At the moment the threshold is taken by averaging the hit counts of some
+ * of the entries in the cache (the first 20 entries across all levels in
+ * ascending order, giving preference to the clean entries at each level).
+ *
+ * We can be much cleverer than this though.  For example, each promotion
+ * could bump up the threshold helping to prevent churn.  Much more to do
+ * here.
+ */
+
+#define MAX_TO_AVERAGE 20
+
+static void check_generation(struct mq_policy *mq)
+{
+	unsigned total = 0, nr = 0, count = 0, level;
+	struct list_head *head;
+	struct entry *e;
+
+	if ((mq->hit_count >= mq->generation_period) && (epool_empty(&mq->cache_pool))) {
+		mq->hit_count = 0;
+		mq->generation++;
+
+		for (level = 0; level < NR_QUEUE_LEVELS && count < MAX_TO_AVERAGE; level++) {
+			head = mq->cache_clean.qs + level;
+			list_for_each_entry(e, head, list) {
+				nr++;
+				total += e->hit_count;
+
+				if (++count >= MAX_TO_AVERAGE)
+					break;
+			}
+
+			head = mq->cache_dirty.qs + level;
+			list_for_each_entry(e, head, list) {
+				nr++;
+				total += e->hit_count;
+
+				if (++count >= MAX_TO_AVERAGE)
+					break;
+			}
+		}
+	}
+}
+
+/*
+ * Whenever we use an entry we bump up it's hit counter, and push it to the
+ * back to it's current level.
+ */
+static void requeue(struct mq_policy *mq, struct entry *e)
+{
+	check_generation(mq);
+	del(mq, e);
+	push(mq, e);
+}
+
+/*
+ * Demote the least recently used entry from the cache to the pre_cache.
+ * Returns the new cache entry to use, and the old origin block it was
+ * mapped to.
+ *
+ * We drop the hit count on the demoted entry back to 1 to stop it bouncing
+ * straight back into the cache if it's subsequently hit.  There are
+ * various options here, and more experimentation would be good:
+ *
+ * - just forget about the demoted entry completely (ie. don't insert it
+     into the pre_cache).
+ * - divide the hit count rather that setting to some hard coded value.
+ * - set the hit count to a hard coded value other than 1, eg, is it better
+ *   if it goes in at level 2?
+ */
+static int demote_cblock(struct mq_policy *mq,
+			 struct policy_locker *locker, dm_oblock_t *oblock)
+{
+	struct entry *demoted = peek(&mq->cache_clean);
+
+	if (!demoted)
+		/*
+		 * We could get a block from mq->cache_dirty, but that
+		 * would add extra latency to the triggering bio as it
+		 * waits for the writeback.  Better to not promote this
+		 * time and hope there's a clean block next time this block
+		 * is hit.
+		 */
+		return -ENOSPC;
+
+	if (locker->fn(locker, demoted->oblock))
+		/*
+		 * We couldn't lock the demoted block.
+		 */
+		return -EBUSY;
+
+	del(mq, demoted);
+	*oblock = demoted->oblock;
+	free_entry(&mq->cache_pool, demoted);
+
+	/*
+	 * We used to put the demoted block into the pre-cache, but I think
+	 * it's simpler to just let it work it's way up from zero again.
+	 * Stops blocks flickering in and out of the cache.
+	 */
+
+	return 0;
+}
+
+/*
+ * Entries in the pre_cache whose hit count passes the promotion
+ * threshold move to the cache proper.  Working out the correct
+ * value for the promotion_threshold is crucial to this policy.
+ */
+static unsigned promote_threshold(struct mq_policy *mq)
+{
+	struct entry *e;
+
+	if (any_free_cblocks(mq))
+		return 0;
+
+	e = peek(&mq->cache_clean);
+	if (e)
+		return e->hit_count;
+
+	e = peek(&mq->cache_dirty);
+	if (e)
+		return e->hit_count + DISCOURAGE_DEMOTING_DIRTY_THRESHOLD;
+
+	/* This should never happen */
+	return 0;
+}
+
+/*
+ * We modify the basic promotion_threshold depending on the specific io.
