1 files changed, 231 insertions, 312 deletions

diff --git a/drivers/md/dm-cache-policy-mq.c b/drivers/md/dm-cache-policy-mq.c
index 444f0bf10b21..782bf854666a 100644
--- a/drivers/md/dm-cache-policy-mq.c
+++ b/drivers/md/dm-cache-policy-mq.c
@@ -26,19 +26,6 @@ static unsigned next_power(unsigned n, unsigned min)
 
 /*----------------------------------------------------------------*/
 
-static unsigned long *alloc_bitset(unsigned nr_entries)
-{
-	size_t s = sizeof(unsigned long) * dm_div_up(nr_entries, BITS_PER_LONG);
-	return vzalloc(s);
-}
-
-static void free_bitset(unsigned long *bits)
-{
-	vfree(bits);
-}
-
-/*----------------------------------------------------------------*/
-
 /*
  * Large, sequential ios are probably better left on the origin device since
  * spindles tend to have good bandwidth.
@@ -233,18 +220,107 @@ struct entry {
 	struct hlist_node hlist;
 	struct list_head list;
 	dm_oblock_t oblock;
-	dm_cblock_t cblock;	/* valid iff in_cache */
 
 	/*
 	 * FIXME: pack these better
 	 */
-	bool in_cache:1;
 	bool dirty:1;
 	unsigned hit_count;
 	unsigned generation;
 	unsigned tick;
 };
 
+/*
+ * 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(&e->list);
+
+	INIT_LIST_HEAD(&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);
+}
+
+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;
 
@@ -254,6 +330,13 @@ struct mq_policy {
 	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
@@ -300,25 +383,6 @@ struct mq_policy {
 	unsigned promote_threshold;
 
 	/*
-	 * We need cache_size entries for the cache, and choose to have
-	 * cache_size entries for the pre_cache too.  One motivation for
-	 * using the same size is to make the hit counts directly
-	 * comparable between pre_cache and cache.
-	 */
-	unsigned nr_entries;
-	unsigned nr_entries_allocated;
-	struct list_head free;
-
-	/*
-	 * Cache blocks may be unallocated.  We store this info in a
-	 * bitset.
-	 */
-	unsigned long *allocation_bitset;
-	unsigned nr_cblocks_allocated;
-	unsigned find_free_nr_words;
-	unsigned find_free_last_word;
-
-	/*
 	 * The hash table allows us to quickly find an entry by origin
 	 * block.  Both pre_cache and cache entries are in here.
 	 */
@@ -328,50 +392,6 @@ struct mq_policy {
 };
 
 /*----------------------------------------------------------------*/
-/* Free/alloc mq cache entry structures. */
-static void concat_queue(struct list_head *lh, struct queue *q)
-{
-	unsigned level;
-
-	for (level = 0; level < NR_QUEUE_LEVELS; level++)
-		list_splice(q->qs + level, lh);
-}
-
-static void free_entries(struct mq_policy *mq)
-{
-	struct entry *e, *tmp;
-
-	concat_queue(&mq->free, &mq->pre_cache);
-	concat_queue(&mq->free, &mq->cache_clean);
-	concat_queue(&mq->free, &mq->cache_dirty);
-
-	list_for_each_entry_safe(e, tmp, &mq->free, list)
-		kmem_cache_free(mq_entry_cache, e);
-}
-
-static int alloc_entries(struct mq_policy *mq, unsigned elts)
-{
-	unsigned u = mq->nr_entries;
-
-	INIT_LIST_HEAD(&mq->free);
-	mq->nr_entries_allocated = 0;
-
-	while (u--) {
-		struct entry *e = kmem_cache_zalloc(mq_entry_cache, GFP_KERNEL);
-
-		if (!e) {
-			free_entries(mq);
-			return -ENOMEM;
-		}
-
-
-		list_add(&e->list, &mq->free);
-	}
-
-	return 0;
-}
-
-/*----------------------------------------------------------------*/
 
 /*
  * Simple hash table implementation.  Should replace with the standard hash
@@ -407,54 +427,9 @@ static void hash_remove(struct entry *e)
 
