[RFC PATCH v4 0/9] mm: Hot page tracking and promotion infrastructure

[RFC PATCH v4 0/9] mm: Hot page tracking and promotion infrastructure

[Bharata B Rao]

Hi,

This is v4 of page hotness tracking and promotion sub-system pghot.

This patchset introduces a new subsystem for hot page tracking and
promotion (pghot) with the following goals:

- Unify hot page detection from multiple sources like hint faults, page table
  scans, hardware hints (IBS).
- Decouple detection from migration.
- Centralize promotion logic via per-lowertier-node kernel thread.
- Move migration rate limiting and associated logic in NUMAB=2 (current NUMA
  Balancing based hot page promotion) from scheduler to pghot sub-system to
  enable broader reuse.
  
Currently, multiple kernel subsystems detect page accesses independently.
This patchset consolidates accesses from these mechanisms by providing:

- A common API for reporting page accesses
- Shared infrastructure for tracking hotness at PFN granularity
- Per-lowertier-node kernel threads for promoting pages.

Here is a brief summary of how this subsystem works:

- Tracks frequency, last access time and accessing node for each recorded
  access.
- These hotness parameters are maintained on a per-PFN in an unsigned long
  variable within the existing mem_section data structure.
  Bits 0-31 are used to store nid, frequency and time.
  Bits 32-62 are unused now.
  Bit 63 is used to indicate the page is ready for migration.
- Classifies pages as hot based on configurable thresholds.
- Pages classified as hot are marked as ready for migration using the ready bit.
- Per-lowertier-node kmigrated threads periodically scan the PFNs of lower tier
  nodes, checking for the migration-ready bit to perform batched migrations.

Four page hotness sources have been integrated with pghot subsystem on
experimental basis:

1. IBS
2. klruscand (based on MGLRU page table walks)
3. NUMA Balancing (mode 2).
4. folio_mark_accessed()

Changes in v4
=============
- Addition of folio_mark_accessed() as source to track and promote unmapped
  page cache pages.
- Per-section indicator for hotness based on which a section is taken up for
  scanning. This should considerably reduce the scanning effort by kmigrated.
  The LSB of the pointer used to store the hotness data for each section is
  reprovisioned as section hotness indicator.
- Added a file under admin-guide to document the usage of pghot sub-system.
- HWhint source IBS is under its own config option now.
- All vmstat counters are under appropriate config options now.
- Most tunables are moved to a dedicated debugfs dir.
- Some code cleanup.

Results
=======
System details
--------------
3 node AMD Zen5 system with 2 regular NUMA nodes (0, 1) and a CXL node (2)

$ numactl -H
available: 3 nodes (0-2)
node 0 cpus: 0-95,192-287
node 0 size: 128460 MB
node 1 cpus: 96-191,288-383
node 1 size: 128893 MB
node 2 cpus:
node 2 size: 257993 MB
node distances:
node   0   1   2 
  0:  10  32  50 
  1:  32  10  60 
  2:  255  255  10

Hotness sources
---------------
NUMAB0 - Without NUMA Balancing in base case and with no source enabled
	 in the patched case. No migrations occur.
NUMAB2 - Existing hot page promotion for the base case and
	 use of hint faults as source in the patched case.
pgtscan - Klruscand (MGLRU based PTE A bit scanning) source
hwhints - IBS as source
FMA - folio_mark_accessed()

==============================================================
Scenario 1 - Enough memory in toptier and hence only promotion
==============================================================
Microbenchmark details
----------------------
Multi-threaded application with 64 threads that access memory at 4K granularity
repetitively and randomly. The number of accesses per thread and the randomness
pattern for each thread are fixed beforehand. The accesses are divided into stores
and loads.

Benchmark threads run on Node 0, while memory is initially provisioned on
CXL node 2 before the accesses start. There are three modes in which the
benchmark is run:

Mode 1: Regular 4K page accesses. The memory is provisioned on CXL node using
mmap(MAP_POPULATE). 50% loads and 50% stores.

Mode 2: mmapped file 4K accesses. The memory is provisioned on CXL node using
mmap(fd, MAP_POPULATE|MAP_SHARED). 100% loads.

Repetitive accesses results in lowertier pages becoming hot and kmigrated
detecting and migrating them. The benchmark score is the time taken to finish
the accesses in microseconds. The sooner it finishes the better it is. All the
numbers shown below are average of 3 runs.

Mode 1 - Time taken (microseconds, lower is better)
------------------------------------------------------
Source		Base		Patched		Change
------------------------------------------------------
NUMAB0		118,986,471	116,240,187	-2.3%
NUMAB2		104,025,651	105,636,591	+1.5%
pgtscan		NA		110,800,511	NA
hwhints		NA		100,442,082	NA
------------------------------------------------------

Mode 1 - Pages migrated (pgpromote_success)
---------------------------------------
Source		Base		Patched
---------------------------------------
NUMAB0		0		0
NUMAB2		2097152		2097152
pgtscan		NA		2097152
hwhints		NA		1232876
---------------------------------------

Mode 2 - Time taken (microseconds, lower is better)
------------------------------------------------------
Source		Base		Patched		Change
------------------------------------------------------
NUMAB0		113,352,595	110,053,021	-2.9%
NUMAB2		72,339,008	84,999,971	+17.5%
pgtscan		NA		66,189,266	NA
hwhints		NA		71,644,577	NA
------------------------------------------------------

Mode 2 - Pages migrated (pgpromote_success)
---------------------------------------
Source		Base		Patched
---------------------------------------
NUMAB0		0		0
NUMAB2		2097152		2095978
pgtscan		NA		1993077
hwhints		NA		2097129
---------------------------------------

==============================================================
Scenario 2 - Toptier memory overcommited, promotion + demotion
==============================================================
Single threaded application that allocates memory on both DRAM and CXL nodes
using mmap(MAP_POPULATE). Every 1G region of allocated memory on CXL node is
accessed at 4K granularity randomly and repetitively to build up the notion
of hotness in the 1GB region that is under access. This should drive promotion.
For promotion to work successfully, the DRAM memory that has been provisioned
(and not being accessed) should be demoted first. There is enough free memory
in the CXL node to for demotions.

In summary, this benchmark creates a memory pressure on DRAM node and does
CXL memory accesses to drive both demotion and promotion.

The number of accesses are fixed and hence, the quicker the accessed pages
get promoted to DRAM, the sooner the benchmark is expected to finish.

DRAM-node			= 1
CXL-node			= 2
Initial DRAM alloc ratio	= 75%
Allocation-size			= 171798691840
Initial DRAM Alloc-size	=	 128849018880
Initial CXL Alloc-size		= 42949672960
Hot-region-size			= 1073741824
Nr-regions			= 160
Nr-regions DRAM			= 120 (provisioned but not accessed)
Nr-hot-regions CXL		= 40
Access pattern			= random
Access granularity		= 4096
Delay b/n accesses		= 0
Load/store ratio		= 50l50s
THP used			= no
Nr accesses			= 42949672960
Nr repetitions			= 1024

Time taken (microseconds, lower is better)
------------------------------------------------------
Source		Base		Patched		Change
------------------------------------------------------
NUMAB0		61,537,418	59,165,269	-3.8%
NUMAB2		62,070,563	63,087,940	+1.6%
pgtscan		NA		66,886,552	NA
hwhints		NA		63,35,4394	NA
------------------------------------------------------

Pages migrated (pgpromote_success)
---------------------------------------
Source		Base		Patched
---------------------------------------
NUMAB0		0		0
NUMAB2		0		0
pgtscan		NA		6481483
hwhints		NA		304
---------------------------------------

===============================================================
Scenario 3 - Numbers from folio_mark_accessed() (FMA) as source
===============================================================
Single threaded microbenchmark that provisions a file of 2G size on
CXL node initially, runs on Node 0 and reads random file pages at
4k granularity iteratively and repetitively. FMA source detects the
reads on unmapped page cache pages residing on CXL node and mark
them for promotion.
------------------------------------------------------------------
			Base		Patched		Patched
					FMA source	FMA cource
					Disabled	Enabled
------------------------------------------------------------------
Time taken(us)		96,511,260	119,332,436	82,807,865
pgpromote_success	0		0		524242
------------------------------------------------------------------

Results summary
===============
- The observations from v3 pretty much remain the same for 1st
  and 2nd scenarios.
- FMA source: Compared to the base kernel, the time taken to complete
  the file accesses decreases with promotion of file pages in the patched
  version. However when the FMA source isn't enabled we see a regression
  compared to base that needs to be investigated.

This v4 patchset applies on top of upstream commit 4941a17751c9 and
can be fetched from:

https://github.com/AMDESE/linux-mm/tree/bharata/pghot-rfcv4

v3: https://lore.kernel.org/linux-mm/20251110052343.208768-1-bharata@amd.com/
v2: https://lore.kernel.org/linux-mm/20250910144653.212066-1-bharata@amd.com/
v1: https://lore.kernel.org/linux-mm/20250814134826.154003-1-bharata@amd.com/
v0: https://lore.kernel.org/linux-mm/20250306054532.221138-1-bharata@amd.com/

TODOs
=====
- Check if the page is still within the hotness time window when
  kmigrated gets to it.
- Bulk access reporting may be desirable for sources like IBS.
- Take care of memory hotplug for allocation/freeing of mem_section->hot_map.
- Currently I am defaulting to node 0 if target NID isn't specified by the
  source. The best fallback target node may have to determined dynamically.
- Provide compatibility alias for the sysctls moved from sched to pghot.
- Wider testing and benchmark coverage.
- Address Ying Huang's comment about merging migrate_misplaced_folio()
  and migrate_misplaced_folios_batch() and correctly handling memcg
  stats counting properly in the latter.