+ *
+ * If the origin block has been discarded then there's no cost to copy it
+ * to the cache.
+ *
+ * We bias towards reads, since they can be demoted at no cost if they
+ * haven't been dirtied.
+ */
+static unsigned adjusted_promote_threshold(struct mq_policy *mq,
+					   bool discarded_oblock, int data_dir)
+{
+	if (data_dir == READ)
+		return promote_threshold(mq) + mq->read_promote_adjustment;
+
+	if (discarded_oblock && (any_free_cblocks(mq) || any_clean_cblocks(mq))) {
+		/*
+		 * We don't need to do any copying at all, so give this a
+		 * very low threshold.
+		 */
+		return mq->discard_promote_adjustment;
+	}
+
+	return promote_threshold(mq) + mq->write_promote_adjustment;
+}
+
+static bool should_promote(struct mq_policy *mq, struct entry *e,
+			   bool discarded_oblock, int data_dir)
+{
+	return e->hit_count >=
+		adjusted_promote_threshold(mq, discarded_oblock, data_dir);
+}
+
+static int cache_entry_found(struct mq_policy *mq,
+			     struct entry *e,
+			     struct policy_result *result)
+{
+	requeue(mq, e);
+
+	if (in_cache(mq, e)) {
+		result->op = POLICY_HIT;
+		result->cblock = infer_cblock(&mq->cache_pool, e);
+	}
+
+	return 0;
+}
+
+/*
+ * Moves an entry from the pre_cache to the cache.  The main work is
+ * finding which cache block to use.
+ */
+static int pre_cache_to_cache(struct mq_policy *mq, struct entry *e,
+			      struct policy_locker *locker,
+			      struct policy_result *result)
+{
+	int r;
+	struct entry *new_e;
+
+	/* Ensure there's a free cblock in the cache */
+	if (epool_empty(&mq->cache_pool)) {
+		result->op = POLICY_REPLACE;
+		r = demote_cblock(mq, locker, &result->old_oblock);
+		if (r) {
+			result->op = POLICY_MISS;
+			return 0;
+		}
+
+	} else
+		result->op = POLICY_NEW;
+
+	new_e = alloc_entry(&mq->cache_pool);
+	BUG_ON(!new_e);
+
+	new_e->oblock = e->oblock;
+	new_e->dirty = false;
+	new_e->hit_count = e->hit_count;
+
+	del(mq, e);
+	free_entry(&mq->pre_cache_pool, e);
+	push(mq, new_e);
+
+	result->cblock = infer_cblock(&mq->cache_pool, new_e);
+
+	return 0;
+}
+
+static int pre_cache_entry_found(struct mq_policy *mq, struct entry *e,
+				 bool can_migrate, bool discarded_oblock,
+				 int data_dir, struct policy_locker *locker,
+				 struct policy_result *result)
+{
+	int r = 0;
+
+	if (!should_promote(mq, e, discarded_oblock, data_dir)) {
+		requeue(mq, e);
+		result->op = POLICY_MISS;
+
+	} else if (!can_migrate)
+		r = -EWOULDBLOCK;
+
+	else {
+		requeue(mq, e);
+		r = pre_cache_to_cache(mq, e, locker, result);
+	}
+
+	return r;
+}
+
+static void insert_in_pre_cache(struct mq_policy *mq,
+				dm_oblock_t oblock)
+{
+	struct entry *e = alloc_entry(&mq->pre_cache_pool);
+
+	if (!e)
+		/*
+		 * There's no spare entry structure, so we grab the least
+		 * used one from the pre_cache.
