nhit promotion policy implementation

Signed-off-by: Jan Musial <jan.musial@intel.com>

inc/ocf_def.h

@@ -210,7 +210,7 @@ typedef enum {
  * OCF supported promotion policy types
  */
 typedef enum {
-	ocf_promotion_nop = 0,
+	ocf_promotion_always = 0,
 		/*!< No promotion policy. Cache inserts are not filtered */
 
 	ocf_promotion_nhit,
@@ -219,7 +219,7 @@ typedef enum {
 	ocf_promotion_max,
 		/*!< Stopper of enumerator */
 
-	ocf_promotion_default = ocf_promotion_nop,
+	ocf_promotion_default = ocf_promotion_always,
 		/*!< Default promotion policy */
 } ocf_promotion_t;
 

src/engine/engine_discard.c

@@ -60,8 +60,6 @@ static void _ocf_discard_core_complete(struct ocf_io *io, int error)
 
 	OCF_DEBUG_RQ(req, "Core DISCARD Completion");
 
-	ocf_promotion_req_purge(req->cache->promotion_policy, req);
-
 	_ocf_discard_complete_req(req, error);
 
 	ocf_io_put(io);
@@ -85,6 +83,8 @@ static int _ocf_discard_core(struct ocf_request *req)
 
 	ocf_volume_submit_discard(io);
 
+	ocf_promotion_req_purge(req->cache->promotion_policy, req);
+
 	return 0;
 }
 

src/promotion/nhit.c

@@ -1,36 +0,0 @@
-/*
- * Copyright(c) 2019 Intel Corporation
- * SPDX-License-Identifier: BSD-3-Clause-Clear
- */
-
-#include "../metadata/metadata.h"
-
-#include "nhit.h"
-
-ocf_error_t nhit_init(ocf_cache_t cache, ocf_promotion_policy_t policy)
-{
-	return 0;
-}
-
-void nhit_deinit(ocf_promotion_policy_t policy)
-{
-
-}
-
-ocf_error_t nhit_set_param(ocf_promotion_policy_t policy, uint8_t param_id,
-		uint64_t param_value)
-{
-	return 0;
-}
-
-void nhit_req_purge(ocf_promotion_policy_t policy,
-		struct ocf_request *req)
-{
-
-}
-
-bool nhit_req_should_promote(ocf_promotion_policy_t policy, struct ocf_request *req)
-{
-	return true;
-}
-

