[PATCH v14 00/10] mm/demotion: Memory tiers and demotion

[PATCH v14 00/10] mm/demotion: Memory tiers and demotion

[Aneesh Kumar K.V]

The current kernel has the basic memory tiering support: Inactive pages on a
higher tier NUMA node can be migrated (demoted) to a lower tier NUMA node to
make room for new allocations on the higher tier NUMA node. Frequently accessed
pages on a lower tier NUMA node can be migrated (promoted) to a higher tier NUMA
node to improve the performance.

In the current kernel, memory tiers are defined implicitly via a demotion path
relationship between NUMA nodes, which is created during the kernel
initialization and updated when a NUMA node is hot-added or hot-removed. The
current implementation puts all nodes with CPU into the highest tier, and builds the
tier hierarchy tier-by-tier by establishing the per-node demotion targets based
on the distances between nodes.

This current memory tier kernel implementation needs to be improved for several
important use cases:

* The current tier initialization code always initializes each memory-only NUMA
  node into a lower tier. But a memory-only NUMA node may have a high
  performance memory device (e.g. a DRAM-backed memory-only node on a virtual
  machine) and that should be put into a higher tier.

* The current tier hierarchy always puts CPU nodes into the top tier. But on a
  system with HBM (e.g. GPU memory) devices, these memory-only HBM NUMA nodes
  should be in the top tier, and DRAM nodes with CPUs are better to be placed
  into the next lower tier.

* Also because the current tier hierarchy always puts CPU nodes into the top
  tier, when a CPU is hot-added (or hot-removed) and triggers a memory node from
  CPU-less into a CPU node (or vice versa), the memory tier hierarchy gets
  changed, even though no memory node is added or removed. This can make the
  tier hierarchy unstable and make it difficult to support tier-based memory
  accounting.

* A higher tier node can only be demoted to nodes with shortest distance on the
  next lower tier as defined by the demotion path, not any other node from any
  lower tier. This strict, demotion order does not work in all use
  cases (e.g. some use cases may want to allow cross-socket demotion to another
  node in the same demotion tier as a fallback when the preferred demotion node
  is out of space), and has resulted in the feature request for an interface to
  override the system-wide, per-node demotion order from the userspace. This
  demotion order is also inconsistent with the page allocation fallback order
  when all the nodes in a higher tier are out of space: The page allocation can
  fall back to any node from any lower tier, whereas the demotion order doesn't
  allow that.

This patch series make the creation of memory tiers explicit under
the control of device driver.

Memory Tier Initialization
==========================

Linux kernel presents memory devices as NUMA nodes and each memory device is of
a specific type. The memory type of a device is represented by its abstract 
distance. A memory tier corresponds to a range of abstract distance. This allows
for classifying memory devices with a specific performance range into a memory
tier.

By default, all memory nodes are assigned to the default tier with
abstract distance 512.

A device driver can move its memory nodes from the default tier. For example,
PMEM can move its memory nodes below the default tier, whereas GPU can move its
memory nodes above the default tier.

The kernel initialization code makes the decision on which exact tier a memory
node should be assigned to based on the requests from the device drivers as well
as the memory device hardware information provided by the firmware.

Hot-adding/removing CPUs doesn't affect memory tier hierarchy.

Changes from v13
* Address review feedback.
* Add path dropping memtier from struct memory_dev_type

Changes from v12
* Fix kernel crash on module unload
* Address review feedback.
* Add node_random patch to this series based on review feedback

Changes from v11:
* smaller abstract distance imply faster(higher) memory tier.

Changes from v10:
* rename performance level to abstract distance
* Thanks to all the good feedback from Huang, Ying <ying.huang@intel.com>.
  Updated the patchset to cover most of the review feedback.

Changes from v9:
* Use performance level for initializing memory tiers.

Changes from v8:
* Drop the sysfs interface patches and  related documentation changes.

Changes from v7:
* Fix kernel crash with demotion.
* Improve documentation.

Changes from v6:
* Drop the usage of rank.
* Address other review feedback.

Changes from v5:
* Remove patch supporting N_MEMORY node removal from memory tiers. memory tiers
  are going to be used for features other than demotion. Hence keep all N_MEMORY
  nodes in memory tiers irrespective of whether they want to participate in promotion or demotion.
* Add NODE_DATA->memtier
* Rearrage patches to add sysfs files later.
* Add support to create memory tiers from userspace.
* Address other review feedback.


Changes from v4:
* Address review feedback.
* Reverse the meaning of "rank": higher rank value means higher tier.
* Add "/sys/devices/system/memtier/default_tier".
* Add node_is_toptier

v4:
Add support for explicit memory tiers and ranks.

v3:
- Modify patch 1 subject to make it more specific
- Remove /sys/kernel/mm/numa/demotion_targets interface, use
  /sys/devices/system/node/demotion_targets instead and make
  it writable to override node_states[N_DEMOTION_TARGETS].
- Add support to view per node demotion targets via sysfs

v2:
In v1, only 1st patch of this patch series was sent, which was
implemented to avoid some of the limitations on the demotion
target sharing, however for certain numa topology, the demotion
targets found by that patch was not most optimal, so 1st patch
in this series is modified according to suggestions from Huang
and Baolin. Different examples of demotion list comparasion
between existing implementation and changed implementation can
be found in the commit message of 1st patch.



Aneesh Kumar K.V (9):
  mm/demotion: Add support for explicit memory tiers
  mm/demotion: Move memory demotion related code
  mm/demotion: Add hotplug callbacks to handle new numa node onlined
  mm/demotion/dax/kmem: Set node's abstract distance to
    MEMTIER_DEFAULT_DAX_ADISTANCE
  mm/demotion: Build demotion targets based on explicit memory tiers
  mm/demotion: Add pg_data_t member to track node memory tier details
  mm/demotion: Drop memtier from memtype
  mm/demotion: Update node_is_toptier to work with memory tiers
  lib/nodemask: Optimize node_random for nodemask with single NUMA node

Jagdish Gediya (1):
  mm/demotion: Demote pages according to allocation fallback order

 drivers/dax/kmem.c           |  42 ++-
 include/linux/memory-tiers.h |  99 ++++++
 include/linux/migrate.h      |  15 -
 include/linux/mmzone.h       |   3 +
 include/linux/node.h         |   5 -
 include/linux/nodemask.h     |  15 +-
 mm/Makefile                  |   1 +
 mm/huge_memory.c             |   1 +
 mm/memory-tiers.c            | 645 +++++++++++++++++++++++++++++++++++
 mm/migrate.c                 | 453 +-----------------------
 mm/mprotect.c                |   1 +
 mm/vmscan.c                  |  59 +++-
 mm/vmstat.c                  |   4 -
 13 files changed, 846 insertions(+), 497 deletions(-)
 create mode 100644 include/linux/memory-tiers.h
 create mode 100644 mm/memory-tiers.c

-- 
2.37.1

[PATCH v14 01/10] mm/demotion: Add support for explicit memory tiers

[Aneesh Kumar K.V]

In the current kernel, memory tiers are defined implicitly via a demotion path
relationship between NUMA nodes, which is created during the kernel
initialization and updated when a NUMA node is hot-added or hot-removed. The
current implementation puts all nodes with CPU into the highest tier, and builds
the tier hierarchy by establishing the per-node demotion targets based on the
distances between nodes.

This current memory tier kernel implementation needs to be improved for several
important use cases,

The current tier initialization code always initializes each memory-only NUMA
node into a lower tier. But a memory-only NUMA node may have a high performance
memory device (e.g. a DRAM-backed memory-only node on a virtual machine) that
should be put into a higher tier.

The current tier hierarchy always puts CPU nodes into the top tier. But on a
system with HBM or GPU devices, the memory-only NUMA nodes mapping these devices
should be in the top tier, and DRAM nodes with CPUs are better to be placed into
the next lower tier.

With current kernel higher tier node can only be demoted to nodes with shortest
distance on the next lower tier as defined by the demotion path, not any other
node from any lower tier. This strict, demotion order does not work in all use
cases (e.g. some use cases may want to allow cross-socket demotion to another
node in the same demotion tier as a fallback when the preferred demotion node is
out of space), This demotion order is also inconsistent with the page allocation
fallback order when all the nodes in a higher tier are out of space: The page
allocation can fall back to any node from any lower tier, whereas the demotion
order doesn't allow that.

This patch series address the above by defining memory tiers explicitly.

Linux kernel presents memory devices as NUMA nodes and each memory device is of
a specific type. The memory type of a device is represented by its abstract
distance. A memory tier corresponds to a range of abstract distance. This allows
for classifying memory devices with a specific performance range into a memory
tier.

This patch configures the range/chunk size to be 128. The default DRAM abstract
distance is 512. We can have 4 memory tiers below the default DRAM with abstract
distance range 0 - 127, 127 - 255, 256- 383, 384 - 511. Faster memory devices
can be placed in these faster(higher) memory tiers. Slower memory devices like
persistent memory will have abstract distance higher than the default DRAM
level.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/memory-tiers.h |  15 ++++
 mm/Makefile                  |   1 +
 mm/memory-tiers.c            | 129 +++++++++++++++++++++++++++++++++++
 3 files changed, 145 insertions(+)
 create mode 100644 include/linux/memory-tiers.h
 create mode 100644 mm/memory-tiers.c

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
new file mode 100644
index 000000000000..bc7c1b799bef
--- /dev/null
+++ b/include/linux/memory-tiers.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MEMORY_TIERS_H
+#define _LINUX_MEMORY_TIERS_H
+
+/*
+ * Each tier cover a abstrace distance chunk size of 128
+ */
+#define MEMTIER_CHUNK_BITS	7
+#define MEMTIER_CHUNK_SIZE	(1 << MEMTIER_CHUNK_BITS)
+/*
+ * Smaller abstract distance value imply faster(higher) memory tiers.
+ */
+#define MEMTIER_ADISTANCE_DRAM	(4 * MEMTIER_CHUNK_SIZE)
+
+#endif  /* _LINUX_MEMORY_TIERS_H */
diff --git a/mm/Makefile b/mm/Makefile
index 9a564f836403..488f604e77e0 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -92,6 +92,7 @@ obj-$(CONFIG_KFENCE) += kfence/
 obj-$(CONFIG_FAILSLAB) += failslab.o
 obj-$(CONFIG_MEMTEST)		+= memtest.o
 obj-$(CONFIG_MIGRATION) += migrate.o
+obj-$(CONFIG_NUMA) += memory-tiers.o
 obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o
 obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o
 obj-$(CONFIG_PAGE_COUNTER) += page_counter.o
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
new file mode 100644
index 000000000000..1f494e69776a
--- /dev/null
+++ b/mm/memory-tiers.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/nodemask.h>
+#include <linux/slab.h>
+#include <linux/lockdep.h>
+#include <linux/memory-tiers.h>
+
+struct memory_tier {
+	/* hierarchy of memory tiers */
+	struct list_head list;
+	/* list of all memory types part of this tier */
+	struct list_head memory_types;
+	/*
+	 * start value of abstract distance. memory tier maps
+	 * an abstract distance  range,
+	 * adistance_start .. adistance_start + MEMTIER_CHUNK_SIZE
+	 */
+	int adistance_start;
+};
+
+struct memory_dev_type {
+	/* list of memory types that are part of same tier as this type */
+	struct list_head tier_sibiling;
+	/* abstract distance for this specific memory type */
+	int adistance;
+	/* Nodes of same abstract distance */
+	nodemask_t nodes;
+	struct memory_tier *memtier;
+};
+
+static DEFINE_MUTEX(memory_tier_lock);
+static LIST_HEAD(memory_tiers);
+static struct memory_dev_type *node_memory_types[MAX_NUMNODES];
+/*
+ * For now we can have 4 faster memory tiers with smaller adistance
+ * than default DRAM tier.
+ */
+static struct memory_dev_type default_dram_type  = {
+	.adistance = MEMTIER_ADISTANCE_DRAM,
+	.tier_sibiling = LIST_HEAD_INIT(default_dram_type.tier_sibiling),
+};
+
+static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype)
+{
+	bool found_slot = false;
+	struct memory_tier *memtier, *new_memtier;
+	int adistance = memtype->adistance;
+	unsigned int memtier_adistance_chunk_size = MEMTIER_CHUNK_SIZE;
+
+	lockdep_assert_held_once(&memory_tier_lock);
+
+	/*
+	 * If the memtype is already part of a memory tier,
+	 * just return that.
+	 */
+	if (memtype->memtier)
+		return memtype->memtier;
+
+	adistance = round_down(adistance, memtier_adistance_chunk_size);
+	list_for_each_entry(memtier, &memory_tiers, list) {
+		if (adistance == memtier->adistance_start) {
+			memtype->memtier = memtier;
+			list_add(&memtype->tier_sibiling, &memtier->memory_types);
+			return memtier;
+		} else if (adistance < memtier->adistance_start) {
+			found_slot = true;
+			break;
+		}
+	}
+
+	new_memtier = kmalloc(sizeof(struct memory_tier), GFP_KERNEL);
+	if (!new_memtier)
+		return ERR_PTR(-ENOMEM);
+
+	new_memtier->adistance_start = adistance;
+	INIT_LIST_HEAD(&new_memtier->list);
+	INIT_LIST_HEAD(&new_memtier->memory_types);
+	if (found_slot)
+		list_add_tail(&new_memtier->list, &memtier->list);
+	else
+		list_add_tail(&new_memtier->list, &memory_tiers);
+	memtype->memtier = new_memtier;
+	list_add(&memtype->tier_sibiling, &new_memtier->memory_types);
+	return new_memtier;
+}
+
+static struct memory_tier *set_node_memory_tier(int node)
+{
+	struct memory_tier *memtier;
+	struct memory_dev_type *memtype;
+
+	lockdep_assert_held_once(&memory_tier_lock);
+
+	if (!node_state(node, N_MEMORY))
+		return ERR_PTR(-EINVAL);
+
+	if (!node_memory_types[node])
+		node_memory_types[node] = &default_dram_type;
+
+	memtype = node_memory_types[node];
+	node_set(node, memtype->nodes);
+	memtier = find_create_memory_tier(memtype);
+	return memtier;
+}
+
+static int __init memory_tier_init(void)
+{
+	int node;
+	struct memory_tier *memtier;
+
+	mutex_lock(&memory_tier_lock);
+	/*
+	 * Look at all the existing N_MEMORY nodes and add them to
+	 * default memory tier or to a tier if we already have memory
+	 * types assigned.
+	 */
+	for_each_node_state(node, N_MEMORY) {
+		memtier = set_node_memory_tier(node);
+		if (IS_ERR(memtier))
+			/*
+			 * Continue with memtiers we are able to setup
+			 */
+			break;
+	}
+	mutex_unlock(&memory_tier_lock);
+
+	return 0;
+}
+subsys_initcall(memory_tier_init);
-- 
2.37.1

[PATCH v14 02/10] mm/demotion: Move memory demotion related code

[Aneesh Kumar K.V]

This move memory demotion related code to mm/memory-tiers.c.
No functional change in this patch.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/memory-tiers.h |  8 +++++
 include/linux/migrate.h      |  2 --
 mm/memory-tiers.c            | 64 ++++++++++++++++++++++++++++++++++++
 mm/migrate.c                 | 60 +--------------------------------
 mm/vmscan.c                  |  1 +
 5 files changed, 74 insertions(+), 61 deletions(-)

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index bc7c1b799bef..9fdd9572fdf9 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -12,4 +12,12 @@
  */
 #define MEMTIER_ADISTANCE_DRAM	(4 * MEMTIER_CHUNK_SIZE)
 
+#ifdef CONFIG_NUMA
+#include <linux/types.h>
+extern bool numa_demotion_enabled;
+
+#else
+
+#define numa_demotion_enabled	false
+#endif	/* CONFIG_NUMA */
 #endif  /* _LINUX_MEMORY_TIERS_H */
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 22c0a0cf5e0c..96f8c84413fe 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -103,7 +103,6 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
 #if defined(CONFIG_MIGRATION) && defined(CONFIG_NUMA)
 extern void set_migration_target_nodes(void);
 extern void migrate_on_reclaim_init(void);
-extern bool numa_demotion_enabled;
 extern int next_demotion_node(int node);
 #else
 static inline void set_migration_target_nodes(void) {}
@@ -112,7 +111,6 @@ static inline int next_demotion_node(int node)
 {
         return NUMA_NO_NODE;
 }
-#define numa_demotion_enabled  false
 #endif
 