+		 */
+		e = pop(mq, &mq->pre_cache);
+
+	if (unlikely(!e)) {
+		DMWARN("couldn't pop from pre cache");
+		return;
+	}
+
+	e->dirty = false;
+	e->oblock = oblock;
+	e->hit_count = 1;
+	push(mq, e);
+}
+
+static void insert_in_cache(struct mq_policy *mq, dm_oblock_t oblock,
+			    struct policy_locker *locker,
+			    struct policy_result *result)
+{
+	int r;
+	struct entry *e;
+
+	if (epool_empty(&mq->cache_pool)) {
+		result->op = POLICY_REPLACE;
+		r = demote_cblock(mq, locker, &result->old_oblock);
+		if (unlikely(r)) {
+			result->op = POLICY_MISS;
+			insert_in_pre_cache(mq, oblock);
+			return;
+		}
+
+		/*
+		 * This will always succeed, since we've just demoted.
+		 */
+		e = alloc_entry(&mq->cache_pool);
+		BUG_ON(!e);
+
+	} else {
+		e = alloc_entry(&mq->cache_pool);
+		result->op = POLICY_NEW;
+	}
+
+	e->oblock = oblock;
+	e->dirty = false;
+	e->hit_count = 1;
+	push(mq, e);
+
+	result->cblock = infer_cblock(&mq->cache_pool, e);
+}
+
+static int no_entry_found(struct mq_policy *mq, dm_oblock_t oblock,
+			  bool can_migrate, bool discarded_oblock,
+			  int data_dir, struct policy_locker *locker,
+			  struct policy_result *result)
+{
+	if (adjusted_promote_threshold(mq, discarded_oblock, data_dir) <= 1) {
+		if (can_migrate)
+			insert_in_cache(mq, oblock, locker, result);
+		else
+			return -EWOULDBLOCK;
+	} else {
+		insert_in_pre_cache(mq, oblock);
+		result->op = POLICY_MISS;
+	}
+
+	return 0;
+}
+
+/*
+ * Looks the oblock up in the hash table, then decides whether to put in
+ * pre_cache, or cache etc.
+ */
+static int map(struct mq_policy *mq, dm_oblock_t oblock,
+	       bool can_migrate, bool discarded_oblock,
+	       int data_dir, struct policy_locker *locker,
+	       struct policy_result *result)
+{
+	int r = 0;
+	struct entry *e = hash_lookup(mq, oblock);
+
+	if (e && in_cache(mq, e))
+		r = cache_entry_found(mq, e, result);
+
+	else if (mq->tracker.thresholds[PATTERN_SEQUENTIAL] &&
+		 iot_pattern(&mq->tracker) == PATTERN_SEQUENTIAL)
+		result->op = POLICY_MISS;
+
+	else if (e)
+		r = pre_cache_entry_found(mq, e, can_migrate, discarded_oblock,
+					  data_dir, locker, result);
+
+	else
+		r = no_entry_found(mq, oblock, can_migrate, discarded_oblock,
+				   data_dir, locker, result);
+
+	if (r == -EWOULDBLOCK)
+		result->op = POLICY_MISS;
+
+	return r;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Public interface, via the policy struct.  See dm-cache-policy.h for a
+ * description of these.