src/promotion/nhit/hash.c

@@ -0,0 +1,393 @@
+/*
+ * Copyright(c) 2019 Intel Corporation
+ * SPDX-License-Identifier: BSD-3-Clause-Clear
+ */
+
+#include "../../ocf_priv.h"
+
+#include "hash.h"
+
+/* Implementation of hashmap-ish structure for tracking core lines in nhit
+ * promotion policy. It consists of two arrays:
+ * 	- hash_map - indexed by hash formed from core id and core lba pairs,
+ * 	contains pointers (indices) to the ring buffer. Each index in this array
+ * 	has its own rwsem.
+ * 	- ring_buffer - contains per-coreline metadata and collision info for
+ * 	open addressing. If we run out of space in this array, we just loop around
+ * 	and insert elements from the beggining. So lifetime of a core line varies
+ * 	depending on insertion and removal rate.
+ *
+ * Operations:
+ * 	- query(core_id, core_lba):
+ *		Check if core line is present in structure, bump up counter and
+ *		return its value.
+ *
+ * 	- insertion(core_id, core_lba):
+ * 		Insert new core line into structure
+ * 		1. get new slot from ring buffer
+ * 			a. check if current slot under rb_pointer is valid
+ * 			and if not - exit
+ * 			b. set current slot as invalid and increment rb_pointer
+ * 		2. lock hash bucket for new item and for ring buffer slot
+ * 		(if non-empty) in ascending bucket id order (to avoid deadlock)
+ * 		3. insert new data, add to collision
+ * 		4. unlock both hash buckets
+ * 		5. commit rb_slot (mark it as valid)
+ *
+ * Insertion explained visually:
+ *
+ * Suppose that we want to add a new core line with hash value H which already has
+ * some colliding core lines
+ *
+ *		hash(core_id, core_lba)
+ *				 +
+ *				 |
+ *				 v
+ *	+--+--+--+--+--+--+--+--++-+--+
+ *	|  |  |I |  |  |  |  |  |H |  | hash_map
+ *	+--+--++-+--+--+--+--+--++-+--+
+ *	     __|   rb_pointer    |        _______
+ *	    |        +           |        |     |
+ *	    v        v           v        |     v
+ *	+--++-+--+---+-+--+--+--++-+--+--++-+--++-+
+ *	|  |  |  |  |X |  |  |  |  |  |  |  |  |  | ring_buffer
+ *	+--++-+--+---+-+--+--+--++-+--+--++-+--+--+
+ *	    |        ^           |        ^
+ *	    |________|           |________|
+ *
+ * Since rb_pointer is pointing to occupied rb slot we need to write-lock hash
+ * bucket I associated with this slot and remove it from collision list.
+ * We've gained an empty slot and we use slot X for new hash H entry.
+ *
+ *	+--+--+--+--+--+--+--+--+--+--+
+ *	|  |  |I |  |  |  |  |  |H |  | hash_map
+ *	+--+--++-+--+--+--+--+--++-+--+
+ *	     __|   rb_pointer    |        _______
+ *	    |           +        |        |     |
+ *	    v           v        v        |     v
+ *	+--++-+--+-----++-+--+--++-+--+--++-+--++-+
+ *	|  |  |  |  |X |  |  |  |  |  |  |  |  |  | ring_buffer
+ *	+--+--+--+---+-+--+--+--++-+--+--++-+--++-+
+ *		     ^           |        ^     |
+ *		     |           |________|     |
+ *		     |__________________________|
+ *
+ * Valid field in nhit_list_elem is guarded by rb_pointer_lock to make sure we
+ * won't try to use the same slot in two threads. That would be possible if in
+ * time between removal from collision and insertion into the new one the
+ * rb_pointer would go around the whole structure (likeliness depends on size of
+ * ring_buffer).
+ */
+
+#define HASH_PRIME 4099
+
+struct nhit_list_elem {
+	ocf_core_id_t core_id;
+	uint64_t core_lba;
+
+	ocf_cache_line_t coll_prev;
+	ocf_cache_line_t coll_next;
+
+	bool valid;
+
+	env_atomic counter;
+};
+
+struct nhit_hash {
+	ocf_cache_line_t hash_entries;
+	uint64_t rb_entries;
+
+	ocf_cache_line_t *hash_map;
+	env_rwsem *hash_locks;
+
+	struct nhit_list_elem *ring_buffer;
+	uint64_t rb_pointer;
+	env_spinlock rb_pointer_lock;
+};
+
+ocf_error_t hash_init(uint64_t hash_size, nhit_hash_t *ctx)
