[RFC PATCH 0/2] Node migration between memory tiers

[RFC PATCH 0/2] Node migration between memory tiers

[sthanneeru.opensrc]

From: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>

The memory tiers feature allows nodes with similar memory types
or performance characteristics to be grouped together in a
memory tier. However, there is currently no provision for
moving a node from one tier to another on demand.

This patch series aims to support node migration between tiers
on demand by sysadmin/root user using the provided sysfs for
node migration. Each tier has a start abstract distance(adistance)
and range.

To migrate a node to a tier, the corresponding node’s sysfs
adistance_offset is written with a value corresponding to
the tier’s adistance.

Example: Move node2 to memory tier5 from its default tier(i.e 4)

1. Check default values:
$cat /sys/devices/virtual/memory_tiering/memory_tier4/nodelist
0-2

$cat /sys/devices/system/node/node0/adistance_offset
0
$cat /sys/devices/system/node/node1/adistance_offset
0
$cat /sys/devices/system/node/node2/adistance_offset
0

2. Move node2 to  tier5:

To move node2 from emory_tier4 (adistance=512) to
emory_tier5 (abstract=640), set the `adistance_offset` of
node 2 to 128 (i.e., 512 + 128 = 640).

Tier4 adistance start can be derved from tier-id
(i.e for tier4, 4 << 7 = 512).

$echo 128 > /sys/devices/system/node/node2/adistance_offset
$cat /sys/devices/system/node/node2/adistance_offset
128

3. Verify node2's tier id:

$cat /sys/devices/virtual/memory_tiering/memory_tier5/nodelist
2
$cat /sys/devices/virtual/memory_tiering/memory_tier4/nodelist
0-1

Srinivasulu Thanneeru (2):
  base/node: Add sysfs for adistance_offset
  memory tier: Support node migration between tiers

 drivers/base/node.c          | 51 +++++++++++++++++++++++
 include/linux/memory-tiers.h | 11 +++++
 include/linux/node.h         |  6 +++
 mm/memory-tiers.c            | 79 ++++++++++++++++++++----------------
 4 files changed, 113 insertions(+), 34 deletions(-)

-- 
2.25.1

[RFC PATCH 1/2] base/node: Add sysfs for adistance_offset

[sthanneeru.opensrc]

From: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>

This patch introduces a new attribute called adistance_offset to the
node_devices structure.
Using adistance_offset, a node can be migrated to a targeted tier.
Target tier's adjacent distance(adistance) is calculated by taking the
adistance offset into account.

Signed-off-by: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>
Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@micron.com>
---
 drivers/base/node.c          | 45 ++++++++++++++++++++++++++++++++++++
 include/linux/memory-tiers.h |  6 +++++
 include/linux/node.h         |  1 +
 mm/memory-tiers.c            | 14 +++++++++++
 4 files changed, 66 insertions(+)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 493d533f8375..1e63c692977b 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -7,6 +7,7 @@
 #include <linux/init.h>
 #include <linux/mm.h>
 #include <linux/memory.h>
+#include <linux/memory-tiers.h>
 #include <linux/vmstat.h>
 #include <linux/notifier.h>
 #include <linux/node.h>
@@ -569,11 +570,54 @@ static ssize_t node_read_distance(struct device *dev,
 }
 static DEVICE_ATTR(distance, 0444, node_read_distance, NULL);
 
+static ssize_t adistance_offset_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	int nid = dev->id;
+	int len = 0;
+
+	/*
+	 * buf is currently PAGE_SIZE in length and each node needs 4 chars
+	 * at the most (distance + space or newline).
+	 */
+	BUILD_BUG_ON(MAX_NUMNODES * 4 > PAGE_SIZE);
+
+	len += sysfs_emit(buf, "%d\n", node_devices[nid]->adistance_offset);
+	return len;
+}
+
+static ssize_t adistance_offset_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t size)
+{
+	int nid = dev->id;
+	int value, ret;
+
+	ret = kstrtoint(buf, 0, &value);
+
+	if (ret)
+		return ret;
+	if (node_devices[nid]->adistance_offset == value)
+		return size;
+	/*
+	 * Request from a node to migrate to a memtier with negative
+	 * adistance is not valid.
+	 */
+	ret = get_target_memtier_adistance(nid, value);
+	if (ret < 0)
+		return -EINVAL;
+
+	node_devices[nid]->adistance_offset = value;
+	return size;
+}
+static DEVICE_ATTR_RW(adistance_offset);
+
 static struct attribute *node_dev_attrs[] = {
 	&dev_attr_meminfo.attr,
 	&dev_attr_numastat.attr,
 	&dev_attr_distance.attr,
 	&dev_attr_vmstat.attr,
+	&dev_attr_adistance_offset.attr,
 	NULL
 };
 