+ */
+
+static struct mq_policy *to_mq_policy(struct dm_cache_policy *p)
+{
+	return container_of(p, struct mq_policy, policy);
+}
+
+static void mq_destroy(struct dm_cache_policy *p)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+
+	vfree(mq->table);
+	epool_exit(&mq->cache_pool);
+	epool_exit(&mq->pre_cache_pool);
+	kfree(mq);
+}
+
+static void update_pre_cache_hits(struct list_head *h, void *context)
+{
+	struct entry *e = container_of(h, struct entry, list);
+	e->hit_count++;
+}
+
+static void update_cache_hits(struct list_head *h, void *context)
+{
+	struct mq_policy *mq = context;
+	struct entry *e = container_of(h, struct entry, list);
+	e->hit_count++;
+	mq->hit_count++;
+}
+
+static void copy_tick(struct mq_policy *mq)
+{
+	unsigned long flags, tick;
+
+	spin_lock_irqsave(&mq->tick_lock, flags);
+	tick = mq->tick_protected;
+	if (tick != mq->tick) {
+		queue_iterate_tick(&mq->pre_cache, update_pre_cache_hits, mq);
+		queue_iterate_tick(&mq->cache_dirty, update_cache_hits, mq);
+		queue_iterate_tick(&mq->cache_clean, update_cache_hits, mq);
+		mq->tick = tick;
+	}
+
+	queue_tick(&mq->pre_cache);
+	queue_tick(&mq->cache_dirty);
+	queue_tick(&mq->cache_clean);
+	queue_update_writeback_sentinels(&mq->cache_dirty);
+	spin_unlock_irqrestore(&mq->tick_lock, flags);
+}
+
+static int mq_map(struct dm_cache_policy *p, dm_oblock_t oblock,
+		  bool can_block, bool can_migrate, bool discarded_oblock,
+		  struct bio *bio, struct policy_locker *locker,
+		  struct policy_result *result)
+{
+	int r;
+	struct mq_policy *mq = to_mq_policy(p);
+
+	result->op = POLICY_MISS;
+
+	if (can_block)
+		mutex_lock(&mq->lock);
+	else if (!mutex_trylock(&mq->lock))
+		return -EWOULDBLOCK;
+
+	copy_tick(mq);
+
+	iot_examine_bio(&mq->tracker, bio);
+	r = map(mq, oblock, can_migrate, discarded_oblock,
+		bio_data_dir(bio), locker, result);
+
+	mutex_unlock(&mq->lock);
+
+	return r;
+}
+
+static int mq_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock)
+{
+	int r;
+	struct mq_policy *mq = to_mq_policy(p);
+	struct entry *e;
+
+	if (!mutex_trylock(&mq->lock))
+		return -EWOULDBLOCK;
+
+	e = hash_lookup(mq, oblock);
+	if (e && in_cache(mq, e)) {
+		*cblock = infer_cblock(&mq->cache_pool, e);
+		r = 0;
+	} else
+		r = -ENOENT;
+
+	mutex_unlock(&mq->lock);
+
+	return r;
+}
+
+static void __mq_set_clear_dirty(struct mq_policy *mq, dm_oblock_t oblock, bool set)
+{
+	struct entry *e;
+
+	e = hash_lookup(mq, oblock);
+	BUG_ON(!e || !in_cache(mq, e));
+
+	del(mq, e);
+	e->dirty = set;
+	push(mq, e);
+}
+
+static void mq_set_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+
+	mutex_lock(&mq->lock);
+	__mq_set_clear_dirty(mq, oblock, true);
+	mutex_unlock(&mq->lock);
+}
+
+static void mq_clear_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+
+	mutex_lock(&mq->lock);
+	__mq_set_clear_dirty(mq, oblock, false);
+	mutex_unlock(&mq->lock);
+}
+
+static int mq_load_mapping(struct dm_cache_policy *p,
+			   dm_oblock_t oblock, dm_cblock_t cblock,
+			   uint32_t hint, bool hint_valid)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+	struct entry *e;
+