 /*----------------------------------------------------------------*/
 
-/*
- * Allocates a new entry structure.  The memory is allocated in one lump,
- * so we just handing it out here.  Returns NULL if all entries have
- * already been allocated.  Cannot fail otherwise.
- */
-static struct entry *alloc_entry(struct mq_policy *mq)
-{
-	struct entry *e;
-
-	if (mq->nr_entries_allocated >= mq->nr_entries) {
-		BUG_ON(!list_empty(&mq->free));
-		return NULL;
-	}
-
-	e = list_entry(list_pop(&mq->free), struct entry, list);
-	INIT_LIST_HEAD(&e->list);
-	INIT_HLIST_NODE(&e->hlist);
-
-	mq->nr_entries_allocated++;
-	return e;
-}
-
-/*----------------------------------------------------------------*/
-
-/*
- * Mark cache blocks allocated or not in the bitset.
- */
-static void alloc_cblock(struct mq_policy *mq, dm_cblock_t cblock)
-{
-	BUG_ON(from_cblock(cblock) > from_cblock(mq->cache_size));
-	BUG_ON(test_bit(from_cblock(cblock), mq->allocation_bitset));
-
-	set_bit(from_cblock(cblock), mq->allocation_bitset);
-	mq->nr_cblocks_allocated++;
-}
-
-static void free_cblock(struct mq_policy *mq, dm_cblock_t cblock)
-{
-	BUG_ON(from_cblock(cblock) > from_cblock(mq->cache_size));
-	BUG_ON(!test_bit(from_cblock(cblock), mq->allocation_bitset));
-
-	clear_bit(from_cblock(cblock), mq->allocation_bitset);
-	mq->nr_cblocks_allocated--;
-}
-
 static bool any_free_cblocks(struct mq_policy *mq)
 {
-	return mq->nr_cblocks_allocated < from_cblock(mq->cache_size);
+	return !epool_empty(&mq->cache_pool);
 }
 
 static bool any_clean_cblocks(struct mq_policy *mq)
@@ -462,48 +437,6 @@ static bool any_clean_cblocks(struct mq_policy *mq)
 	return !queue_empty(&mq->cache_clean);
 }
 
-/*
- * Fills result out with a cache block that isn't in use, or return
- * -ENOSPC.  This does _not_ mark the cblock as allocated, the caller is
- * reponsible for that.
- */
-static int __find_free_cblock(struct mq_policy *mq, unsigned begin, unsigned end,
-			      dm_cblock_t *result, unsigned *last_word)
-{
-	int r = -ENOSPC;
-	unsigned w;
-
-	for (w = begin; w < end; w++) {
-		/*
-		 * ffz is undefined if no zero exists
-		 */
-		if (mq->allocation_bitset[w] != ~0UL) {
-			*last_word = w;
-			*result = to_cblock((w * BITS_PER_LONG) + ffz(mq->allocation_bitset[w]));
-			if (from_cblock(*result) < from_cblock(mq->cache_size))
-				r = 0;
-
-			break;
-		}
-	}
-
-	return r;
-}
-
-static int find_free_cblock(struct mq_policy *mq, dm_cblock_t *result)
-{
-	int r;
-
-	if (!any_free_cblocks(mq))
-		return -ENOSPC;
-
-	r = __find_free_cblock(mq, mq->find_free_last_word, mq->find_free_nr_words, result, &mq->find_free_last_word);
-	if (r == -ENOSPC && mq->find_free_last_word)
-		r = __find_free_cblock(mq, 0, mq->find_free_last_word, result, &mq->find_free_last_word);
-
-	return r;
-}
-
 /*----------------------------------------------------------------*/
 
 /*
@@ -520,34 +453,35 @@ 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.
+ * 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)
 {
 	e->tick = mq->tick;
 	hash_insert(mq, e);
 
-	if (e->in_cache) {
-		alloc_cblock(mq, e->cblock);
+	if (in_cache(mq, e))
 		queue_push(e->dirty ? &mq->cache_dirty : &mq->cache_clean,
 			   queue_level(e), &e->list);
-	} else
+	else
 		queue_push(&mq->pre_cache, queue_level(e), &e->list);
 }
 