 #ifdef CONFIG_COMPACTION
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 1f494e69776a..f3dc3318d931 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -3,6 +3,8 @@
 #include <linux/nodemask.h>
 #include <linux/slab.h>
 #include <linux/lockdep.h>
+#include <linux/sysfs.h>
+#include <linux/kobject.h>
 #include <linux/memory-tiers.h>
 
 struct memory_tier {
@@ -127,3 +129,65 @@ static int __init memory_tier_init(void)
 	return 0;
 }
 subsys_initcall(memory_tier_init);
+
+bool numa_demotion_enabled = false;
+
+#ifdef CONFIG_MIGRATION
+#ifdef CONFIG_SYSFS
+static ssize_t numa_demotion_enabled_show(struct kobject *kobj,
+					  struct kobj_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%s\n",
+			  numa_demotion_enabled ? "true" : "false");
+}
+
+static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
+					   struct kobj_attribute *attr,
+					   const char *buf, size_t count)
+{
+	ssize_t ret;
+
+	ret = kstrtobool(buf, &numa_demotion_enabled);
+	if (ret)
+		return ret;
+
+	return count;
+}
+
+static struct kobj_attribute numa_demotion_enabled_attr =
+	__ATTR(demotion_enabled, 0644, numa_demotion_enabled_show,
+	       numa_demotion_enabled_store);
+
+static struct attribute *numa_attrs[] = {
+	&numa_demotion_enabled_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group numa_attr_group = {
+	.attrs = numa_attrs,
+};
+
+static int __init numa_init_sysfs(void)
+{
+	int err;
+	struct kobject *numa_kobj;
+
+	numa_kobj = kobject_create_and_add("numa", mm_kobj);
+	if (!numa_kobj) {
+		pr_err("failed to create numa kobject\n");
+		return -ENOMEM;
+	}
+	err = sysfs_create_group(numa_kobj, &numa_attr_group);
+	if (err) {
+		pr_err("failed to register numa group\n");
+		goto delete_obj;
+	}
+	return 0;
+
+delete_obj:
+	kobject_put(numa_kobj);
+	return err;
+}
+subsys_initcall(numa_init_sysfs);
+#endif /* CONFIG_SYSFS */
+#endif
diff --git a/mm/migrate.c b/mm/migrate.c
index 6a1597c92261..5d7fb417edbf 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2562,64 +2562,6 @@ void __init migrate_on_reclaim_init(void)
 	set_migration_target_nodes();
 	cpus_read_unlock();
 }
+#endif /* CONFIG_NUMA */
 
-bool numa_demotion_enabled = false;
-
-#ifdef CONFIG_SYSFS
-static ssize_t numa_demotion_enabled_show(struct kobject *kobj,
-					  struct kobj_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "%s\n",
-			  numa_demotion_enabled ? "true" : "false");
-}
-
-static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
-					   struct kobj_attribute *attr,
-					   const char *buf, size_t count)
-{
-	ssize_t ret;
-
-	ret = kstrtobool(buf, &numa_demotion_enabled);
-	if (ret)
-		return ret;
-
-	return count;
-}
-
-static struct kobj_attribute numa_demotion_enabled_attr =
-	__ATTR(demotion_enabled, 0644, numa_demotion_enabled_show,
-	       numa_demotion_enabled_store);
-
-static struct attribute *numa_attrs[] = {
-	&numa_demotion_enabled_attr.attr,
-	NULL,
-};
-
-static const struct attribute_group numa_attr_group = {
-	.attrs = numa_attrs,
-};
-
-static int __init numa_init_sysfs(void)
-{
-	int err;
-	struct kobject *numa_kobj;
 
-	numa_kobj = kobject_create_and_add("numa", mm_kobj);
-	if (!numa_kobj) {
-		pr_err("failed to create numa kobject\n");
-		return -ENOMEM;
-	}
-	err = sysfs_create_group(numa_kobj, &numa_attr_group);
-	if (err) {
-		pr_err("failed to register numa group\n");
-		goto delete_obj;
-	}
-	return 0;
-
-delete_obj:
-	kobject_put(numa_kobj);
-	return err;
-}
-subsys_initcall(numa_init_sysfs);
-#endif /* CONFIG_SYSFS */
-#endif /* CONFIG_NUMA */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b2b1431352dc..224de380ac88 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -49,6 +49,7 @@
 #include <linux/printk.h>
 #include <linux/dax.h>
 #include <linux/psi.h>
+#include <linux/memory-tiers.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
-- 
2.37.1

[PATCH v14 03/10] mm/demotion: Add hotplug callbacks to handle new numa node onlined

[Aneesh Kumar K.V]

If the new NUMA node onlined doesn't have a abstract distance assigned,
the kernel adds the NUMA node to default memory tier.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/memory-tiers.h |  1 +
 mm/memory-tiers.c            | 68 ++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index 9fdd9572fdf9..cc89876899a6 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -11,6 +11,7 @@
  * Smaller abstract distance value imply faster(higher) memory tiers.
  */
 #define MEMTIER_ADISTANCE_DRAM	(4 * MEMTIER_CHUNK_SIZE)
+#define MEMTIER_HOTPLUG_PRIO	100
 
 #ifdef CONFIG_NUMA
 #include <linux/types.h>
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index f3dc3318d931..05f05395468a 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -5,6 +5,7 @@
 #include <linux/lockdep.h>
 #include <linux/sysfs.h>
 #include <linux/kobject.h>
+#include <linux/memory.h>
 #include <linux/memory-tiers.h>
 
 struct memory_tier {
@@ -105,6 +106,72 @@ static struct memory_tier *set_node_memory_tier(int node)
 	return memtier;
 }
 
+static struct memory_tier *__node_get_memory_tier(int node)
+{
+	struct memory_dev_type *memtype;
+
+	memtype = node_memory_types[node];
+	if (memtype && node_isset(node, memtype->nodes))
+		return memtype->memtier;
+	return NULL;
+}
+
+static void destroy_memory_tier(struct memory_tier *memtier)
+{
+	list_del(&memtier->list);
+	kfree(memtier);
+}
+
+static bool clear_node_memory_tier(int node)
+{
+	bool cleared = false;
+	struct memory_tier *memtier;
+
+	memtier = __node_get_memory_tier(node);
+	if (memtier) {
+		struct memory_dev_type *memtype;
+
+		memtype = node_memory_types[node];
+		node_clear(node, memtype->nodes);
+		if (nodes_empty(memtype->nodes)) {
+			list_del(&memtype->tier_sibiling);
+			memtype->memtier = NULL;
+			if (list_empty(&memtier->memory_types))
+				destroy_memory_tier(memtier);
+		}
+		cleared = true;
+	}
+	return cleared;
+}
+
+static int __meminit memtier_hotplug_callback(struct notifier_block *self,
+					      unsigned long action, void *_arg)
+{
+	struct memory_notify *arg = _arg;
+
+	/*
+	 * Only update the node migration order when a node is
+	 * changing status, like online->offline.
+	 */
+	if (arg->status_change_nid < 0)
+		return notifier_from_errno(0);
+
+	switch (action) {
+	case MEM_OFFLINE:
+		mutex_lock(&memory_tier_lock);
+		clear_node_memory_tier(arg->status_change_nid);
+		mutex_unlock(&memory_tier_lock);
+		break;
+	case MEM_ONLINE:
+		mutex_lock(&memory_tier_lock);
+		set_node_memory_tier(arg->status_change_nid);
+		mutex_unlock(&memory_tier_lock);
+		break;
+	}
+
+	return notifier_from_errno(0);
+}
+
 static int __init memory_tier_init(void)
 {
 	int node;
@@ -126,6 +193,7 @@ static int __init memory_tier_init(void)
 	}
 	mutex_unlock(&memory_tier_lock);
 
+	hotplug_memory_notifier(memtier_hotplug_callback, MEMTIER_HOTPLUG_PRIO);
 	return 0;
 }
 subsys_initcall(memory_tier_init);
-- 
2.37.1

[PATCH v14 04/10] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE

[Aneesh Kumar K.V]

By default, all nodes are assigned to the default memory tier which
is the memory tier designated for nodes with DRAM

Set dax kmem device node's tier to slower memory tier by assigning
abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE. Low-level drivers
like papr_scm or ACPI NFIT can initialize memory device type to a
more accurate value based on device tree details or HMAT. If the
kernel doesn't find the memory type initialized, a default slower
memory type is assigned by the kmem driver.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 drivers/dax/kmem.c           | 42 +++++++++++++++--
 include/linux/memory-tiers.h | 42 ++++++++++++++++-
 mm/memory-tiers.c            | 91 +++++++++++++++++++++++++++---------
 3 files changed, 149 insertions(+), 26 deletions(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index a37622060fff..d88814f1c414 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -11,9 +11,17 @@
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
+#include <linux/memory-tiers.h>
 #include "dax-private.h"
 #include "bus.h"
 
+/*
+ * Default abstract distance assigned to the NUMA node onlined
+ * by DAX/kmem if the low level platform driver didn't initialize
+ * one for this NUMA node.
+ */
+#define MEMTIER_DEFAULT_DAX_ADISTANCE	(MEMTIER_ADISTANCE_DRAM * 2)
+
 /* Memory resource name used for add_memory_driver_managed(). */
 static const char *kmem_name;
 /* Set if any memory will remain added when the driver will be unloaded. */
@@ -41,6 +49,7 @@ struct dax_kmem_data {
 	struct resource *res[];
 };
 
+static struct memory_dev_type *dax_slowmem_type;
 static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 {
 	struct device *dev = &dev_dax->dev;
@@ -79,11 +88,13 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 		return -EINVAL;
 	}
 
+	init_node_memory_type(numa_node, dax_slowmem_type);
+
+	rc = -ENOMEM;
 	data = kzalloc(struct_size(data, res, dev_dax->nr_range), GFP_KERNEL);
 	if (!data)
-		return -ENOMEM;
+		goto err_dax_kmem_data;
 
-	rc = -ENOMEM;
 	data->res_name = kstrdup(dev_name(dev), GFP_KERNEL);
 	if (!data->res_name)
 		goto err_res_name;
@@ -155,6 +166,8 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 	kfree(data->res_name);
 err_res_name:
 	kfree(data);
+err_dax_kmem_data:
+	clear_node_memory_type(numa_node, dax_slowmem_type);
 	return rc;
 }
 
@@ -162,6 +175,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
 {
 	int i, success = 0;
+	int node = dev_dax->target_node;
 	struct device *dev = &dev_dax->dev;
 	struct dax_kmem_data *data = dev_get_drvdata(dev);
 
@@ -198,6 +212,14 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
 		kfree(data->res_name);
 		kfree(data);
 		dev_set_drvdata(dev, NULL);
+		/*
+		 * Clear the memtype association on successful unplug.
+		 * If not, we have memory blocks left which can be
+		 * offlined/onlined later. We need to keep memory_dev_type
+		 * for that. This implies this reference will be around
+		 * till next reboot.
+		 */
+		clear_node_memory_type(node, dax_slowmem_type);
 	}
 }
 #else
@@ -228,9 +250,22 @@ static int __init dax_kmem_init(void)
 	if (!kmem_name)
 		return -ENOMEM;
 
+	dax_slowmem_type = alloc_memory_type(MEMTIER_DEFAULT_DAX_ADISTANCE);
+	if (IS_ERR(dax_slowmem_type)) {
+		rc = PTR_ERR(dax_slowmem_type);
+		goto err_dax_slowmem_type;
+	}
+
 	rc = dax_driver_register(&device_dax_kmem_driver);
 	if (rc)
-		kfree_const(kmem_name);
+		goto error_dax_driver;
+
+	return rc;
+
+error_dax_driver:
+	destroy_memory_type(dax_slowmem_type);
+err_dax_slowmem_type:
+	kfree_const(kmem_name);
 	return rc;
 }
 
@@ -239,6 +274,7 @@ static void __exit dax_kmem_exit(void)
 	dax_driver_unregister(&device_dax_kmem_driver);
 	if (!any_hotremove_failed)
 		kfree_const(kmem_name);
+	destroy_memory_type(dax_slowmem_type);
 }
 
 MODULE_AUTHOR("Intel Corporation");
diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index cc89876899a6..0c739508517a 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -2,6 +2,9 @@
 #ifndef _LINUX_MEMORY_TIERS_H
 #define _LINUX_MEMORY_TIERS_H
 
+#include <linux/types.h>
+#include <linux/nodemask.h>
+#include <linux/kref.h>
 /*
  * Each tier cover a abstrace distance chunk size of 128
  */
@@ -13,12 +16,49 @@
 #define MEMTIER_ADISTANCE_DRAM	(4 * MEMTIER_CHUNK_SIZE)
 #define MEMTIER_HOTPLUG_PRIO	100
 
+struct memory_tier;
+struct memory_dev_type {
+	/* list of memory types that are part of same tier as this type */
+	struct list_head tier_sibiling;
+	/* abstract distance for this specific memory type */
+	int adistance;
+	/* Nodes of same abstract distance */
+	nodemask_t nodes;
+	struct kref kref;
+	struct memory_tier *memtier;
+};
+
 #ifdef CONFIG_NUMA
-#include <linux/types.h>
 extern bool numa_demotion_enabled;
+struct memory_dev_type *alloc_memory_type(int adistance);
+void destroy_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);
 
 #else
 
 #define numa_demotion_enabled	false
+/*
+ * CONFIG_NUMA implementation returns non NULL error.
+ */
+static inline struct memory_dev_type *alloc_memory_type(int adistance)
+{
+	return NULL;
+}
+
+static inline void destroy_memory_type(struct memory_dev_type *memtype)
+{
+
+}
+
+static inline void init_node_memory_type(int node, struct memory_dev_type *default_type)
+{
+
+}
+
+static inline void clear_node_memory_type(int node, struct memory_dev_type *memtype)
+{
+
+}
 #endif	/* CONFIG_NUMA */
 #endif  /* _LINUX_MEMORY_TIERS_H */
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 05f05395468a..e52ccbcb2b27 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -1,6 +1,4 @@
 // SPDX-License-Identifier: GPL-2.0
-#include <linux/types.h>
-#include <linux/nodemask.h>
 #include <linux/slab.h>
 #include <linux/lockdep.h>
 #include <linux/sysfs.h>
@@ -21,27 +19,10 @@ struct memory_tier {
 	int adistance_start;
 };
 
-struct memory_dev_type {
-	/* list of memory types that are part of same tier as this type */
-	struct list_head tier_sibiling;
-	/* abstract distance for this specific memory type */
-	int adistance;
-	/* Nodes of same abstract distance */
-	nodemask_t nodes;
-	struct memory_tier *memtier;
-};
-
 static DEFINE_MUTEX(memory_tier_lock);
 static LIST_HEAD(memory_tiers);
 static struct memory_dev_type *node_memory_types[MAX_NUMNODES];
-/*
- * For now we can have 4 faster memory tiers with smaller adistance
- * than default DRAM tier.
- */
-static struct memory_dev_type default_dram_type  = {
-	.adistance = MEMTIER_ADISTANCE_DRAM,
-	.tier_sibiling = LIST_HEAD_INIT(default_dram_type.tier_sibiling),
-};
+static struct memory_dev_type *default_dram_type;
 
 static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype)
 {
@@ -87,6 +68,14 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
 	return new_memtier;
 }
 
+static inline void __init_node_memory_type(int node, struct memory_dev_type *default_type)
+{
+	if (!node_memory_types[node]) {
+		node_memory_types[node] = default_type;
+		kref_get(&default_type->kref);
+	}
+}
+
 static struct memory_tier *set_node_memory_tier(int node)
 {
 	struct memory_tier *memtier;
@@ -97,8 +86,7 @@ static struct memory_tier *set_node_memory_tier(int node)
 	if (!node_state(node, N_MEMORY))
 		return ERR_PTR(-EINVAL);
 
-	if (!node_memory_types[node])
-		node_memory_types[node] = &default_dram_type;
+	__init_node_memory_type(node, default_dram_type);
 
 	memtype = node_memory_types[node];
 	node_set(node, memtype->nodes);
@@ -144,6 +132,57 @@ static bool clear_node_memory_tier(int node)
 	return cleared;
 }
 