+	e = alloc_particular_entry(&mq->cache_pool, cblock);
+	e->oblock = oblock;
+	e->dirty = false;	/* this gets corrected in a minute */
+	e->hit_count = hint_valid ? hint : 1;
+	push(mq, e);
+
+	return 0;
+}
+
+static int mq_save_hints(struct mq_policy *mq, struct queue *q,
+			 policy_walk_fn fn, void *context)
+{
+	int r;
+	unsigned level;
+	struct list_head *h;
+	struct entry *e;
+
+	for (level = 0; level < NR_QUEUE_LEVELS; level++)
+		list_for_each(h, q->qs + level) {
+			if (is_sentinel(q, h))
+				continue;
+
+			e = container_of(h, struct entry, list);
+			r = fn(context, infer_cblock(&mq->cache_pool, e),
+			       e->oblock, e->hit_count);
+			if (r)
+				return r;
+		}
+
+	return 0;
+}
+
+static int mq_walk_mappings(struct dm_cache_policy *p, policy_walk_fn fn,
+			    void *context)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+	int r = 0;
+
+	mutex_lock(&mq->lock);
+
+	r = mq_save_hints(mq, &mq->cache_clean, fn, context);
+	if (!r)
+		r = mq_save_hints(mq, &mq->cache_dirty, fn, context);
+
+	mutex_unlock(&mq->lock);
+
+	return r;
+}
+
+static void __remove_mapping(struct mq_policy *mq, dm_oblock_t oblock)
+{
+	struct entry *e;
+
+	e = hash_lookup(mq, oblock);
+	BUG_ON(!e || !in_cache(mq, e));
+
+	del(mq, e);
+	free_entry(&mq->cache_pool, e);
+}
+
+static void mq_remove_mapping(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+
+	mutex_lock(&mq->lock);
+	__remove_mapping(mq, oblock);
+	mutex_unlock(&mq->lock);
+}
+
+static int __remove_cblock(struct mq_policy *mq, dm_cblock_t cblock)
+{
+	struct entry *e = epool_find(&mq->cache_pool, cblock);
+
+	if (!e)
+		return -ENODATA;
+
+	del(mq, e);
+	free_entry(&mq->cache_pool, e);
+
+	return 0;
+}
+
+static int mq_remove_cblock(struct dm_cache_policy *p, dm_cblock_t cblock)
+{
+	int r;
+	struct mq_policy *mq = to_mq_policy(p);
+
+	mutex_lock(&mq->lock);
+	r = __remove_cblock(mq, cblock);
+	mutex_unlock(&mq->lock);
+
+	return r;
+}
+
+#define CLEAN_TARGET_PERCENTAGE 25
+
+static bool clean_target_met(struct mq_policy *mq)
+{
+	/*
+	 * Cache entries may not be populated.  So we're cannot rely on the
+	 * size of the clean queue.
+	 */
+	unsigned nr_clean = from_cblock(mq->cache_size) - queue_size(&mq->cache_dirty);
+	unsigned target = from_cblock(mq->cache_size) * CLEAN_TARGET_PERCENTAGE / 100;
+
+	return nr_clean >= target;
+}
+
+static int __mq_writeback_work(struct mq_policy *mq, dm_oblock_t *oblock,
+			      dm_cblock_t *cblock)
+{
+	struct entry *e = pop_old(mq, &mq->cache_dirty);
+
+	if (!e && !clean_target_met(mq))
+		e = pop(mq, &mq->cache_dirty);
+
+	if (!e)
+		return -ENODATA;
+
+	*oblock = e->oblock;
+	*cblock = infer_cblock(&mq->cache_pool, e);
+	e->dirty = false;
+	push(mq, e);
+
+	return 0;
+}
+
+static int mq_writeback_work(struct dm_cache_policy *p, dm_oblock_t *oblock,
+			     dm_cblock_t *cblock)
+{
+	int r;
+	struct mq_policy *mq = to_mq_policy(p);
+
+	mutex_lock(&mq->lock);
+	r = __mq_writeback_work(mq, oblock, cblock);
+	mutex_unlock(&mq->lock);
+
+	return r;
+}
+
+static void __force_mapping(struct mq_policy *mq,
+			    dm_oblock_t current_oblock, dm_oblock_t new_oblock)
+{