Bharata B Rao (6):
  mm: migrate: Allow misplaced migration without VMA too
  mm: Hot page tracking and promotion
  x86: ibs: In-kernel IBS driver for memory access profiling
  x86: ibs: Enable IBS profiling for memory accesses
  mm: sched: Move hot page promotion from NUMAB=2 to pghot tracking
  mm: pghot: Add folio_mark_accessed() as hotness source

Gregory Price (1):
  migrate: implement migrate_misplaced_folios_batch

Kinsey Ho (2):
  mm: mglru: generalize page table walk
  mm: klruscand: use mglru scanning for page promotion

 Documentation/admin-guide/mm/pghot.txt |  64 +++
 arch/x86/events/amd/ibs.c              |  10 +
 arch/x86/include/asm/entry-common.h    |   3 +
 arch/x86/include/asm/hardirq.h         |   2 +
 arch/x86/include/asm/msr-index.h       |  16 +
 arch/x86/mm/Makefile                   |   1 +
 arch/x86/mm/ibs.c                      | 348 ++++++++++++++++
 include/linux/migrate.h                |   6 +
 include/linux/mmzone.h                 |  19 +
 include/linux/pghot.h                  |  87 ++++
 include/linux/vm_event_item.h          |  26 ++
 kernel/sched/debug.c                   |   1 -
 kernel/sched/fair.c                    | 152 +------
 mm/Kconfig                             |  32 ++
 mm/Makefile                            |   2 +
 mm/huge_memory.c                       |  26 +-
 mm/internal.h                          |   4 +
 mm/klruscand.c                         | 110 +++++
 mm/memory.c                            |  31 +-
 mm/migrate.c                           |  41 +-
 mm/mm_init.c                           |  10 +
 mm/pghot-debug.c                       | 187 +++++++++
 mm/pghot.c                             | 533 +++++++++++++++++++++++++
 mm/swap.c                              |   8 +
 mm/vmscan.c                            | 181 ++++++---
 mm/vmstat.c                            |  26 ++
 26 files changed, 1686 insertions(+), 240 deletions(-)
 create mode 100644 Documentation/admin-guide/mm/pghot.txt
 create mode 100644 arch/x86/mm/ibs.c
 create mode 100644 include/linux/pghot.h
 create mode 100644 mm/klruscand.c
 create mode 100644 mm/pghot-debug.c
 create mode 100644 mm/pghot.c

-- 
2.34.1

[RFC PATCH v4 1/9] mm: migrate: Allow misplaced migration without VMA too

[Bharata B Rao]

We want isolation of misplaced folios to work in contexts
where VMA isn't available, typically when performing migrations
from a kernel thread context. In order to prepare for that
allow migrate_misplaced_folio_prepare() to be called with
a NULL VMA.

When migrate_misplaced_folio_prepare() is called with non-NULL
VMA, it will check if the folio is mapped shared and that requires
holding PTL lock. This path isn't taken when the function is
invoked with NULL VMA (migration outside of process context).
Hence for such cases, it is not necessary this function be
called with PTL lock held.

Signed-off-by: Bharata B Rao <bharata@amd.com>
---
 mm/migrate.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index c0e9f15be2a2..189d0548d4ce 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2644,7 +2644,8 @@ static struct folio *alloc_misplaced_dst_folio(struct folio *src,
 
 /*
  * Prepare for calling migrate_misplaced_folio() by isolating the folio if
- * permitted. Must be called with the PTL still held.
+ * permitted. Must be called with the PTL still held if called with a non-NULL
+ * vma.
  */
 int migrate_misplaced_folio_prepare(struct folio *folio,
 		struct vm_area_struct *vma, int node)
@@ -2661,7 +2662,7 @@ int migrate_misplaced_folio_prepare(struct folio *folio,
 		 * See folio_maybe_mapped_shared() on possible imprecision
 		 * when we cannot easily detect if a folio is shared.
 		 */
-		if ((vma->vm_flags & VM_EXEC) && folio_maybe_mapped_shared(folio))
+		if (vma && (vma->vm_flags & VM_EXEC) && folio_maybe_mapped_shared(folio))
 			return -EACCES;
 
 		/*
-- 
2.34.1

[RFC PATCH v4 2/9] migrate: implement migrate_misplaced_folios_batch

[Bharata B Rao]

From: Gregory Price <gourry@gourry.net>

Tiered memory systems often require migrating multiple folios at once.
Currently, migrate_misplaced_folio() handles only one folio per call,
which is inefficient for batch operations. This patch introduces
migrate_misplaced_folios_batch(), a batch variant that leverages
migrate_pages() internally for improved performance.

The caller must isolate folios beforehand using
migrate_misplaced_folio_prepare(). On return, the folio list will be
empty regardless of success or failure.

Signed-off-by: Gregory Price <gourry@gourry.net>
[Rewrote commit description]
Signed-off-by: Bharata B Rao <bharata@amd.com>
---
 include/linux/migrate.h |  6 ++++++
 mm/migrate.c            | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 1f0ac122c3bf..2ace66772c16 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -103,6 +103,7 @@ static inline int set_movable_ops(const struct movable_operations *ops, enum pag
 int migrate_misplaced_folio_prepare(struct folio *folio,
 		struct vm_area_struct *vma, int node);
 int migrate_misplaced_folio(struct folio *folio, int node);
+int migrate_misplaced_folios_batch(struct list_head *foliolist, int node);
 #else
 static inline int migrate_misplaced_folio_prepare(struct folio *folio,
 		struct vm_area_struct *vma, int node)
@@ -113,6 +114,11 @@ static inline int migrate_misplaced_folio(struct folio *folio, int node)
 {
 	return -EAGAIN; /* can't migrate now */
 }
+static inline int migrate_misplaced_folios_batch(struct list_head *foliolist,
+						 int node)
+{
+	return -EAGAIN; /* can't migrate now */
+}
 #endif /* CONFIG_NUMA_BALANCING */
 
 #ifdef CONFIG_MIGRATION
diff --git a/mm/migrate.c b/mm/migrate.c
index 189d0548d4ce..2bf756123d55 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2739,5 +2739,41 @@ int migrate_misplaced_folio(struct folio *folio, int node)
 	BUG_ON(!list_empty(&migratepages));
 	return nr_remaining ? -EAGAIN : 0;
 }
+
+/**
+ * migrate_misplaced_folios_batch - Batch variant of migrate_misplaced_folio.
+ * Attempts to migrate a folio list to the specified destination.
+ * @folio_list - Isolated list of folios to be batch-migrated.
+ * @node - The NUMA node ID to where the folios should be migrated.
+ *
+ * Caller is expected to have isolated the folios by calling
+ * migrate_misplaced_folio_prepare(), which will result in an
+ * elevated reference count on the folio.
+ *
+ * This function will un-isolate the folios, dereference them, and
+ * remove them from the list before returning.
+ *
+ * Return: 0 on success and -EAGAIN on failure or partial migration.
+ *         On return, @folio_list will be empty regardless of success/failure.
+ */
+int migrate_misplaced_folios_batch(struct list_head *folio_list, int node)
+{
+	pg_data_t *pgdat = NODE_DATA(node);
+	unsigned int nr_succeeded;
+	int nr_remaining;
+
+	nr_remaining = migrate_pages(folio_list, alloc_misplaced_dst_folio,
+				     NULL, node, MIGRATE_ASYNC,
+				     MR_NUMA_MISPLACED, &nr_succeeded);
+	if (nr_remaining)
+		putback_movable_pages(folio_list);
+
+	if (nr_succeeded) {
+		count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
+		mod_node_page_state(pgdat, PGPROMOTE_SUCCESS, nr_succeeded);
+	}
+	BUG_ON(!list_empty(folio_list));
+	return nr_remaining ? -EAGAIN : 0;
+}
 #endif /* CONFIG_NUMA_BALANCING */
 #endif /* CONFIG_NUMA */
-- 
2.34.1

[RFC PATCH v4 3/9] mm: Hot page tracking and promotion

[Bharata B Rao]

This introduces a sub-system for collecting memory access
information from different sources. It maintains the hotness
information based on the access history and time of access.

Additionally, it provides per-lowertier-node kernel threads
(named kmigrated) that periodically promote the pages that
are eligible for promotion.

Sub-systems that generate hot page access info can report that
using this API:

int pghot_record_access(unsigned long pfn, int nid, int src,
                        unsigned long time)

@pfn: The PFN of the memory accessed
@nid: The accessing NUMA node ID
@src: The temperature source (sub-system) that generated the
      access info
@time: The access time in jiffies

Some temperature sources may not provide the nid from which
the page was accessed. This is true for sources that use
page table scanning for PTE Accessed bit. For such sources,
the default toptier node to which such pages should be promoted
is hard coded.

The hotness information is stored for every page of lower
tier memory in an unsigned long variable that is part of
mem_section data structure.

kmigrated is a per-lowertier-node kernel thread that migrates
the folios marked for migration in batches. Each kmigrated
thread walks the PFN range spanning its node and checks
for potential migration candidates.

A bunch of tunables for enabling different hotness sources,
setting target_nid, frequency threshold are provided in debugfs.

