[PATCH v6 00/13] mm/demotion: Memory tiers and demotion

[PATCH v6 00/13] 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 top 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 interface 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
  device attached via CXL.mem or a DRAM-backed memory-only node on
  a virtual machine) and 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 selected nodes on the
  next lower tier as defined by the demotion path, not any other
  node from any lower tier.  This strict, hard-coded 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.

* There are no interfaces for the userspace to learn about the memory
  tier hierarchy in order to optimize its memory allocations.

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

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

By default, all memory nodes are assigned to the default tier (1).
The default tier device has a rank value (200).

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

Memory Allocation for Demotion
==============================
This patch series keep the demotion target page allocation logic same.
The demotion page allocation pick the closest NUMA node in the
next lower tier to the current NUMA node allocating pages from.

This will be later improved to use the same page allocation strategy
using fallback list.

Sysfs Interface:
=======================
Listing current list of memory tiers and rank details:

:/sys/devices/system/memtier$ ls
default_tier max_tier  memtier1  power  uevent
:/sys/devices/system/memtier$ cat default_tier
memtier1
:/sys/devices/system/memtier$ cat max_tier 
3
:/sys/devices/system/memtier$ 

Per node memory tier details:

For a cpu only NUMA node:

:/sys/devices/system/node# cat node0/memtier 
:/sys/devices/system/node# echo 1 > node0/memtier 
:/sys/devices/system/node# cat node0/memtier 
:/sys/devices/system/node# 

For a NUMA node with memory:
:/sys/devices/system/node# cat node1/memtier 
1
:/sys/devices/system/node# ls ../memtier/
default_tier  max_tier  memtier1  power  uevent
:/sys/devices/system/node# echo 2 > node1/memtier 
:/sys/devices/system/node# 
:/sys/devices/system/node# ls ../memtier/
default_tier  max_tier  memtier1  memtier2  power  uevent
:/sys/devices/system/node# cat node1/memtier 
2
:/sys/devices/system/node# 
:/sys/devices/system/node# cat ../memtier/memtier2/rank 
100
:/sys/devices/system/node# 
:/sys/devices/system/node# cat ../memtier/memtier1/rank 
200
:/sys/devices/system/node#

Removing a NUMA node from demotion:
:/sys/devices/system/node# cat node1/memtier 
2
:/sys/devices/system/node# echo none > node1/memtier 
:/sys/devices/system/node# 
:/sys/devices/system/node# cat node1/memtier 
:/sys/devices/system/node# 
:/sys/devices/system/node# ls ../memtier/
default_tier  max_tier  memtier1  power  uevent
:/sys/devices/system/node# 

The above also resulted in removal of memtier2 which was created in the earlier step.


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 (11):
  mm/demotion: Add support for explicit memory tiers
  mm/demotion: Move memory demotion related code
  mm/demotion: Return error on write to numa_demotion sysfs
  mm/demotion/dax/kmem: Set node's memory tier to MEMORY_TIER_PMEM
  mm/demotion: Build demotion targets based on explicit memory tiers
  mm/demotion: Expose memory tier details via sysfs
  mm/demotion: Add per node memory tier attribute to sysfs
  mm/demotion: Add support for memory tier creation from userspace
  mm/demotion: Add pg_data_t member to track node memory tier details
  mm/demotion: Update node_is_toptier to work with memory tiers
  mm/demotion: Add sysfs ABI documentation

Jagdish Gediya (2):
  mm/demotion: Demote pages according to allocation fallback order
  mm/demotion: Add documentation for memory tiering

 .../ABI/testing/sysfs-kernel-mm-memory-tiers  |  87 ++
 Documentation/admin-guide/mm/index.rst        |   1 +
 .../admin-guide/mm/memory-tiering.rst         | 181 ++++
 drivers/base/node.c                           |  39 +
 drivers/dax/kmem.c                            |   4 +
 include/linux/memory-tiers.h                  |  63 ++
 include/linux/migrate.h                       |  15 -
 include/linux/mmzone.h                        |   3 +
 include/linux/node.h                          |   5 -
 mm/Kconfig                                    |   3 +
 mm/Makefile                                   |   1 +
 mm/huge_memory.c                              |   1 +
 mm/memory-tiers.c                             | 888 ++++++++++++++++++
 mm/migrate.c                                  | 453 +--------
 mm/mprotect.c                                 |   1 +
 mm/vmscan.c                                   |  57 +-
 mm/vmstat.c                                   |   4 -
 17 files changed, 1316 insertions(+), 490 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers
 create mode 100644 Documentation/admin-guide/mm/memory-tiering.rst
 create mode 100644 include/linux/memory-tiers.h
 create mode 100644 mm/memory-tiers.c

-- 
2.36.1

[PATCH v6 01/13] 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 top 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 interface 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
device attached via CXL.mem or a DRAM-backed memory-only node on
a virtual machine) and 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 selected nodes on the
next lower tier as defined by the demotion path, not any other
node from any lower tier.  This strict, hard-coded 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.

The current kernel also don't provide any interfaces for the
userspace to learn about the memory tier hierarchy in order to
optimize its memory allocations.