 /*
  * Removes an entry from pre_cache or cache.  Removes from the hash table.
- * Frees off the cache block if necc.
  */
 static void del(struct mq_policy *mq, struct entry *e)
 {
 	queue_remove(&e->list);
 	hash_remove(e);
-	if (e->in_cache)
-		free_cblock(mq, e->cblock);
 }
 
 /*
@@ -564,8 +498,6 @@ static struct entry *pop(struct mq_policy *mq, struct queue *q)
 
 	e = container_of(h, struct entry, list);
 	hash_remove(e);
-	if (e->in_cache)
-		free_cblock(mq, e->cblock);
 
 	return e;
 }
@@ -599,9 +531,7 @@ static void check_generation(struct mq_policy *mq)
 	struct list_head *head;
 	struct entry *e;
 
-	if ((mq->hit_count >= mq->generation_period) &&
-	    (mq->nr_cblocks_allocated == from_cblock(mq->cache_size))) {
-
+	if ((mq->hit_count >= mq->generation_period) && (epool_empty(&mq->cache_pool))) {
 		mq->hit_count = 0;
 		mq->generation++;
 
@@ -668,7 +598,7 @@ static void requeue_and_update_tick(struct mq_policy *mq, struct entry *e)
  * - 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, dm_oblock_t *oblock, dm_cblock_t *cblock)
+static int demote_cblock(struct mq_policy *mq, dm_oblock_t *oblock)
 {
 	struct entry *demoted = pop(mq, &mq->cache_clean);
 
@@ -682,12 +612,14 @@ static int demote_cblock(struct mq_policy *mq, dm_oblock_t *oblock, dm_cblock_t
 		 */
 		return -ENOSPC;
 
-	*cblock = demoted->cblock;
 	*oblock = demoted->oblock;
-	demoted->in_cache = false;
-	demoted->dirty = false;
-	demoted->hit_count = 1;
-	push(mq, demoted);
+	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;
 }
@@ -735,9 +667,9 @@ static int cache_entry_found(struct mq_policy *mq,
 {
 	requeue_and_update_tick(mq, e);
 
-	if (e->in_cache) {
+	if (in_cache(mq, e)) {
 		result->op = POLICY_HIT;
-		result->cblock = e->cblock;
+		result->cblock = infer_cblock(&mq->cache_pool, e);
 	}
 
 	return 0;
@@ -751,11 +683,12 @@ static int pre_cache_to_cache(struct mq_policy *mq, struct entry *e,
 			      struct policy_result *result)
 {
 	int r;
-	dm_cblock_t cblock;
+	struct entry *new_e;
 
-	if (find_free_cblock(mq, &cblock) == -ENOSPC) {
+	/* Ensure there's a free cblock in the cache */
+	if (epool_empty(&mq->cache_pool)) {
 		result->op = POLICY_REPLACE;
-		r = demote_cblock(mq, &result->old_oblock, &cblock);
+		r = demote_cblock(mq, &result->old_oblock);
 		if (r) {
 			result->op = POLICY_MISS;
 			return 0;
@@ -763,12 +696,20 @@ static int pre_cache_to_cache(struct mq_policy *mq, struct entry *e,
 	} else
 		result->op = POLICY_NEW;
 
-	result->cblock = e->cblock = cblock;
+	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;
+	new_e->generation = e->generation;
+	new_e->tick = e->tick;
 
 	del(mq, e);
-	e->in_cache = true;
-	e->dirty = false;
-	push(mq, e);
+	free_entry(&mq->pre_cache_pool, e);
+	push(mq, new_e);
+
+	result->cblock = infer_cblock(&mq->cache_pool, new_e);
 
 	return 0;
 }
@@ -793,21 +734,10 @@ static int pre_cache_entry_found(struct mq_policy *mq, struct entry *e,
 	return r;
 }
 