@@ -883,6 +927,7 @@ int __register_one_node(int nid)
 
 	INIT_LIST_HEAD(&node_devices[nid]->access_list);
 	node_init_caches(nid);
+	node_devices[nid]->adistance_offset = 0;
 
 	return error;
 }
diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index 1e39d27bee41..ff4e7136ab40 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -48,6 +48,7 @@ int mt_calc_adistance(int node, int *adist);
 int mt_set_default_dram_perf(int nid, struct node_hmem_attrs *perf,
 			     const char *source);
 int mt_perf_to_adistance(struct node_hmem_attrs *perf, int *adist);
+int get_target_memtier_adistance(int node, int adistance_offset);
 #ifdef CONFIG_MIGRATION
 int next_demotion_node(int node);
 void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
@@ -136,5 +137,10 @@ static inline int mt_perf_to_adistance(struct node_hmem_attrs *perf, int *adist)
 {
 	return -EIO;
 }
+
+static int get_target_memtier_adistance(int node, int adistance_offset)
+{
+	return 0;
+}
 #endif	/* CONFIG_NUMA */
 #endif  /* _LINUX_MEMORY_TIERS_H */
diff --git a/include/linux/node.h b/include/linux/node.h
index 427a5975cf40..fd0f4f3177f8 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -83,6 +83,7 @@ static inline void node_set_perf_attrs(unsigned int nid,
 struct node {
 	struct device	dev;
 	struct list_head access_list;
+	int adistance_offset;
 #ifdef CONFIG_HMEM_REPORTING
 	struct list_head cache_attrs;
 	struct device *cache_dev;
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 8d5291add2bc..a40d4d4383d7 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -167,6 +167,20 @@ static const struct attribute_group *memtier_dev_groups[] = {
 	NULL
 };
 
+int get_target_memtier_adistance(int node, int adistance_offset)
+{
+	struct memory_dev_type *memtype;
+	int node_adistance;
+
+	memtype = node_memory_types[node].memtype;
+	/*
+	 * Calculate the targeted memtier abstract distance from
+	 * memtype adistance and node adistance offset.
+	 */
+	node_adistance = memtype->adistance + adistance_offset;
+	return node_adistance;
+}
+
 static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype)
 {
 	int ret;
-- 
2.25.1

[RFC PATCH 2/2] memory tier: Support node migration between tiers

[sthanneeru.opensrc]

From: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>

Node migration enables the grouping or migration of nodes
between tiers based on nodes' latencies and bandwidth characteristics.
Since nodes of the same memory-type can exist in different tiers and can
migrate from one tier to another, it is necessary to maintain nodes
per tier instead of maintaining a list of nodes grouped using
memory type(siblings) within the tier.

To migrate a node from one tier to another, remove the node from the
current tier and insert it into the target tier. If the target tier does
not exist, create a new one.

Signed-off-by: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>
---
 drivers/base/node.c          |  6 ++++
 include/linux/memory-tiers.h |  5 +++
 include/linux/node.h         |  5 +++
 mm/memory-tiers.c            | 65 +++++++++++++++++-------------------
 4 files changed, 47 insertions(+), 34 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 1e63c692977b..8290ea96b439 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -608,10 +608,16 @@ static ssize_t adistance_offset_store(struct device *dev,
 		return -EINVAL;
 
 	node_devices[nid]->adistance_offset = value;
+	node_memtier_change(nid);
 	return size;
 }
 static DEVICE_ATTR_RW(adistance_offset);
 
+int get_node_adistance_offset(int nid)
+{
+	return node_devices[nid]->adistance_offset;
+}
+
 static struct attribute *node_dev_attrs[] = {
 	&dev_attr_meminfo.attr,
 	&dev_attr_numastat.attr,
diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index ff4e7136ab40..e86c23873334 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -49,6 +49,7 @@ int mt_set_default_dram_perf(int nid, struct node_hmem_attrs *perf,
 			     const char *source);
 int mt_perf_to_adistance(struct node_hmem_attrs *perf, int *adist);
 int get_target_memtier_adistance(int node, int adistance_offset);
+void node_memtier_change(int node);
 #ifdef CONFIG_MIGRATION
 int next_demotion_node(int node);
 void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
@@ -142,5 +143,9 @@ static int get_target_memtier_adistance(int node, int adistance_offset)
 {
 	return 0;
 }
+
+static inline void node_memtier_change(int node)
+{
+}
 #endif	/* CONFIG_NUMA */
 #endif  /* _LINUX_MEMORY_TIERS_H */
diff --git a/include/linux/node.h b/include/linux/node.h
index fd0f4f3177f8..5150215b4922 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -139,6 +139,7 @@ extern void unregister_memory_block_under_nodes(struct memory_block *mem_blk);
 extern int register_memory_node_under_compute_node(unsigned int mem_nid,
 						   unsigned int cpu_nid,
 						   unsigned access);
+extern int get_node_adistance_offset(int nid);
 #else
 static inline void node_dev_init(void)
 {
@@ -166,6 +167,10 @@ static inline int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
 static inline void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
 {
 }
+static inline int get_node_adistance_offset(int nid)
+{
+	return 0;
+}
 #endif
 