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

This patch introduce explicity memory tiers with ranks. The rank
value of a memory tier is used to derive the demotion order between
NUMA nodes. The memory tiers present in a system can be found at

"Rank" is an opaque value. Its absolute value doesn't have any
special meaning. But the rank values of different memtiers can be
compared with each other to determine the memory tier order.

For example, if we have 3 memtiers: memtier0, memtier1, memiter2, and
their rank values are 300, 200, 100, then the memory tier order is:
memtier0 -> memtier1 -> memtier2, where memtier0 is the highest tier
and memtier2 is the lowest tier.

The rank value of each memtier should be unique.

A higher rank memory tier will appear first in the demotion order
than a lower rank memory tier. ie. while reclaim we choose a node
in higher rank memory tier to demote pages to as compared to a node
in a lower rank memory tier.

This patchset introduce 3 memory tiers (memtier0, memtier1 and memtier2)
which are created by different kernel subsystems. The default memory
tier created by the kernel is memtier1. Once created these memory tiers
are not destroyed even if they don't have any NUMA nodes assigned to
them.

This patch is based on the proposal sent by Wei Xu <weixugc@google.com> at [1].

[1] https://lore.kernel.org/linux-mm/CAAPL-u9Wv+nH1VOZTj=9p9S70Y3Qz3+63EkqncRDdHfubsrjfw@mail.gmail.com

/sys/devices/system/memtier/memtierN/

The nodes which are part of a specific memory tier can be listed
via
/sys/devices/system/memtier/memtierN/nodelist

Suggested-by: Wei Xu <weixugc@google.com>
Signed-off-by: Jagdish Gediya <jvgediya@linux.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 include/linux/memory-tiers.h | 20 ++++++++
 mm/Kconfig                   |  3 ++
 mm/Makefile                  |  1 +
 mm/memory-tiers.c            | 89 ++++++++++++++++++++++++++++++++++++
 4 files changed, 113 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..e17f6b4ee177
--- /dev/null
+++ b/include/linux/memory-tiers.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MEMORY_TIERS_H
+#define _LINUX_MEMORY_TIERS_H
+
+#ifdef CONFIG_TIERED_MEMORY
+
+#define MEMORY_TIER_HBM_GPU	0
+#define MEMORY_TIER_DRAM	1
+#define MEMORY_TIER_PMEM	2
+
+#define MEMORY_RANK_HBM_GPU	300
+#define MEMORY_RANK_DRAM	200
+#define MEMORY_RANK_PMEM	100
+
+#define DEFAULT_MEMORY_TIER	MEMORY_TIER_DRAM
+#define MAX_MEMORY_TIERS  3
+
+#endif	/* CONFIG_TIERED_MEMORY */
+
+#endif
diff --git a/mm/Kconfig b/mm/Kconfig
index 169e64192e48..bb5aa585ab41 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -614,6 +614,9 @@ config ARCH_ENABLE_HUGEPAGE_MIGRATION
 config ARCH_ENABLE_THP_MIGRATION
 	bool
 
+config TIERED_MEMORY
+	def_bool NUMA
+
 config HUGETLB_PAGE_SIZE_VARIABLE
 	def_bool n
 	help
diff --git a/mm/Makefile b/mm/Makefile
index 6f9ffa968a1a..482557fbc9d1 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-$(CONFIG_TIERED_MEMORY) += memory-tiers.o
 obj-$(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..d9fa955f208e
--- /dev/null
+++ b/mm/memory-tiers.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/nodemask.h>
+#include <linux/slab.h>
+#include <linux/memory-tiers.h>
+
+struct memory_tier {
+	struct list_head list;
+	nodemask_t nodelist;
+	int id;
+	int rank;
+};
+
+static DEFINE_MUTEX(memory_tier_lock);
+static LIST_HEAD(memory_tiers);
+
+/*
+ * Keep it simple by having  direct mapping between
+ * tier index and rank value.
+ */
+static inline int get_rank_from_tier(unsigned int tier)
+{
+	switch (tier) {
+	case MEMORY_TIER_HBM_GPU:
+		return MEMORY_RANK_HBM_GPU;
+	case MEMORY_TIER_DRAM:
+		return MEMORY_RANK_DRAM;
+	case MEMORY_TIER_PMEM:
+		return MEMORY_RANK_PMEM;
+	}
+	return -1;
+}
+
+static void insert_memory_tier(struct memory_tier *memtier)
+{
+	struct list_head *ent;
+	struct memory_tier *tmp_memtier;
+
+	list_for_each(ent, &memory_tiers) {
+		tmp_memtier = list_entry(ent, struct memory_tier, list);
+		if (tmp_memtier->rank < memtier->rank) {
+			list_add_tail(&memtier->list, ent);
+			return;
+		}
+	}
+	list_add_tail(&memtier->list, &memory_tiers);
+}
+
+static struct memory_tier *register_memory_tier(unsigned int tier,
+						unsigned int rank)
+{
+	struct memory_tier *memtier;
+
+	if (tier >= MAX_MEMORY_TIERS)
+		return ERR_PTR(-EINVAL);
+
+	memtier = kzalloc(sizeof(struct memory_tier), GFP_KERNEL);
+	if (!memtier)
+		return ERR_PTR(-ENOMEM);
+
+	memtier->id   = tier;
+	memtier->rank = rank;
+
+	insert_memory_tier(memtier);
+
+	return memtier;
+}
+
+static int __init memory_tier_init(void)
+{
+	struct memory_tier *memtier;
+
+	/*
+	 * Register only default memory tier to hide all empty
+	 * memory tier from sysfs.
+	 */
+	memtier = register_memory_tier(DEFAULT_MEMORY_TIER,
+				       get_rank_from_tier(DEFAULT_MEMORY_TIER));
+
+	if (IS_ERR(memtier))
+		panic("%s() failed to register memory tier: %ld\n",
+		      __func__, PTR_ERR(memtier));
+
+	/* CPU only nodes are not part of memory tiers. */
+	memtier->nodelist = node_states[N_MEMORY];
+
+	return 0;
+}
+subsys_initcall(memory_tier_init);
-- 
2.36.1