+	struct entry *e = hash_lookup(mq, current_oblock);
+
+	if (e && in_cache(mq, e)) {
+		del(mq, e);
+		e->oblock = new_oblock;
+		e->dirty = true;
+		push(mq, e);
+	}
+}
+
+static void mq_force_mapping(struct dm_cache_policy *p,
+			     dm_oblock_t current_oblock, dm_oblock_t new_oblock)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+
+	mutex_lock(&mq->lock);
+	__force_mapping(mq, current_oblock, new_oblock);
+	mutex_unlock(&mq->lock);
+}
+
+static dm_cblock_t mq_residency(struct dm_cache_policy *p)
+{
+	dm_cblock_t r;
+	struct mq_policy *mq = to_mq_policy(p);
+
+	mutex_lock(&mq->lock);
+	r = to_cblock(mq->cache_pool.nr_allocated);
+	mutex_unlock(&mq->lock);
+
+	return r;
+}
+
+static void mq_tick(struct dm_cache_policy *p)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+	unsigned long flags;
+
+	spin_lock_irqsave(&mq->tick_lock, flags);
+	mq->tick_protected++;
+	spin_unlock_irqrestore(&mq->tick_lock, flags);
+}
+
+static int mq_set_config_value(struct dm_cache_policy *p,
+			       const char *key, const char *value)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+	unsigned long tmp;
+
+	if (kstrtoul(value, 10, &tmp))
+		return -EINVAL;
+
+	if (!strcasecmp(key, "random_threshold")) {
+		mq->tracker.thresholds[PATTERN_RANDOM] = tmp;
+
+	} else if (!strcasecmp(key, "sequential_threshold")) {
+		mq->tracker.thresholds[PATTERN_SEQUENTIAL] = tmp;
+
+	} else if (!strcasecmp(key, "discard_promote_adjustment"))
+		mq->discard_promote_adjustment = tmp;
+
+	else if (!strcasecmp(key, "read_promote_adjustment"))
+		mq->read_promote_adjustment = tmp;
+
+	else if (!strcasecmp(key, "write_promote_adjustment"))
+		mq->write_promote_adjustment = tmp;
+
+	else
+		return -EINVAL;
+
+	return 0;
+}
+
+static int mq_emit_config_values(struct dm_cache_policy *p, char *result, unsigned maxlen)
+{
+	ssize_t sz = 0;
+	struct mq_policy *mq = to_mq_policy(p);
+
+	DMEMIT("10 random_threshold %u "
+	       "sequential_threshold %u "
+	       "discard_promote_adjustment %u "
+	       "read_promote_adjustment %u "
+	       "write_promote_adjustment %u",
+	       mq->tracker.thresholds[PATTERN_RANDOM],
+	       mq->tracker.thresholds[PATTERN_SEQUENTIAL],
+	       mq->discard_promote_adjustment,
+	       mq->read_promote_adjustment,
+	       mq->write_promote_adjustment);
+
+	return 0;
+}
+
+/* Init the policy plugin interface function pointers. */
+static void init_policy_functions(struct mq_policy *mq)
+{
+	mq->policy.destroy = mq_destroy;
+	mq->policy.map = mq_map;
+	mq->policy.lookup = mq_lookup;
+	mq->policy.set_dirty = mq_set_dirty;
+	mq->policy.clear_dirty = mq_clear_dirty;
+	mq->policy.load_mapping = mq_load_mapping;
+	mq->policy.walk_mappings = mq_walk_mappings;
+	mq->policy.remove_mapping = mq_remove_mapping;
+	mq->policy.remove_cblock = mq_remove_cblock;
+	mq->policy.writeback_work = mq_writeback_work;
+	mq->policy.force_mapping = mq_force_mapping;
+	mq->policy.residency = mq_residency;
+	mq->policy.tick = mq_tick;
+	mq->policy.emit_config_values = mq_emit_config_values;
+	mq->policy.set_config_value = mq_set_config_value;
+}
+
+static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