+{
+	int result = 0;
+	struct nhit_hash *new_ctx;
+	uint64_t i;
+
+	new_ctx = env_vzalloc(sizeof(*new_ctx));
+	if (!new_ctx) {
+		result = -OCF_ERR_NO_MEM;
+		goto exit;
+	}
+
+	new_ctx->rb_entries = hash_size;
+	new_ctx->hash_entries = OCF_DIV_ROUND_UP(
+			new_ctx->rb_entries / 4,
+			HASH_PRIME) * HASH_PRIME - 1;
+
+	new_ctx->hash_map = env_vzalloc(
+			new_ctx->hash_entries * sizeof(*new_ctx->hash_map));
+	if (!new_ctx->hash_map) {
+		result = -OCF_ERR_NO_MEM;
+		goto dealloc_ctx;
+	}
+	for (i = 0; i < new_ctx->hash_entries; i++)
+		new_ctx->hash_map[i] = new_ctx->rb_entries;
+
+	new_ctx->hash_locks = env_vzalloc(
+			new_ctx->hash_entries * sizeof(*new_ctx->hash_locks));
+	if (!new_ctx->hash_locks) {
+		result = -OCF_ERR_NO_MEM;
+		goto dealloc_hash;
+	}
+
+	for (i = 0; i < new_ctx->hash_entries; i++) {
+		if (env_rwsem_init(&new_ctx->hash_locks[i])) {
+			result = -OCF_ERR_UNKNOWN;
+			goto dealloc_locks;
+		}
+	}
+
+	new_ctx->ring_buffer = env_vzalloc(
+			new_ctx->rb_entries * sizeof(*new_ctx->ring_buffer));
+	if (!new_ctx->ring_buffer) {
+		result = -OCF_ERR_NO_MEM;
+		goto dealloc_locks;
+	}
+	for (i = 0; i < new_ctx->rb_entries; i++) {
+		new_ctx->ring_buffer[i].core_id = OCF_CORE_ID_INVALID;
+		new_ctx->ring_buffer[i].valid = true;
+		env_atomic_set(&new_ctx->ring_buffer[i].counter, 0);
+	}
+
+	env_spinlock_init(&new_ctx->rb_pointer_lock);
+	new_ctx->rb_pointer = 0;
+
+	*ctx = new_ctx;
+	return 0;
+
+dealloc_locks:
+	for (i = 0; i < new_ctx->hash_entries; i++)
+		ENV_BUG_ON(env_rwsem_destroy(&new_ctx->hash_locks[i]));
+	env_vfree(new_ctx->hash_locks);
+dealloc_hash:
+	env_vfree(new_ctx->hash_map);
+dealloc_ctx:
+	env_vfree(new_ctx);
+exit:
+	return result;
+}
+
+void hash_deinit(nhit_hash_t ctx)
+{
+	ocf_cache_line_t i;
+
+	env_spinlock_destroy(&ctx->rb_pointer_lock);
+	for (i = 0; i < ctx->hash_entries; i++)
+		ENV_BUG_ON(env_rwsem_destroy(&ctx->hash_locks[i]));
+
+	env_vfree(ctx->ring_buffer);
+	env_vfree(ctx->hash_locks);
+	env_vfree(ctx->hash_map);
+	env_vfree(ctx);
+}
+
+static ocf_cache_line_t hash_function(ocf_core_id_t core_id, uint64_t core_lba,
+		uint64_t limit)
+{
+	if (core_id == OCF_CORE_ID_INVALID)
+		return limit;
+
+	return (ocf_cache_line_t) ((core_lba * HASH_PRIME + core_id) % limit);
+}
+
+static ocf_cache_line_t core_line_lookup(nhit_hash_t ctx,
+		ocf_core_id_t core_id, uint64_t core_lba)
+{
+	ocf_cache_line_t hash = hash_function(core_id, core_lba,
+			ctx->hash_entries);
+	ocf_cache_line_t needle = ctx->rb_entries;
+	ocf_cache_line_t cur;
+
+	for (cur = ctx->hash_map[hash]; cur != ctx->rb_entries;
+			cur = ctx->ring_buffer[cur].coll_next) {
+		struct nhit_list_elem *cur_elem = &ctx->ring_buffer[cur];
+
+		if (cur_elem->core_lba == core_lba &&
+				cur_elem->core_id == core_id) {
+			needle = cur;
+			break;
+		}
+	}
+
+	return needle;
+}
+
+static inline bool get_rb_slot(nhit_hash_t ctx, uint64_t *slot)
+{
+	bool result = true;
+
+	OCF_CHECK_NULL(slot);
+
+	env_spinlock_lock(&ctx->rb_pointer_lock);
+
+	*slot = ctx->rb_pointer;
+	result = ctx->ring_buffer[*slot].valid;
+
+	ctx->ring_buffer[*slot].valid = false;
+
+	ctx->rb_pointer = (*slot + 1) % ctx->rb_entries;
+
+	env_spinlock_unlock(&ctx->rb_pointer_lock);
+
+	return result;
+}
+
+static inline void commit_rb_slot(nhit_hash_t ctx, uint64_t slot)
+{
+	env_spinlock_lock(&ctx->rb_pointer_lock);
+
+	ctx->ring_buffer[slot].valid = true;
+
+	env_spinlock_unlock(&ctx->rb_pointer_lock);
+}
+
+static void collision_remove(nhit_hash_t ctx, uint64_t slot_id)
+{
+	struct nhit_list_elem *slot = &ctx->ring_buffer[slot_id];
+	ocf_cache_line_t hash = hash_function(slot->core_id, slot->core_lba,
+			ctx->hash_entries);
+
+	if (slot->core_id == OCF_CORE_ID_INVALID)
+		return;
+
+	slot->core_id = OCF_CORE_ID_INVALID;