[PATCH v6 02/13] 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 |  6 ++++
 include/linux/migrate.h      |  2 --
 mm/memory-tiers.c            | 61 ++++++++++++++++++++++++++++++++++++
 mm/migrate.c                 | 60 +----------------------------------
 mm/vmscan.c                  |  1 +
 5 files changed, 69 insertions(+), 61 deletions(-)

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index e17f6b4ee177..44c3c3b16a36 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -2,6 +2,8 @@
 #ifndef _LINUX_MEMORY_TIERS_H
 #define _LINUX_MEMORY_TIERS_H
 
+#include <linux/types.h>
+
 #ifdef CONFIG_TIERED_MEMORY
 
 #define MEMORY_TIER_HBM_GPU	0
@@ -15,6 +17,10 @@
 #define DEFAULT_MEMORY_TIER	MEMORY_TIER_DRAM
 #define MAX_MEMORY_TIERS  3
 
+extern bool numa_demotion_enabled;
+#else
+#define numa_demotion_enabled	false
+
 #endif	/* CONFIG_TIERED_MEMORY */
 
 #endif
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 069a89e847f3..43e737215f33 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -78,7 +78,6 @@ 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) {}
@@ -87,7 +86,6 @@ 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 d9fa955f208e..9c6b40d7e0bf 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/types.h>
+#include <linux/device.h>
 #include <linux/nodemask.h>
 #include <linux/slab.h>
 #include <linux/memory-tiers.h>
@@ -87,3 +88,63 @@ static int __init memory_tier_init(void)
 	return 0;
 }
 subsys_initcall(memory_tier_init);
+
+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 */
diff --git a/mm/migrate.c b/mm/migrate.c
index e51588e95f57..29cacc217e38 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2508,64 +2508,6 @@ 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 f7d9a683e3a7..3a8f78277f99 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -50,6 +50,7 @@
 #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>
-- 
2.36.1

[PATCH v6 03/13] mm/demotion: Return error on write to numa_demotion sysfs

[Aneesh Kumar K.V]

With CONFIG_MIGRATION disabled return EINVAL on write.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 mm/memory-tiers.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 9c6b40d7e0bf..c3123a457d90 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -105,6 +105,9 @@ static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
 {
 	ssize_t ret;
 
+	if (!IS_ENABLED(CONFIG_MIGRATION))
+		return -EINVAL;
+
 	ret = kstrtobool(buf, &numa_demotion_enabled);
 	if (ret)
 		return ret;
-- 
2.36.1

[PATCH v6 04/13] mm/demotion/dax/kmem: Set node's memory tier to MEMORY_TIER_PMEM

[Aneesh Kumar K.V]

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

Set dax kmem device node's tier to MEMORY_TIER_PMEM. MEMORY_TIER_PMEM
is assigned a default rank value of 100 and appears below DEFAULT_MEMORY_TIER
in demotion order.

Signed-off-by: Jagdish Gediya <jvgediya@linux.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 drivers/dax/kmem.c           |  4 ++
 include/linux/memory-tiers.h |  1 +
 mm/memory-tiers.c            | 78 ++++++++++++++++++++++++++++++++++++
 3 files changed, 83 insertions(+)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index a37622060fff..0cb3de3d138f 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -11,6 +11,7 @@
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
+#include <linux/memory-tiers.h>
 #include "dax-private.h"
 #include "bus.h"
 
@@ -147,6 +148,9 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 
 	dev_set_drvdata(dev, data);
 
+#ifdef CONFIG_TIERED_MEMORY
+	node_create_and_set_memory_tier(numa_node, MEMORY_TIER_PMEM);
+#endif
 	return 0;
 
 err_request_mem:
diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index 44c3c3b16a36..e102ec73ab80 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -18,6 +18,7 @@
 #define MAX_MEMORY_TIERS  3
 
 extern bool numa_demotion_enabled;
+int node_create_and_set_memory_tier(int node, int tier);
 #else
 #define numa_demotion_enabled	false
 
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index c3123a457d90..00d393a5a628 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -67,6 +67,84 @@ static struct memory_tier *register_memory_tier(unsigned int tier,
 	return memtier;
 }
 