Signed-off-by: Bharata B Rao <bharata@amd.com>
---
 Documentation/admin-guide/mm/pghot.txt |  63 ++++
 include/linux/mmzone.h                 |  14 +
 include/linux/pghot.h                  |  71 +++++
 include/linux/vm_event_item.h          |   6 +
 mm/Kconfig                             |  11 +
 mm/Makefile                            |   1 +
 mm/mm_init.c                           |  10 +
 mm/pghot-debug.c                       | 180 +++++++++++
 mm/pghot.c                             | 402 +++++++++++++++++++++++++
 mm/vmstat.c                            |   6 +
 10 files changed, 764 insertions(+)
 create mode 100644 Documentation/admin-guide/mm/pghot.txt
 create mode 100644 include/linux/pghot.h
 create mode 100644 mm/pghot-debug.c
 create mode 100644 mm/pghot.c

diff --git a/Documentation/admin-guide/mm/pghot.txt b/Documentation/admin-guide/mm/pghot.txt
new file mode 100644
index 000000000000..13b87bcfa6a4
--- /dev/null
+++ b/Documentation/admin-guide/mm/pghot.txt
@@ -0,0 +1,63 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================
+PGHOT: Hot Page Tracking Tunables
+=================================
+
+Overview
+========
+The PGHOT subsystem tracks frequently accessed pages in lower-tier memory and
+promotes them to faster tiers. It uses per-PFN hotness metadata and asynchronous
+migration via per-node kernel threads (kmigrated).
+
+This document describes tunables available via **debugfs** and **sysctl** for
+PGHOT.
+
+Debugfs Interface
+=================
+Path: /sys/kernel/debug/pghot/
+
+1. **enabled_sources**
+   - Bitmask to enable/disable hotness sources.
+   - Bits:
+     - 0: Hardware hints (value 0x1)
+     - 1: Page table scan (value 0x2)
+     - 2: Hint faults (value 0x4)
+   - Default: 0 (disabled)
+   - Example:
+     # echo 0x7 > /sys/kernel/debug/pghot/enabled_sources
+     Enables all sources.
+
+2. **target_nid**
+   - NUMA node ID to which hot pages should be promoted when source does not provide nid.
+   - Default: 0
+   - Example:
+     # echo 1 > /sys/kernel/debug/pghot/target_nid
+
+3. **freq_threshold**
+   - Minimum access frequency before a page is marked ready for promotion.
+   - Range: 1 to 8
+   - Default: 2
+   - Example:
+     # echo 3 > /sys/kernel/debug/pghot/freq_threshold
+
+4. **kmigrated_sleep_ms**
+   - Sleep interval (ms) for kmigrated thread between scans.
+   - Default: 100
+
+5. **kmigrated_batch_nr**
+   - Maximum number of folios migrated in one batch.
+   - Default: 512
+
+Sysctl Interface
+================
+1. pghot_promote_freq_window_ms
+
+Path: /proc/sys/vm/pghot_promote_freq_window_ms
+
+- Controls the time window (in ms) for counting access frequency. A page is
+  considered hot only when **freq_threshold** number of accesses occur with
+  this time period.
+- Default: 5000 (5 seconds)
+- Example:
+  # sysctl vm.pghot_promote_freq_window_ms=3000
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 7fb7331c5725..fde851990394 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1068,6 +1068,7 @@ enum pgdat_flags {
 					 * many pages under writeback
 					 */
 	PGDAT_RECLAIM_LOCKED,		/* prevents concurrent reclaim */
+	PGDAT_KMIGRATED_ACTIVATE,	/* activates kmigrated */
 };
 
 enum zone_flags {
@@ -1522,6 +1523,10 @@ typedef struct pglist_data {
 #ifdef CONFIG_MEMORY_FAILURE
 	struct memory_failure_stats mf_stats;
 #endif
+#ifdef CONFIG_PGHOT
+	struct task_struct *kmigrated;
+	wait_queue_head_t kmigrated_wait;
+#endif
 } pg_data_t;
 
 #define node_present_pages(nid)	(NODE_DATA(nid)->node_present_pages)
@@ -1920,12 +1925,21 @@ struct mem_section {
 	unsigned long section_mem_map;
 
 	struct mem_section_usage *usage;
+#ifdef CONFIG_PGHOT
+	/*
+	 * Per-PFN hotness data for this section.
+	 */
+	unsigned long *hot_map;
+#endif
 #ifdef CONFIG_PAGE_EXTENSION
 	/*
 	 * If SPARSEMEM, pgdat doesn't have page_ext pointer. We use
 	 * section. (see page_ext.h about this.)
 	 */
 	struct page_ext *page_ext;
+#endif
+#if (defined(CONFIG_PGHOT) && !defined(CONFIG_PAGE_EXTENSION)) || \
+		(!defined(CONFIG_PGHOT) && defined(CONFIG_PAGE_EXTENSION))
 	unsigned long pad;
 #endif
 	/*
diff --git a/include/linux/pghot.h b/include/linux/pghot.h
new file mode 100644
index 000000000000..802240d574a6
--- /dev/null
+++ b/include/linux/pghot.h
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PGHOT_H
+#define _LINUX_PGHOT_H
+
+/* Page hotness temperature sources */
+enum pghot_src {
+	PGHOT_HW_HINTS,
+	PGHOT_PGTABLE_SCAN,
+	PGHOT_HINT_FAULT,
+};
+
+#ifdef CONFIG_PGHOT
+/*
+ * Bit positions to enable individual sources in pghot/records_enabled
+ * of debugfs.
+ */
+enum pghot_src_enabed {
+	PGHOT_HWHINTS_BIT	= 0,
+	PGHOT_PGTSCAN_BIT,
+	PGHOT_HINTFAULT_BIT,
+	PGHOT_MAX_BIT
+};
+
+#define PGHOT_HWHINTS_ENABLED	BIT(PGHOT_HWHINTS_BIT)
+#define PGHOT_PGTSCAN_ENABLED	BIT(PGHOT_PGTSCAN_BIT)
+#define PGHOT_HINTFAULT_ENABLED	BIT(PGHOT_HINTFAULT_BIT)
+#define PGHOT_SRC_ENABLED_MASK	GENMASK(PGHOT_MAX_BIT - 1, 0)
+
+#define PGHOT_DEFAULT_FREQ_WINDOW	(5 * MSEC_PER_SEC)
+#define PGHOT_DEFAULT_FREQ_THRESHOLD	2
+
+#define KMIGRATED_DEFAULT_SLEEP_MS	100
+#define KMIGRATED_DEFAULT_BATCH_NR	512
+
+#define PGHOT_DEFAULT_NODE	0
+
+/*
+ * Bits 0-31 are used to store nid, frequency and time.
+ * Bits 32-62 are unused now.
+ * Bit 63 is used to indicate the page is ready for migration.
+ */
+#define PGHOT_MIGRATE_READY	63
+
+#define PGHOT_NID_WIDTH		10
+#define PGHOT_FREQ_WIDTH	3
+/* time is stored in 19 bits which can represent up to 8.73s with HZ=1000 */
+#define PGHOT_TIME_WIDTH	19
+
+#define PGHOT_NID_SHIFT		0
+#define PGHOT_FREQ_SHIFT	(PGHOT_NID_SHIFT + PGHOT_NID_WIDTH)
+#define PGHOT_TIME_SHIFT	(PGHOT_FREQ_SHIFT + PGHOT_FREQ_WIDTH)
+
+#define PGHOT_NID_MASK		((1UL << PGHOT_NID_SHIFT) - 1)
+#define PGHOT_FREQ_MASK		((1UL << PGHOT_FREQ_SHIFT) - 1)
+#define PGHOT_TIME_MASK		((1UL << PGHOT_TIME_SHIFT) - 1)
+
+#define PGHOT_NID_MAX		(1 << PGHOT_NID_WIDTH)
+#define PGHOT_FREQ_MAX		(1 << PGHOT_FREQ_WIDTH)
+#define PGHOT_TIME_MAX		(1 << PGHOT_TIME_WIDTH)
+
+#define PGHOT_SECTION_HOT_BIT	BIT(0)
+#define PGHOT_SECTION_HOT_MASK	GENMASK(PGHOT_SECTION_HOT_BIT - 1, 0)
+
+int pghot_record_access(unsigned long pfn, int nid, int src, unsigned long now);
+#else
+static inline int pghot_record_access(unsigned long pfn, int nid, int src, unsigned long now)
+{
+	return 0;
+}
+#endif /* CONFIG_PGHOT */
+#endif /* _LINUX_PGHOT_H */
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 92f80b4d69a6..5b8fd93b55fd 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -188,6 +188,12 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		KSTACK_REST,
 #endif
 #endif /* CONFIG_DEBUG_STACK_USAGE */
+#ifdef CONFIG_PGHOT
+		PGHOT_RECORDED_ACCESSES,
+		PGHOT_RECORD_HWHINTS,
+		PGHOT_RECORD_PGTSCANS,
+		PGHOT_RECORD_HINTFAULTS,
+#endif /* CONFIG_PGHOT */
 		NR_VM_EVENT_ITEMS
 };
 
diff --git a/mm/Kconfig b/mm/Kconfig
index ca3f146bc705..472975da69e1 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1379,6 +1379,17 @@ config PT_RECLAIM
 config FIND_NORMAL_PAGE
 	def_bool n
 
+config PGHOT
+	bool "Hot page tracking and promotion"
+	def_bool n
+	depends on NUMA && MIGRATION && SPARSEMEM && MMU
+	help
+	  A sub-system to track page accesses in lower tier memory and
+	  maintain hot page information. Promotes hot pages from lower
+	  tiers to top tier by using the memory access information provided
+	  by various sources. Asynchronous promotion is done by per-node
+	  kernel threads.
+
 source "mm/damon/Kconfig"
 
 endmenu
diff --git a/mm/Makefile b/mm/Makefile
index 21abb3353550..a6fac171c36e 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -146,3 +146,4 @@ obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
 obj-$(CONFIG_EXECMEM) += execmem.o
 obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o
 obj-$(CONFIG_PT_RECLAIM) += pt_reclaim.o
+obj-$(CONFIG_PGHOT) += pghot.o
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 7712d887b696..c2a8e5309417 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1401,6 +1401,15 @@ static void pgdat_init_kcompactd(struct pglist_data *pgdat)
 static void pgdat_init_kcompactd(struct pglist_data *pgdat) {}
 #endif
 