-static void insert_entry_in_pre_cache(struct mq_policy *mq,
-				      struct entry *e, dm_oblock_t oblock)
-{
-	e->in_cache = false;
-	e->dirty = false;
-	e->oblock = oblock;
-	e->hit_count = 1;
-	e->generation = mq->generation;
-	push(mq, e);
-}
-
 static void insert_in_pre_cache(struct mq_policy *mq,
 				dm_oblock_t oblock)
 {
-	struct entry *e = alloc_entry(mq);
+	struct entry *e = alloc_entry(&mq->pre_cache_pool);
 
 	if (!e)
 		/*
@@ -821,7 +751,11 @@ static void insert_in_pre_cache(struct mq_policy *mq,
 		return;
 	}
 
-	insert_entry_in_pre_cache(mq, e, oblock);
+	e->dirty = false;
+	e->oblock = oblock;
+	e->hit_count = 1;
+	e->generation = mq->generation;
+	push(mq, e);
 }
 
 static void insert_in_cache(struct mq_policy *mq, dm_oblock_t oblock,
@@ -829,10 +763,10 @@ static void insert_in_cache(struct mq_policy *mq, dm_oblock_t oblock,
 {
 	int r;
 	struct entry *e;
-	dm_cblock_t cblock;
 
-	if (find_free_cblock(mq, &cblock) == -ENOSPC) {
-		r = demote_cblock(mq, &result->old_oblock, &cblock);
+	if (epool_empty(&mq->cache_pool)) {
+		result->op = POLICY_REPLACE;
+		r = demote_cblock(mq, &result->old_oblock);
 		if (unlikely(r)) {
 			result->op = POLICY_MISS;
 			insert_in_pre_cache(mq, oblock);
@@ -842,31 +776,21 @@ static void insert_in_cache(struct mq_policy *mq, dm_oblock_t oblock,
 		/*
 		 * This will always succeed, since we've just demoted.
 		 */
-		e = pop(mq, &mq->pre_cache);
-		result->op = POLICY_REPLACE;
+		e = alloc_entry(&mq->cache_pool);
+		BUG_ON(!e);
 
 	} else {
-		e = alloc_entry(mq);
-		if (unlikely(!e))
-			e = pop(mq, &mq->pre_cache);
-
-		if (unlikely(!e)) {
-			result->op = POLICY_MISS;
-			return;
-		}
-
+		e = alloc_entry(&mq->cache_pool);
 		result->op = POLICY_NEW;
 	}
 
 	e->oblock = oblock;
-	e->cblock = cblock;
-	e->in_cache = true;
 	e->dirty = false;
 	e->hit_count = 1;
 	e->generation = mq->generation;
 	push(mq, e);
 
-	result->cblock = e->cblock;
+	result->cblock = infer_cblock(&mq->cache_pool, e);
 }
 
 static int no_entry_found(struct mq_policy *mq, dm_oblock_t oblock,
@@ -897,13 +821,16 @@ static int map(struct mq_policy *mq, dm_oblock_t oblock,
 	int r = 0;
 	struct entry *e = hash_lookup(mq, oblock);
 
-	if (e && e->in_cache)
+	if (e && in_cache(mq, e))
 		r = cache_entry_found(mq, e, result);
+
 	else if (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, result);
+
 	else
 		r = no_entry_found(mq, oblock, can_migrate, discarded_oblock,
 				   data_dir, result);
@@ -930,9 +857,9 @@ static void mq_destroy(struct dm_cache_policy *p)
 {
 	struct mq_policy *mq = to_mq_policy(p);
 
-	free_bitset(mq->allocation_bitset);
 	kfree(mq->table);
-	free_entries(mq);
+	epool_exit(&mq->cache_pool);
+	epool_exit(&mq->pre_cache_pool);
 	kfree(mq);
 }
 
@@ -980,8 +907,8 @@ static int mq_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t
 		return -EWOULDBLOCK;
 
 	e = hash_lookup(mq, oblock);
-	if (e && e->in_cache) {
-		*cblock = e->cblock;
+	if (e && in_cache(mq, e)) {
+		*cblock = infer_cblock(&mq->cache_pool, e);
 		r = 0;
 	} else
 		r = -ENOENT;
@@ -991,38 +918,34 @@ static int mq_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t
 	return r;
 }
 