 #define to_node(device) container_of(device, struct node, dev)
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index a40d4d4383d7..b6cd86977731 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -23,6 +23,8 @@ struct memory_tier {
 	struct device dev;
 	/* All the nodes that are part of all the lower memory tiers. */
 	nodemask_t lower_tier_mask;
+	/* Nodes linked to this tier*/
+	nodemask_t nodes;
 };
 
 struct demotion_nodes {
@@ -120,13 +122,7 @@ static inline struct memory_tier *to_memory_tier(struct device *device)
 
 static __always_inline nodemask_t get_memtier_nodemask(struct memory_tier *memtier)
 {
-	nodemask_t nodes = NODE_MASK_NONE;
-	struct memory_dev_type *memtype;
-
-	list_for_each_entry(memtype, &memtier->memory_types, tier_sibling)
-		nodes_or(nodes, nodes, memtype->nodes);
-
-	return nodes;
+	return memtier->nodes;
 }
 
 static void memory_tier_device_release(struct device *dev)
@@ -181,33 +177,22 @@ int get_target_memtier_adistance(int node, int adistance_offset)
 	return node_adistance;
 }
 
-static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype)
+static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype,
+						   int tier_adistance)
 {
 	int ret;
 	bool found_slot = false;
 	struct memory_tier *memtier, *new_memtier;
-	int adistance = memtype->adistance;
+	int adistance;
 	unsigned int memtier_adistance_chunk_size = MEMTIER_CHUNK_SIZE;
 
 	lockdep_assert_held_once(&memory_tier_lock);
 
-	adistance = round_down(adistance, memtier_adistance_chunk_size);
-	/*
-	 * If the memtype is already part of a memory tier,
-	 * just return that.
-	 */
-	if (!list_empty(&memtype->tier_sibling)) {
-		list_for_each_entry(memtier, &memory_tiers, list) {
-			if (adistance == memtier->adistance_start)
-				return memtier;
-		}
-		WARN_ON(1);
-		return ERR_PTR(-EINVAL);
-	}
+	adistance = round_down(tier_adistance, memtier_adistance_chunk_size);
 
 	list_for_each_entry(memtier, &memory_tiers, list) {
 		if (adistance == memtier->adistance_start) {
-			goto link_memtype;
+			return memtier;
 		} else if (adistance < memtier->adistance_start) {
 			found_slot = true;
 			break;
@@ -238,9 +223,6 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
 		return ERR_PTR(ret);
 	}
 	memtier = new_memtier;
-
-link_memtype:
-	list_add(&memtype->tier_sibling, &memtier->memory_types);
 	return memtier;
 }
 
@@ -499,7 +481,7 @@ static struct memory_tier *set_node_memory_tier(int node)
 	struct memory_tier *memtier;
 	struct memory_dev_type *memtype;
 	pg_data_t *pgdat = NODE_DATA(node);
-
+	int tier_adistance;
 
 	lockdep_assert_held_once(&memory_tier_lock);
 
@@ -510,9 +492,13 @@ static struct memory_tier *set_node_memory_tier(int node)
 
 	memtype = node_memory_types[node].memtype;
 	node_set(node, memtype->nodes);
-	memtier = find_create_memory_tier(memtype);
+	tier_adistance = get_node_adistance_offset(node);
+	tier_adistance = memtype->adistance + tier_adistance;
+
+	memtier = find_create_memory_tier(memtype, tier_adistance);
 	if (!IS_ERR(memtier))
 		rcu_assign_pointer(pgdat->memtier, memtier);
+	node_set(node, memtier->nodes);
 	return memtier;
 }
 