+#ifdef CONFIG_PGHOT
+static void pgdat_init_kmigrated(struct pglist_data *pgdat)
+{
+	init_waitqueue_head(&pgdat->kmigrated_wait);
+}
+#else
+static inline void pgdat_init_kmigrated(struct pglist_data *pgdat) {}
+#endif
+
 static void __meminit pgdat_init_internals(struct pglist_data *pgdat)
 {
 	int i;
@@ -1410,6 +1419,7 @@ static void __meminit pgdat_init_internals(struct pglist_data *pgdat)
 
 	pgdat_init_split_queue(pgdat);
 	pgdat_init_kcompactd(pgdat);
+	pgdat_init_kmigrated(pgdat);
 
 	init_waitqueue_head(&pgdat->kswapd_wait);
 	init_waitqueue_head(&pgdat->pfmemalloc_wait);
diff --git a/mm/pghot-debug.c b/mm/pghot-debug.c
new file mode 100644
index 000000000000..b6bee0f32389
--- /dev/null
+++ b/mm/pghot-debug.c
@@ -0,0 +1,180 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * pghot tunables in debugfs
+ */
+#include <linux/debugfs.h>
+
+static struct dentry *debugfs_pghot;
+
+static ssize_t pghot_freq_th_write(struct file *filp, const char __user *ubuf,
+				   size_t cnt, loff_t *ppos)
+{
+	char buf[16];
+	unsigned int freq;
+
+	if (cnt > 15)
+		cnt = 15;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+	buf[cnt] = '\0';
+
+	if (kstrtouint(buf, 10, &freq))
+		return -EINVAL;
+
+	if (!freq || freq > PGHOT_FREQ_MAX)
+		return -EINVAL;
+
+	pghot_freq_threshold = freq;
+
+	*ppos += cnt;
+	return cnt;
+}
+
+static int pghot_freq_th_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "%d\n", pghot_freq_threshold);
+	return 0;
+}
+
+static int pghot_freq_th_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, pghot_freq_th_show, NULL);
+}
+
+static const struct file_operations pghot_freq_th_fops = {
+	.open		= pghot_freq_th_open,
+	.write		= pghot_freq_th_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static ssize_t pghot_target_nid_write(struct file *filp, const char __user *ubuf,
+				      size_t cnt, loff_t *ppos)
+{
+	char buf[16];
+	unsigned int nid;
+
+	if (cnt > 15)
+		cnt = 15;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+	buf[cnt] = '\0';
+
+	if (kstrtouint(buf, 10, &nid))
+		return -EINVAL;
+
+	if (nid > PGHOT_NID_MAX || !node_online(nid) || !node_is_toptier(nid))
+		return -EINVAL;
+	pghot_target_nid = nid;
+
+	*ppos += cnt;
+	return cnt;
+}
+
+static int pghot_target_nid_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "%d\n", pghot_target_nid);
+	return 0;
+}
+
+static int pghot_target_nid_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, pghot_target_nid_show, NULL);
+}
+
+static const struct file_operations pghot_target_nid_fops = {
+	.open		= pghot_target_nid_open,
+	.write		= pghot_target_nid_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static void pghot_src_enabled_update(unsigned int enabled)
+{
+	unsigned int changed = pghot_src_enabled ^ enabled;
+
+	if (changed & PGHOT_HWHINTS_ENABLED) {
+		if (enabled & PGHOT_HWHINTS_ENABLED)
+			static_branch_enable(&pghot_src_hwhints);
+		else
+			static_branch_disable(&pghot_src_hwhints);
+	}
+
+	if (changed & PGHOT_PGTSCAN_ENABLED) {
+		if (enabled & PGHOT_PGTSCAN_ENABLED)
+			static_branch_enable(&pghot_src_pghtscans);
+		else
+			static_branch_disable(&pghot_src_pghtscans);
+	}
+
+	if (changed & PGHOT_HINTFAULT_ENABLED) {
+		if (enabled & PGHOT_HINTFAULT_ENABLED)
+			static_branch_enable(&pghot_src_hintfaults);
+		else
+			static_branch_disable(&pghot_src_hintfaults);
+	}
+}
+
+static ssize_t pghot_src_enabled_write(struct file *filp, const char __user *ubuf,
+					   size_t cnt, loff_t *ppos)
+{
+	char buf[16];
+	unsigned int enabled;
+
+	if (cnt > 15)
+		cnt = 15;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+	buf[cnt] = '\0';
+
+	if (kstrtouint(buf, 0, &enabled))
+		return -EINVAL;
+
+	if (enabled & ~PGHOT_SRC_ENABLED_MASK)
+		return -EINVAL;
+
+	pghot_src_enabled_update(enabled);
+	pghot_src_enabled = enabled;
+
+	*ppos += cnt;
+	return cnt;
+}
+
+static int pghot_src_enabled_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "%d\n", pghot_src_enabled);
+	return 0;
+}
+
+static int pghot_src_enabled_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, pghot_src_enabled_show, NULL);
+}
+
+static const struct file_operations pghot_src_enabled_fops = {
+	.open		= pghot_src_enabled_open,
+	.write		= pghot_src_enabled_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static void pghot_debug_init(void)
+{
+	debugfs_pghot = debugfs_create_dir("pghot", NULL);
+	debugfs_create_file("enabled_sources", 0644, debugfs_pghot, NULL,
+			    &pghot_src_enabled_fops);
+	debugfs_create_file("target_nid", 0644, debugfs_pghot, NULL,
+			    &pghot_target_nid_fops);
+	debugfs_create_file("freq_threshold", 0644, debugfs_pghot, NULL,
+			    &pghot_freq_th_fops);
+	debugfs_create_u32("kmigrated_sleep_ms", 0644, debugfs_pghot,
+			    &kmigrated_sleep_ms);
+	debugfs_create_u32("kmigrated_batch_nr", 0644, debugfs_pghot,
+			    &kmigrated_batch_nr);
+}
diff --git a/mm/pghot.c b/mm/pghot.c
new file mode 100644
index 000000000000..a3f52d4e8750
--- /dev/null
+++ b/mm/pghot.c
@@ -0,0 +1,402 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Maintains information about hot pages from slower tier nodes and
+ * promotes them.
+ *
+ * Per-PFN hotness information is stored for lower tier nodes in
+ * mem_section. An unsigned long variable is used to store the
+ * frequency of access, last access time and the nid to which the
+ * page needs to be migrated.
+ *
+ * A kernel thread named kmigrated is provided to migrate or promote
+ * the hot pages. kmigrated runs for each lower tier node. It iterates
+ * over the node's PFNs and  migrates pages marked for migration into
+ * their targeted nodes.
+ */
+#include <linux/mm.h>
+#include <linux/migrate.h>
+#include <linux/memory-tiers.h>
+#include <linux/cpuhotplug.h>
+#include <linux/pghot.h>
+
+static unsigned int pghot_target_nid = PGHOT_DEFAULT_NODE;
+static unsigned int pghot_src_enabled;
+static unsigned int pghot_freq_threshold = PGHOT_DEFAULT_FREQ_THRESHOLD;
+static unsigned int kmigrated_sleep_ms = KMIGRATED_DEFAULT_SLEEP_MS;
+static unsigned int kmigrated_batch_nr = KMIGRATED_DEFAULT_BATCH_NR;
+
+static unsigned int sysctl_pghot_freq_window = PGHOT_DEFAULT_FREQ_WINDOW;
+
+static DEFINE_STATIC_KEY_FALSE(pghot_src_hwhints);
+static DEFINE_STATIC_KEY_FALSE(pghot_src_pghtscans);
+static DEFINE_STATIC_KEY_FALSE(pghot_src_hintfaults);
+
+#include "pghot-debug.c"
+
+#ifdef CONFIG_SYSCTL
+static const struct ctl_table pghot_sysctls[] = {
+	{
+		.procname       = "pghot_promote_freq_window_ms",
+		.data           = &sysctl_pghot_freq_window,
+		.maxlen         = sizeof(unsigned int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec_minmax,
+		.extra1         = SYSCTL_ZERO,
+	},
+};
+#endif
+
+static bool kmigrated_started __ro_after_init;
+
+/**
+ *
+ * pghot_record_access - Record page accesses from lower tier memory
+ * for the purpose of tracking page hotness and subsequent promotion.
+ *
+ * @pfn - PFN of the page
+ * @nid - Target NID to were the page needs to be migrated
+ * @src - The identifier of the sub-system that reports the access
+ * @now - Access time in jiffies
+ *
+ * Updates the NID, frequency and time of access and marks the page as
+ * ready for migration if the frequency crosses a threshold. The pages
+ * marked for migration are migrated by kmigrated kernel thread.
+ *
+ * Return: 0 on success and -EAGAIN on failure to record the access.
+ */
+int pghot_record_access(unsigned long pfn, int nid, int src, unsigned long now)
+{
+	unsigned long *phi, *hot_map, old_hotness, hotness;
+	unsigned long time = now & PGHOT_TIME_MASK;
+	unsigned long old_nid, old_freq, old_time;
+	bool new_window = false;
+	struct mem_section *ms;
+	struct folio *folio;
+	struct page *page;
+	unsigned long freq;
+
+	if (!kmigrated_started)
+		return -EINVAL;
+
+	if (nid >= PGHOT_NID_MAX)
+		return -EINVAL;
+
+	switch (src) {
+	case PGHOT_HW_HINTS:
+		if (!static_branch_likely(&pghot_src_hwhints))
+			return -EINVAL;
+		count_vm_event(PGHOT_RECORD_HWHINTS);
+		break;
+	case PGHOT_PGTABLE_SCAN:
+		if (!static_branch_likely(&pghot_src_pghtscans))
+			return -EINVAL;
+		count_vm_event(PGHOT_RECORD_PGTSCANS);
+		break;
+	case PGHOT_HINT_FAULT:
+		if (!static_branch_likely(&pghot_src_hintfaults))
+			return -EINVAL;
+		count_vm_event(PGHOT_RECORD_HINTFAULTS);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/*
+	 * Record only accesses from lower tiers.
+	 */