+
+	if (slot->coll_prev != ctx->rb_entries)
+		ctx->ring_buffer[slot->coll_prev].coll_next = slot->coll_next;
+
+	if (slot->coll_next != ctx->rb_entries)
+		ctx->ring_buffer[slot->coll_next].coll_prev = slot->coll_prev;
+
+	if (ctx->hash_map[hash] == slot_id)
+		ctx->hash_map[hash] = slot->coll_next;
+}
+
+static void collision_insert_new(nhit_hash_t ctx,
+		uint64_t slot_id, ocf_core_id_t core_id,
+		uint64_t core_lba)
+{
+	ocf_cache_line_t hash = hash_function(core_id, core_lba,
+			ctx->hash_entries);
+	struct nhit_list_elem *slot = &ctx->ring_buffer[slot_id];
+
+	slot->core_id = core_id;
+	slot->core_lba = core_lba;
+	slot->coll_next = ctx->hash_map[hash];
+	slot->coll_prev = ctx->rb_entries;
+	env_atomic_set(&slot->counter, 1);
+
+	if (ctx->hash_map[hash] != ctx->rb_entries)
+		ctx->ring_buffer[ctx->hash_map[hash]].coll_prev = slot_id;
+
+	ctx->hash_map[hash] = slot_id;
+}
+
+static inline void write_lock_hashes(nhit_hash_t ctx, ocf_core_id_t core_id1,
+		uint64_t core_lba1, ocf_core_id_t core_id2, uint64_t core_lba2)
+{
+	ocf_cache_line_t hash1 = hash_function(core_id1, core_lba1,
+			ctx->hash_entries);
+	ocf_cache_line_t hash2 = hash_function(core_id2, core_lba2,
+			ctx->hash_entries);
+	ocf_cache_line_t lock_order[2] = {
+		OCF_MIN(hash1, hash2),
+		OCF_MAX(hash1, hash2)};
+
+	if (lock_order[0] != ctx->hash_entries)
+		env_rwsem_down_write(&ctx->hash_locks[lock_order[0]]);
+
+	if (lock_order[1] != ctx->hash_entries)
+		env_rwsem_down_write(&ctx->hash_locks[lock_order[1]]);
+}
+
+static inline void write_unlock_hashes(nhit_hash_t ctx, ocf_core_id_t core_id1,
+		uint64_t core_lba1, ocf_core_id_t core_id2, uint64_t core_lba2)
+{
+	ocf_cache_line_t hash1 = hash_function(core_id1, core_lba1,
+			ctx->hash_entries);
+	ocf_cache_line_t hash2 = hash_function(core_id2, core_lba2,
+			ctx->hash_entries);
+
+	if (hash1 != ctx->hash_entries)
+		env_rwsem_up_write(&ctx->hash_locks[hash1]);
+
+	if (hash2 != ctx->hash_entries)
+		env_rwsem_up_write(&ctx->hash_locks[hash2]);
+}
+
+void hash_insert(nhit_hash_t ctx, ocf_core_id_t core_id, uint64_t core_lba)
+{
+	uint64_t slot_id;
+	struct nhit_list_elem *slot;
+	ocf_core_id_t slot_core_id;
+	uint64_t slot_core_lba;
+
+	if (!get_rb_slot(ctx, &slot_id))
+		return;
+
+	slot = &ctx->ring_buffer[slot_id];
+	slot_core_id = slot->core_id;
+	slot_core_lba = slot->core_lba;
+
+	write_lock_hashes(ctx, core_id, core_lba, slot_core_id, slot_core_lba);
+
+	collision_remove(ctx, slot_id);
+	collision_insert_new(ctx, slot_id, core_id, core_lba);
+
+	write_unlock_hashes(ctx, core_id, core_lba, slot_core_id, slot_core_lba);
+
+	commit_rb_slot(ctx, slot_id);
+}
+
+bool hash_query(nhit_hash_t ctx, ocf_core_id_t core_id, uint64_t core_lba,
+		int32_t *counter)
+{
+	OCF_CHECK_NULL(counter);
+
+	ocf_cache_line_t hash = hash_function(core_id, core_lba,
+			ctx->hash_entries);
+	uint64_t rb_idx;
+
+	env_rwsem_down_read(&ctx->hash_locks[hash]);
+	rb_idx = core_line_lookup(ctx, core_id, core_lba);
+
+	if (rb_idx == ctx->rb_entries) {
+		env_rwsem_up_read(&ctx->hash_locks[hash]);
+		return false;
+	}
+
+	*counter = env_atomic_inc_return(&ctx->ring_buffer[rb_idx].counter);
+
+	env_rwsem_up_read(&ctx->hash_locks[hash]);
+
+	return true;
+}
+
+void hash_set_occurences(nhit_hash_t ctx, ocf_core_id_t core_id,
+		uint64_t core_lba, int32_t occurences)
+{
+	ocf_cache_line_t hash = hash_function(core_id, core_lba,
+			ctx->hash_entries);
+	uint64_t rb_idx;
+
+	env_rwsem_down_read(&ctx->hash_locks[hash]);
+	rb_idx = core_line_lookup(ctx, core_id, core_lba);
+
+	if (rb_idx == ctx->rb_entries) {
+		env_rwsem_up_read(&ctx->hash_locks[hash]);
+		return;
+	}
+
+	env_atomic_set(&ctx->ring_buffer[rb_idx].counter, occurences);
+
+	env_rwsem_up_read(&ctx->hash_locks[hash]);
+}
+