+static struct memory_tier *__node_get_memory_tier(int node)
+{
+	struct memory_tier *memtier;
+
+	list_for_each_entry(memtier, &memory_tiers, list) {
+		if (node_isset(node, memtier->nodelist))
+			return memtier;
+	}
+	return NULL;
+}
+
+static struct memory_tier *__get_memory_tier_from_id(int id)
+{
+	struct memory_tier *memtier;
+
+	list_for_each_entry(memtier, &memory_tiers, list) {
+		if (memtier->id == id)
+			return memtier;
+	}
+	return NULL;
+}
+
+static int __node_create_and_set_memory_tier(int node, int tier)
+{
+	int ret = 0;
+	struct memory_tier *memtier;
+
+	memtier = __get_memory_tier_from_id(tier);
+	if (!memtier) {
+		int rank;
+
+		rank = get_rank_from_tier(tier);
+		if (rank == -1) {
+			ret = -EINVAL;
+			goto out;
+		}
+		memtier = register_memory_tier(tier, rank);
+		if (!memtier) {
+			ret = -EINVAL;
+			goto out;
+		}
+	}
+	node_set(node, memtier->nodelist);
+out:
+	return ret;
+}
+
+int node_create_and_set_memory_tier(int node, int tier)
+{
+	struct memory_tier *current_tier;
+	int ret = 0;
+
+	mutex_lock(&memory_tier_lock);
+
+	current_tier = __node_get_memory_tier(node);
+	if (!current_tier) {
+		ret = __node_create_and_set_memory_tier(node, tier);
+		goto out;
+	}
+
+	if (current_tier->id == tier)
+		goto out;
+
+	node_clear(node, current_tier->nodelist);
+
+	ret = __node_create_and_set_memory_tier(node, tier);
+	if (ret) {
+		/* reset it back to older tier */
+		node_set(node, current_tier->nodelist);
+		goto out;
+	}
+out:
+	mutex_unlock(&memory_tier_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(node_create_and_set_memory_tier);
+
 static int __init memory_tier_init(void)
 {
 	struct memory_tier *memtier;
-- 
2.36.1

[PATCH v6 05/13] 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 tier 1 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.

The rank approach allows us to keep memory tier device IDs stable even if there
is a need to change the tier ordering among different memory tiers. e.g. DRAM
nodes with CPUs will always be on memtier1, no matter how many tiers are higher
or lower than these nodes. A new memory tier can be inserted into the tier
hierarchy for a new set of nodes without affecting the node assignment of any
existing memtier, provided that there is enough gap in the rank values for the
new memtier.

The absolute value of "rank" of a memtier doesn't necessarily carry any meaning.
Its value relative to other memtiers decides the level of this memtier in the tier
hierarchy.

For now, This patch supports hardcoded rank values which are 300, 200, & 100 for
memory tiers 0,1 & 2 respectively.

Suggested-by: Wei Xu <weixugc@google.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

Below is the sysfs interface to read the rank values of memory tier,
/sys/devices/system/memtier/memtierN/rank

This interface is read only for now. Write support can be added when there is
a need of flexibility of more number of memory tiers(> 3) with flexibile ordering
requirement among them.
---
 include/linux/memory-tiers.h |   5 +
 include/linux/migrate.h      |  13 --
 mm/memory-tiers.c            | 291 ++++++++++++++++++++++++++
 mm/migrate.c                 | 394 -----------------------------------
 mm/vmstat.c                  |   4 -
 5 files changed, 296 insertions(+), 411 deletions(-)

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index e102ec73ab80..18dd1ab7b96e 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -19,8 +19,13 @@
 
 extern bool numa_demotion_enabled;
 int node_create_and_set_memory_tier(int node, int tier);
+int next_demotion_node(int node);
 #else
 #define numa_demotion_enabled	false
+static inline int next_demotion_node(int node)
+{
+	return NUMA_NO_NODE;
+}
 
 #endif	/* CONFIG_TIERED_MEMORY */
 
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 43e737215f33..93fab62e6548 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -75,19 +75,6 @@ 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
 extern int PageMovable(struct page *page);
 extern void __SetPageMovable(struct page *page, struct address_space *mapping);
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 00d393a5a628..2f116912de43 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -4,6 +4,10 @@
 #include <linux/nodemask.h>
 #include <linux/slab.h>
 #include <linux/memory-tiers.h>
+#include <linux/random.h>
+#include <linux/memory.h>
+
+#include "internal.h"
 
 struct memory_tier {
 	struct list_head list;
@@ -12,9 +16,76 @@ struct memory_tier {
 	int rank;
 };
 
+struct demotion_nodes {
+	nodemask_t preferred;
+};
+
+static void establish_migration_targets(void);
 static DEFINE_MUTEX(memory_tier_lock);
 static LIST_HEAD(memory_tiers);
 
+/*
+ * 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_tiers[0] = <empty>
+ * memory_tiers[1] = 0-1
+ * memory_tiers[2] = 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_tiers[0] = <empty>
+ * memory_tiers[1] = 0-2
+ * memory_tiers[2] = <empty>
+ *
+ * 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_tiers[0] = 1
+ * memory_tiers[1] = 0
+ * memory_tiers[2] = 2
+ *
+ * node_demotion[0].preferred = 2
+ * node_demotion[1].preferred = 0
+ * node_demotion[2].preferred = <empty>
+ *
+ */
+static struct demotion_nodes *node_demotion __read_mostly;
+
 /*
  * Keep it simple by having  direct mapping between
  * tier index and rank value.
@@ -124,6 +195,7 @@ int node_create_and_set_memory_tier(int node, int tier)
 	current_tier = __node_get_memory_tier(node);
 	if (!current_tier) {
 		ret = __node_create_and_set_memory_tier(node, tier);
+		establish_migration_targets();
 		goto out;
 	}
 