+	if (node_is_toptier(pfn_to_nid(pfn)))
+		return 0;
+
+	/*
+	 * Reject the non-migratable pages right away.
+	 */
+	page = pfn_to_online_page(pfn);
+	if (!page || is_zone_device_page(page))
+		return 0;
+
+	folio = page_folio(page);
+	if (!folio_test_lru(folio))
+		return 0;
+
+	/* Get the hotness slot corresponding to the 1st PFN of the folio */
+	pfn = folio_pfn(folio);
+	ms = __pfn_to_section(pfn);
+	if (!ms)
+		return -EINVAL;
+	hot_map = (unsigned long *)(((unsigned long)(ms->hot_map)) & ~PGHOT_SECTION_HOT_MASK);
+	phi = &hot_map[pfn % PAGES_PER_SECTION];
+
+	count_vm_event(PGHOT_RECORDED_ACCESSES);
+	/*
+	 * Update the hotness parameters.
+	 */
+	old_hotness = READ_ONCE(*phi);
+	do {
+		hotness = old_hotness;
+		old_nid = (hotness >> PGHOT_NID_SHIFT) & PGHOT_NID_MASK;
+		old_freq = (hotness >> PGHOT_FREQ_SHIFT) & PGHOT_FREQ_MASK;
+		old_time = (hotness >> PGHOT_TIME_SHIFT) & PGHOT_TIME_MASK;
+
+		if (((time - old_time) > msecs_to_jiffies(sysctl_pghot_freq_window))
+		    || (nid != NUMA_NO_NODE && old_nid != nid))
+			new_window = true;
+
+		if (new_window)
+			freq = 1;
+		else if (old_freq < PGHOT_FREQ_MAX)
+			freq = old_freq + 1;
+		nid = (nid == NUMA_NO_NODE) ? pghot_target_nid : nid;
+
+		hotness &= ~(PGHOT_NID_MASK << PGHOT_NID_SHIFT);
+		hotness &= ~(PGHOT_FREQ_MASK << PGHOT_FREQ_SHIFT);
+		hotness &= ~(PGHOT_TIME_MASK << PGHOT_TIME_SHIFT);
+
+		hotness |= (nid & PGHOT_NID_MASK) << PGHOT_NID_SHIFT;
+		hotness |= (freq & PGHOT_FREQ_MASK) << PGHOT_FREQ_SHIFT;
+		hotness |= (time & PGHOT_TIME_MASK) << PGHOT_TIME_SHIFT;
+
+		if (freq >= pghot_freq_threshold)
+			set_bit(PGHOT_MIGRATE_READY, &hotness);
+	} while (unlikely(!try_cmpxchg(phi, &old_hotness, hotness)));
+
+	if (test_bit(PGHOT_MIGRATE_READY, &hotness)) {
+		set_bit(PGHOT_SECTION_HOT_BIT, ms->hot_map);
+		set_bit(PGDAT_KMIGRATED_ACTIVATE, &page_pgdat(page)->flags);
+	}
+	return 0;
+}
+
+static int pghot_get_hotness(unsigned long pfn, unsigned long *nid, unsigned long *freq,
+				    unsigned long *time)
+{
+	unsigned long *phi, old_hotness, hotness;
+	struct mem_section *ms;
+
+	ms = __pfn_to_section(pfn);
+	if (!ms)
+		return -EINVAL;
+
+	phi = &ms->hot_map[pfn % PAGES_PER_SECTION];
+	if (!test_and_clear_bit(PGHOT_MIGRATE_READY, phi))
+		return -EINVAL;
+
+	old_hotness = READ_ONCE(*phi);
+	do {
+		hotness = old_hotness;
+		*nid = (hotness >> PGHOT_NID_SHIFT) & PGHOT_NID_MASK;
+		*freq = (hotness >> PGHOT_FREQ_SHIFT) & PGHOT_FREQ_MASK;
+		*time = (hotness >> PGHOT_TIME_SHIFT) & PGHOT_TIME_MASK;
+		hotness = 0;
+
+	} while (unlikely(!try_cmpxchg(phi, &old_hotness, hotness)));
+	return 0;
+}
+
+/*
+ * Walks the PFNs of the zone, isolates and migrates them in batches.
+ */
+static void kmigrated_walk_zone(unsigned long start_pfn, unsigned long end_pfn,
+				int src_nid)
+{
+	int cur_nid = NUMA_NO_NODE;
+	LIST_HEAD(migrate_list);
+	int batch_count = 0;
+	struct folio *folio;
+	struct page *page;
+	unsigned long pfn;
+
+	pfn = start_pfn;
+	do {
+		unsigned long nid = NUMA_NO_NODE, freq = 0, time = 0, nr = 1;
+
+		if (!pfn_valid(pfn))
+			goto out_next;
+
+		page = pfn_to_online_page(pfn);
+		if (!page)
+			goto out_next;
+
+		folio = page_folio(page);
+		nr = folio_nr_pages(folio);
+		if (folio_nid(folio) != src_nid)
+			goto out_next;
+
+		if (!folio_test_lru(folio))
+			goto out_next;
+
+		if (pghot_get_hotness(pfn, &nid, &freq, &time))
+			goto out_next;
+
+		if (nid == NUMA_NO_NODE)
+			goto out_next;
+
+		if (folio_nid(folio) == nid)
+			goto out_next;
+
+		if (migrate_misplaced_folio_prepare(folio, NULL, nid))
+			goto out_next;
+
+		if (cur_nid != NUMA_NO_NODE)
+			cur_nid = nid;
+
+		if (++batch_count >= kmigrated_batch_nr || cur_nid != nid) {
+			migrate_misplaced_folios_batch(&migrate_list, cur_nid);
+			cur_nid = nid;
+			batch_count = 0;
+			cond_resched();
+		}
+		list_add(&folio->lru, &migrate_list);
+out_next:
+		pfn += nr;
+	} while (pfn < end_pfn);
+	if (!list_empty(&migrate_list))
+		migrate_misplaced_folios_batch(&migrate_list, cur_nid);
+}
+
+static void kmigrated_do_work(pg_data_t *pgdat)
+{
+	unsigned long section_nr, s_begin, start_pfn;
+	struct mem_section *ms;
+	int nid;
+
+	clear_bit(PGDAT_KMIGRATED_ACTIVATE, &pgdat->flags);
+	/* s_begin = first_present_section_nr(); */
+	s_begin = next_present_section_nr(-1);
+	for_each_present_section_nr(s_begin, section_nr) {
+		start_pfn = section_nr_to_pfn(section_nr);
+		ms = __nr_to_section(section_nr);
+
+		if (!pfn_valid(start_pfn))
+			continue;
+
+		nid = pfn_to_nid(start_pfn);
+		if (node_is_toptier(nid) || nid != pgdat->node_id)
+			continue;
+
+		if (!test_and_clear_bit(PGHOT_SECTION_HOT_BIT, ms->hot_map))
+			continue;
+
+		kmigrated_walk_zone(start_pfn, start_pfn + PAGES_PER_SECTION,
+				    pgdat->node_id);
+	}
+}
+
+static inline bool kmigrated_work_requested(pg_data_t *pgdat)
+{
+	return test_bit(PGDAT_KMIGRATED_ACTIVATE, &pgdat->flags);
+}
+
+/*
+ * Per-node kthread that iterates over its PFNs and migrates the
+ * pages that have been marked for migration.
+ */
+static int kmigrated(void *p)
+{
+	long timeout = msecs_to_jiffies(kmigrated_sleep_ms);
+	pg_data_t *pgdat = p;
+
+	while (!kthread_should_stop()) {
+		if (wait_event_timeout(pgdat->kmigrated_wait, kmigrated_work_requested(pgdat),
+				       timeout))
+			kmigrated_do_work(pgdat);
+	}
+	return 0;
+}
+
+static int kmigrated_run(int nid)
+{
+	pg_data_t *pgdat = NODE_DATA(nid);
+	int ret;
+
+	if (node_is_toptier(nid))
+		return 0;
+
+	if (!pgdat->kmigrated) {
+		pgdat->kmigrated = kthread_create_on_node(kmigrated, pgdat, nid,
+							  "kmigrated%d", nid);
+		if (IS_ERR(pgdat->kmigrated)) {
+			ret = PTR_ERR(pgdat->kmigrated);
+			pgdat->kmigrated = NULL;
+			pr_err("Failed to start kmigrated%d, ret %d\n", nid, ret);
+			return ret;
+		}
+		pr_info("pghot: Started kmigrated thread for node %d\n", nid);
+	}
+	wake_up_process(pgdat->kmigrated);
+	return 0;
+}
+
+static void pghot_free_hot_map(void)
+{
+	unsigned long section_nr, s_begin;
+	struct mem_section *ms;
+
+	/* s_begin = first_present_section_nr(); */
+	s_begin = next_present_section_nr(-1);
+	for_each_present_section_nr(s_begin, section_nr) {
+		ms = __nr_to_section(section_nr);
+		kfree(ms->hot_map);
+	}
+}
+
+static int pghot_alloc_hot_map(void)
+{
+	unsigned long section_nr, s_begin, start_pfn;
+	struct mem_section *ms;
+	int nid;
+
+	/* s_begin = first_present_section_nr(); */
+	s_begin = next_present_section_nr(-1);
+	for_each_present_section_nr(s_begin, section_nr) {
+		ms = __nr_to_section(section_nr);
+		start_pfn = section_nr_to_pfn(section_nr);
+		nid = pfn_to_nid(start_pfn);
+
+		if (node_is_toptier(nid) || !pfn_valid(start_pfn))
+			continue;
+
+		ms->hot_map = kcalloc_node(PAGES_PER_SECTION, sizeof(*ms->hot_map), GFP_KERNEL,
+					   nid);
+		if (!ms->hot_map)
+			goto out_free_hot_map;
+	}
+	return 0;
+
+out_free_hot_map:
+	pghot_free_hot_map();
+	return -ENOMEM;
+}
+
+static int __init pghot_init(void)
+{
+	pg_data_t *pgdat;
+	int nid, ret;
+
+	ret = pghot_alloc_hot_map();
+	if (ret)
+		return ret;
+
+	for_each_node_state(nid, N_MEMORY) {
+		ret = kmigrated_run(nid);
+		if (ret)
+			goto out_stop_kthread;
+	}
+	register_sysctl_init("vm", pghot_sysctls);
+	pghot_debug_init();
+
+	kmigrated_started = true;
+	return 0;
+
+out_stop_kthread:
+	for_each_node_state(nid, N_MEMORY) {
+		pgdat = NODE_DATA(nid);
+		if (pgdat->kmigrated) {
+			kthread_stop(pgdat->kmigrated);
+			pgdat->kmigrated = NULL;
+		}
+	}
+	pghot_free_hot_map();
+	return ret;
+}
+
+late_initcall_sync(pghot_init)
diff --git a/mm/vmstat.c b/mm/vmstat.c
index bb09c032eecf..10745e498e3a 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1496,6 +1496,12 @@ const char * const vmstat_text[] = {
 	[I(KSTACK_REST)]			= "kstack_rest",
 #endif
 #endif
+#ifdef CONFIG_PGHOT
+	[I(PGHOT_RECORDED_ACCESSES)]		= "pghot_recorded_accesses",
+	[I(PGHOT_RECORD_HWHINTS)]		= "pghot_recorded_hwhints",
+	[I(PGHOT_RECORD_PGTSCANS)]		= "pghot_recorded_pgtscans",
+	[I(PGHOT_RECORD_HINTFAULTS)]		= "pghot_recorded_hintfaults",
+#endif /* CONFIG_PGHOT */
 #undef I
 #endif /* CONFIG_VM_EVENT_COUNTERS */
 };
-- 
2.34.1

[RFC PATCH v4 4/9] x86: ibs: In-kernel IBS driver for memory access profiling

[Bharata B Rao]

Use IBS (Instruction Based Sampling) feature present
in AMD processors for memory access tracking. The access
information obtained from IBS via NMI is fed to pghot
sub-system for futher action.