src/promotion/nhit/hash.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright(c) 2019 Intel Corporation
+ * SPDX-License-Identifier: BSD-3-Clause-Clear
+ */
+
+#ifndef NHIT_HASH_H_
+#define NHIT_HASH_H_
+
+#include "ocf/ocf.h"
+
+typedef struct nhit_hash *nhit_hash_t;
+
+ocf_error_t hash_init(uint64_t hash_size, nhit_hash_t *ctx);
+
+void hash_deinit(nhit_hash_t ctx);
+
+void hash_insert(nhit_hash_t ctx, ocf_core_id_t core_id, uint64_t core_lba);
+
+bool hash_query(nhit_hash_t ctx, ocf_core_id_t core_id, uint64_t core_lba,
+		int32_t *counter);
+
+void hash_set_occurences(nhit_hash_t ctx, ocf_core_id_t core_id,
+		uint64_t core_lba, int32_t occurences);
+
+#endif /* NHIT_HASH_H_ */

src/promotion/nhit/nhit.c

@@ -0,0 +1,182 @@
+/*
+ * Copyright(c) 2019 Intel Corporation
+ * SPDX-License-Identifier: BSD-3-Clause-Clear
+ */
+
+#include "hash.h"
+#include "../../metadata/metadata.h"
+#include "../../ocf_priv.h"
+#include "../../engine/engine_common.h"
+
+#include "nhit.h"
+#include "../ops.h"
+
+#define NHIT_MAPPING_RATIO 2
+
+#define NHIT_MIN_THRESHOLD 1
+#define NHIT_MAX_THRESHOLD 1000
+#define NHIT_THRESHOLD_DEFAULT 3
+
+struct nhit_policy_context {
+	nhit_hash_t hash_map;
+
+	/* Configurable parameters */
+	env_atomic insertion_threshold;
+};
+
+ocf_error_t nhit_init(ocf_cache_t cache, ocf_promotion_policy_t policy)
+{
+	struct nhit_policy_context *ctx;
+	int result = 0;
+
+	ctx = env_vmalloc(sizeof(*ctx));
+	if (!ctx) {
+		result = -OCF_ERR_NO_MEM;
+		goto exit;
+	}
+
+	result = hash_init(ocf_metadata_get_cachelines_count(cache) *
+			NHIT_MAPPING_RATIO, &ctx->hash_map);
+	if (result)
+		goto dealloc_ctx;
+
+	env_atomic_set(&ctx->insertion_threshold, NHIT_THRESHOLD_DEFAULT);
+
+	policy->ctx = ctx;
+
+	return 0;
+
+dealloc_ctx:
+	env_vfree(ctx);
+exit:
+	ocf_cache_log(cache, log_err, "Error initializing nhit promotion policy\n");
+	return result;
+}
+
+void nhit_deinit(ocf_promotion_policy_t policy)
+{
+	struct nhit_policy_context *ctx = policy->ctx;
+
+	hash_deinit(ctx->hash_map);
+
+	env_vfree(ctx);
+	policy->ctx = NULL;
+}
+
+ocf_error_t nhit_set_param(ocf_promotion_policy_t policy, uint8_t param_id,
+		uint64_t param_value)
+{
+	struct nhit_policy_context *ctx = policy->ctx;
+	ocf_error_t result = 0;
+
+	switch (param_id) {
+	case nhit_insertion_threshold:
+		if (param_value > NHIT_MIN_THRESHOLD &&
+				param_value < NHIT_MAX_THRESHOLD) {
+			env_atomic_set(&ctx->insertion_threshold, param_value);
+		} else {
+			ocf_cache_log(policy->owner, log_err, "Invalid nhit "
+					"promotion policy insertion threshold!\n");
+			result = -OCF_ERR_INVAL;
+		}
+		break;
+
+	default:
+		ocf_cache_log(policy->owner, log_err, "Invalid nhit "
+				"promotion policy parameter (%u)!\n",
+				param_id);
+		result = -OCF_ERR_INVAL;
+
+		break;
+	}
+
+	return result;
+}
+
+ocf_error_t nhit_get_param(ocf_promotion_policy_t policy, uint8_t param_id,
+		uint64_t *param_value)
+{
+	struct nhit_policy_context *ctx = policy->ctx;
+	ocf_error_t result = 0;