+static void release_memtype(struct kref *kref)
+{
+	struct memory_dev_type *memtype;
+
+	memtype = container_of(kref, struct memory_dev_type, kref);
+	kfree(memtype);
+}
+
+struct memory_dev_type *alloc_memory_type(int adistance)
+{
+	struct memory_dev_type *memtype;
+
+	memtype = kmalloc(sizeof(*memtype), GFP_KERNEL);
+	if (!memtype)
+		return ERR_PTR(-ENOMEM);
+
+	memtype->adistance = adistance;
+	INIT_LIST_HEAD(&memtype->tier_sibiling);
+	memtype->nodes  = NODE_MASK_NONE;
+	memtype->memtier = NULL;
+	kref_init(&memtype->kref);
+	return memtype;
+}
+EXPORT_SYMBOL_GPL(alloc_memory_type);
+
+void destroy_memory_type(struct memory_dev_type *memtype)
+{
+	kref_put(&memtype->kref, release_memtype);
+}
+EXPORT_SYMBOL_GPL(destroy_memory_type);
+
+void init_node_memory_type(int node, struct memory_dev_type *default_type)
+{
+
+	mutex_lock(&memory_tier_lock);
+	__init_node_memory_type(node, default_type);
+	mutex_unlock(&memory_tier_lock);
+}
+EXPORT_SYMBOL_GPL(init_node_memory_type);
+
+void clear_node_memory_type(int node, struct memory_dev_type *memtype)
+{
+	mutex_lock(&memory_tier_lock);
+	if (node_memory_types[node] == memtype) {
+		node_memory_types[node] = NULL;
+		kref_put(&memtype->kref, release_memtype);
+	}
+	mutex_unlock(&memory_tier_lock);
+}
+EXPORT_SYMBOL_GPL(clear_node_memory_type);
+
 static int __meminit memtier_hotplug_callback(struct notifier_block *self,
 					      unsigned long action, void *_arg)
 {
@@ -178,6 +217,14 @@ static int __init memory_tier_init(void)
 	struct memory_tier *memtier;
 
 	mutex_lock(&memory_tier_lock);
+	/*
+	 * For now we can have 4 faster memory tiers with smaller adistance
+	 * than default DRAM tier.
+	 */
+	default_dram_type = alloc_memory_type(MEMTIER_ADISTANCE_DRAM);
+	if (!default_dram_type)
+		panic("%s() failed to allocate default DRAM tier\n", __func__);
+
 	/*
 	 * Look at all the existing N_MEMORY nodes and add them to
 	 * default memory tier or to a tier if we already have memory
-- 
2.37.1

[PATCH v14 05/10] mm/demotion: Build demotion targets based on explicit memory tiers

[Aneesh Kumar K.V]

This patch switch the demotion target building logic to use memory tiers
instead of NUMA distance. All N_MEMORY NUMA nodes will be placed in the
default memory tier and additional memory tiers will be added by drivers like
dax kmem.

This patch builds the demotion target for a NUMA node by looking at all
memory tiers below the tier to which the NUMA node belongs. The closest node
in the immediately following memory tier is used as a demotion target.

Since we are now only building demotion target for N_MEMORY NUMA nodes
the CPU hotplug calls are removed in this patch.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/memory-tiers.h |  13 ++
 include/linux/migrate.h      |  13 --
 mm/memory-tiers.c            | 238 +++++++++++++++++++--
 mm/migrate.c                 | 394 -----------------------------------
 mm/vmstat.c                  |   4 -
 5 files changed, 239 insertions(+), 423 deletions(-)

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index 0c739508517a..d0490ea4e35b 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -34,6 +34,14 @@ struct memory_dev_type *alloc_memory_type(int adistance);
 void destroy_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);
+#ifdef CONFIG_MIGRATION
+int next_demotion_node(int node);
+#else
+static inline int next_demotion_node(int node)
+{
+	return NUMA_NO_NODE;
+}
+#endif
 
 #else
 
@@ -60,5 +68,10 @@ static inline void clear_node_memory_type(int node, struct memory_dev_type *memt
 {
 
 }
+
+static inline int next_demotion_node(int node)
+{
+	return NUMA_NO_NODE;
+}
 #endif	/* CONFIG_NUMA */
 #endif  /* _LINUX_MEMORY_TIERS_H */
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 96f8c84413fe..704a04f5a074 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -100,19 +100,6 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
 
 #endif /* CONFIG_MIGRATION */
 
-#if defined(CONFIG_MIGRATION) && defined(CONFIG_NUMA)
-extern void set_migration_target_nodes(void);
-extern void migrate_on_reclaim_init(void);
-extern int next_demotion_node(int node);
-#else
-static inline void set_migration_target_nodes(void) {}
-static inline void migrate_on_reclaim_init(void) {}
-static inline int next_demotion_node(int node)
-{
-        return NUMA_NO_NODE;
-}
-#endif
-
 #ifdef CONFIG_COMPACTION
 bool PageMovable(struct page *page);
 void __SetPageMovable(struct page *page, const struct movable_operations *ops);
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index e52ccbcb2b27..41a0bc06d169 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -6,6 +6,8 @@
 #include <linux/memory.h>
 #include <linux/memory-tiers.h>
 
+#include "internal.h"
+
 struct memory_tier {
 	/* hierarchy of memory tiers */
 	struct list_head list;
@@ -19,10 +21,74 @@ struct memory_tier {
 	int adistance_start;
 };
 
+struct demotion_nodes {
+	nodemask_t preferred;
+};
+
 static DEFINE_MUTEX(memory_tier_lock);
 static LIST_HEAD(memory_tiers);
 static struct memory_dev_type *node_memory_types[MAX_NUMNODES];
 static struct memory_dev_type *default_dram_type;
+#ifdef CONFIG_MIGRATION
+/*
+ * node_demotion[] examples:
+ *
+ * Example 1:
+ *
+ * Node 0 & 1 are CPU + DRAM nodes, node 2 & 3 are PMEM nodes.
+ *
+ * node distances:
+ * node   0    1    2    3
+ *    0  10   20   30   40
+ *    1  20   10   40   30
+ *    2  30   40   10   40
+ *    3  40   30   40   10
+ *
+ * memory_tiers0 = 0-1
+ * memory_tiers1 = 2-3
+ *
+ * node_demotion[0].preferred = 2
+ * node_demotion[1].preferred = 3
+ * node_demotion[2].preferred = <empty>
+ * node_demotion[3].preferred = <empty>
+ *
+ * Example 2:
+ *
+ * Node 0 & 1 are CPU + DRAM nodes, node 2 is memory-only DRAM node.
+ *
+ * node distances:
+ * node   0    1    2
+ *    0  10   20   30
+ *    1  20   10   30
+ *    2  30   30   10
+ *
+ * memory_tiers0 = 0-2
+ *
+ * node_demotion[0].preferred = <empty>
+ * node_demotion[1].preferred = <empty>
+ * node_demotion[2].preferred = <empty>
+ *
+ * Example 3:
+ *
+ * Node 0 is CPU + DRAM nodes, Node 1 is HBM node, node 2 is PMEM node.
+ *
+ * node distances:
+ * node   0    1    2
+ *    0  10   20   30
+ *    1  20   10   40
+ *    2  30   40   10
+ *
+ * memory_tiers0 = 1
+ * memory_tiers1 = 0
+ * memory_tiers2 = 2
+ *
+ * node_demotion[0].preferred = 2
+ * node_demotion[1].preferred = 0
+ * node_demotion[2].preferred = <empty>
+ *
+ */
+static struct demotion_nodes *node_demotion __read_mostly;
+#endif /* CONFIG_MIGRATION */
 
 static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype)
 {
@@ -68,6 +134,154 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
 	return new_memtier;
 }
 
+static struct memory_tier *__node_get_memory_tier(int node)
+{
+	struct memory_dev_type *memtype;
+
+	memtype = node_memory_types[node];
+	if (memtype && node_isset(node, memtype->nodes))
+		return memtype->memtier;
+	return NULL;
+}
+
+#ifdef CONFIG_MIGRATION
+/**
+ * next_demotion_node() - Get the next node in the demotion path
+ * @node: The starting node to lookup the next node
+ *
+ * Return: node id for next memory node in the demotion path hierarchy
+ * from @node; NUMA_NO_NODE if @node is terminal.  This does not keep
+ * @node online or guarantee that it *continues* to be the next demotion
+ * target.
+ */
+int next_demotion_node(int node)
+{
+	struct demotion_nodes *nd;
+	int target;
+
+	if (!node_demotion)
+		return NUMA_NO_NODE;
+
+	nd = &node_demotion[node];
+
+	/*
+	 * node_demotion[] is updated without excluding this
+	 * function from running.
+	 *
+	 * Make sure to use RCU over entire code blocks if
+	 * node_demotion[] reads need to be consistent.
+	 */
+	rcu_read_lock();
+	/*
+	 * If there are multiple target nodes, just select one
+	 * target node randomly.
+	 *
+	 * In addition, we can also use round-robin to select
+	 * target node, but we should introduce another variable
+	 * for node_demotion[] to record last selected target node,
+	 * that may cause cache ping-pong due to the changing of
+	 * last target node. Or introducing per-cpu data to avoid
+	 * caching issue, which seems more complicated. So selecting
+	 * target node randomly seems better until now.
+	 */
+	target = node_random(&nd->preferred);
+	rcu_read_unlock();
+
+	return target;
+}
+
+static void disable_all_demotion_targets(void)
+{
+	int node;
+
+	for_each_node_state(node, N_MEMORY)
+		node_demotion[node].preferred = NODE_MASK_NONE;
+	/*
+	 * Ensure that the "disable" is visible across the system.
+	 * Readers will see either a combination of before+disable
+	 * state or disable+after.  They will never see before and
+	 * after state together.
+	 */
+	synchronize_rcu();
+}
+
+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_sibiling)
+		nodes_or(nodes, nodes, memtype->nodes);
+
+	return nodes;
+}
+
+/*
+ * Find an automatic demotion target for all memory
+ * nodes. Failing here is OK.  It might just indicate
+ * being at the end of a chain.
+ */
+static void establish_demotion_targets(void)
+{
+	struct memory_tier *memtier;
+	struct demotion_nodes *nd;
+	int target = NUMA_NO_NODE, node;
+	int distance, best_distance;
+	nodemask_t tier_nodes;
+
+	lockdep_assert_held_once(&memory_tier_lock);
+
+	if (!node_demotion || !IS_ENABLED(CONFIG_MIGRATION))
+		return;
+
+	disable_all_demotion_targets();
+
+	for_each_node_state(node, N_MEMORY) {
+		best_distance = -1;
+		nd = &node_demotion[node];
+
+		memtier = __node_get_memory_tier(node);
+		if (!memtier || list_is_last(&memtier->list, &memory_tiers))
+			continue;
+		/*
+		 * Get the lower memtier to find the  demotion node list.
+		 */
+		memtier = list_next_entry(memtier, list);
+		tier_nodes = get_memtier_nodemask(memtier);
+		/*
+		 * find_next_best_node, use 'used' nodemask as a skip list.
+		 * Add all memory nodes except the selected memory tier
+		 * nodelist to skip list so that we find the best node from the
+		 * memtier nodelist.
+		 */
+		nodes_andnot(tier_nodes, node_states[N_MEMORY], tier_nodes);
+
+		/*
+		 * Find all the nodes in the memory tier node list of same best distance.
+		 * add them to the preferred mask. We randomly select between nodes
+		 * in the preferred mask when allocating pages during demotion.
+		 */
+		do {
+			target = find_next_best_node(node, &tier_nodes);
+			if (target == NUMA_NO_NODE)
+				break;
+
+			distance = node_distance(node, target);
+			if (distance == best_distance || best_distance == -1) {
+				best_distance = distance;
+				node_set(target, nd->preferred);
+			} else {
+				break;
+			}
+		} while (1);
+	}
+}
+
+#else
+static inline void disable_all_demotion_targets(void) {}
+static inline void establish_demotion_targets(void) {}
+#endif /* CONFIG_MIGRATION */
+
 static inline void __init_node_memory_type(int node, struct memory_dev_type *default_type)
 {
 	if (!node_memory_types[node]) {
@@ -94,16 +308,6 @@ static struct memory_tier *set_node_memory_tier(int node)
 	return memtier;
 }
 
-static struct memory_tier *__node_get_memory_tier(int node)
-{
-	struct memory_dev_type *memtype;
-
-	memtype = node_memory_types[node];
-	if (memtype && node_isset(node, memtype->nodes))
-		return memtype->memtier;
-	return NULL;
-}
-
 static void destroy_memory_tier(struct memory_tier *memtier)
 {
 	list_del(&memtier->list);
@@ -186,6 +390,7 @@ EXPORT_SYMBOL_GPL(clear_node_memory_type);
 static int __meminit memtier_hotplug_callback(struct notifier_block *self,
 					      unsigned long action, void *_arg)
 {
+	struct memory_tier *memtier;
 	struct memory_notify *arg = _arg;
 
 	/*
@@ -198,12 +403,15 @@ static int __meminit memtier_hotplug_callback(struct notifier_block *self,
 	switch (action) {
 	case MEM_OFFLINE:
 		mutex_lock(&memory_tier_lock);
-		clear_node_memory_tier(arg->status_change_nid);
+		if (clear_node_memory_tier(arg->status_change_nid))
+			establish_demotion_targets();
 		mutex_unlock(&memory_tier_lock);
 		break;
 	case MEM_ONLINE:
 		mutex_lock(&memory_tier_lock);
-		set_node_memory_tier(arg->status_change_nid);
+		memtier = set_node_memory_tier(arg->status_change_nid);
+		if (!IS_ERR(memtier))
+			establish_demotion_targets();
 		mutex_unlock(&memory_tier_lock);
 		break;
 	}
@@ -216,6 +424,11 @@ static int __init memory_tier_init(void)
 	int node;
 	struct memory_tier *memtier;
 
+#ifdef CONFIG_MIGRATION
+	node_demotion = kcalloc(nr_node_ids, sizeof(struct demotion_nodes),
+				GFP_KERNEL);
+	WARN_ON(!node_demotion);
+#endif
 	mutex_lock(&memory_tier_lock);
 	/*
 	 * For now we can have 4 faster memory tiers with smaller adistance
@@ -238,6 +451,7 @@ static int __init memory_tier_init(void)
 			 */
 			break;
 	}
+	establish_demotion_targets();
 	mutex_unlock(&memory_tier_lock);
 
