memory tiering: add abstract distance calculation algorithms management

Patch series "memory tiering: calculate abstract distance based on ACPI
HMAT".

We have the explicit memory tiers framework to manage systems with
multiple types of memory, e.g., DRAM in DIMM slots and CXL memory
devices.  Where, same kind of memory devices will be grouped into
memory types, then put into memory tiers.  To describe the performance
of a memory type, abstract distance is defined.  Which is in direct
proportion to the memory latency and inversely proportional to the
memory bandwidth.  To keep the code as simple as possible, fixed
abstract distance is used in dax/kmem to describe slow memory such as
Optane DCPMM.

To support more memory types, in this series, we added the abstract
distance calculation algorithm management mechanism, provided a
algorithm implementation based on ACPI HMAT, and used the general
abstract distance calculation interface in dax/kmem driver.  So,
dax/kmem can support HBM (high bandwidth memory) in addition to the
original Optane DCPMM.


This patch (of 4):

The abstract distance may be calculated by various drivers, such as ACPI
HMAT, CXL CDAT, etc.  While it may be used by various code which hot-add
memory node, such as dax/kmem etc.  To decouple the algorithm users and
the providers, the abstract distance calculation algorithms management
mechanism is implemented in this patch.  It provides interface for the
providers to register the implementation, and interface for the users.

Multiple algorithm implementations can cooperate via calculating abstract
distance for different memory nodes.  The preference of algorithm
implementations can be specified via priority (notifier_block.priority).

Link: https://lkml.kernel.org/r/20230721012932.190742-1-ying.huang@intel.com
Link: https://lkml.kernel.org/r/20230721012932.190742-2-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Rafael J Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: yhuang-intel

include/linux/memory-tiers.h

@@ -6,6 +6,7 @@
 #include <linux/nodemask.h>
 #include <linux/kref.h>
 #include <linux/mmzone.h>
+#include <linux/notifier.h>
 /*
  * Each tier cover a abstrace distance chunk size of 128
  */
@@ -36,6 +37,9 @@ struct memory_dev_type *alloc_memory_type(int adistance);
 void put_memory_type(struct memory_dev_type *memtype);
 void init_node_memory_type(int node, struct memory_dev_type *default_type);
 void clear_node_memory_type(int node, struct memory_dev_type *memtype);
+int register_mt_adistance_algorithm(struct notifier_block *nb);
+int unregister_mt_adistance_algorithm(struct notifier_block *nb);
+int mt_calc_adistance(int node, int *adist);
 #ifdef CONFIG_MIGRATION
 int next_demotion_node(int node);
 void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
@@ -97,5 +101,20 @@ static inline bool node_is_toptier(int node)
 {
 	return true;
 }
+
+static inline int register_mt_adistance_algorithm(struct notifier_block *nb)
+{
+	return 0;
+}
+
+static inline int unregister_mt_adistance_algorithm(struct notifier_block *nb)
+{
+	return 0;
+}
+
+static inline int mt_calc_adistance(int node, int *adist)
+{
+	return NOTIFY_DONE;
+}
 #endif	/* CONFIG_NUMA */
 #endif  /* _LINUX_MEMORY_TIERS_H */

mm/memory-tiers.c

@@ -5,6 +5,7 @@
 #include <linux/kobject.h>
 #include <linux/memory.h>
 #include <linux/memory-tiers.h>
+#include <linux/notifier.h>
 
 #include "internal.h"
 
@@ -105,6 +106,8 @@ static int top_tier_adistance;
 static struct demotion_nodes *node_demotion __read_mostly;
 #endif /* CONFIG_MIGRATION */
 
+static BLOCKING_NOTIFIER_HEAD(mt_adistance_algorithms);
+
 static inline struct memory_tier *to_memory_tier(struct device *device)
 {
 	return container_of(device, struct memory_tier, dev);
@@ -592,6 +595,62 @@ void clear_node_memory_type(int node, struct memory_dev_type *memtype)
 }
 EXPORT_SYMBOL_GPL(clear_node_memory_type);
 
+/**
+ * register_mt_adistance_algorithm() - Register memory tiering abstract distance algorithm
+ * @nb: The notifier block which describe the algorithm
+ *
+ * Return: 0 on success, errno on error.
+ *
+ * Every memory tiering abstract distance algorithm provider needs to
+ * register the algorithm with register_mt_adistance_algorithm().  To
+ * calculate the abstract distance for a specified memory node, the
+ * notifier function will be called unless some high priority
+ * algorithm has provided result.  The prototype of the notifier
+ * function is as follows,
+ *
+ *   int (*algorithm_notifier)(struct notifier_block *nb,
+ *                             unsigned long nid, void *data);
+ *
+ * Where "nid" specifies the memory node, "data" is the pointer to the
+ * returned abstract distance (that is, "int *adist").  If the
+ * algorithm provides the result, NOTIFY_STOP should be returned.
+ * Otherwise, return_value & %NOTIFY_STOP_MASK == 0 to allow the next
+ * algorithm in the chain to provide the result.
+ */
+int register_mt_adistance_algorithm(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&mt_adistance_algorithms, nb);
+}
+EXPORT_SYMBOL_GPL(register_mt_adistance_algorithm);
+
+/**
+ * unregister_mt_adistance_algorithm() - Unregister memory tiering abstract distance algorithm
+ * @nb: the notifier block which describe the algorithm
+ *
+ * Return: 0 on success, errno on error.
+ */
+int unregister_mt_adistance_algorithm(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&mt_adistance_algorithms, nb);
+}
+EXPORT_SYMBOL_GPL(unregister_mt_adistance_algorithm);
+
+/**
+ * mt_calc_adistance() - Calculate abstract distance with registered algorithms
+ * @node: the node to calculate abstract distance for
+ * @adist: the returned abstract distance
+ *
+ * Return: if return_value & %NOTIFY_STOP_MASK != 0, then some
+ * abstract distance algorithm provides the result, and return it via
+ * @adist.  Otherwise, no algorithm can provide the result and @adist
+ * will be kept as it is.
+ */
+int mt_calc_adistance(int node, int *adist)
+{
+	return blocking_notifier_call_chain(&mt_adistance_algorithms, node, adist);
+}
+EXPORT_SYMBOL_GPL(mt_calc_adistance);
+
 static int __meminit memtier_hotplug_callback(struct notifier_block *self,
 					      unsigned long action, void *_arg)
 {