@@ -548,11 +534,9 @@ static bool clear_node_memory_tier(int node)
 		synchronize_rcu();
 		memtype = node_memory_types[node].memtype;
 		node_clear(node, memtype->nodes);
-		if (nodes_empty(memtype->nodes)) {
-			list_del_init(&memtype->tier_sibling);
-			if (list_empty(&memtier->memory_types))
-				destroy_memory_tier(memtier);
-		}
+		node_clear(node, memtier->nodes);
+		if (nodes_empty(memtier->nodes))
+			destroy_memory_tier(memtier);
 		cleared = true;
 	}
 	return cleared;
@@ -575,7 +559,6 @@ struct memory_dev_type *alloc_memory_type(int adistance)
 		return ERR_PTR(-ENOMEM);
 
 	memtype->adistance = adistance;
-	INIT_LIST_HEAD(&memtype->tier_sibling);
 	memtype->nodes  = NODE_MASK_NONE;
 	kref_init(&memtype->kref);
 	return memtype;
@@ -615,6 +598,20 @@ void clear_node_memory_type(int node, struct memory_dev_type *memtype)
 }
 EXPORT_SYMBOL_GPL(clear_node_memory_type);
 
+void node_memtier_change(int node)
+{
+	struct memory_tier *memtier;
+
+	mutex_lock(&memory_tier_lock);
+	if (clear_node_memory_tier(node))
+		establish_demotion_targets();
+	memtier = set_node_memory_tier(node);
+	if (!IS_ERR(memtier))
+		establish_demotion_targets();
+	mutex_unlock(&memory_tier_lock);
+}
+
+
 static void dump_hmem_attrs(struct node_hmem_attrs *attrs, const char *prefix)
 {
 	pr_info(
-- 
2.25.1

Re: [RFC PATCH 0/2] Node migration between memory tiers

[Huang, Ying]

<sthanneeru.opensrc@micron.com> writes:

> From: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>
>
> The memory tiers feature allows nodes with similar memory types
> or performance characteristics to be grouped together in a
> memory tier. However, there is currently no provision for
> moving a node from one tier to another on demand.
>
> This patch series aims to support node migration between tiers
> on demand by sysadmin/root user using the provided sysfs for
> node migration. Each tier has a start abstract distance(adistance)
> and range.

We have discussed migrating nodes (in fact nodes of a memory type)
between tiers by sysadmin/root before.  The basic idea comes from
Johannes.  It is summarized in page 11 of [1],

[1] https://lpc.events/event/16/contributions/1209/attachments/1042/1995/Live%20In%20a%20World%20With%20Multiple%20Memory%20Types.pdf

The abstract distance of a memory type (e.g., GPU HBM) can be adjusted
via a sysfs knob (<memory_type>/abstract_distance_offset).

I still think that the memory type is better to be used to change
the abstract distance of nodes.  Do you agree?

--
Best Regards,
Huang, Ying

> To migrate a node to a tier, the corresponding node’s sysfs
> adistance_offset is written with a value corresponding to
> the tier’s adistance.
>
> Example: Move node2 to memory tier5 from its default tier(i.e 4)
>
> 1. Check default values:
> $cat /sys/devices/virtual/memory_tiering/memory_tier4/nodelist
> 0-2
>
> $cat /sys/devices/system/node/node0/adistance_offset
> 0
> $cat /sys/devices/system/node/node1/adistance_offset
> 0
> $cat /sys/devices/system/node/node2/adistance_offset
> 0
>
> 2. Move node2 to  tier5:
>
> To move node2 from emory_tier4 (adistance=512) to
> emory_tier5 (abstract=640), set the `adistance_offset` of
> node 2 to 128 (i.e., 512 + 128 = 640).
>
> Tier4 adistance start can be derved from tier-id
> (i.e for tier4, 4 << 7 = 512).
>
> $echo 128 > /sys/devices/system/node/node2/adistance_offset
> $cat /sys/devices/system/node/node2/adistance_offset
> 128
>
> 3. Verify node2's tier id:
>
> $cat /sys/devices/virtual/memory_tiering/memory_tier5/nodelist
> 2
> $cat /sys/devices/virtual/memory_tiering/memory_tier4/nodelist
> 0-1
>
> Srinivasulu Thanneeru (2):
>   base/node: Add sysfs for adistance_offset
>   memory tier: Support node migration between tiers
>
>  drivers/base/node.c          | 51 +++++++++++++++++++++++
>  include/linux/memory-tiers.h | 11 +++++
>  include/linux/node.h         |  6 +++
>  mm/memory-tiers.c            | 79 ++++++++++++++++++++----------------
>  4 files changed, 113 insertions(+), 34 deletions(-)

[RFC PATCH 1/2] base/node: Add sysfs for adistance_offset

[sthanneeru.opensrc]

From: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>

This patch introduces a new attribute called adistance_offset to the
node_devices structure.
Using adistance_offset, a node can be migrated to a targeted tier.
Target tier's adjacent distance(adistance) is calculated by taking the
adistance offset into account.