 	hotplug_memory_notifier(memtier_hotplug_callback, MEMTIER_HOTPLUG_PRIO);
diff --git a/mm/migrate.c b/mm/migrate.c
index 5d7fb417edbf..ea86594f4bc5 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2170,398 +2170,4 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
 	return 0;
 }
 #endif /* CONFIG_NUMA_BALANCING */
-
-/*
- * node_demotion[] example:
- *
- * Consider a system with two sockets.  Each socket has
- * three classes of memory attached: fast, medium and slow.
- * Each memory class is placed in its own NUMA node.  The
- * CPUs are placed in the node with the "fast" memory.  The
- * 6 NUMA nodes (0-5) might be split among the sockets like
- * this:
- *
- *	Socket A: 0, 1, 2
- *	Socket B: 3, 4, 5
- *
- * When Node 0 fills up, its memory should be migrated to
- * Node 1.  When Node 1 fills up, it should be migrated to
- * Node 2.  The migration path start on the nodes with the
- * processors (since allocations default to this node) and
- * fast memory, progress through medium and end with the
- * slow memory:
- *
- *	0 -> 1 -> 2 -> stop
- *	3 -> 4 -> 5 -> stop
- *
- * This is represented in the node_demotion[] like this:
- *
- *	{  nr=1, nodes[0]=1 }, // Node 0 migrates to 1
- *	{  nr=1, nodes[0]=2 }, // Node 1 migrates to 2
- *	{  nr=0, nodes[0]=-1 }, // Node 2 does not migrate
- *	{  nr=1, nodes[0]=4 }, // Node 3 migrates to 4
- *	{  nr=1, nodes[0]=5 }, // Node 4 migrates to 5
- *	{  nr=0, nodes[0]=-1 }, // Node 5 does not migrate
- *
- * Moreover some systems may have multiple slow memory nodes.
- * Suppose a system has one socket with 3 memory nodes, node 0
- * is fast memory type, and node 1/2 both are slow memory
- * type, and the distance between fast memory node and slow
- * memory node is same. So the migration path should be:
- *
- *	0 -> 1/2 -> stop
- *
- * This is represented in the node_demotion[] like this:
- *	{ nr=2, {nodes[0]=1, nodes[1]=2} }, // Node 0 migrates to node 1 and node 2
- *	{ nr=0, nodes[0]=-1, }, // Node 1 dose not migrate
- *	{ nr=0, nodes[0]=-1, }, // Node 2 does not migrate
- */
-
-/*
- * Writes to this array occur without locking.  Cycles are
- * not allowed: Node X demotes to Y which demotes to X...
- *
- * If multiple reads are performed, a single rcu_read_lock()
- * must be held over all reads to ensure that no cycles are
- * observed.
- */
-#define DEFAULT_DEMOTION_TARGET_NODES 15
-
-#if MAX_NUMNODES < DEFAULT_DEMOTION_TARGET_NODES
-#define DEMOTION_TARGET_NODES	(MAX_NUMNODES - 1)
-#else
-#define DEMOTION_TARGET_NODES	DEFAULT_DEMOTION_TARGET_NODES
-#endif
-
-struct demotion_nodes {
-	unsigned short nr;
-	short nodes[DEMOTION_TARGET_NODES];
-};
-
-static struct demotion_nodes *node_demotion __read_mostly;
-
-/**
- * next_demotion_node() - Get the next node in the demotion path
- * @node: The starting node to lookup the next node
- *
- * Return: node id for next memory node in the demotion path hierarchy
- * from @node; NUMA_NO_NODE if @node is terminal.  This does not keep
- * @node online or guarantee that it *continues* to be the next demotion
- * target.
- */
-int next_demotion_node(int node)
-{
-	struct demotion_nodes *nd;
-	unsigned short target_nr, index;
-	int target;
-
-	if (!node_demotion)
-		return NUMA_NO_NODE;
-
-	nd = &node_demotion[node];
-
-	/*
-	 * node_demotion[] is updated without excluding this
-	 * function from running.  RCU doesn't provide any
-	 * compiler barriers, so the READ_ONCE() is required
-	 * to avoid compiler reordering or read merging.
-	 *
-	 * Make sure to use RCU over entire code blocks if
-	 * node_demotion[] reads need to be consistent.
-	 */
-	rcu_read_lock();
-	target_nr = READ_ONCE(nd->nr);
-
-	switch (target_nr) {
-	case 0:
-		target = NUMA_NO_NODE;
-		goto out;
-	case 1:
-		index = 0;
-		break;
-	default:
-		/*
-		 * If there are multiple target nodes, just select one
-		 * target node randomly.
-		 *
-		 * In addition, we can also use round-robin to select
-		 * target node, but we should introduce another variable
-		 * for node_demotion[] to record last selected target node,
-		 * that may cause cache ping-pong due to the changing of
-		 * last target node. Or introducing per-cpu data to avoid
-		 * caching issue, which seems more complicated. So selecting
-		 * target node randomly seems better until now.
-		 */
-		index = get_random_int() % target_nr;
-		break;
-	}
-
-	target = READ_ONCE(nd->nodes[index]);
-
-out:
-	rcu_read_unlock();
-	return target;
-}
-
-/* Disable reclaim-based migration. */
-static void __disable_all_migrate_targets(void)
-{
-	int node, i;
-
-	if (!node_demotion)
-		return;
-
-	for_each_online_node(node) {
-		node_demotion[node].nr = 0;
-		for (i = 0; i < DEMOTION_TARGET_NODES; i++)
-			node_demotion[node].nodes[i] = NUMA_NO_NODE;
-	}
-}
-
-static void disable_all_migrate_targets(void)
-{
-	__disable_all_migrate_targets();
-
-	/*
-	 * Ensure that the "disable" is visible across the system.
-	 * Readers will see either a combination of before+disable
-	 * state or disable+after.  They will never see before and
-	 * after state together.
-	 *
-	 * The before+after state together might have cycles and
-	 * could cause readers to do things like loop until this
-	 * function finishes.  This ensures they can only see a
-	 * single "bad" read and would, for instance, only loop
-	 * once.
-	 */
-	synchronize_rcu();
-}
-
-/*
- * Find an automatic demotion target for 'node'.
- * Failing here is OK.  It might just indicate
- * being at the end of a chain.
- */
-static int establish_migrate_target(int node, nodemask_t *used,
-				    int best_distance)
-{
-	int migration_target, index, val;
-	struct demotion_nodes *nd;
-
-	if (!node_demotion)
-		return NUMA_NO_NODE;
-
-	nd = &node_demotion[node];
-
-	migration_target = find_next_best_node(node, used);
-	if (migration_target == NUMA_NO_NODE)
-		return NUMA_NO_NODE;
-
-	/*
-	 * If the node has been set a migration target node before,
-	 * which means it's the best distance between them. Still
-	 * check if this node can be demoted to other target nodes
-	 * if they have a same best distance.
-	 */
-	if (best_distance != -1) {
-		val = node_distance(node, migration_target);
-		if (val > best_distance)
-			goto out_clear;
-	}
-
-	index = nd->nr;
-	if (WARN_ONCE(index >= DEMOTION_TARGET_NODES,
-		      "Exceeds maximum demotion target nodes\n"))
-		goto out_clear;
-
-	nd->nodes[index] = migration_target;
-	nd->nr++;
-
-	return migration_target;
-out_clear:
-	node_clear(migration_target, *used);
-	return NUMA_NO_NODE;
-}
-
-/*
- * When memory fills up on a node, memory contents can be
- * automatically migrated to another node instead of
- * discarded at reclaim.
- *
- * Establish a "migration path" which will start at nodes
- * with CPUs and will follow the priorities used to build the
- * page allocator zonelists.
- *
- * The difference here is that cycles must be avoided.  If
- * node0 migrates to node1, then neither node1, nor anything
- * node1 migrates to can migrate to node0. Also one node can
- * be migrated to multiple nodes if the target nodes all have
- * a same best-distance against the source node.
- *
- * This function can run simultaneously with readers of
- * node_demotion[].  However, it can not run simultaneously
- * with itself.  Exclusion is provided by memory hotplug events
- * being single-threaded.
- */
-static void __set_migration_target_nodes(void)
-{
-	nodemask_t next_pass;
-	nodemask_t this_pass;
-	nodemask_t used_targets = NODE_MASK_NONE;
-	int node, best_distance;
-
-	/*
-	 * Avoid any oddities like cycles that could occur
-	 * from changes in the topology.  This will leave
-	 * a momentary gap when migration is disabled.
-	 */
-	disable_all_migrate_targets();
-
-	/*
-	 * Allocations go close to CPUs, first.  Assume that
-	 * the migration path starts at the nodes with CPUs.
-	 */
-	next_pass = node_states[N_CPU];
-again:
-	this_pass = next_pass;
-	next_pass = NODE_MASK_NONE;
-	/*
-	 * To avoid cycles in the migration "graph", ensure
-	 * that migration sources are not future targets by
-	 * setting them in 'used_targets'.  Do this only
-	 * once per pass so that multiple source nodes can
-	 * share a target node.
-	 *
-	 * 'used_targets' will become unavailable in future
-	 * passes.  This limits some opportunities for
-	 * multiple source nodes to share a destination.
-	 */
-	nodes_or(used_targets, used_targets, this_pass);
-
-	for_each_node_mask(node, this_pass) {
-		best_distance = -1;
-
-		/*
-		 * Try to set up the migration path for the node, and the target
-		 * migration nodes can be multiple, so doing a loop to find all
-		 * the target nodes if they all have a best node distance.
-		 */
-		do {
-			int target_node =
-				establish_migrate_target(node, &used_targets,
-							 best_distance);
-
-			if (target_node == NUMA_NO_NODE)
-				break;
-
-			if (best_distance == -1)
-				best_distance = node_distance(node, target_node);
-
-			/*
-			 * Visit targets from this pass in the next pass.
-			 * Eventually, every node will have been part of
-			 * a pass, and will become set in 'used_targets'.
-			 */
-			node_set(target_node, next_pass);
-		} while (1);
-	}
-	/*
-	 * 'next_pass' contains nodes which became migration
-	 * targets in this pass.  Make additional passes until
-	 * no more migrations targets are available.
-	 */
-	if (!nodes_empty(next_pass))
-		goto again;
-}
-
-/*
- * For callers that do not hold get_online_mems() already.
- */
-void set_migration_target_nodes(void)
-{
-	get_online_mems();
-	__set_migration_target_nodes();
-	put_online_mems();
-}
-
-/*
- * This leaves migrate-on-reclaim transiently disabled between
- * the MEM_GOING_OFFLINE and MEM_OFFLINE events.  This runs
- * whether reclaim-based migration is enabled or not, which
- * ensures that the user can turn reclaim-based migration at
- * any time without needing to recalculate migration targets.
- *
- * These callbacks already hold get_online_mems().  That is why
- * __set_migration_target_nodes() can be used as opposed to
- * set_migration_target_nodes().
- */
-#ifdef CONFIG_MEMORY_HOTPLUG
-static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
-						 unsigned long action, void *_arg)
-{
-	struct memory_notify *arg = _arg;
-
-	/*
-	 * Only update the node migration order when a node is
-	 * changing status, like online->offline.  This avoids
-	 * the overhead of synchronize_rcu() in most cases.
-	 */
-	if (arg->status_change_nid < 0)
-		return notifier_from_errno(0);
-
-	switch (action) {
-	case MEM_GOING_OFFLINE:
-		/*
-		 * Make sure there are not transient states where
-		 * an offline node is a migration target.  This
-		 * will leave migration disabled until the offline
-		 * completes and the MEM_OFFLINE case below runs.
-		 */
-		disable_all_migrate_targets();
-		break;
-	case MEM_OFFLINE:
-	case MEM_ONLINE:
-		/*
-		 * Recalculate the target nodes once the node
-		 * reaches its final state (online or offline).
-		 */
-		__set_migration_target_nodes();
-		break;
-	case MEM_CANCEL_OFFLINE:
-		/*
-		 * MEM_GOING_OFFLINE disabled all the migration
-		 * targets.  Reenable them.
-		 */
-		__set_migration_target_nodes();
-		break;
-	case MEM_GOING_ONLINE:
-	case MEM_CANCEL_ONLINE:
-		break;
-	}
-
-	return notifier_from_errno(0);
-}
-#endif
-
-void __init migrate_on_reclaim_init(void)
-{
-	node_demotion = kcalloc(nr_node_ids,
-				sizeof(struct demotion_nodes),
-				GFP_KERNEL);
-	WARN_ON(!node_demotion);
-#ifdef CONFIG_MEMORY_HOTPLUG
-	hotplug_memory_notifier(migrate_on_reclaim_callback, 100);
-#endif
-	/*
-	 * At this point, all numa nodes with memory/CPus have their state
-	 * properly set, so we can build the demotion order now.
-	 * Let us hold the cpu_hotplug lock just, as we could possibily have
-	 * CPU hotplug events during boot.
-	 */
-	cpus_read_lock();
-	set_migration_target_nodes();
-	cpus_read_unlock();
-}
 #endif /* CONFIG_NUMA */
-
-
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 373d2730fcf2..35c6ff97cf29 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -28,7 +28,6 @@
 #include <linux/mm_inline.h>
 #include <linux/page_ext.h>
 #include <linux/page_owner.h>
-#include <linux/migrate.h>
 
 #include "internal.h"
 
@@ -2060,7 +2059,6 @@ static int vmstat_cpu_online(unsigned int cpu)
 
 	if (!node_state(cpu_to_node(cpu), N_CPU)) {
 		node_set_state(cpu_to_node(cpu), N_CPU);
-		set_migration_target_nodes();
 	}
 
 	return 0;
@@ -2085,7 +2083,6 @@ static int vmstat_cpu_dead(unsigned int cpu)
 		return 0;
 
 	node_clear_state(node, N_CPU);
-	set_migration_target_nodes();
 
 	return 0;
 }
@@ -2118,7 +2115,6 @@ void __init init_mm_internals(void)
 
 	start_shepherd_timer();
 #endif
-	migrate_on_reclaim_init();
 #ifdef CONFIG_PROC_FS
 	proc_create_seq("buddyinfo", 0444, NULL, &fragmentation_op);
 	proc_create_seq("pagetypeinfo", 0400, NULL, &pagetypeinfo_op);
-- 
2.37.1

[PATCH v14 06/10] mm/demotion: Add pg_data_t member to track node memory tier details

[Aneesh Kumar K.V]

Also update different helpes to use NODE_DATA()->memtier. Since
node specific memtier can change based on the reassignment of
NUMA node to a different memory tiers, accessing NODE_DATA()->memtier
needs to happen under an rcu read lock or memory_tier_lock.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/mmzone.h |  3 +++
 mm/memory-tiers.c      | 40 +++++++++++++++++++++++++++++++++++-----
 2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index e24b40c52468..7d78133fe8dd 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1012,6 +1012,9 @@ typedef struct pglist_data {
 	/* Per-node vmstats */
 	struct per_cpu_nodestat __percpu *per_cpu_nodestats;
 	atomic_long_t		vm_stat[NR_VM_NODE_STAT_ITEMS];
+#ifdef CONFIG_NUMA
+	struct memory_tier __rcu *memtier;
+#endif
 } pg_data_t;
 
 #define node_present_pages(nid)	(NODE_DATA(nid)->node_present_pages)
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 41a0bc06d169..315b9fe14c48 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -4,6 +4,7 @@
 #include <linux/sysfs.h>
 #include <linux/kobject.h>
 #include <linux/memory.h>
+#include <linux/mmzone.h>
 #include <linux/memory-tiers.h>
 
 #include "internal.h"
@@ -136,12 +137,18 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
 
 static struct memory_tier *__node_get_memory_tier(int node)
 {
-	struct memory_dev_type *memtype;
+	pg_data_t *pgdat;
 
-	memtype = node_memory_types[node];
-	if (memtype && node_isset(node, memtype->nodes))
-		return memtype->memtier;
-	return NULL;
+	pgdat = NODE_DATA(node);
+	if (!pgdat)
+		return NULL;
+	/*
+	 * Since we hold memory_tier_lock, we can avoid
+	 * RCU read locks when accessing the details. No
+	 * parallel updates are possible here.
+	 */
+	return rcu_dereference_check(pgdat->memtier,
+				     lockdep_is_held(&memory_tier_lock));
 }
 
 #ifdef CONFIG_MIGRATION
@@ -294,6 +301,8 @@ 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);
+
 
 	lockdep_assert_held_once(&memory_tier_lock);
 
@@ -305,24 +314,45 @@ static struct memory_tier *set_node_memory_tier(int node)
 	memtype = node_memory_types[node];
 	node_set(node, memtype->nodes);
 	memtier = find_create_memory_tier(memtype);
+	if (!IS_ERR(memtier))
+		rcu_assign_pointer(pgdat->memtier, memtier);
 	return memtier;
 }
 
 static void destroy_memory_tier(struct memory_tier *memtier)
 {
 	list_del(&memtier->list);
+	/*
+	 * synchronize_rcu in clear_node_memory_tier makes sure
+	 * we don't have rcu access to this memory tier.
+	 */
 	kfree(memtier);
 }
 
 static bool clear_node_memory_tier(int node)
 {
 	bool cleared = false;
+	pg_data_t *pgdat;
 	struct memory_tier *memtier;
 
+	pgdat = NODE_DATA(node);
+	if (!pgdat)
+		return false;
+
+	/*
+	 * Make sure that anybody looking at NODE_DATA who finds
+	 * a valid memtier finds memory_dev_types with nodes still
+	 * linked to the memtier. We achieve this by waiting for
+	 * rcu read section to finish using synchronize_rcu.
+	 * This also enables us to free the destroyed memory tier
+	 * with kfree instead of kfree_rcu
+	 */
 	memtier = __node_get_memory_tier(node);
 	if (memtier) {
 		struct memory_dev_type *memtype;
 
+		rcu_assign_pointer(pgdat->memtier, NULL);
+		synchronize_rcu();
 		memtype = node_memory_types[node];
 		node_clear(node, memtype->nodes);
 		if (nodes_empty(memtype->nodes)) {
-- 
2.37.1

[PATCH v14 07/10] mm/demotion: Drop memtier from memtype

[Aneesh Kumar K.V]