+
+	OCF_CHECK_NULL(param_value);
+
+	switch (param_id) {
+	case nhit_insertion_threshold:
+		*param_value = env_atomic_read(&ctx->insertion_threshold);
+		break;
+
+	default:
+		ocf_cache_log(policy->owner, log_err, "Invalid nhit "
+				"promotion policy parameter (%u)!\n",
+				param_id);
+		result = -OCF_ERR_INVAL;
+
+		break;
+	}
+
+	return result;
+}
+
+static void core_line_purge(struct nhit_policy_context *ctx, ocf_core_id_t core_id,
+		uint64_t core_lba)
+{
+	hash_set_occurences(ctx->hash_map, core_id, core_lba, 0);
+}
+
+void nhit_req_purge(ocf_promotion_policy_t policy,
+		struct ocf_request *req)
+{
+	struct nhit_policy_context *ctx = policy->ctx;
+	uint32_t i;
+	uint64_t core_line;
+
+	for (i = 0, core_line = req->core_line_first;
+			core_line <= req->core_line_last; core_line++, i++) {
+		struct ocf_map_info *entry = &(req->map[i]);
+
+		core_line_purge(ctx, entry->core_id, entry->core_line);
+	}
+}
+
+static bool core_line_should_promote(struct nhit_policy_context *ctx,
+		ocf_core_id_t core_id, uint64_t core_lba)
+{
+	bool hit;
+	int32_t counter;
+
+	hit = hash_query(ctx->hash_map, core_id, core_lba, &counter);
+	if (hit) {
+		/* we have a hit, return now */
+		return env_atomic_read(&ctx->insertion_threshold) <= counter;
+	}
+
+	hash_insert(ctx->hash_map, core_id, core_lba);
+
+	return false;
+}
+
+bool nhit_req_should_promote(ocf_promotion_policy_t policy,
+		struct ocf_request *req)
+{
+	struct nhit_policy_context *ctx = policy->ctx;
+	bool result = true;
+	uint32_t i;
+	uint64_t core_line;
+
+	for (i = 0, core_line = req->core_line_first;
+			core_line <= req->core_line_last; core_line++, i++) {
+		struct ocf_map_info *entry = &(req->map[i]);
+
+		if (!core_line_should_promote(ctx, entry->core_id,
+					entry->core_line)) {
+			result = false;
+		}
+	}
+
+	/* We don't want to reject even partially
+	 * hit requests - this way we could trigger passthrough and invalidation.
+	 * Let's let it in! */
+	return result || req->info.hit_no;
+}
+

src/promotion/nhit/nhit.h

@@ -7,8 +7,13 @@
 #define NHIT_PROMOTION_POLICY_H_
 
 #include "ocf/ocf.h"
-#include "../ocf_request.h"
-#include "promotion.h"
+#include "../../ocf_request.h"
+#include "../promotion.h"
+
+enum nhit_param {
+	nhit_insertion_threshold,
+	nhit_param_max
+};
 
 ocf_error_t nhit_init(ocf_cache_t cache, ocf_promotion_policy_t policy);
 
@@ -17,6 +22,9 @@ void nhit_deinit(ocf_promotion_policy_t policy);
 ocf_error_t nhit_set_param(ocf_promotion_policy_t policy, uint8_t param_id,
 		uint64_t param_value);
 
+ocf_error_t nhit_get_param(ocf_promotion_policy_t policy, uint8_t param_id,
+		uint64_t *param_value);
+
 void nhit_req_purge(ocf_promotion_policy_t policy,
 		struct ocf_request *req);
 

src/promotion/ops.h

@@ -10,6 +10,7 @@
 #include "promotion.h"
 
 struct ocf_promotion_policy {
+	ocf_cache_t owner;
 	ocf_promotion_t type;
 	void *ctx;
 };
@@ -28,6 +29,10 @@ struct promotion_policy_ops {
 			uint64_t param_value);
 		/*!< Set promotion policy parameter */
 