@@ -138,6 +210,7 @@ int node_create_and_set_memory_tier(int node, int tier)
 		node_set(node, current_tier->nodelist);
 		goto out;
 	}
+	establish_migration_targets();
 out:
 	mutex_unlock(&memory_tier_lock);
 
@@ -145,6 +218,223 @@ int node_create_and_set_memory_tier(int node, int tier)
 }
 EXPORT_SYMBOL_GPL(node_create_and_set_memory_tier);
 
+static int __node_set_memory_tier(int node, int tier)
+{
+	int ret = 0;
+	struct memory_tier *memtier;
+
+	memtier = __get_memory_tier_from_id(tier);
+	if (!memtier) {
+		ret = -EINVAL;
+		goto out;
+	}
+	node_set(node, memtier->nodelist);
+out:
+	return ret;
+}
+
+int node_set_memory_tier(int node, int tier)
+{
+	struct memory_tier *memtier;
+	int ret = 0;
+
+	mutex_lock(&memory_tier_lock);
+	memtier = __node_get_memory_tier(node);
+	/*
+	 * if node is already part of the tier proceed with the
+	 * current tier value, because we might want to establish
+	 * new migration paths now. The node might be added to a tier
+	 * before it was made part of N_MEMORY, hence estabilish_migration_targets
+	 * will have skipped this node.
+	 */
+	if (!memtier)
+		ret = __node_set_memory_tier(node, tier);
+	establish_migration_targets();
+
+	mutex_unlock(&memory_tier_lock);
+
+	return ret;
+}
+
+/**
+ * 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;
+}
+
+/* Disable reclaim-based migration. */
+static void __disable_all_migrate_targets(void)
+{
+	int node;
+
+	for_each_node_state(node, N_MEMORY)
+		node_demotion[node].preferred = NODE_MASK_NONE;
+}
+
+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.
+	 */
+	synchronize_rcu();
+}
+
+/*
+ * 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_migration_targets(void)
+{
+	struct memory_tier *memtier;
+	struct demotion_nodes *nd;
+	int target = NUMA_NO_NODE, node;
+	int distance, best_distance;
+	nodemask_t used;
+
+	if (!node_demotion || !IS_ENABLED(CONFIG_MIGRATION))
+		return;
+
+	disable_all_migrate_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 next memtier to find the  demotion node list.
+		 */
+		memtier = list_next_entry(memtier, list);
+
+		/*
+		 * 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(used, node_states[N_MEMORY], memtier->nodelist);
+
+		/*
+		 * 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, &used);
+			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);
+	}
+}
+
+/*
+ * 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.
+ */
+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.
+	 */
+	if (arg->status_change_nid < 0)
+		return notifier_from_errno(0);
+
+	switch (action) {
+	case MEM_OFFLINE:
+		/*
+		 * In case we are moving out of N_MEMORY. Keep the node
+		 * in the memory tier so that when we bring memory online,
+		 * they appear in the right memory tier. We still need
+		 * to rebuild the demotion order.
+		 */
+		mutex_lock(&memory_tier_lock);
+		establish_migration_targets();
+		mutex_unlock(&memory_tier_lock);
+		break;
+	case MEM_ONLINE:
+		/*
+		 * We ignore the error here, if the node already have the tier
+		 * registered, we will continue to use that for the new memory
+		 * we are adding here.
+		 */
+		node_set_memory_tier(arg->status_change_nid, DEFAULT_MEMORY_TIER);
+		break;
+	}
+
+	return notifier_from_errno(0);
+}
+
+static void __init migrate_on_reclaim_init(void)
+{
+
+	if (IS_ENABLED(CONFIG_MIGRATION)) {
+		node_demotion = kcalloc(MAX_NUMNODES, sizeof(struct demotion_nodes),
+					GFP_KERNEL);
+		WARN_ON(!node_demotion);
+	}
+	hotplug_memory_notifier(migrate_on_reclaim_callback, 100);
+}
+
 static int __init memory_tier_init(void)
 {
 	struct memory_tier *memtier;
@@ -162,6 +452,7 @@ static int __init memory_tier_init(void)
 
 	/* CPU only nodes are not part of memory tiers. */
 	memtier->nodelist = node_states[N_MEMORY];
+	migrate_on_reclaim_init();
 
 	return 0;
 }
diff --git a/mm/migrate.c b/mm/migrate.c
index 29cacc217e38..0b554625a219 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2116,398 +2116,4 @@ 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);
-- 
2.36.1

[PATCH v6 06/13] mm/demotion: Expose memory tier details via sysfs

[Aneesh Kumar K.V]

This patch adds /sys/devices/system/memtier/ where all memory tier
related details can be found. All created memory tiers will be
listed there as /sys/devices/system/memtier/memtierN/

The nodes which are part of a specific memory tier can be listed
via /sys/devices/system/memtier/memtierN/nodelist

The rank value of a memory tier can be listed via
via /sys/devices/system/memtier/memtierN/rank

/sys/devices/system/memtier/max_tier shows the maximum number of memory
tiers that can be created.