Now that we track node-specific memtier in pg_data_t, we can drop
memtier from memtype.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/memory-tiers.h |  1 -
 mm/memory-tiers.c            | 16 +++++++++-------
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index d0490ea4e35b..dd86323d2ba0 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -25,7 +25,6 @@ struct memory_dev_type {
 	/* Nodes of same abstract distance */
 	nodemask_t nodes;
 	struct kref kref;
-	struct memory_tier *memtier;
 };
 
 #ifdef CONFIG_NUMA
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 315b9fe14c48..9d53d4c14a5e 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -100,17 +100,22 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
 
 	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 (memtype->memtier)
-		return memtype->memtier;
+	if (!list_empty(&memtype->tier_sibiling)) {
+		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(adistance, memtier_adistance_chunk_size);
 	list_for_each_entry(memtier, &memory_tiers, list) {
 		if (adistance == memtier->adistance_start) {
-			memtype->memtier = memtier;
 			list_add(&memtype->tier_sibiling, &memtier->memory_types);
 			return memtier;
 		} else if (adistance < memtier->adistance_start) {
@@ -130,7 +135,6 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
 		list_add_tail(&new_memtier->list, &memtier->list);
 	else
 		list_add_tail(&new_memtier->list, &memory_tiers);
-	memtype->memtier = new_memtier;
 	list_add(&memtype->tier_sibiling, &new_memtier->memory_types);
 	return new_memtier;
 }
@@ -357,7 +361,6 @@ static bool clear_node_memory_tier(int node)
 		node_clear(node, memtype->nodes);
 		if (nodes_empty(memtype->nodes)) {
 			list_del(&memtype->tier_sibiling);
-			memtype->memtier = NULL;
 			if (list_empty(&memtier->memory_types))
 				destroy_memory_tier(memtier);
 		}
@@ -385,7 +388,6 @@ struct memory_dev_type *alloc_memory_type(int adistance)
 	memtype->adistance = adistance;
 	INIT_LIST_HEAD(&memtype->tier_sibiling);
 	memtype->nodes  = NODE_MASK_NONE;
-	memtype->memtier = NULL;
 	kref_init(&memtype->kref);
 	return memtype;
 }
-- 
2.37.1

[PATCH v14 08/10] mm/demotion: Demote pages according to allocation fallback order

[Aneesh Kumar K.V]

From: Jagdish Gediya <jvgediya.oss@gmail.com>

Currently, a higher tier node can only be demoted to selected nodes on the next
lower tier as defined by the demotion path. This strict demotion order does not
work in all use cases (e.g. some use cases may want to allow cross-socket
demotion to another node in the same demotion tier as a fallback when the
preferred demotion node is out of space). This demotion order is also
inconsistent with the page allocation fallback order when all the nodes in a
higher tier are out of space: The page allocation can fall back to any node from
any lower tier, whereas the demotion order doesn't allow that currently.

This patch adds support to get all the allowed demotion targets for a memory
tier. demote_page_list() function is now modified to utilize this allowed node
mask as the fallback allocation mask.

Signed-off-by: Jagdish Gediya <jvgediya.oss@gmail.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/memory-tiers.h | 12 ++++++++
 mm/memory-tiers.c            | 51 +++++++++++++++++++++++++++++--
 mm/vmscan.c                  | 58 ++++++++++++++++++++++++++----------
 3 files changed, 103 insertions(+), 18 deletions(-)

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index dd86323d2ba0..6fdff436c205 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -5,6 +5,7 @@
 #include <linux/types.h>
 #include <linux/nodemask.h>
 #include <linux/kref.h>
+#include <linux/mmzone.h>
 /*
  * Each tier cover a abstrace distance chunk size of 128
  */
@@ -35,11 +36,17 @@ 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);
 #ifdef CONFIG_MIGRATION
 int next_demotion_node(int node);
+void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
 #else
 static inline int next_demotion_node(int node)
 {
 	return NUMA_NO_NODE;
 }
+
+static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
+{
+	*targets = NODE_MASK_NONE;
+}
 #endif
 
 #else
@@ -72,5 +79,10 @@ static inline int next_demotion_node(int node)
 {
 	return NUMA_NO_NODE;
 }
+
+static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
+{
+	*targets = NODE_MASK_NONE;
+}
 #endif	/* CONFIG_NUMA */
 #endif  /* _LINUX_MEMORY_TIERS_H */
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 9d53d4c14a5e..2db4b4116a28 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -4,7 +4,6 @@
 #include <linux/sysfs.h>
 #include <linux/kobject.h>
 #include <linux/memory.h>
-#include <linux/mmzone.h>
 #include <linux/memory-tiers.h>
 
 #include "internal.h"
@@ -20,6 +19,8 @@ struct memory_tier {
 	 * adistance_start .. adistance_start + MEMTIER_CHUNK_SIZE
 	 */
 	int adistance_start;
+	/* All the nodes that are part of all the lower memory tiers. */
+	nodemask_t lower_tier_mask;
 };
 
 struct demotion_nodes {
@@ -156,6 +157,24 @@ static struct memory_tier *__node_get_memory_tier(int node)
 }
 
 #ifdef CONFIG_MIGRATION
+void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
+{
+	struct memory_tier *memtier;
+
+	/*
+	 * pg_data_t.memtier updates includes a synchronize_rcu()
+	 * which ensures that we either find NULL or a valid memtier
+	 * in NODE_DATA. protect the access via rcu_read_lock();
+	 */
+	rcu_read_lock();
+	memtier = rcu_dereference(pgdat->memtier);
+	if (memtier)
+		*targets = memtier->lower_tier_mask;
+	else
+		*targets = NODE_MASK_NONE;
+	rcu_read_unlock();
+}
+
 /**
  * next_demotion_node() - Get the next node in the demotion path
  * @node: The starting node to lookup the next node
@@ -203,10 +222,19 @@ int next_demotion_node(int node)
 
 static void disable_all_demotion_targets(void)
 {
+	struct memory_tier *memtier;
 	int node;
 
-	for_each_node_state(node, N_MEMORY)
+	for_each_node_state(node, N_MEMORY) {
 		node_demotion[node].preferred = NODE_MASK_NONE;
+		/*
+		 * We are holding memory_tier_lock, it is safe
+		 * to access pgda->memtier.
+		 */
+		memtier = __node_get_memory_tier(node);
+		if (memtier)
+			memtier->lower_tier_mask = NODE_MASK_NONE;
+	}
 	/*
 	 * Ensure that the "disable" is visible across the system.
 	 * Readers will see either a combination of before+disable
@@ -238,7 +266,7 @@ static void establish_demotion_targets(void)
 	struct demotion_nodes *nd;
 	int target = NUMA_NO_NODE, node;
 	int distance, best_distance;
-	nodemask_t tier_nodes;
+	nodemask_t tier_nodes, lower_tier;
 
 	lockdep_assert_held_once(&memory_tier_lock);
 
@@ -286,6 +314,23 @@ static void establish_demotion_targets(void)
 			}
 		} while (1);
 	}
+	/*
+	 * Now build the lower_tier mask for each node collecting node mask from
+	 * all memory tier below it. This allows us to fallback demotion page
+	 * allocation to a set of nodes that is closer the above selected
+	 * perferred node.
+	 */
+	lower_tier = node_states[N_MEMORY];
+	list_for_each_entry(memtier, &memory_tiers, list) {
+		/*
+		 * Keep removing current tier from lower_tier nodes,
+		 * This will remove all nodes in current and above
+		 * memory tier from the lower_tier mask.
+		 */
+		tier_nodes = get_memtier_nodemask(memtier);
+		nodes_andnot(lower_tier, lower_tier, tier_nodes);
+		memtier->lower_tier_mask = lower_tier;
+	}
 }
 
 #else
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 224de380ac88..500b9054be18 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1521,21 +1521,34 @@ static void folio_check_dirty_writeback(struct folio *folio,
 		mapping->a_ops->is_dirty_writeback(folio, dirty, writeback);
 }
 
-static struct page *alloc_demote_page(struct page *page, unsigned long node)
+static struct page *alloc_demote_page(struct page *page, unsigned long private)
 {
-	struct migration_target_control mtc = {
-		/*
-		 * Allocate from 'node', or fail quickly and quietly.
-		 * When this happens, 'page' will likely just be discarded
-		 * instead of migrated.
-		 */
-		.gfp_mask = (GFP_HIGHUSER_MOVABLE & ~__GFP_RECLAIM) |
-			    __GFP_THISNODE  | __GFP_NOWARN |
-			    __GFP_NOMEMALLOC | GFP_NOWAIT,
-		.nid = node
-	};
+	struct page *target_page;
+	nodemask_t *allowed_mask;
+	struct migration_target_control *mtc;
+
+	mtc = (struct migration_target_control *)private;
+
+	allowed_mask = mtc->nmask;
+	/*
+	 * make sure we allocate from the target node first also trying to
+	 * demote or reclaim pages from the target node via kswapd if we are
+	 * low on free memory on target node. If we don't do this and if
+	 * we have free memory on the slower(lower) memtier, we would start
+	 * allocating pages from slower(lower) memory tiers without even forcing
+	 * a demotion of cold pages from the target memtier. This can result
+	 * in the kernel placing hot pages in slower(lower) memory tiers.
+	 */
+	mtc->nmask = NULL;
+	mtc->gfp_mask |= __GFP_THISNODE;
+	target_page = alloc_migration_target(page, (unsigned long)mtc);
+	if (target_page)
+		return target_page;
 
-	return alloc_migration_target(page, (unsigned long)&mtc);
+	mtc->gfp_mask &= ~__GFP_THISNODE;
+	mtc->nmask = allowed_mask;
+
+	return alloc_migration_target(page, (unsigned long)mtc);
 }
 
 /*
@@ -1548,6 +1561,19 @@ static unsigned int demote_page_list(struct list_head *demote_pages,
 {
 	int target_nid = next_demotion_node(pgdat->node_id);
 	unsigned int nr_succeeded;
+	nodemask_t allowed_mask;
+
+	struct migration_target_control mtc = {
+		/*
+		 * Allocate from 'node', or fail quickly and quietly.
+		 * When this happens, 'page' will likely just be discarded
+		 * instead of migrated.
+		 */
+		.gfp_mask = (GFP_HIGHUSER_MOVABLE & ~__GFP_RECLAIM) | __GFP_NOWARN |
+			__GFP_NOMEMALLOC | GFP_NOWAIT,
+		.nid = target_nid,
+		.nmask = &allowed_mask
+	};
 
 	if (list_empty(demote_pages))
 		return 0;
@@ -1555,10 +1581,12 @@ static unsigned int demote_page_list(struct list_head *demote_pages,
 	if (target_nid == NUMA_NO_NODE)
 		return 0;
 
+	node_get_allowed_targets(pgdat, &allowed_mask);
+
 	/* Demotion ignores all cpuset and mempolicy settings */
 	migrate_pages(demote_pages, alloc_demote_page, NULL,
-			    target_nid, MIGRATE_ASYNC, MR_DEMOTION,
-			    &nr_succeeded);
+		      (unsigned long)&mtc, MIGRATE_ASYNC, MR_DEMOTION,
+		      &nr_succeeded);
 
 	if (current_is_kswapd())
 		__count_vm_events(PGDEMOTE_KSWAPD, nr_succeeded);
-- 
2.37.1

[PATCH v14 09/10] mm/demotion: Update node_is_toptier to work with memory tiers

[Aneesh Kumar K.V]

With memory tier support we can have memory only NUMA nodes
in the top tier from which we want to avoid promotion tracking NUMA
faults. Update node_is_toptier to work with memory tiers.
All NUMA nodes are by default top tier nodes. With lower(slower) memory
tiers added we consider all memory tiers above a memory tier having
CPU NUMA nodes as a top memory tier

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/memory-tiers.h | 11 +++++++++
 include/linux/node.h         |  5 ----
 mm/huge_memory.c             |  1 +
 mm/memory-tiers.c            | 46 ++++++++++++++++++++++++++++++++++++
 mm/migrate.c                 |  1 +
 mm/mprotect.c                |  1 +
 6 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index 6fdff436c205..9198d69afaa9 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -37,6 +37,7 @@ void clear_node_memory_type(int node, struct memory_dev_type *memtype);
 #ifdef CONFIG_MIGRATION
 int next_demotion_node(int node);
 void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
+bool node_is_toptier(int node);
 #else
 static inline int next_demotion_node(int node)
 {
@@ -47,6 +48,11 @@ static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *target
 {
 	*targets = NODE_MASK_NONE;
 }
+
+static inline bool node_is_toptier(int node)
+{
+	return true;
+}
 #endif
 
 #else
@@ -84,5 +90,10 @@ static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *target
 {
 	*targets = NODE_MASK_NONE;
 }
+
+static inline bool node_is_toptier(int node)
+{
+	return true;
+}
 #endif	/* CONFIG_NUMA */
 #endif  /* _LINUX_MEMORY_TIERS_H */
diff --git a/include/linux/node.h b/include/linux/node.h
index 40d641a8bfb0..9ec680dd607f 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -185,9 +185,4 @@ static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
 
 #define to_node(device) container_of(device, struct node, dev)
 
-static inline bool node_is_toptier(int node)
-{
-	return node_state(node, N_CPU);
-}
-
 #endif /* _LINUX_NODE_H_ */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8a7c1b344abe..1e9357576f2d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -36,6 +36,7 @@
 #include <linux/numa.h>
 #include <linux/page_owner.h>
 #include <linux/sched/sysctl.h>
+#include <linux/memory-tiers.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 2db4b4116a28..165ebbbac30d 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -32,6 +32,7 @@ static LIST_HEAD(memory_tiers);
 static struct memory_dev_type *node_memory_types[MAX_NUMNODES];
 static struct memory_dev_type *default_dram_type;
 #ifdef CONFIG_MIGRATION
+static int top_tier_adistance;
 /*
  * node_demotion[] examples:
  *
@@ -157,6 +158,31 @@ static struct memory_tier *__node_get_memory_tier(int node)
 }
 
 #ifdef CONFIG_MIGRATION
+bool node_is_toptier(int node)
+{
+	bool toptier;
+	pg_data_t *pgdat;
+	struct memory_tier *memtier;
+
+	pgdat = NODE_DATA(node);
+	if (!pgdat)
+		return false;
+
+	rcu_read_lock();
+	memtier = rcu_dereference(pgdat->memtier);
+	if (!memtier) {
+		toptier = true;
+		goto out;
+	}
+	if (memtier->adistance_start < top_tier_adistance)
+		toptier = true;
+	else
+		toptier = false;
+out:
+	rcu_read_unlock();
+	return toptier;
+}
+
 void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
 {
 	struct memory_tier *memtier;
@@ -314,6 +340,26 @@ static void establish_demotion_targets(void)
 			}
 		} while (1);
 	}
+	/*
+	 * Promotion is allowed from a memory tier to higher
+	 * memory tier only if the memory tier doesn't include
+	 * compute. We want to skip promotion from a memory tier,
+	 * if any node that is part of the memory tier have CPUs.
+	 * Once we detect such a memory tier, we consider that tier
+	 * as top tiper from which promotion is not allowed.
+	 */
+	list_for_each_entry_reverse(memtier, &memory_tiers, list) {
+		tier_nodes = get_memtier_nodemask(memtier);
+		nodes_and(tier_nodes, node_states[N_CPU], tier_nodes);
+		if (!nodes_empty(tier_nodes)) {
+			/*
+			 * abstract distance below the max value of this memtier
+			 * is considered toptier.
+			 */
+			top_tier_adistance = memtier->adistance_start + MEMTIER_CHUNK_SIZE;
+			break;
+		}
+	}
 	/*
 	 * Now build the lower_tier mask for each node collecting node mask from
 	 * all memory tier below it. This allows us to fallback demotion page
diff --git a/mm/migrate.c b/mm/migrate.c
index ea86594f4bc5..55e7718cfe45 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -50,6 +50,7 @@
 #include <linux/memory.h>
 #include <linux/random.h>
 #include <linux/sched/sysctl.h>
+#include <linux/memory-tiers.h>
 
 #include <asm/tlbflush.h>
 
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 3a23dde73723..61cd80831b04 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -31,6 +31,7 @@
 #include <linux/pgtable.h>
 #include <linux/sched/sysctl.h>
 #include <linux/userfaultfd_k.h>
+#include <linux/memory-tiers.h>
 #include <asm/cacheflush.h>
 #include <asm/mmu_context.h>
 #include <asm/tlbflush.h>
-- 
2.37.1

[PATCH v14 10/10] lib/nodemask: Optimize node_random for nodemask with single NUMA node

[Aneesh Kumar K.V]

The most common case for certain node_random usage (demotion nodemask) is with
nodemask weight 1. We can avoid calling get_random_init() in that case and
always return the only node set in the nodemask.