In addition to many other information related to the memory
access, IBS provides physical (and virtual) address of the access
and indicates if the access came from slower tier. Only memory
accesses originating from slower tiers are further acted upon
by this driver.

The samples are initially accumulated in percpu buffers which
are flushed to pghot hot page tracking mechanism using irq_work.

TODO: Many counters are added to vmstat just as debugging aid
for now.

About IBS
---------
IBS can be programmed to provide data about instruction
execution periodically. This is done by programming a desired
sample count (number of ops) in a control register. When the
programmed number of ops are dispatched, a micro-op gets tagged,
various information about the tagged micro-op's execution is
populated in IBS execution MSRs and an interrupt is raised.
While IBS provides a lot of data for each sample, for the
purpose of  memory access profiling, we are interested in
linear and physical address of the memory access that reached
DRAM. Recent AMD processors provide further filtering where
it is possible to limit the sampling to those ops that had
an L3 miss which greately reduces the non-useful samples.

While IBS provides capability to sample instruction fetch
and execution, only IBS execution sampling is used here
to collect data about memory accesses that occur during
the instruction execution.

More information about IBS is available in Sec 13.3 of
AMD64 Architecture Programmer's Manual, Volume 2:System
Programming which is present at:
https://bugzilla.kernel.org/attachment.cgi?id=288923

Information about MSRs used for programming IBS can be
found in Sec 2.1.14.4 of PPR Vol 1 for AMD Family 19h
Model 11h B1 which is currently present at:
https://www.amd.com/system/files/TechDocs/55901_0.25.zip

Signed-off-by: Bharata B Rao <bharata@amd.com>
---
 arch/x86/events/amd/ibs.c        |  10 +
 arch/x86/include/asm/msr-index.h |  16 ++
 arch/x86/mm/Makefile             |   1 +
 arch/x86/mm/ibs.c                | 316 +++++++++++++++++++++++++++++++
 include/linux/pghot.h            |   6 +
 include/linux/vm_event_item.h    |  19 ++
 mm/Kconfig                       |  13 ++
 mm/vmstat.c                      |  19 ++
 8 files changed, 400 insertions(+)
 create mode 100644 arch/x86/mm/ibs.c

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 112f43b23ebf..e387c18c91f8 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -13,6 +13,7 @@
 #include <linux/ptrace.h>
 #include <linux/syscore_ops.h>
 #include <linux/sched/clock.h>
+#include <linux/pghot.h>
 
 #include <asm/apic.h>
 #include <asm/msr.h>
@@ -1756,6 +1757,15 @@ static __init int amd_ibs_init(void)
 {
 	u32 caps;
 
+	/*
+	 * TODO: Find a clean way to disable perf IBS so that IBS
+	 * can be used for memory access profiling.
+	 */
+	if (hwmem_access_profiler_inuse()) {
+		pr_info("IBS isn't available for perf use\n");
+		return 0;
+	}
+
 	caps = __get_ibs_caps();
 	if (!caps)
 		return -ENODEV;	/* ibs not supported by the cpu */
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 9e1720d73244..59657bd768c9 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -760,6 +760,22 @@
 /* AMD Last Branch Record MSRs */
 #define MSR_AMD64_LBR_SELECT			0xc000010e
 
+/* AMD IBS MSR bits */
+#define MSR_AMD64_IBSOPDATA2_DATASRC			0x7
+#define MSR_AMD64_IBSOPDATA2_DATASRC_LCL_CACHE		0x1
+#define MSR_AMD64_IBSOPDATA2_DATASRC_PEER_CACHE_NEAR	0x2
+#define MSR_AMD64_IBSOPDATA2_DATASRC_DRAM		0x3
+#define MSR_AMD64_IBSOPDATA2_DATASRC_FAR_CCX_CACHE	0x5
+#define MSR_AMD64_IBSOPDATA2_DATASRC_EXT_MEM		0x8
+#define	MSR_AMD64_IBSOPDATA2_RMTNODE			0x10
+
+#define MSR_AMD64_IBSOPDATA3_LDOP		BIT_ULL(0)
+#define MSR_AMD64_IBSOPDATA3_STOP		BIT_ULL(1)
+#define MSR_AMD64_IBSOPDATA3_DCMISS		BIT_ULL(7)
+#define MSR_AMD64_IBSOPDATA3_LADDR_VALID	BIT_ULL(17)
+#define MSR_AMD64_IBSOPDATA3_PADDR_VALID	BIT_ULL(18)
+#define MSR_AMD64_IBSOPDATA3_L2MISS		BIT_ULL(20)
+
 /* Zen4 */
 #define MSR_ZEN4_BP_CFG                 0xc001102e
 #define MSR_ZEN4_BP_CFG_BP_SPEC_REDUCE_BIT 4
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index 5b9908f13dcf..361a456582e9 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -57,3 +57,4 @@ obj-$(CONFIG_X86_MEM_ENCRYPT)	+= mem_encrypt.o
 obj-$(CONFIG_AMD_MEM_ENCRYPT)	+= mem_encrypt_amd.o
 