/sys/devices/system/memtier/default_tier shows the memory tier to which
NUMA nodes get added by default if not assigned a specific memory tier.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 mm/memory-tiers.c | 99 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 95 insertions(+), 4 deletions(-)

diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 2f116912de43..51210f5efc1f 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -11,8 +11,8 @@
 
 struct memory_tier {
 	struct list_head list;
+	struct device dev;
 	nodemask_t nodelist;
-	int id;
 	int rank;
 };
 
@@ -20,6 +20,7 @@ struct demotion_nodes {
 	nodemask_t preferred;
 };
 
+#define to_memory_tier(device) container_of(device, struct memory_tier, dev)
 static void establish_migration_targets(void);
 static DEFINE_MUTEX(memory_tier_lock);
 static LIST_HEAD(memory_tiers);
@@ -86,6 +87,52 @@ static LIST_HEAD(memory_tiers);
  */
 static struct demotion_nodes *node_demotion __read_mostly;
 
+static struct bus_type memory_tier_subsys = {
+	.name = "memtier",
+	.dev_name = "memtier",
+};
+
+static ssize_t nodelist_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct memory_tier *memtier = to_memory_tier(dev);
+
+	return sysfs_emit(buf, "%*pbl\n",
+			  nodemask_pr_args(&memtier->nodelist));
+}
+static DEVICE_ATTR_RO(nodelist);
+
+static ssize_t rank_show(struct device *dev,
+			 struct device_attribute *attr, char *buf)
+{
+	struct memory_tier *memtier = to_memory_tier(dev);
+
+	return sysfs_emit(buf, "%d\n", memtier->rank);
+}
+static DEVICE_ATTR_RO(rank);
+
+static struct attribute *memory_tier_dev_attrs[] = {
+	&dev_attr_nodelist.attr,
+	&dev_attr_rank.attr,
+	NULL
+};
+
+static const struct attribute_group memory_tier_dev_group = {
+	.attrs = memory_tier_dev_attrs,
+};
+
+static const struct attribute_group *memory_tier_dev_groups[] = {
+	&memory_tier_dev_group,
+	NULL
+};
+
+static void memory_tier_device_release(struct device *dev)
+{
+	struct memory_tier *tier = to_memory_tier(dev);
+
+	kfree(tier);
+}
+
 /*
  * Keep it simple by having  direct mapping between
  * tier index and rank value.
@@ -121,6 +168,7 @@ static void insert_memory_tier(struct memory_tier *memtier)
 static struct memory_tier *register_memory_tier(unsigned int tier,
 						unsigned int rank)
 {
+	int error;
 	struct memory_tier *memtier;
 
 	if (tier >= MAX_MEMORY_TIERS)
@@ -130,11 +178,20 @@ static struct memory_tier *register_memory_tier(unsigned int tier,
 	if (!memtier)
 		return ERR_PTR(-ENOMEM);
 
-	memtier->id   = tier;
+	memtier->dev.id = tier;
 	memtier->rank = rank;
+	memtier->dev.bus = &memory_tier_subsys;
+	memtier->dev.release = memory_tier_device_release;
+	memtier->dev.groups = memory_tier_dev_groups;
 
 	insert_memory_tier(memtier);
 
+	error = device_register(&memtier->dev);
+	if (error) {
+		list_del(&memtier->list);
+		put_device(&memtier->dev);
+		return ERR_PTR(error);
+	}
 	return memtier;
 }
 
@@ -154,7 +211,7 @@ static struct memory_tier *__get_memory_tier_from_id(int id)
 	struct memory_tier *memtier;
 
 	list_for_each_entry(memtier, &memory_tiers, list) {
-		if (memtier->id == id)
+		if (memtier->dev.id == id)
 			return memtier;
 	}
 	return NULL;
@@ -199,7 +256,7 @@ int node_create_and_set_memory_tier(int node, int tier)
 		goto out;
 	}
 
-	if (current_tier->id == tier)
+	if (current_tier->dev.id == tier)
 		goto out;
 
 	node_clear(node, current_tier->nodelist);
@@ -435,10 +492,44 @@ static void __init migrate_on_reclaim_init(void)
 	hotplug_memory_notifier(migrate_on_reclaim_callback, 100);
 }
 
+static ssize_t
+max_tier_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%d\n", MAX_MEMORY_TIERS);
+}
+static DEVICE_ATTR_RO(max_tier);
+
+static ssize_t
+default_tier_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "memtier%d\n", DEFAULT_MEMORY_TIER);
+}
+static DEVICE_ATTR_RO(default_tier);
+
+static struct attribute *memory_tier_attrs[] = {
+	&dev_attr_max_tier.attr,
+	&dev_attr_default_tier.attr,
+	NULL
+};
+
+static const struct attribute_group memory_tier_attr_group = {
+	.attrs = memory_tier_attrs,
+};
+
+static const struct attribute_group *memory_tier_attr_groups[] = {
+	&memory_tier_attr_group,
+	NULL,
+};
+
 static int __init memory_tier_init(void)
 {
+	int ret;
 	struct memory_tier *memtier;
 