A simple test as below
  before = rdtsc_ordered();
  for (i= 0; i < 100; i++) {
      rand = node_random(&nmask);
  }
  after = rdtsc_ordered();

Without fix after - before : 16438
With fix after - before : 816

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/nodemask.h | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
index 4b71a96190a8..ac5b6a371be5 100644
--- a/include/linux/nodemask.h
+++ b/include/linux/nodemask.h
@@ -504,12 +504,21 @@ static inline int num_node_state(enum node_states state)
 static inline int node_random(const nodemask_t *maskp)
 {
 #if defined(CONFIG_NUMA) && (MAX_NUMNODES > 1)
-	int w, bit = NUMA_NO_NODE;
+	int w, bit;
 
 	w = nodes_weight(*maskp);
-	if (w)
+	switch (w) {
+	case 0:
+		bit = NUMA_NO_NODE;
+		break;
+	case 1:
+		bit = first_node(*maskp);
+		break;
+	default:
 		bit = bitmap_ord_to_pos(maskp->bits,
-			get_random_int() % w, MAX_NUMNODES);
+					get_random_int() % w, MAX_NUMNODES);
+		break;
+	}
 	return bit;
 #else
 	return 0;
-- 
2.37.1

Re: [PATCH v14 04/10] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE

[Huang, Ying]

"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:

> By default, all nodes are assigned to the default memory tier which
> is the memory tier designated for nodes with DRAM
>
> Set dax kmem device node's tier to slower memory tier by assigning
> abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE. Low-level drivers
> like papr_scm or ACPI NFIT can initialize memory device type to a
> more accurate value based on device tree details or HMAT. If the
> kernel doesn't find the memory type initialized, a default slower
> memory type is assigned by the kmem driver.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  drivers/dax/kmem.c           | 42 +++++++++++++++--
>  include/linux/memory-tiers.h | 42 ++++++++++++++++-
>  mm/memory-tiers.c            | 91 +++++++++++++++++++++++++++---------
>  3 files changed, 149 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index a37622060fff..d88814f1c414 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -11,9 +11,17 @@
>  #include <linux/fs.h>
>  #include <linux/mm.h>
>  #include <linux/mman.h>
> +#include <linux/memory-tiers.h>
>  #include "dax-private.h"
>  #include "bus.h"
>  
> +/*
> + * Default abstract distance assigned to the NUMA node onlined
> + * by DAX/kmem if the low level platform driver didn't initialize
> + * one for this NUMA node.
> + */
> +#define MEMTIER_DEFAULT_DAX_ADISTANCE	(MEMTIER_ADISTANCE_DRAM * 2)
> +
>  /* Memory resource name used for add_memory_driver_managed(). */
>  static const char *kmem_name;
>  /* Set if any memory will remain added when the driver will be unloaded. */
> @@ -41,6 +49,7 @@ struct dax_kmem_data {
>  	struct resource *res[];
>  };
>  
> +static struct memory_dev_type *dax_slowmem_type;
>  static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  {
>  	struct device *dev = &dev_dax->dev;
> @@ -79,11 +88,13 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  		return -EINVAL;
>  	}
>  
> +	init_node_memory_type(numa_node, dax_slowmem_type);
> +
> +	rc = -ENOMEM;
>  	data = kzalloc(struct_size(data, res, dev_dax->nr_range), GFP_KERNEL);
>  	if (!data)
> -		return -ENOMEM;
> +		goto err_dax_kmem_data;
>  
> -	rc = -ENOMEM;
>  	data->res_name = kstrdup(dev_name(dev), GFP_KERNEL);
>  	if (!data->res_name)
>  		goto err_res_name;
> @@ -155,6 +166,8 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  	kfree(data->res_name);
>  err_res_name:
>  	kfree(data);
> +err_dax_kmem_data:
> +	clear_node_memory_type(numa_node, dax_slowmem_type);
>  	return rc;
>  }
>  
> @@ -162,6 +175,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
>  {
>  	int i, success = 0;
> +	int node = dev_dax->target_node;
>  	struct device *dev = &dev_dax->dev;
>  	struct dax_kmem_data *data = dev_get_drvdata(dev);
>  
> @@ -198,6 +212,14 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
>  		kfree(data->res_name);
>  		kfree(data);
>  		dev_set_drvdata(dev, NULL);
> +		/*
> +		 * Clear the memtype association on successful unplug.
> +		 * If not, we have memory blocks left which can be
> +		 * offlined/onlined later. We need to keep memory_dev_type
> +		 * for that. This implies this reference will be around
> +		 * till next reboot.
> +		 */
> +		clear_node_memory_type(node, dax_slowmem_type);
>  	}
>  }
>  #else
> @@ -228,9 +250,22 @@ static int __init dax_kmem_init(void)
>  	if (!kmem_name)
>  		return -ENOMEM;
>  
> +	dax_slowmem_type = alloc_memory_type(MEMTIER_DEFAULT_DAX_ADISTANCE);
> +	if (IS_ERR(dax_slowmem_type)) {
> +		rc = PTR_ERR(dax_slowmem_type);
> +		goto err_dax_slowmem_type;
> +	}
> +
>  	rc = dax_driver_register(&device_dax_kmem_driver);
>  	if (rc)
> -		kfree_const(kmem_name);
> +		goto error_dax_driver;
> +
> +	return rc;
> +
> +error_dax_driver:
> +	destroy_memory_type(dax_slowmem_type);
> +err_dax_slowmem_type:
> +	kfree_const(kmem_name);
>  	return rc;
>  }
>  
> @@ -239,6 +274,7 @@ static void __exit dax_kmem_exit(void)
>  	dax_driver_unregister(&device_dax_kmem_driver);
>  	if (!any_hotremove_failed)
>  		kfree_const(kmem_name);
> +	destroy_memory_type(dax_slowmem_type);
>  }
>  
>  MODULE_AUTHOR("Intel Corporation");
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index cc89876899a6..0c739508517a 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -2,6 +2,9 @@
>  #ifndef _LINUX_MEMORY_TIERS_H
>  #define _LINUX_MEMORY_TIERS_H
>  
> +#include <linux/types.h>
> +#include <linux/nodemask.h>
> +#include <linux/kref.h>
>  /*
>   * Each tier cover a abstrace distance chunk size of 128
>   */
> @@ -13,12 +16,49 @@
>  #define MEMTIER_ADISTANCE_DRAM	(4 * MEMTIER_CHUNK_SIZE)
>  #define MEMTIER_HOTPLUG_PRIO	100
>  
> +struct memory_tier;
> +struct memory_dev_type {
> +	/* list of memory types that are part of same tier as this type */
> +	struct list_head tier_sibiling;
> +	/* abstract distance for this specific memory type */
> +	int adistance;
> +	/* Nodes of same abstract distance */
> +	nodemask_t nodes;
> +	struct kref kref;
> +	struct memory_tier *memtier;
> +};
> +
>  #ifdef CONFIG_NUMA
> -#include <linux/types.h>
>  extern bool numa_demotion_enabled;
> +struct memory_dev_type *alloc_memory_type(int adistance);
> +void destroy_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);
>  
>  #else
>  
>  #define numa_demotion_enabled	false
> +/*
> + * CONFIG_NUMA implementation returns non NULL error.
> + */
> +static inline struct memory_dev_type *alloc_memory_type(int adistance)
> +{
> +	return NULL;
> +}
> +
> +static inline void destroy_memory_type(struct memory_dev_type *memtype)
> +{
> +
> +}
> +
> +static inline void init_node_memory_type(int node, struct memory_dev_type *default_type)
> +{
> +
> +}
> +
> +static inline void clear_node_memory_type(int node, struct memory_dev_type *memtype)
> +{
> +
> +}
>  #endif	/* CONFIG_NUMA */
>  #endif  /* _LINUX_MEMORY_TIERS_H */
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 05f05395468a..e52ccbcb2b27 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -1,6 +1,4 @@
>  // SPDX-License-Identifier: GPL-2.0
> -#include <linux/types.h>
> -#include <linux/nodemask.h>
>  #include <linux/slab.h>
>  #include <linux/lockdep.h>
>  #include <linux/sysfs.h>
> @@ -21,27 +19,10 @@ struct memory_tier {
>  	int adistance_start;
>  };
>  
> -struct memory_dev_type {
> -	/* list of memory types that are part of same tier as this type */
> -	struct list_head tier_sibiling;
> -	/* abstract distance for this specific memory type */
> -	int adistance;
> -	/* Nodes of same abstract distance */
> -	nodemask_t nodes;
> -	struct memory_tier *memtier;
> -};
> -
>  static DEFINE_MUTEX(memory_tier_lock);
>  static LIST_HEAD(memory_tiers);
>  static struct memory_dev_type *node_memory_types[MAX_NUMNODES];
> -/*
> - * For now we can have 4 faster memory tiers with smaller adistance
> - * than default DRAM tier.
> - */
> -static struct memory_dev_type default_dram_type  = {
> -	.adistance = MEMTIER_ADISTANCE_DRAM,
> -	.tier_sibiling = LIST_HEAD_INIT(default_dram_type.tier_sibiling),
> -};
> +static struct memory_dev_type *default_dram_type;
>  
>  static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype)
>  {
> @@ -87,6 +68,14 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
>  	return new_memtier;
>  }
>  
> +static inline void __init_node_memory_type(int node, struct memory_dev_type *default_type)

Why the parameter is named as "default_type"?  I don't think we will
have an explicit "type" here.  So why not just "mem_type" or "type"?

Best Regards,
Huang, Ying

> +{
> +	if (!node_memory_types[node]) {
> +		node_memory_types[node] = default_type;
> +		kref_get(&default_type->kref);
> +	}
> +}
> +
>  static struct memory_tier *set_node_memory_tier(int node)
>  {
>  	struct memory_tier *memtier;
> @@ -97,8 +86,7 @@ static struct memory_tier *set_node_memory_tier(int node)
>  	if (!node_state(node, N_MEMORY))
>  		return ERR_PTR(-EINVAL);
>  
> -	if (!node_memory_types[node])
> -		node_memory_types[node] = &default_dram_type;
> +	__init_node_memory_type(node, default_dram_type);
>  
>  	memtype = node_memory_types[node];
>  	node_set(node, memtype->nodes);
> @@ -144,6 +132,57 @@ static bool clear_node_memory_tier(int node)
>  	return cleared;
>  }
>  
> +static void release_memtype(struct kref *kref)
> +{
> +	struct memory_dev_type *memtype;
> +
> +	memtype = container_of(kref, struct memory_dev_type, kref);
> +	kfree(memtype);
> +}
> +
> +struct memory_dev_type *alloc_memory_type(int adistance)
> +{
> +	struct memory_dev_type *memtype;
> +
> +	memtype = kmalloc(sizeof(*memtype), GFP_KERNEL);
> +	if (!memtype)
> +		return ERR_PTR(-ENOMEM);
> +
> +	memtype->adistance = adistance;
> +	INIT_LIST_HEAD(&memtype->tier_sibiling);
> +	memtype->nodes  = NODE_MASK_NONE;
> +	memtype->memtier = NULL;
> +	kref_init(&memtype->kref);
> +	return memtype;
> +}
> +EXPORT_SYMBOL_GPL(alloc_memory_type);
> +
> +void destroy_memory_type(struct memory_dev_type *memtype)
> +{
> +	kref_put(&memtype->kref, release_memtype);
> +}
> +EXPORT_SYMBOL_GPL(destroy_memory_type);
> +
> +void init_node_memory_type(int node, struct memory_dev_type *default_type)
> +{
> +
> +	mutex_lock(&memory_tier_lock);
> +	__init_node_memory_type(node, default_type);
> +	mutex_unlock(&memory_tier_lock);
> +}
> +EXPORT_SYMBOL_GPL(init_node_memory_type);
> +
> +void clear_node_memory_type(int node, struct memory_dev_type *memtype)
> +{
> +	mutex_lock(&memory_tier_lock);
> +	if (node_memory_types[node] == memtype) {
> +		node_memory_types[node] = NULL;
> +		kref_put(&memtype->kref, release_memtype);
> +	}
> +	mutex_unlock(&memory_tier_lock);
> +}
> +EXPORT_SYMBOL_GPL(clear_node_memory_type);
> +
>  static int __meminit memtier_hotplug_callback(struct notifier_block *self,
>  					      unsigned long action, void *_arg)
>  {
> @@ -178,6 +217,14 @@ static int __init memory_tier_init(void)
>  	struct memory_tier *memtier;
>  
>  	mutex_lock(&memory_tier_lock);
> +	/*
> +	 * For now we can have 4 faster memory tiers with smaller adistance
> +	 * than default DRAM tier.
> +	 */
> +	default_dram_type = alloc_memory_type(MEMTIER_ADISTANCE_DRAM);
> +	if (!default_dram_type)
> +		panic("%s() failed to allocate default DRAM tier\n", __func__);
> +
>  	/*
>  	 * Look at all the existing N_MEMORY nodes and add them to
>  	 * default memory tier or to a tier if we already have memory

Re: [PATCH v14 04/10] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE

[Huang, Ying]

"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:

> By default, all nodes are assigned to the default memory tier which
> is the memory tier designated for nodes with DRAM
>
> Set dax kmem device node's tier to slower memory tier by assigning
> abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE. Low-level drivers
> like papr_scm or ACPI NFIT can initialize memory device type to a
> more accurate value based on device tree details or HMAT. If the
> kernel doesn't find the memory type initialized, a default slower
> memory type is assigned by the kmem driver.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  drivers/dax/kmem.c           | 42 +++++++++++++++--
>  include/linux/memory-tiers.h | 42 ++++++++++++++++-
>  mm/memory-tiers.c            | 91 +++++++++++++++++++++++++++---------
>  3 files changed, 149 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index a37622060fff..d88814f1c414 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -11,9 +11,17 @@
>  #include <linux/fs.h>
>  #include <linux/mm.h>
>  #include <linux/mman.h>
> +#include <linux/memory-tiers.h>
>  #include "dax-private.h"
>  #include "bus.h"
>  
> +/*
> + * Default abstract distance assigned to the NUMA node onlined
> + * by DAX/kmem if the low level platform driver didn't initialize
> + * one for this NUMA node.
> + */
> +#define MEMTIER_DEFAULT_DAX_ADISTANCE	(MEMTIER_ADISTANCE_DRAM * 2)

If my understanding were correct, this is targeting Optane DCPMM for
now.  The measured results in the following paper is,

https://arxiv.org/pdf/2002.06018.pdf

Section: 2.1 Read/Write Latencies

"
For read access, the latency of DCPMM was 400.1% higher than that of
DRAM. For write access, it was 407.1% higher.
"

Section: 2.2 Read/Write Bandwidths

"
For read access, the throughput of DCPMM was 37.1% of DRAM. For write
access, it was 7.8%
"

According to the above data, I think the MEMTIER_DEFAULT_DAX_ADISTANCE
can be "5 * MEMTIER_ADISTANCE_DRAM".