 obj-$(CONFIG_AMD_MEM_ENCRYPT)	+= mem_encrypt_boot.o
+obj-$(CONFIG_HWMEM_PROFILER)	+= ibs.o
diff --git a/arch/x86/mm/ibs.c b/arch/x86/mm/ibs.c
new file mode 100644
index 000000000000..946f3a82ca11
--- /dev/null
+++ b/arch/x86/mm/ibs.c
@@ -0,0 +1,316 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/init.h>
+#include <linux/pghot.h>
+#include <linux/percpu.h>
+#include <linux/workqueue.h>
+#include <linux/irq_work.h>
+
+#include <asm/nmi.h>
+#include <asm/perf_event.h> /* TODO: Move defns like IBS_OP_ENABLE into non-perf header */
+#include <asm/apic.h>
+
+bool hwmem_access_profiling;
+
+static u64 ibs_config __read_mostly;
+static u32 ibs_caps;
+
+#define IBS_NR_SAMPLES	150
+
+/*
+ * Basic access info captured for each memory access.
+ */
+struct ibs_sample {
+	unsigned long pfn;
+	unsigned long time;	/* jiffies when accessed */
+	int nid;		/* Accessing node ID, if known */
+};
+
+/*
+ * Percpu buffer of access samples. Samples are accumulated here
+ * before pushing them to pghot sub-system for further action.
+ */
+struct ibs_sample_pcpu {
+	struct ibs_sample samples[IBS_NR_SAMPLES];
+	int head, tail;
+};
+
+struct ibs_sample_pcpu __percpu *ibs_s;
+
+/*
+ * The workqueue for pushing the percpu access samples to pghot sub-system.
+ */
+static struct work_struct ibs_work;
+static struct irq_work ibs_irq_work;
+
+bool hwmem_access_profiler_inuse(void)
+{
+	return hwmem_access_profiling;
+}
+
+/*
+ * Record the IBS-reported access sample in percpu buffer.
+ * Called from IBS NMI handler.
+ */
+static int ibs_push_sample(unsigned long pfn, int nid, unsigned long time)
+{
+	struct ibs_sample_pcpu *ibs_pcpu = raw_cpu_ptr(ibs_s);
+	int next = ibs_pcpu->head + 1;
+
+	if (next >= IBS_NR_SAMPLES)
+		next = 0;
+
+	if (next == ibs_pcpu->tail)
+		return 0;
+
+	ibs_pcpu->samples[ibs_pcpu->head].pfn = pfn;
+	ibs_pcpu->samples[ibs_pcpu->head].time = time;
+	ibs_pcpu->head = next;
+	return 1;
+}
+
+static int ibs_pop_sample(struct ibs_sample *s)
+{
+	struct ibs_sample_pcpu *ibs_pcpu = raw_cpu_ptr(ibs_s);
+
+	int next = ibs_pcpu->tail + 1;
+
+	if (ibs_pcpu->head == ibs_pcpu->tail)
+		return 0;
+
+	if (next >= IBS_NR_SAMPLES)
+		next = 0;
+
+	*s = ibs_pcpu->samples[ibs_pcpu->tail];
+	ibs_pcpu->tail = next;
+	return 1;
+}
+
+/*
+ * Remove access samples from percpu buffer and send them
+ * to pghot sub-system for further action.
+ */
+static void ibs_work_handler(struct work_struct *work)
+{
+	struct ibs_sample s;
+
+	while (ibs_pop_sample(&s))
+		pghot_record_access(s.pfn, s.nid, PGHOT_HW_HINTS, s.time);
+}
+
+static void ibs_irq_handler(struct irq_work *i)
+{
+	schedule_work_on(smp_processor_id(), &ibs_work);
+}
+
+/*
+ * IBS NMI handler: Process the memory access info reported by IBS.
+ *
+ * Reads the MSRs to collect all the information about the reported
+ * memory access, validates the access, stores the valid sample and
+ * schedules the work on this CPU to further process the sample.
+ */
+static int ibs_overflow_handler(unsigned int cmd, struct pt_regs *regs)
+{
+	struct mm_struct *mm = current->mm;
+	u64 ops_ctl, ops_data3, ops_data2;
+	u64 laddr = -1, paddr = -1;
+	u64 data_src, rmt_node;
+	struct page *page;
+	unsigned long pfn;
+
+	rdmsrl(MSR_AMD64_IBSOPCTL, ops_ctl);
+
+	/*
+	 * When IBS sampling period is reprogrammed via read-modify-update
+	 * of MSR_AMD64_IBSOPCTL, overflow NMIs could be generated with
+	 * IBS_OP_ENABLE not set. For such cases, return as HANDLED.
+	 *
+	 * With this, the handler will say "handled" for all NMIs that
+	 * aren't related to this NMI.  This stems from the limitation of
+	 * having both status and control bits in one MSR.
+	 */
+	if (!(ops_ctl & IBS_OP_VAL))
+		goto handled;
+
+	wrmsrl(MSR_AMD64_IBSOPCTL, ops_ctl & ~IBS_OP_VAL);
+
+	count_vm_event(HWHINT_NR_EVENTS);
+
+	if (!user_mode(regs)) {
+		count_vm_event(HWHINT_KERNEL);
+		goto handled;
+	}
+
+	if (!mm) {
+		count_vm_event(HWHINT_KTHREAD);
+		goto handled;
+	}
+
+	rdmsrl(MSR_AMD64_IBSOPDATA3, ops_data3);
+
+	/* Load/Store ops only */
+	/* TODO: DataSrc isn't valid for stores, so filter out stores? */
+	if (!(ops_data3 & (MSR_AMD64_IBSOPDATA3_LDOP |
+			   MSR_AMD64_IBSOPDATA3_STOP))) {
+		count_vm_event(HWHINT_NON_LOAD_STORES);
+		goto handled;
+	}
+
+	/* Discard the sample if it was L1 or L2 hit */
+	if (!(ops_data3 & (MSR_AMD64_IBSOPDATA3_DCMISS |
+			   MSR_AMD64_IBSOPDATA3_L2MISS))) {
+		count_vm_event(HWHINT_DC_L2_HITS);
+		goto handled;
+	}
+
+	rdmsrl(MSR_AMD64_IBSOPDATA2, ops_data2);
+	data_src = ops_data2 & MSR_AMD64_IBSOPDATA2_DATASRC;
+	if (ibs_caps & IBS_CAPS_ZEN4)
+		data_src |= ((ops_data2 & 0xC0) >> 3);
+
+	switch (data_src) {
+	case MSR_AMD64_IBSOPDATA2_DATASRC_LCL_CACHE:
+		count_vm_event(HWHINT_LOCAL_L3L1L2);
+		break;
+	case MSR_AMD64_IBSOPDATA2_DATASRC_PEER_CACHE_NEAR:
+		count_vm_event(HWHINT_LOCAL_PEER_CACHE_NEAR);
+		break;
+	case MSR_AMD64_IBSOPDATA2_DATASRC_DRAM:
+		count_vm_event(HWHINT_DRAM_ACCESSES);
+		break;
+	case MSR_AMD64_IBSOPDATA2_DATASRC_EXT_MEM:
+		count_vm_event(HWHINT_CXL_ACCESSES);
+		break;
+	case MSR_AMD64_IBSOPDATA2_DATASRC_FAR_CCX_CACHE:
+		count_vm_event(HWHINT_FAR_CACHE_HITS);
+		break;
+	}
+
+	rmt_node = ops_data2 & MSR_AMD64_IBSOPDATA2_RMTNODE;
+	if (rmt_node)
+		count_vm_event(HWHINT_REMOTE_NODE);
+
+	/* Is linear addr valid? */
+	if (ops_data3 & MSR_AMD64_IBSOPDATA3_LADDR_VALID)
+		rdmsrl(MSR_AMD64_IBSDCLINAD, laddr);
+	else {
+		count_vm_event(HWHINT_LADDR_INVALID);
+		goto handled;
+	}
+
+	/* Discard kernel address accesses */
+	if (laddr & (1UL << 63)) {
+		count_vm_event(HWHINT_KERNEL_ADDR);
+		goto handled;
+	}
+
+	/* Is phys addr valid? */
+	if (ops_data3 & MSR_AMD64_IBSOPDATA3_PADDR_VALID)
+		rdmsrl(MSR_AMD64_IBSDCPHYSAD, paddr);
+	else {
+		count_vm_event(HWHINT_PADDR_INVALID);
+		goto handled;
+	}
+
+	pfn = PHYS_PFN(paddr);
+	page = pfn_to_online_page(pfn);
+	if (!page)
+		goto handled;
+
+	if (!PageLRU(page)) {
+		count_vm_event(HWHINT_NON_LRU);
+		goto handled;
+	}
+
+	if (!ibs_push_sample(pfn, numa_node_id(), jiffies)) {
+		count_vm_event(HWHINT_BUFFER_FULL);
+		goto handled;
+	}
+
+	irq_work_queue(&ibs_irq_work);
+	count_vm_event(HWHINT_USEFUL_SAMPLES);
+
+handled:
+	return NMI_HANDLED;
+}
+
+static inline int get_ibs_lvt_offset(void)
+{
+	u64 val;
+
+	rdmsrl(MSR_AMD64_IBSCTL, val);
+	if (!(val & IBSCTL_LVT_OFFSET_VALID))
+		return -EINVAL;
+
+	return val & IBSCTL_LVT_OFFSET_MASK;
+}
+
+static void setup_APIC_ibs(void)
+{
+	int offset;
+
+	offset = get_ibs_lvt_offset();
+	if (offset < 0)
+		goto failed;
+
+	if (!setup_APIC_eilvt(offset, 0, APIC_EILVT_MSG_NMI, 0))
+		return;
+failed:
+	pr_warn("IBS APIC setup failed on cpu #%d\n",
+		smp_processor_id());
+}
+
+static void clear_APIC_ibs(void)
+{
+	int offset;
+
+	offset = get_ibs_lvt_offset();
+	if (offset >= 0)
+		setup_APIC_eilvt(offset, 0, APIC_EILVT_MSG_FIX, 1);
+}
+
+static int x86_amd_ibs_access_profile_startup(unsigned int cpu)
+{
+	setup_APIC_ibs();
+	return 0;
+}
+
+static int x86_amd_ibs_access_profile_teardown(unsigned int cpu)
+{
+	clear_APIC_ibs();
+	return 0;
+}
+
+static int __init ibs_access_profiling_init(void)
+{
+	if (!boot_cpu_has(X86_FEATURE_IBS)) {
+		pr_info("IBS capability is unavailable for access profiling\n");
+		return 0;
+	}
+
+	ibs_s = alloc_percpu_gfp(struct ibs_sample_pcpu, GFP_KERNEL | __GFP_ZERO);
+	if (!ibs_s)
+		return 0;
+
+	INIT_WORK(&ibs_work, ibs_work_handler);
+	init_irq_work(&ibs_irq_work, ibs_irq_handler);
+
+	/* Uses IBS Op sampling */
+	ibs_config = IBS_OP_CNT_CTL | IBS_OP_ENABLE;
+	ibs_caps = cpuid_eax(IBS_CPUID_FEATURES);
+	if (ibs_caps & IBS_CAPS_ZEN4)
+		ibs_config |= IBS_OP_L3MISSONLY;
+
+	register_nmi_handler(NMI_LOCAL, ibs_overflow_handler, 0, "ibs");
+
+	cpuhp_setup_state(CPUHP_AP_PERF_X86_AMD_IBS_STARTING,
+			  "x86/amd/ibs_access_profile:starting",
+			  x86_amd_ibs_access_profile_startup,
+			  x86_amd_ibs_access_profile_teardown);
+
+	pr_info("IBS setup for memory access profiling\n");
+	return 0;
+}
+
+arch_initcall(ibs_access_profiling_init);
diff --git a/include/linux/pghot.h b/include/linux/pghot.h
index 802240d574a6..6410cb131d3d 100644
--- a/include/linux/pghot.h
+++ b/include/linux/pghot.h
@@ -2,6 +2,12 @@
 #ifndef _LINUX_PGHOT_H
 #define _LINUX_PGHOT_H
 
+#ifdef CONFIG_HWMEM_PROFILER
+bool hwmem_access_profiler_inuse(void);
+#else
+static inline bool hwmem_access_profiler_inuse(void) { return false; }
+#endif
+
 /* Page hotness temperature sources */
 enum pghot_src {
 	PGHOT_HW_HINTS,
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 5b8fd93b55fd..67efbca9051c 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -193,6 +193,25 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		PGHOT_RECORD_HWHINTS,
 		PGHOT_RECORD_PGTSCANS,
 		PGHOT_RECORD_HINTFAULTS,
+#ifdef CONFIG_HWMEM_PROFILER
+		HWHINT_NR_EVENTS,
+		HWHINT_KERNEL,
+		HWHINT_KTHREAD,
+		HWHINT_NON_LOAD_STORES,
+		HWHINT_DC_L2_HITS,
+		HWHINT_LOCAL_L3L1L2,
+		HWHINT_LOCAL_PEER_CACHE_NEAR,
+		HWHINT_FAR_CACHE_HITS,
+		HWHINT_DRAM_ACCESSES,
+		HWHINT_CXL_ACCESSES,
+		HWHINT_REMOTE_NODE,
+		HWHINT_LADDR_INVALID,
+		HWHINT_KERNEL_ADDR,
+		HWHINT_PADDR_INVALID,
+		HWHINT_NON_LRU,
+		HWHINT_BUFFER_FULL,
+		HWHINT_USEFUL_SAMPLES,
+#endif /* CONFIG_HWMEM_PROFILER */
 #endif /* CONFIG_PGHOT */
 		NR_VM_EVENT_ITEMS
 };
diff --git a/mm/Kconfig b/mm/Kconfig
index 472975da69e1..6057c96b9cd3 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1390,6 +1390,19 @@ config PGHOT
 	  by various sources. Asynchronous promotion is done by per-node
 	  kernel threads.
 