+	ret = subsys_system_register(&memory_tier_subsys, memory_tier_attr_groups);
+	if (ret)
+		pr_err("%s() failed to register subsystem: %d\n", __func__, ret);
+
 	/*
 	 * Register only default memory tier to hide all empty
 	 * memory tier from sysfs.
-- 
2.36.1

Re: [PATCH v6 00/13] mm/demotion: Memory tiers and demotion

[Hesham Almatary]

On Fri, 10 Jun 2022 19:19:53 +0530
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> wrote:

> 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 top 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 interface 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
>   device attached via CXL.mem or a DRAM-backed memory-only node on
>   a virtual machine) and 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 selected nodes on the
>   next lower tier as defined by the demotion path, not any other
>   node from any lower tier.  This strict, hard-coded 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.
> 
> * There are no interfaces for the userspace to learn about the memory
>   tier hierarchy in order to optimize its memory allocations.
> 
> This patch series make the creation of memory tiers explicit under
> the control of userspace or device driver.
> 
> Memory Tier Initialization
> ==========================
> 
> By default, all memory nodes are assigned to the default tier (1).
> The default tier device has a rank value (200).
> 
> A device driver can move up or down its memory nodes from the default
> tier.  For example, PMEM can move down its memory nodes below the
> default tier, whereas GPU can move up 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.
> 
> Memory Allocation for Demotion
> ==============================
> This patch series keep the demotion target page allocation logic same.
> The demotion page allocation pick the closest NUMA node in the
> next lower tier to the current NUMA node allocating pages from.
> 
> This will be later improved to use the same page allocation strategy
> using fallback list.
> 
> Sysfs Interface:
> =======================
> Listing current list of memory tiers and rank details:
> 
> :/sys/devices/system/memtier$ ls
> default_tier max_tier  memtier1  power  uevent
> :/sys/devices/system/memtier$ cat default_tier
> memtier1
> :/sys/devices/system/memtier$ cat max_tier 
> 3
Should this be renamed to max_tiers or tiers_count? Otherwise one might
confuse max_tier as the highest allowed tier ID.

> :/sys/devices/system/memtier$ 
> 
> Per node memory tier details:
> 
> For a cpu only NUMA node:
> 
> :/sys/devices/system/node# cat node0/memtier 
> :/sys/devices/system/node# echo 1 > node0/memtier 
> :/sys/devices/system/node# cat node0/memtier 
> :/sys/devices/system/node# 
> 
> For a NUMA node with memory:
> :/sys/devices/system/node# cat node1/memtier 
> 1
> :/sys/devices/system/node# ls ../memtier/
> default_tier  max_tier  memtier1  power  uevent
> :/sys/devices/system/node# echo 2 > node1/memtier 
> :/sys/devices/system/node# 
> :/sys/devices/system/node# ls ../memtier/
> default_tier  max_tier  memtier1  memtier2  power  uevent
> :/sys/devices/system/node# cat node1/memtier 
> 2
> :/sys/devices/system/node# 
> :/sys/devices/system/node# cat ../memtier/memtier2/rank 
> 100
> :/sys/devices/system/node# 
> :/sys/devices/system/node# cat ../memtier/memtier1/rank 
> 200
> :/sys/devices/system/node#
> 
> Removing a NUMA node from demotion:
> :/sys/devices/system/node# cat node1/memtier 
> 2
> :/sys/devices/system/node# echo none > node1/memtier 
> :/sys/devices/system/node# 
> :/sys/devices/system/node# cat node1/memtier 
> :/sys/devices/system/node# 
> :/sys/devices/system/node# ls ../memtier/
> default_tier  max_tier  memtier1  power  uevent
> :/sys/devices/system/node# 
> 
> The above also resulted in removal of memtier2 which was created in
> the earlier step.
> 
> 
> 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 (11):
>   mm/demotion: Add support for explicit memory tiers
>   mm/demotion: Move memory demotion related code
>   mm/demotion: Return error on write to numa_demotion sysfs
>   mm/demotion/dax/kmem: Set node's memory tier to MEMORY_TIER_PMEM
>   mm/demotion: Build demotion targets based on explicit memory tiers
>   mm/demotion: Expose memory tier details via sysfs
>   mm/demotion: Add per node memory tier attribute to sysfs
>   mm/demotion: Add support for memory tier creation from userspace
>   mm/demotion: Add pg_data_t member to track node memory tier details
>   mm/demotion: Update node_is_toptier to work with memory tiers
>   mm/demotion: Add sysfs ABI documentation
> 
> Jagdish Gediya (2):
>   mm/demotion: Demote pages according to allocation fallback order
>   mm/demotion: Add documentation for memory tiering
> 
>  .../ABI/testing/sysfs-kernel-mm-memory-tiers  |  87 ++
>  Documentation/admin-guide/mm/index.rst        |   1 +
>  .../admin-guide/mm/memory-tiering.rst         | 181 ++++
>  drivers/base/node.c                           |  39 +
>  drivers/dax/kmem.c                            |   4 +
>  include/linux/memory-tiers.h                  |  63 ++
>  include/linux/migrate.h                       |  15 -
>  include/linux/mmzone.h                        |   3 +
>  include/linux/node.h                          |   5 -
>  mm/Kconfig                                    |   3 +
>  mm/Makefile                                   |   1 +
>  mm/huge_memory.c                              |   1 +
>  mm/memory-tiers.c                             | 888
> ++++++++++++++++++ mm/migrate.c                                  |
> 453 +-------- mm/mprotect.c                                 |   1 +
>  mm/vmscan.c                                   |  57 +-
>  mm/vmstat.c                                   |   4 -
>  17 files changed, 1316 insertions(+), 490 deletions(-)
>  create mode 100644
> Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers create mode
> 100644 Documentation/admin-guide/mm/memory-tiering.rst create mode
> 100644 include/linux/memory-tiers.h create mode 100644
> mm/memory-tiers.c
> 