Best Regards,
Huang, Ying

> +
>  /* Memory resource name used for add_memory_driver_managed(). */
>  static const char *kmem_name;
>  /* Set if any memory will remain added when the driver will be unloaded. */
> @@ -41,6 +49,7 @@ struct dax_kmem_data {
>  	struct resource *res[];
>  };
>  
> +static struct memory_dev_type *dax_slowmem_type;
>  static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  {
>  	struct device *dev = &dev_dax->dev;
> @@ -79,11 +88,13 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  		return -EINVAL;
>  	}
>  
> +	init_node_memory_type(numa_node, dax_slowmem_type);
> +
> +	rc = -ENOMEM;
>  	data = kzalloc(struct_size(data, res, dev_dax->nr_range), GFP_KERNEL);
>  	if (!data)
> -		return -ENOMEM;
> +		goto err_dax_kmem_data;
>  
> -	rc = -ENOMEM;
>  	data->res_name = kstrdup(dev_name(dev), GFP_KERNEL);
>  	if (!data->res_name)
>  		goto err_res_name;
> @@ -155,6 +166,8 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  	kfree(data->res_name);
>  err_res_name:
>  	kfree(data);
> +err_dax_kmem_data:
> +	clear_node_memory_type(numa_node, dax_slowmem_type);
>  	return rc;
>  }
>  
> @@ -162,6 +175,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
>  {
>  	int i, success = 0;
> +	int node = dev_dax->target_node;
>  	struct device *dev = &dev_dax->dev;
>  	struct dax_kmem_data *data = dev_get_drvdata(dev);
>  
> @@ -198,6 +212,14 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
>  		kfree(data->res_name);
>  		kfree(data);
>  		dev_set_drvdata(dev, NULL);
> +		/*
> +		 * Clear the memtype association on successful unplug.
> +		 * If not, we have memory blocks left which can be
> +		 * offlined/onlined later. We need to keep memory_dev_type
> +		 * for that. This implies this reference will be around
> +		 * till next reboot.
> +		 */
> +		clear_node_memory_type(node, dax_slowmem_type);
>  	}
>  }
>  #else
> @@ -228,9 +250,22 @@ static int __init dax_kmem_init(void)
>  	if (!kmem_name)
>  		return -ENOMEM;
>  
> +	dax_slowmem_type = alloc_memory_type(MEMTIER_DEFAULT_DAX_ADISTANCE);
> +	if (IS_ERR(dax_slowmem_type)) {
> +		rc = PTR_ERR(dax_slowmem_type);
> +		goto err_dax_slowmem_type;
> +	}
> +
>  	rc = dax_driver_register(&device_dax_kmem_driver);
>  	if (rc)
> -		kfree_const(kmem_name);
> +		goto error_dax_driver;
> +
> +	return rc;
> +
> +error_dax_driver:
> +	destroy_memory_type(dax_slowmem_type);
> +err_dax_slowmem_type:
> +	kfree_const(kmem_name);
>  	return rc;
>  }
>  
> @@ -239,6 +274,7 @@ static void __exit dax_kmem_exit(void)
>  	dax_driver_unregister(&device_dax_kmem_driver);
>  	if (!any_hotremove_failed)
>  		kfree_const(kmem_name);
> +	destroy_memory_type(dax_slowmem_type);
>  }
>  
>  MODULE_AUTHOR("Intel Corporation");
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index cc89876899a6..0c739508517a 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -2,6 +2,9 @@
>  #ifndef _LINUX_MEMORY_TIERS_H
>  #define _LINUX_MEMORY_TIERS_H
>  
> +#include <linux/types.h>
> +#include <linux/nodemask.h>
> +#include <linux/kref.h>
>  /*
>   * Each tier cover a abstrace distance chunk size of 128
>   */
> @@ -13,12 +16,49 @@
>  #define MEMTIER_ADISTANCE_DRAM	(4 * MEMTIER_CHUNK_SIZE)
>  #define MEMTIER_HOTPLUG_PRIO	100
>  
> +struct memory_tier;
> +struct memory_dev_type {
> +	/* list of memory types that are part of same tier as this type */
> +	struct list_head tier_sibiling;
> +	/* abstract distance for this specific memory type */
> +	int adistance;
> +	/* Nodes of same abstract distance */
> +	nodemask_t nodes;
> +	struct kref kref;
> +	struct memory_tier *memtier;
> +};
> +
>  #ifdef CONFIG_NUMA
> -#include <linux/types.h>
>  extern bool numa_demotion_enabled;
> +struct memory_dev_type *alloc_memory_type(int adistance);
> +void destroy_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);
>  
>  #else
>  
>  #define numa_demotion_enabled	false
> +/*
> + * CONFIG_NUMA implementation returns non NULL error.
> + */
> +static inline struct memory_dev_type *alloc_memory_type(int adistance)
> +{
> +	return NULL;
> +}
> +
> +static inline void destroy_memory_type(struct memory_dev_type *memtype)
> +{
> +
> +}
> +
> +static inline void init_node_memory_type(int node, struct memory_dev_type *default_type)
> +{
> +
> +}
> +
> +static inline void clear_node_memory_type(int node, struct memory_dev_type *memtype)
> +{
> +
> +}
>  #endif	/* CONFIG_NUMA */
>  #endif  /* _LINUX_MEMORY_TIERS_H */
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 05f05395468a..e52ccbcb2b27 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -1,6 +1,4 @@
>  // SPDX-License-Identifier: GPL-2.0
> -#include <linux/types.h>
> -#include <linux/nodemask.h>
>  #include <linux/slab.h>
>  #include <linux/lockdep.h>
>  #include <linux/sysfs.h>
> @@ -21,27 +19,10 @@ struct memory_tier {
>  	int adistance_start;
>  };
>  
> -struct memory_dev_type {
> -	/* list of memory types that are part of same tier as this type */
> -	struct list_head tier_sibiling;
> -	/* abstract distance for this specific memory type */
> -	int adistance;
> -	/* Nodes of same abstract distance */
> -	nodemask_t nodes;
> -	struct memory_tier *memtier;
> -};
> -
>  static DEFINE_MUTEX(memory_tier_lock);
>  static LIST_HEAD(memory_tiers);
>  static struct memory_dev_type *node_memory_types[MAX_NUMNODES];
> -/*
> - * For now we can have 4 faster memory tiers with smaller adistance
> - * than default DRAM tier.
> - */
> -static struct memory_dev_type default_dram_type  = {
> -	.adistance = MEMTIER_ADISTANCE_DRAM,
> -	.tier_sibiling = LIST_HEAD_INIT(default_dram_type.tier_sibiling),
> -};
> +static struct memory_dev_type *default_dram_type;
>  
>  static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype)
>  {
> @@ -87,6 +68,14 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
>  	return new_memtier;
>  }
>  
> +static inline void __init_node_memory_type(int node, struct memory_dev_type *default_type)
> +{
> +	if (!node_memory_types[node]) {
> +		node_memory_types[node] = default_type;
> +		kref_get(&default_type->kref);
> +	}
> +}
> +
>  static struct memory_tier *set_node_memory_tier(int node)
>  {
>  	struct memory_tier *memtier;
> @@ -97,8 +86,7 @@ static struct memory_tier *set_node_memory_tier(int node)
>  	if (!node_state(node, N_MEMORY))
>  		return ERR_PTR(-EINVAL);
>  
> -	if (!node_memory_types[node])
> -		node_memory_types[node] = &default_dram_type;
> +	__init_node_memory_type(node, default_dram_type);
>  
>  	memtype = node_memory_types[node];
>  	node_set(node, memtype->nodes);
> @@ -144,6 +132,57 @@ static bool clear_node_memory_tier(int node)
>  	return cleared;
>  }
>  
> +static void release_memtype(struct kref *kref)
> +{
> +	struct memory_dev_type *memtype;
> +
> +	memtype = container_of(kref, struct memory_dev_type, kref);
> +	kfree(memtype);
> +}
> +
> +struct memory_dev_type *alloc_memory_type(int adistance)
> +{
> +	struct memory_dev_type *memtype;
> +
> +	memtype = kmalloc(sizeof(*memtype), GFP_KERNEL);
> +	if (!memtype)
> +		return ERR_PTR(-ENOMEM);
> +
> +	memtype->adistance = adistance;
> +	INIT_LIST_HEAD(&memtype->tier_sibiling);
> +	memtype->nodes  = NODE_MASK_NONE;
> +	memtype->memtier = NULL;
> +	kref_init(&memtype->kref);
> +	return memtype;
> +}
> +EXPORT_SYMBOL_GPL(alloc_memory_type);
> +
> +void destroy_memory_type(struct memory_dev_type *memtype)
> +{
> +	kref_put(&memtype->kref, release_memtype);
> +}
> +EXPORT_SYMBOL_GPL(destroy_memory_type);
> +
> +void init_node_memory_type(int node, struct memory_dev_type *default_type)
> +{
> +
> +	mutex_lock(&memory_tier_lock);
> +	__init_node_memory_type(node, default_type);
> +	mutex_unlock(&memory_tier_lock);
> +}
> +EXPORT_SYMBOL_GPL(init_node_memory_type);
> +
> +void clear_node_memory_type(int node, struct memory_dev_type *memtype)
> +{
> +	mutex_lock(&memory_tier_lock);
> +	if (node_memory_types[node] == memtype) {
> +		node_memory_types[node] = NULL;
> +		kref_put(&memtype->kref, release_memtype);
> +	}
> +	mutex_unlock(&memory_tier_lock);
> +}
> +EXPORT_SYMBOL_GPL(clear_node_memory_type);
> +
>  static int __meminit memtier_hotplug_callback(struct notifier_block *self,
>  					      unsigned long action, void *_arg)
>  {
> @@ -178,6 +217,14 @@ static int __init memory_tier_init(void)
>  	struct memory_tier *memtier;
>  
>  	mutex_lock(&memory_tier_lock);
> +	/*
> +	 * For now we can have 4 faster memory tiers with smaller adistance
> +	 * than default DRAM tier.
> +	 */
> +	default_dram_type = alloc_memory_type(MEMTIER_ADISTANCE_DRAM);
> +	if (!default_dram_type)
> +		panic("%s() failed to allocate default DRAM tier\n", __func__);
> +
>  	/*
>  	 * Look at all the existing N_MEMORY nodes and add them to
>  	 * default memory tier or to a tier if we already have memory

Re: [PATCH v14 00/10] mm/demotion: Memory tiers and demotion

[Huang, Ying]

"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:

> The current kernel has the basic memory tiering support: Inactive pages on a
> higher tier NUMA node can be migrated (demoted) to a lower tier NUMA node to
> make room for new allocations on the higher tier NUMA node. Frequently accessed
> pages on a lower tier NUMA node can be migrated (promoted) to a higher tier NUMA
> node to improve the performance.
>
> In the current kernel, memory tiers are defined implicitly via a demotion path
> relationship between NUMA nodes, which is created during the kernel
> initialization and updated when a NUMA node is hot-added or hot-removed. The
> current implementation puts all nodes with CPU into the highest tier, and builds the
> tier hierarchy tier-by-tier by establishing the per-node demotion targets based
> on the distances between nodes.
>
> This current memory tier kernel implementation needs to be improved for several
> important use cases:
>
> * The current tier initialization code always initializes each memory-only NUMA
>   node into a lower tier. But a memory-only NUMA node may have a high
>   performance memory device (e.g. a DRAM-backed memory-only node on a virtual
>   machine) and that should be put into a higher tier.
>
> * The current tier hierarchy always puts CPU nodes into the top tier. But on a
>   system with HBM (e.g. GPU memory) devices, these memory-only HBM NUMA nodes
>   should be in the top tier, and DRAM nodes with CPUs are better to be placed
>   into the next lower tier.
>
> * Also because the current tier hierarchy always puts CPU nodes into the top
>   tier, when a CPU is hot-added (or hot-removed) and triggers a memory node from
>   CPU-less into a CPU node (or vice versa), the memory tier hierarchy gets
>   changed, even though no memory node is added or removed. This can make the
>   tier hierarchy unstable and make it difficult to support tier-based memory
>   accounting.
>
> * A higher tier node can only be demoted to nodes with shortest distance on the
>   next lower tier as defined by the demotion path, not any other node from any
>   lower tier. This strict, demotion order does not work in all use
>   cases (e.g. some use cases may want to allow cross-socket demotion to another
>   node in the same demotion tier as a fallback when the preferred demotion node
>   is out of space), and has resulted in the feature request for an interface to
>   override the system-wide, per-node demotion order from the userspace. This
>   demotion order is also inconsistent with the page allocation fallback order
>   when all the nodes in a higher tier are out of space: The page allocation can
>   fall back to any node from any lower tier, whereas the demotion order doesn't
>   allow that.
>
> This patch series make the creation of memory tiers explicit under
> the control of device driver.
>
> Memory Tier Initialization
> ==========================
>
> Linux kernel presents memory devices as NUMA nodes and each memory device is of
> a specific type. The memory type of a device is represented by its abstract 
> distance. A memory tier corresponds to a range of abstract distance. This allows
> for classifying memory devices with a specific performance range into a memory
> tier.
>
> By default, all memory nodes are assigned to the default tier with
> abstract distance 512.
>
> A device driver can move its memory nodes from the default tier. For example,
> PMEM can move its memory nodes below the default tier, whereas GPU can move its
> memory nodes above the default tier.
>
> The kernel initialization code makes the decision on which exact tier a memory
> node should be assigned to based on the requests from the device drivers as well
> as the memory device hardware information provided by the firmware.
>
> Hot-adding/removing CPUs doesn't affect memory tier hierarchy.
>
> Changes from v13
> * Address review feedback.
> * Add path dropping memtier from struct memory_dev_type
>
> Changes from v12
> * Fix kernel crash on module unload
> * Address review feedback.
> * Add node_random patch to this series based on review feedback
>
> Changes from v11:
> * smaller abstract distance imply faster(higher) memory tier.
>
> Changes from v10:
> * rename performance level to abstract distance
> * Thanks to all the good feedback from Huang, Ying <ying.huang@intel.com>.
>   Updated the patchset to cover most of the review feedback.
>
> Changes from v9:
> * Use performance level for initializing memory tiers.
>
> Changes from v8:
> * Drop the sysfs interface patches and  related documentation changes.
>
> Changes from v7:
> * Fix kernel crash with demotion.
> * Improve documentation.
>
> Changes from v6:
> * Drop the usage of rank.
> * Address other review feedback.
>
> Changes from v5:
> * Remove patch supporting N_MEMORY node removal from memory tiers. memory tiers
>   are going to be used for features other than demotion. Hence keep all N_MEMORY
>   nodes in memory tiers irrespective of whether they want to participate in promotion or demotion.
> * Add NODE_DATA->memtier
> * Rearrage patches to add sysfs files later.
> * Add support to create memory tiers from userspace.
> * Address other review feedback.
>
>
> Changes from v4:
> * Address review feedback.
> * Reverse the meaning of "rank": higher rank value means higher tier.
> * Add "/sys/devices/system/memtier/default_tier".
> * Add node_is_toptier
>
> v4:
> Add support for explicit memory tiers and ranks.
>
> v3:
> - Modify patch 1 subject to make it more specific
> - Remove /sys/kernel/mm/numa/demotion_targets interface, use
>   /sys/devices/system/node/demotion_targets instead and make
>   it writable to override node_states[N_DEMOTION_TARGETS].
> - Add support to view per node demotion targets via sysfs
>
> v2:
> In v1, only 1st patch of this patch series was sent, which was
> implemented to avoid some of the limitations on the demotion
> target sharing, however for certain numa topology, the demotion
> targets found by that patch was not most optimal, so 1st patch
> in this series is modified according to suggestions from Huang
> and Baolin. Different examples of demotion list comparasion
> between existing implementation and changed implementation can
> be found in the commit message of 1st patch.
>
>
>
> Aneesh Kumar K.V (9):
>   mm/demotion: Add support for explicit memory tiers
>   mm/demotion: Move memory demotion related code
>   mm/demotion: Add hotplug callbacks to handle new numa node onlined
>   mm/demotion/dax/kmem: Set node's abstract distance to
>     MEMTIER_DEFAULT_DAX_ADISTANCE
>   mm/demotion: Build demotion targets based on explicit memory tiers
>   mm/demotion: Add pg_data_t member to track node memory tier details
>   mm/demotion: Drop memtier from memtype
>   mm/demotion: Update node_is_toptier to work with memory tiers
>   lib/nodemask: Optimize node_random for nodemask with single NUMA node
>
> Jagdish Gediya (1):
>   mm/demotion: Demote pages according to allocation fallback order
>
>  drivers/dax/kmem.c           |  42 ++-
>  include/linux/memory-tiers.h |  99 ++++++
>  include/linux/migrate.h      |  15 -
>  include/linux/mmzone.h       |   3 +
>  include/linux/node.h         |   5 -
>  include/linux/nodemask.h     |  15 +-
>  mm/Makefile                  |   1 +
>  mm/huge_memory.c             |   1 +
>  mm/memory-tiers.c            | 645 +++++++++++++++++++++++++++++++++++
>  mm/migrate.c                 | 453 +-----------------------
>  mm/mprotect.c                |   1 +
>  mm/vmscan.c                  |  59 +++-
>  mm/vmstat.c                  |   4 -
>  13 files changed, 846 insertions(+), 497 deletions(-)
>  create mode 100644 include/linux/memory-tiers.h
>  create mode 100644 mm/memory-tiers.c

Except some minor comments, the series looks good to me.  Thanks!  Feel
free to add

Reviewed-by: "Huang, Ying" <ying.huang@intel.com>

for the whole series.