Signed-off-by: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>
Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@micron.com>
---
 drivers/base/node.c          | 45 ++++++++++++++++++++++++++++++++++++
 include/linux/memory-tiers.h |  6 +++++
 include/linux/node.h         |  1 +
 mm/memory-tiers.c            | 14 +++++++++++
 4 files changed, 66 insertions(+)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 493d533f8375..1e63c692977b 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -7,6 +7,7 @@
 #include <linux/init.h>
 #include <linux/mm.h>
 #include <linux/memory.h>
+#include <linux/memory-tiers.h>
 #include <linux/vmstat.h>
 #include <linux/notifier.h>
 #include <linux/node.h>
@@ -569,11 +570,54 @@ static ssize_t node_read_distance(struct device *dev,
 }
 static DEVICE_ATTR(distance, 0444, node_read_distance, NULL);
 
+static ssize_t adistance_offset_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	int nid = dev->id;
+	int len = 0;
+
+	/*
+	 * buf is currently PAGE_SIZE in length and each node needs 4 chars
+	 * at the most (distance + space or newline).
+	 */
+	BUILD_BUG_ON(MAX_NUMNODES * 4 > PAGE_SIZE);
+
+	len += sysfs_emit(buf, "%d\n", node_devices[nid]->adistance_offset);
+	return len;
+}
+
+static ssize_t adistance_offset_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t size)
+{
+	int nid = dev->id;
+	int value, ret;
+
+	ret = kstrtoint(buf, 0, &value);
+
+	if (ret)
+		return ret;
+	if (node_devices[nid]->adistance_offset == value)
+		return size;
+	/*
+	 * Request from a node to migrate to a memtier with negative
+	 * adistance is not valid.
+	 */
+	ret = get_target_memtier_adistance(nid, value);
+	if (ret < 0)
+		return -EINVAL;
+
+	node_devices[nid]->adistance_offset = value;
+	return size;
+}
+static DEVICE_ATTR_RW(adistance_offset);
+
 static struct attribute *node_dev_attrs[] = {
 	&dev_attr_meminfo.attr,
 	&dev_attr_numastat.attr,
 	&dev_attr_distance.attr,
 	&dev_attr_vmstat.attr,
+	&dev_attr_adistance_offset.attr,
 	NULL
 };
 
@@ -883,6 +927,7 @@ int __register_one_node(int nid)
 
 	INIT_LIST_HEAD(&node_devices[nid]->access_list);
 	node_init_caches(nid);
+	node_devices[nid]->adistance_offset = 0;
 
 	return error;
 }
diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index 1e39d27bee41..ff4e7136ab40 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -48,6 +48,7 @@ int mt_calc_adistance(int node, int *adist);
 int mt_set_default_dram_perf(int nid, struct node_hmem_attrs *perf,
 			     const char *source);
 int mt_perf_to_adistance(struct node_hmem_attrs *perf, int *adist);
+int get_target_memtier_adistance(int node, int adistance_offset);
 #ifdef CONFIG_MIGRATION
 int next_demotion_node(int node);
 void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
@@ -136,5 +137,10 @@ static inline int mt_perf_to_adistance(struct node_hmem_attrs *perf, int *adist)
 {
 	return -EIO;
 }
+
+static int get_target_memtier_adistance(int node, int adistance_offset)
+{
+	return 0;
+}
 #endif	/* CONFIG_NUMA */
 #endif  /* _LINUX_MEMORY_TIERS_H */
diff --git a/include/linux/node.h b/include/linux/node.h
index 427a5975cf40..fd0f4f3177f8 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -83,6 +83,7 @@ static inline void node_set_perf_attrs(unsigned int nid,
 struct node {
 	struct device	dev;
 	struct list_head access_list;
+	int adistance_offset;
 #ifdef CONFIG_HMEM_REPORTING
 	struct list_head cache_attrs;
 	struct device *cache_dev;
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 8d5291add2bc..a40d4d4383d7 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -167,6 +167,20 @@ static const struct attribute_group *memtier_dev_groups[] = {
 	NULL
 };
 
+int get_target_memtier_adistance(int node, int adistance_offset)
+{
+	struct memory_dev_type *memtype;
+	int node_adistance;
+
+	memtype = node_memory_types[node].memtype;
+	/*
+	 * Calculate the targeted memtier abstract distance from
+	 * memtype adistance and node adistance offset.
+	 */
+	node_adistance = memtype->adistance + adistance_offset;
+	return node_adistance;
+}
+
 static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype)
 {
 	int ret;
-- 
2.25.1