-/*
- * FIXME: __mq_set_clear_dirty can block due to mutex.
- * Ideally a policy should not block in functions called
- * from the map() function.  Explore using RCU.
- */
-static void __mq_set_clear_dirty(struct dm_cache_policy *p, dm_oblock_t oblock, bool set)
+static void __mq_set_clear_dirty(struct mq_policy *mq, dm_oblock_t oblock, bool set)
 {
-	struct mq_policy *mq = to_mq_policy(p);
 	struct entry *e;
 
-	mutex_lock(&mq->lock);
 	e = hash_lookup(mq, oblock);
-	if (!e)
-		DMWARN("__mq_set_clear_dirty called for a block that isn't in the cache");
-	else {
-		BUG_ON(!e->in_cache);
+	BUG_ON(!e || !in_cache(mq, e));
 
-		del(mq, e);
-		e->dirty = set;
-		push(mq, e);
-	}
-	mutex_unlock(&mq->lock);
+	del(mq, e);
+	e->dirty = set;
+	push(mq, e);
 }
 
 static void mq_set_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
 {
-	__mq_set_clear_dirty(p, oblock, true);
+	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)
 {
-	__mq_set_clear_dirty(p, oblock, false);
+	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,
@@ -1032,13 +955,8 @@ static int mq_load_mapping(struct dm_cache_policy *p,
 	struct mq_policy *mq = to_mq_policy(p);
 	struct entry *e;
 
-	e = alloc_entry(mq);
-	if (!e)
-		return -ENOMEM;
-
-	e->cblock = cblock;
+	e = alloc_particular_entry(&mq->cache_pool, cblock);
 	e->oblock = oblock;
-	e->in_cache = true;
 	e->dirty = false;	/* this gets corrected in a minute */
 	e->hit_count = hint_valid ? hint : 1;
 	e->generation = mq->generation;
@@ -1047,52 +965,58 @@ static int mq_load_mapping(struct dm_cache_policy *p,
 	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 entry *e;
+
+	for (level = 0; level < NR_QUEUE_LEVELS; level++)
+		list_for_each_entry(e, q->qs + level, 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;
-	struct entry *e;
-	unsigned level;
 
 	mutex_lock(&mq->lock);
 
-	for (level = 0; level < NR_QUEUE_LEVELS; level++)
-		list_for_each_entry(e, &mq->cache_clean.qs[level], list) {
-			r = fn(context, e->cblock, e->oblock, e->hit_count);
-			if (r)
-				goto out;
-		}
-
-	for (level = 0; level < NR_QUEUE_LEVELS; level++)
-		list_for_each_entry(e, &mq->cache_dirty.qs[level], list) {
-			r = fn(context, e->cblock, e->oblock, e->hit_count);
-			if (r)
-				goto out;
-		}
+	r = mq_save_hints(mq, &mq->cache_clean, fn, context);
+	if (!r)
+		r = mq_save_hints(mq, &mq->cache_dirty, fn, context);
 
-out:
 	mutex_unlock(&mq->lock);
 
 	return r;
 }
 
-static void mq_remove_mapping(struct dm_cache_policy *p, dm_oblock_t oblock)
+static void __remove_mapping(struct mq_policy *mq, dm_oblock_t oblock)
 {
-	struct mq_policy *mq = to_mq_policy(p);
 	struct entry *e;
 
-	mutex_lock(&mq->lock);
-
 	e = hash_lookup(mq, oblock);
-
-	BUG_ON(!e || !e->in_cache);
+	BUG_ON(!e || !in_cache(mq, e));
 
 	del(mq, e);
-	e->in_cache = false;
-	e->dirty = false;
-	push(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);
 }
 
@@ -1105,7 +1029,7 @@ static int __mq_writeback_work(struct mq_policy *mq, dm_oblock_t *oblock,
 		return -ENODATA;
 
 	*oblock = e->oblock;
-	*cblock = e->cblock;
+	*cblock = infer_cblock(&mq->cache_pool, e);
 	e->dirty = false;
 	push(mq, e);
 