Best Regards,
Huang, Ying

Re: [PATCH v14 04/10] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE

[Aneesh Kumar K V]

On 8/15/22 8:09 AM, Huang, Ying wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> 
>> By default, all nodes are assigned to the default memory tier which
>> is the memory tier designated for nodes with DRAM
>>
>> Set dax kmem device node's tier to slower memory tier by assigning
>> abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE. Low-level drivers
>> like papr_scm or ACPI NFIT can initialize memory device type to a
>> more accurate value based on device tree details or HMAT. If the
>> kernel doesn't find the memory type initialized, a default slower
>> memory type is assigned by the kmem driver.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>>  drivers/dax/kmem.c           | 42 +++++++++++++++--
>>  include/linux/memory-tiers.h | 42 ++++++++++++++++-
>>  mm/memory-tiers.c            | 91 +++++++++++++++++++++++++++---------
>>  3 files changed, 149 insertions(+), 26 deletions(-)
>>
>> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
>> index a37622060fff..d88814f1c414 100644
>> --- a/drivers/dax/kmem.c
>> +++ b/drivers/dax/kmem.c
>> @@ -11,9 +11,17 @@
>>  #include <linux/fs.h>
>>  #include <linux/mm.h>
>>  #include <linux/mman.h>
>> +#include <linux/memory-tiers.h>
>>  #include "dax-private.h"
>>  #include "bus.h"
>>  
>> +/*
>> + * Default abstract distance assigned to the NUMA node onlined
>> + * by DAX/kmem if the low level platform driver didn't initialize
>> + * one for this NUMA node.
>> + */
>> +#define MEMTIER_DEFAULT_DAX_ADISTANCE	(MEMTIER_ADISTANCE_DRAM * 2)
> 
> If my understanding were correct, this is targeting Optane DCPMM for
> now.  The measured results in the following paper is,
> 
> https://arxiv.org/pdf/2002.06018.pdf
> 
> Section: 2.1 Read/Write Latencies
> 
> "
> For read access, the latency of DCPMM was 400.1% higher than that of
> DRAM. For write access, it was 407.1% higher.
> "
> 
> Section: 2.2 Read/Write Bandwidths
> 
> "
> For read access, the throughput of DCPMM was 37.1% of DRAM. For write
> access, it was 7.8%
> "
> 
> According to the above data, I think the MEMTIER_DEFAULT_DAX_ADISTANCE
> can be "5 * MEMTIER_ADISTANCE_DRAM".
> 

If we look at mapping every 100% increase in latency as a memory tier, we essentially
will have 4 memory tier here. Each memory tier is covering a range of abstract distance 128.
which makes a total adistance increase from MEMTIER_ADISTANCE_DRAM by 512. This puts 
DEFAULT_DAX_DISTANCE at 1024 or  MEMTIER_ADISTANCE_DRAM * 2

-aneesh

Re: [PATCH v14 04/10] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE

[huang ying]

On Tue, Aug 16, 2022 at 1:10 PM Aneesh Kumar K V
<aneesh.kumar@linux.ibm.com> wrote:
>
> On 8/15/22 8:09 AM, Huang, Ying wrote:
> > "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> >

[snip]

> >>
> >> +/*
> >> + * Default abstract distance assigned to the NUMA node onlined
> >> + * by DAX/kmem if the low level platform driver didn't initialize
> >> + * one for this NUMA node.
> >> + */
> >> +#define MEMTIER_DEFAULT_DAX_ADISTANCE       (MEMTIER_ADISTANCE_DRAM * 2)
> >
> > If my understanding were correct, this is targeting Optane DCPMM for
> > now.  The measured results in the following paper is,
> >
> > https://arxiv.org/pdf/2002.06018.pdf
> >
> > Section: 2.1 Read/Write Latencies
> >
> > "
> > For read access, the latency of DCPMM was 400.1% higher than that of
> > DRAM. For write access, it was 407.1% higher.
> > "
> >
> > Section: 2.2 Read/Write Bandwidths
> >
> > "
> > For read access, the throughput of DCPMM was 37.1% of DRAM. For write
> > access, it was 7.8%
> > "
> >
> > According to the above data, I think the MEMTIER_DEFAULT_DAX_ADISTANCE
> > can be "5 * MEMTIER_ADISTANCE_DRAM".
> >
>
> If we look at mapping every 100% increase in latency as a memory tier, we essentially
> will have 4 memory tier here. Each memory tier is covering a range of abstract distance 128.
> which makes a total adistance increase from MEMTIER_ADISTANCE_DRAM by 512. This puts
> DEFAULT_DAX_DISTANCE at 1024 or  MEMTIER_ADISTANCE_DRAM * 2

If my understanding were correct, you are suggesting to use a kind of
logarithmic mapping from latency to abstract distance?  That is,

  abstract_distance = log2(latency)

While I am suggesting to use a kind of linear mapping from latency to
abstract distance.  That is,

  abstract_distance = C * latency

I think that linear mapping is easy to understand.

Are there some good reasons to use logarithmic mapping?

Best Regards,
Huang, Ying

Re: [PATCH v14 04/10] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE

[Bharata B Rao]

On 8/16/2022 12:58 PM, huang ying wrote:
> On Tue, Aug 16, 2022 at 1:10 PM Aneesh Kumar K V
> <aneesh.kumar@linux.ibm.com> wrote:
>>
>> On 8/15/22 8:09 AM, Huang, Ying wrote:
>>> "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
>>>
> 
> [snip]
> 
>>>>
>>>> +/*
>>>> + * Default abstract distance assigned to the NUMA node onlined
>>>> + * by DAX/kmem if the low level platform driver didn't initialize
>>>> + * one for this NUMA node.
>>>> + */
>>>> +#define MEMTIER_DEFAULT_DAX_ADISTANCE       (MEMTIER_ADISTANCE_DRAM * 2)
>>>
>>> If my understanding were correct, this is targeting Optane DCPMM for
>>> now.  The measured results in the following paper is,
>>>
>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Farxiv.org%2Fpdf%2F2002.06018.pdf&amp;data=05%7C01%7Cbharata%40amd.com%7C1c5015b55ff849e5275408da7f58e67d%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637962317187856589%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=SxSC8WaKEeTyfZXoqtI%2FZAoBXXp82PnTeyyavrV%2FGGg%3D&amp;reserved=0
>>>
>>> Section: 2.1 Read/Write Latencies
>>>
>>> "
>>> For read access, the latency of DCPMM was 400.1% higher than that of
>>> DRAM. For write access, it was 407.1% higher.
>>> "
>>>
>>> Section: 2.2 Read/Write Bandwidths
>>>
>>> "
>>> For read access, the throughput of DCPMM was 37.1% of DRAM. For write
>>> access, it was 7.8%
>>> "
>>>
>>> According to the above data, I think the MEMTIER_DEFAULT_DAX_ADISTANCE
>>> can be "5 * MEMTIER_ADISTANCE_DRAM".
>>>
>>
>> If we look at mapping every 100% increase in latency as a memory tier, we essentially
>> will have 4 memory tier here. Each memory tier is covering a range of abstract distance 128.
>> which makes a total adistance increase from MEMTIER_ADISTANCE_DRAM by 512. This puts
>> DEFAULT_DAX_DISTANCE at 1024 or  MEMTIER_ADISTANCE_DRAM * 2
> 
> If my understanding were correct, you are suggesting to use a kind of
> logarithmic mapping from latency to abstract distance?  That is,
> 
>   abstract_distance = log2(latency)
> 
> While I am suggesting to use a kind of linear mapping from latency to
> abstract distance.  That is,
> 
>   abstract_distance = C * latency
> 
> I think that linear mapping is easy to understand.
> 
> Are there some good reasons to use logarithmic mapping?

Also, what is the recommendation for using bandwidth measure which
may be available from HMAT for CXL memory? How is bandwidth going
to influence the abstract distance?

Regards,
Bharata.

Re: [PATCH v14 04/10] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE

[huang ying]

On Tue, Aug 16, 2022 at 4:12 PM Bharata B Rao <bharata@amd.com> wrote:
>
> On 8/16/2022 12:58 PM, huang ying wrote:
> > On Tue, Aug 16, 2022 at 1:10 PM Aneesh Kumar K V
> > <aneesh.kumar@linux.ibm.com> wrote:
> >>
> >> On 8/15/22 8:09 AM, Huang, Ying wrote:
> >>> "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> >>>
> >
> > [snip]
> >
> >>>>
> >>>> +/*
> >>>> + * Default abstract distance assigned to the NUMA node onlined
> >>>> + * by DAX/kmem if the low level platform driver didn't initialize
> >>>> + * one for this NUMA node.
> >>>> + */
> >>>> +#define MEMTIER_DEFAULT_DAX_ADISTANCE       (MEMTIER_ADISTANCE_DRAM * 2)
> >>>
> >>> If my understanding were correct, this is targeting Optane DCPMM for
> >>> now.  The measured results in the following paper is,
> >>>
> >>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Farxiv.org%2Fpdf%2F2002.06018.pdf&amp;data=05%7C01%7Cbharata%40amd.com%7C1c5015b55ff849e5275408da7f58e67d%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637962317187856589%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=SxSC8WaKEeTyfZXoqtI%2FZAoBXXp82PnTeyyavrV%2FGGg%3D&amp;reserved=0
> >>>
> >>> Section: 2.1 Read/Write Latencies
> >>>
> >>> "
> >>> For read access, the latency of DCPMM was 400.1% higher than that of
> >>> DRAM. For write access, it was 407.1% higher.
> >>> "
> >>>
> >>> Section: 2.2 Read/Write Bandwidths
> >>>
> >>> "
> >>> For read access, the throughput of DCPMM was 37.1% of DRAM. For write
> >>> access, it was 7.8%
> >>> "
> >>>
> >>> According to the above data, I think the MEMTIER_DEFAULT_DAX_ADISTANCE
> >>> can be "5 * MEMTIER_ADISTANCE_DRAM".
> >>>
> >>
> >> If we look at mapping every 100% increase in latency as a memory tier, we essentially
> >> will have 4 memory tier here. Each memory tier is covering a range of abstract distance 128.
> >> which makes a total adistance increase from MEMTIER_ADISTANCE_DRAM by 512. This puts
> >> DEFAULT_DAX_DISTANCE at 1024 or  MEMTIER_ADISTANCE_DRAM * 2
> >
> > If my understanding were correct, you are suggesting to use a kind of
> > logarithmic mapping from latency to abstract distance?  That is,
> >
> >   abstract_distance = log2(latency)
> >
> > While I am suggesting to use a kind of linear mapping from latency to
> > abstract distance.  That is,
> >
> >   abstract_distance = C * latency
> >
> > I think that linear mapping is easy to understand.
> >
> > Are there some good reasons to use logarithmic mapping?
>
> Also, what is the recommendation for using bandwidth measure which
> may be available from HMAT for CXL memory? How is bandwidth going
> to influence the abstract distance?

This is a good question.

Per my understanding, latency stands for idle latency by default.  But
in practice, the latency under some reasonable memory accessing
throughput is the "real" latency.  So the memory with lower bandwidth
should have a larger abstract distance than the memory with higher
bandwidth even if the idle latency is the same.  But I don't have a
perfect formula to combine idle latency and bandwidth into abstract
distance.  One possibility is to increase abstract distance if the
bandwidth of the memory is much lower than that of DRAM.

Best Regards,
Huang, Ying

Re: [PATCH v14 01/10] mm/demotion: Add support for explicit memory tiers

[huang ying]

On Fri, Aug 12, 2022 at 1:58 PM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:

[snip]

> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> new file mode 100644
> index 000000000000..bc7c1b799bef
> --- /dev/null
> +++ b/include/linux/memory-tiers.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_MEMORY_TIERS_H
> +#define _LINUX_MEMORY_TIERS_H
> +
> +/*
> + * Each tier cover a abstrace distance chunk size of 128
> + */
> +#define MEMTIER_CHUNK_BITS     7
> +#define MEMTIER_CHUNK_SIZE     (1 << MEMTIER_CHUNK_BITS)
> +/*
> + * Smaller abstract distance value imply faster(higher) memory tiers.
> + */
> +#define MEMTIER_ADISTANCE_DRAM (4 * MEMTIER_CHUNK_SIZE)

This will make the abstract distance of DRAM the start of its memory
tier.  So that any memory type that is slightly slower than DRAM will
be put in a lower memory tier.  So I think it's better to put the DRAM
at the middle of its memory tier by default.  For example,

    4 * MEMTIER_CHUNK_SIZE + MEMTIER_CHUNK_SIZE / 2

> +
> +#endif  /* _LINUX_MEMORY_TIERS_H */

[snip]

Best Regards,
Huang, Ying

Re: [PATCH v14 04/10] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE

[Bharata B Rao]

On 8/16/2022 1:56 PM, huang ying wrote:
<snip>
>>>
>>> If my understanding were correct, you are suggesting to use a kind of
>>> logarithmic mapping from latency to abstract distance?  That is,
>>>
>>>   abstract_distance = log2(latency)
>>>
>>> While I am suggesting to use a kind of linear mapping from latency to
>>> abstract distance.  That is,
>>>
>>>   abstract_distance = C * latency
>>>
>>> I think that linear mapping is easy to understand.
>>>
>>> Are there some good reasons to use logarithmic mapping?
>>
>> Also, what is the recommendation for using bandwidth measure which
>> may be available from HMAT for CXL memory? How is bandwidth going
>> to influence the abstract distance?
> 
> This is a good question.
> 
> Per my understanding, latency stands for idle latency by default.  But
> in practice, the latency under some reasonable memory accessing
> throughput is the "real" latency.  So the memory with lower bandwidth
> should have a larger abstract distance than the memory with higher
> bandwidth even if the idle latency is the same.  But I don't have a
> perfect formula to combine idle latency and bandwidth into abstract
> distance.  One possibility is to increase abstract distance if the
> bandwidth of the memory is much lower than that of DRAM.

So if the firmware/platforms differ in their definition of latency and
bandwidth (like idle vs real value etc) in the firmware tables
(like HMAT), then the low level drivers (like ACPI) would have to be
aware of these and handle the conversion from latency and bw to
abstract distance correctly?

Regards,
Bharata.

Re: [PATCH v14 04/10] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE

[Huang, Ying]

Bharata B Rao <bharata@amd.com> writes:

> On 8/16/2022 1:56 PM, huang ying wrote:
> <snip>
>>>>
>>>> If my understanding were correct, you are suggesting to use a kind of
>>>> logarithmic mapping from latency to abstract distance?  That is,
>>>>
>>>>   abstract_distance = log2(latency)
>>>>
>>>> While I am suggesting to use a kind of linear mapping from latency to
>>>> abstract distance.  That is,
>>>>
>>>>   abstract_distance = C * latency
>>>>
>>>> I think that linear mapping is easy to understand.
>>>>
>>>> Are there some good reasons to use logarithmic mapping?
>>>
>>> Also, what is the recommendation for using bandwidth measure which
>>> may be available from HMAT for CXL memory? How is bandwidth going
>>> to influence the abstract distance?
>> 
>> This is a good question.
>> 
>> Per my understanding, latency stands for idle latency by default.  But
>> in practice, the latency under some reasonable memory accessing
>> throughput is the "real" latency.  So the memory with lower bandwidth
>> should have a larger abstract distance than the memory with higher
>> bandwidth even if the idle latency is the same.  But I don't have a
>> perfect formula to combine idle latency and bandwidth into abstract
>> distance.  One possibility is to increase abstract distance if the
>> bandwidth of the memory is much lower than that of DRAM.
>
> So if the firmware/platforms differ in their definition of latency and
> bandwidth (like idle vs real value etc) in the firmware tables
> (like HMAT), then the low level drivers (like ACPI) would have to be
> aware of these and handle the conversion from latency and bw to
> abstract distance correctly?

One possible way to make this a little easier is that we plan to add a
knob (as user space interface via sysfs) for each memory type, so that
the default abstract distance can be offset.  If so, at least we have
way to deal with difference in firmware/platforms.

Best Regards,
Huang, Ying