+					 sector_t origin_size,
+					 sector_t cache_block_size)
+{
+	struct mq_policy *mq = kzalloc(sizeof(*mq), GFP_KERNEL);
+
+	if (!mq)
+		return NULL;
+
+	init_policy_functions(mq);
+	iot_init(&mq->tracker, SEQUENTIAL_THRESHOLD_DEFAULT, RANDOM_THRESHOLD_DEFAULT);
+	mq->cache_size = cache_size;
+
+	if (epool_init(&mq->pre_cache_pool, from_cblock(cache_size))) {
+		DMERR("couldn't initialize pool of pre-cache entries");
+		goto bad_pre_cache_init;
+	}
+
+	if (epool_init(&mq->cache_pool, from_cblock(cache_size))) {
+		DMERR("couldn't initialize pool of cache entries");
+		goto bad_cache_init;
+	}
+
+	mq->tick_protected = 0;
+	mq->tick = 0;
+	mq->hit_count = 0;
+	mq->generation = 0;
+	mq->discard_promote_adjustment = DEFAULT_DISCARD_PROMOTE_ADJUSTMENT;
+	mq->read_promote_adjustment = DEFAULT_READ_PROMOTE_ADJUSTMENT;
+	mq->write_promote_adjustment = DEFAULT_WRITE_PROMOTE_ADJUSTMENT;
+	mutex_init(&mq->lock);
+	spin_lock_init(&mq->tick_lock);
+
+	queue_init(&mq->pre_cache);
+	queue_init(&mq->cache_clean);
+	queue_init(&mq->cache_dirty);
+
+	mq->generation_period = max((unsigned) from_cblock(cache_size), 1024U);
+
+	mq->nr_buckets = next_power(from_cblock(cache_size) / 2, 16);
+	mq->hash_bits = ffs(mq->nr_buckets) - 1;
+	mq->table = vzalloc(sizeof(*mq->table) * mq->nr_buckets);
+	if (!mq->table)
+		goto bad_alloc_table;
+
+	return &mq->policy;
+
+bad_alloc_table:
+	epool_exit(&mq->cache_pool);
+bad_cache_init:
+	epool_exit(&mq->pre_cache_pool);
+bad_pre_cache_init:
+	kfree(mq);
+
+	return NULL;
+}
+
+/*----------------------------------------------------------------*/
+
+static struct dm_cache_policy_type mq_policy_type = {
+	.name = "mq",
+	.version = {1, 3, 0},
+	.hint_size = 4,
+	.owner = THIS_MODULE,
+	.create = mq_create
+};
+
+static struct dm_cache_policy_type default_policy_type = {
+	.name = "default",
+	.version = {1, 3, 0},
+	.hint_size = 4,
+	.owner = THIS_MODULE,
+	.create = mq_create,
+	.real = &mq_policy_type
+};
+
+static int __init mq_init(void)
+{
+	int r;
+
+	mq_entry_cache = kmem_cache_create("dm_mq_policy_cache_entry",
+					   sizeof(struct entry),
+					   __alignof__(struct entry),
+					   0, NULL);
+	if (!mq_entry_cache)
+		goto bad;
+
+	r = dm_cache_policy_register(&mq_policy_type);
+	if (r) {
+		DMERR("register failed %d", r);
+		goto bad_register_mq;
+	}
+
+	r = dm_cache_policy_register(&default_policy_type);
+	if (!r) {
+		DMINFO("version %u.%u.%u loaded",
+		       mq_policy_type.version[0],
+		       mq_policy_type.version[1],
+		       mq_policy_type.version[2]);
+		return 0;
+	}
+
+	DMERR("register failed (as default) %d", r);
+
+	dm_cache_policy_unregister(&mq_policy_type);
+bad_register_mq:
+	kmem_cache_destroy(mq_entry_cache);
+bad:
+	return -ENOMEM;
+}
+
+static void __exit mq_exit(void)
+{
+	dm_cache_policy_unregister(&mq_policy_type);
+	dm_cache_policy_unregister(&default_policy_type);
+
+	kmem_cache_destroy(mq_entry_cache);
+}
+
+module_init(mq_init);
+module_exit(mq_exit);
+
+MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("mq cache policy");
+
+MODULE_ALIAS("dm-cache-default");