@@ -1125,17 +1049,17 @@ static int mq_writeback_work(struct dm_cache_policy *p, dm_oblock_t *oblock,
 	return r;
 }
 
-static void force_mapping(struct mq_policy *mq,
-			  dm_oblock_t current_oblock, dm_oblock_t new_oblock)
+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);
 
-	BUG_ON(!e || !e->in_cache);
-
-	del(mq, e);
-	e->oblock = new_oblock;
-	e->dirty = true;
-	push(mq, e);
+	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,
@@ -1144,7 +1068,7 @@ static void mq_force_mapping(struct dm_cache_policy *p,
 	struct mq_policy *mq = to_mq_policy(p);
 
 	mutex_lock(&mq->lock);
-	force_mapping(mq, current_oblock, new_oblock);
+	__force_mapping(mq, current_oblock, new_oblock);
 	mutex_unlock(&mq->lock);
 }
 
@@ -1154,7 +1078,7 @@ static dm_cblock_t mq_residency(struct dm_cache_policy *p)
 	struct mq_policy *mq = to_mq_policy(p);
 
 	mutex_lock(&mq->lock);
-	r = to_cblock(mq->nr_cblocks_allocated);
+	r = to_cblock(mq->cache_pool.nr_allocated);
 	mutex_unlock(&mq->lock);
 
 	return r;
@@ -1227,7 +1151,6 @@ static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
 					 sector_t origin_size,
 					 sector_t cache_block_size)
 {
-	int r;
 	struct mq_policy *mq = kzalloc(sizeof(*mq), GFP_KERNEL);
 
 	if (!mq)
@@ -1235,8 +1158,18 @@ static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
 
 	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;
@@ -1244,8 +1177,6 @@ static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
 	mq->promote_threshold = 0;
 	mutex_init(&mq->lock);
 	spin_lock_init(&mq->tick_lock);
-	mq->find_free_nr_words = dm_div_up(from_cblock(mq->cache_size), BITS_PER_LONG);
-	mq->find_free_last_word = 0;
 
 	queue_init(&mq->pre_cache);
 	queue_init(&mq->cache_clean);
@@ -1253,31 +1184,19 @@ static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
 
 	mq->generation_period = max((unsigned) from_cblock(cache_size), 1024U);
 
-	mq->nr_entries = 2 * from_cblock(cache_size);
-	r = alloc_entries(mq, mq->nr_entries);
-	if (r)
-		goto bad_cache_alloc;
-
-	mq->nr_entries_allocated = 0;
-	mq->nr_cblocks_allocated = 0;
-
 	mq->nr_buckets = next_power(from_cblock(cache_size) / 2, 16);
 	mq->hash_bits = ffs(mq->nr_buckets) - 1;
 	mq->table = kzalloc(sizeof(*mq->table) * mq->nr_buckets, GFP_KERNEL);
 	if (!mq->table)
 		goto bad_alloc_table;
 
-	mq->allocation_bitset = alloc_bitset(from_cblock(cache_size));
-	if (!mq->allocation_bitset)
-		goto bad_alloc_bitset;
-
 	return &mq->policy;
 
-bad_alloc_bitset:
-	kfree(mq->table);
 bad_alloc_table:
-	free_entries(mq);
-bad_cache_alloc:
+	epool_exit(&mq->cache_pool);
+bad_cache_init:
+	epool_exit(&mq->pre_cache_pool);
+bad_pre_cache_init:
 	kfree(mq);
 
 	return NULL;
@@ -1287,7 +1206,7 @@ bad_cache_alloc:
 
 static struct dm_cache_policy_type mq_policy_type = {
 	.name = "mq",
-	.version = {1, 0, 0},
+	.version = {1, 1, 0},
 	.hint_size = 4,
 	.owner = THIS_MODULE,
 	.create = mq_create
@@ -1295,7 +1214,7 @@ static struct dm_cache_policy_type mq_policy_type = {
 
 static struct dm_cache_policy_type default_policy_type = {
 	.name = "default",
-	.version = {1, 0, 0},
+	.version = {1, 1, 0},
 	.hint_size = 4,
 	.owner = THIS_MODULE,
 	.create = mq_create