[PATCH v6 00/13] 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 top 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 interface 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
  device attached via CXL.mem or a DRAM-backed memory-only node on
  a virtual machine) and 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 selected nodes on the
  next lower tier as defined by the demotion path, not any other
  node from any lower tier.  This strict, hard-coded 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.

* There are no interfaces for the userspace to learn about the memory
  tier hierarchy in order to optimize its memory allocations.

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

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

By default, all memory nodes are assigned to the default tier (1).
The default tier device has a rank value (200).

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

Memory Allocation for Demotion
==============================
This patch series keep the demotion target page allocation logic same.
The demotion page allocation pick the closest NUMA node in the
next lower tier to the current NUMA node allocating pages from.

This will be later improved to use the same page allocation strategy
using fallback list.

Sysfs Interface:
=======================
Listing current list of memory tiers and rank details:

:/sys/devices/system/memtier$ ls
default_tier max_tier  memtier1  power  uevent
:/sys/devices/system/memtier$ cat default_tier
memtier1
:/sys/devices/system/memtier$ cat max_tier 
3
:/sys/devices/system/memtier$ 

Per node memory tier details:

For a cpu only NUMA node:

:/sys/devices/system/node# cat node0/memtier 
:/sys/devices/system/node# echo 1 > node0/memtier 
:/sys/devices/system/node# cat node0/memtier 
:/sys/devices/system/node# 

For a NUMA node with memory:
:/sys/devices/system/node# cat node1/memtier 
1
:/sys/devices/system/node# ls ../memtier/
default_tier  max_tier  memtier1  power  uevent
:/sys/devices/system/node# echo 2 > node1/memtier 
:/sys/devices/system/node# 
:/sys/devices/system/node# ls ../memtier/
default_tier  max_tier  memtier1  memtier2  power  uevent
:/sys/devices/system/node# cat node1/memtier 
2
:/sys/devices/system/node# 
:/sys/devices/system/node# cat ../memtier/memtier2/rank 
100
:/sys/devices/system/node# 
:/sys/devices/system/node# cat ../memtier/memtier1/rank 
200
:/sys/devices/system/node#

Removing a NUMA node from demotion:
:/sys/devices/system/node# cat node1/memtier 
2
:/sys/devices/system/node# echo none > node1/memtier 
:/sys/devices/system/node# 
:/sys/devices/system/node# cat node1/memtier 
:/sys/devices/system/node# 
:/sys/devices/system/node# ls ../memtier/
default_tier  max_tier  memtier1  power  uevent
:/sys/devices/system/node# 

The above also resulted in removal of memtier2 which was created in the earlier step.


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 (11):
  mm/demotion: Add support for explicit memory tiers
  mm/demotion: Move memory demotion related code
  mm/demotion: Return error on write to numa_demotion sysfs
  mm/demotion/dax/kmem: Set node's memory tier to MEMORY_TIER_PMEM
  mm/demotion: Build demotion targets based on explicit memory tiers
  mm/demotion: Expose memory tier details via sysfs
  mm/demotion: Add per node memory tier attribute to sysfs
  mm/demotion: Add support for memory tier creation from userspace
  mm/demotion: Add pg_data_t member to track node memory tier details
  mm/demotion: Update node_is_toptier to work with memory tiers
  mm/demotion: Add sysfs ABI documentation

Jagdish Gediya (2):
  mm/demotion: Demote pages according to allocation fallback order
  mm/demotion: Add documentation for memory tiering

 .../ABI/testing/sysfs-kernel-mm-memory-tiers  |  87 ++
 Documentation/admin-guide/mm/index.rst        |   1 +
 .../admin-guide/mm/memory-tiering.rst         | 181 ++++
 drivers/base/node.c                           |  39 +
 drivers/dax/kmem.c                            |   4 +
 include/linux/memory-tiers.h                  |  63 ++
 include/linux/migrate.h                       |  15 -
 include/linux/mmzone.h                        |   3 +
 include/linux/node.h                          |   5 -
 mm/Kconfig                                    |   3 +
 mm/Makefile                                   |   1 +
 mm/huge_memory.c                              |   1 +
 mm/memory-tiers.c                             | 888 ++++++++++++++++++
 mm/migrate.c                                  | 453 +--------
 mm/mprotect.c                                 |   1 +
 mm/vmscan.c                                   |  57 +-
 mm/vmstat.c                                   |   4 -
 17 files changed, 1316 insertions(+), 490 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers
 create mode 100644 Documentation/admin-guide/mm/memory-tiering.rst
 create mode 100644 include/linux/memory-tiers.h
 create mode 100644 mm/memory-tiers.c

-- 
2.36.1