+	ocf_error_t (*get_param)(ocf_promotion_policy_t policy, uint8_t param_id,
+			uint64_t *param_value);
+		/*!< Get promotion policy parameter */
+
 	void (*req_purge)(ocf_promotion_policy_t policy,
 			struct ocf_request *req);
 		/*!< Call when request core lines have been inserted or it is

src/promotion/promotion.c

@@ -7,11 +7,11 @@
 
 #include "promotion.h"
 #include "ops.h"
-#include "nhit.h"
+#include "nhit/nhit.h"
 
 struct promotion_policy_ops ocf_promotion_policies[ocf_promotion_max] = {
-	[ocf_promotion_nop] = {
-		.name = "nop",
+	[ocf_promotion_always] = {
+		.name = "always",
 	},
 	[ocf_promotion_nhit] = {
 		.name = "nhit",
@@ -35,6 +35,7 @@ ocf_error_t ocf_promotion_init(ocf_cache_t cache, ocf_promotion_policy_t *policy
 		return -OCF_ERR_NO_MEM;
 
 	(*policy)->type = type;
+	(*policy)->owner = cache;
 
 	if (ocf_promotion_policies[type].init)
 		result = ocf_promotion_policies[type].init(cache, *policy);
@@ -70,6 +71,22 @@ ocf_error_t ocf_promotion_set_param(ocf_promotion_policy_t policy,
 	return result;
 }
 
+ocf_error_t ocf_promotion_get_param(ocf_promotion_policy_t policy,
+		uint8_t param_id, uint64_t *param_value)
+{
+	ocf_promotion_t type = policy->type;
+	ocf_error_t result = 0;
+
+	ENV_BUG_ON(type >= ocf_promotion_max);
+
+	if (ocf_promotion_policies[type].get_param) {
+		result = ocf_promotion_policies[type].get_param(policy, param_id,
+				param_value);
+	}
+
+	return result;
+}
+
 void ocf_promotion_req_purge(ocf_promotion_policy_t policy,
 		struct ocf_request *req)
 {

src/promotion/promotion.h

@@ -43,6 +43,18 @@ void ocf_promotion_deinit(ocf_promotion_policy_t policy);
 ocf_error_t ocf_promotion_set_param(ocf_promotion_policy_t policy,
 		uint8_t param_id, uint64_t param_value);
 
+/**
+ * @brief Get promotion policy parameter
+ *
+ * @param[in] policy promotion policy handle
+ * @param[in] param_id id of parameter to be set
+ * @param[out] param_value value of parameter to be set
+ *
+ * @retval ocf_error_t
+ */
+ocf_error_t ocf_promotion_get_param(ocf_promotion_policy_t policy,
+		uint8_t param_id, uint64_t *param_value);
+
 /**
  * @brief Update promotion policy after cache lines have been promoted to cache
  * or discarded from core device

tests/unit/framework/tests_config.py

@@ -14,13 +14,14 @@ MAIN_DIRECTORY_OF_UNIT_TESTS = "../tests/"
 # Paths to all directories, in which tests are stored. All paths should be relative to
 # MAIN_DIRECTORY_OF_UNIT_TESTS
 DIRECTORIES_WITH_TESTS_LIST = ["cleaning/", "metadata/", "mngt/", "concurrency/", "engine/",
-                               "eviction/", "utils/"]
+                               "eviction/", "utils/", "promotion/"]
 
 # Paths to all directories containing files with sources. All paths should be relative to
 # MAIN_DIRECTORY_OF_TESTED_PROJECT
 DIRECTORIES_TO_INCLUDE_FROM_PROJECT_LIST = ["src/", "src/cleaning/", "src/engine/", "src/metadata/",
                                             "src/eviction/", "src/mngt/", "src/concurrency/",
-                                            "src/utils/", "inc/"]
+                                            "src/utils/", "inc/", "src/promotion/",
+                                            "src/promotion/nhit/"]
 
 # Paths to all directories from directory with tests, which should also be included
 DIRECTORIES_TO_INCLUDE_FROM_UT_LIST = ["ocf_env/"]