+config HWMEM_PROFILER
+	bool "HW based memory access profiling"
+	def_bool n
+	depends on PGHOT
+	depends on X86_64
+	help
+	  Some hardware platforms are capable of providing memory access
+	  information in direct and actionable manner. Instruction Based
+	  Sampling (IBS) present on AMD Zen CPUs in one such example.
+	  Memory accesses obtained via such HW based mechanisms are
+	  rolled up to PGHOT sub-system for further action like hot page
+	  promotion or NUMA Balancing
+
 source "mm/damon/Kconfig"
 
 endmenu
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 10745e498e3a..4160476c4ee5 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1501,6 +1501,25 @@ const char * const vmstat_text[] = {
 	[I(PGHOT_RECORD_HWHINTS)]		= "pghot_recorded_hwhints",
 	[I(PGHOT_RECORD_PGTSCANS)]		= "pghot_recorded_pgtscans",
 	[I(PGHOT_RECORD_HINTFAULTS)]		= "pghot_recorded_hintfaults",
+#ifdef CONFIG_HWMEM_PROFILER
+	[I(HWHINT_NR_EVENTS)]			= "hwhint_nr_events",
+	[I(HWHINT_KERNEL)]			= "hwhint_kernel",
+	[I(HWHINT_KTHREAD)]			= "hwhint_kthread",
+	[I(HWHINT_NON_LOAD_STORES)]		= "hwhint_non_load_stores",
+	[I(HWHINT_DC_L2_HITS)]			= "hwhint_dc_l2_hits",
+	[I(HWHINT_LOCAL_L3L1L2)]		= "hwhint_local_l3l1l2",
+	[I(HWHINT_LOCAL_PEER_CACHE_NEAR)]	= "hwhint_local_peer_cache_near",
+	[I(HWHINT_FAR_CACHE_HITS)]		= "hwhint_far_cache_hits",
+	[I(HWHINT_DRAM_ACCESSES)]		= "hwhint_dram_accesses",
+	[I(HWHINT_CXL_ACCESSES)]		= "hwhint_cxl_accesses",
+	[I(HWHINT_REMOTE_NODE)]			= "hwhint_remote_node",
+	[I(HWHINT_LADDR_INVALID)]		= "hwhint_invalid_laddr",
+	[I(HWHINT_KERNEL_ADDR)]			= "hwhint_kernel_addr",
+	[I(HWHINT_PADDR_INVALID)]		= "hwhint_invalid_paddr",
+	[I(HWHINT_NON_LRU)]			= "hwhint_non_lru",
+	[I(HWHINT_BUFFER_FULL)]			= "hwhint_buffer_full",
+	[I(HWHINT_USEFUL_SAMPLES)]		= "hwhint_useful_samples",
+#endif /* CONFIG_HWMEM_PROFILER */
 #endif /* CONFIG_PGHOT */
 #undef I
 #endif /* CONFIG_VM_EVENT_COUNTERS */
-- 
2.34.1

[RFC PATCH v4 5/9] x86: ibs: Enable IBS profiling for memory accesses

[Bharata B Rao]

Enable IBS memory access data collection for user memory
accesses by programming the required MSRs. The profiling
is turned ON only for user mode execution and turned OFF
for kernel mode execution. Profiling is explicitly disabled
for NMI handler too.

TODOs:

- IBS sampling rate is kept fixed for now.
- Arch/vendor separation/isolation of the code needs relook.

Signed-off-by: Bharata B Rao <bharata@amd.com>
---
 arch/x86/include/asm/entry-common.h |  3 +++
 arch/x86/include/asm/hardirq.h      |  2 ++
 arch/x86/mm/ibs.c                   | 32 +++++++++++++++++++++++++++++
 include/linux/pghot.h               |  4 ++++
 4 files changed, 41 insertions(+)

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index ce3eb6d5fdf9..0f381a63669e 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -4,6 +4,7 @@
 
 #include <linux/randomize_kstack.h>
 #include <linux/user-return-notifier.h>
+#include <linux/pghot.h>
 
 #include <asm/nospec-branch.h>
 #include <asm/io_bitmap.h>
@@ -13,6 +14,7 @@
 /* Check that the stack and regs on entry from user mode are sane. */
 static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs)
 {
+	hwmem_access_profiling_stop();
 	if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) {
 		/*
 		 * Make sure that the entry code gave us a sensible EFLAGS
@@ -106,6 +108,7 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
 static __always_inline void arch_exit_to_user_mode(void)
 {
 	amd_clear_divider();
+	hwmem_access_profiling_start();
 }
 #define arch_exit_to_user_mode arch_exit_to_user_mode
 
diff --git a/arch/x86/include/asm/hardirq.h b/arch/x86/include/asm/hardirq.h
index f00c09ffe6a9..281dd76f5efb 100644
--- a/arch/x86/include/asm/hardirq.h
+++ b/arch/x86/include/asm/hardirq.h
@@ -91,4 +91,6 @@ static __always_inline bool kvm_get_cpu_l1tf_flush_l1d(void)
 static __always_inline void kvm_set_cpu_l1tf_flush_l1d(void) { }
 #endif /* IS_ENABLED(CONFIG_KVM_INTEL) */
 
+#define arch_nmi_enter()	hwmem_access_profiling_stop()
+#define arch_nmi_exit()		hwmem_access_profiling_start()
 #endif /* _ASM_X86_HARDIRQ_H */
diff --git a/arch/x86/mm/ibs.c b/arch/x86/mm/ibs.c
index 946f3a82ca11..cf21052118c9 100644
--- a/arch/x86/mm/ibs.c
+++ b/arch/x86/mm/ibs.c
@@ -16,6 +16,7 @@ static u64 ibs_config __read_mostly;
 static u32 ibs_caps;
 
 #define IBS_NR_SAMPLES	150
+#define IBS_SAMPLE_PERIOD      10000
 
 /*
  * Basic access info captured for each memory access.
@@ -43,6 +44,36 @@ struct ibs_sample_pcpu __percpu *ibs_s;
 static struct work_struct ibs_work;
 static struct irq_work ibs_irq_work;
 
+void hwmem_access_profiling_stop(void)
+{
+	u64 ops_ctl;
+
+	if (!hwmem_access_profiling)
+		return;
+
+	rdmsrl(MSR_AMD64_IBSOPCTL, ops_ctl);
+	wrmsrl(MSR_AMD64_IBSOPCTL, ops_ctl & ~IBS_OP_ENABLE);
+}
+
+void hwmem_access_profiling_start(void)
+{
+	u64 config = 0;
+	unsigned int period = IBS_SAMPLE_PERIOD;
+
+	if (!hwmem_access_profiling)
+		return;
+
+	/* Disable IBS for kernel thread */
+	if (!current->mm)
+		goto out;
+
+	config = (period >> 4) & IBS_OP_MAX_CNT;
+	config |= (period & IBS_OP_MAX_CNT_EXT_MASK);
+	config |= ibs_config;
+out:
+	wrmsrl(MSR_AMD64_IBSOPCTL, config);
+}
+
 bool hwmem_access_profiler_inuse(void)
 {
 	return hwmem_access_profiling;
@@ -309,6 +340,7 @@ static int __init ibs_access_profiling_init(void)
 			  x86_amd_ibs_access_profile_startup,
 			  x86_amd_ibs_access_profile_teardown);
 
+	hwmem_access_profiling = true;
 	pr_info("IBS setup for memory access profiling\n");
 	return 0;
 }
diff --git a/include/linux/pghot.h b/include/linux/pghot.h
index 6410cb131d3d..00f450f79c86 100644
--- a/include/linux/pghot.h
+++ b/include/linux/pghot.h
@@ -4,8 +4,12 @@
 
 #ifdef CONFIG_HWMEM_PROFILER
 bool hwmem_access_profiler_inuse(void);
+void hwmem_access_profiling_start(void);
+void hwmem_access_profiling_stop(void);
 #else
 static inline bool hwmem_access_profiler_inuse(void) { return false; }
+static inline void hwmem_access_profiling_start(void) {}
+static inline void hwmem_access_profiling_stop(void) {}
 #endif
 
 /* Page hotness temperature sources */
-- 
2.34.1

[RFC PATCH v4 6/9] mm: mglru: generalize page table walk

[Bharata B Rao]

From: Kinsey Ho <kinseyho@google.com>

Refactor the existing MGLRU page table walking logic to make it
resumable.

Additionally, introduce two hooks into the MGLRU page table walk:
accessed callback and flush callback. The accessed callback is called
for each accessed page detected via the scanned accessed bit. The flush
callback is called when the accessed callback reports that a flush is
required. This allows for processing pages in batches for efficiency.

With a generalised page table walk, introduce a new scan function which
repeatedly scans on the same young generation and does not add a new
young generation.

Signed-off-by: Kinsey Ho <kinseyho@google.com>
Signed-off-by: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Bharata B Rao <bharata@amd.com>
---
 include/linux/mmzone.h |   5 ++
 mm/internal.h          |   4 +
 mm/vmscan.c            | 181 +++++++++++++++++++++++++++++++----------
 3 files changed, 145 insertions(+), 45 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fde851990394..421b012fb60c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -548,6 +548,8 @@ struct lru_gen_mm_walk {
 	unsigned long seq;
 	/* the next address within an mm to scan */
 	unsigned long next_addr;
+	/* called for each accessed pte/pmd */
+	bool (*accessed_cb)(unsigned long pfn);
 	/* to batch promoted pages */
 	int nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
 	/* to batch the mm stats */
@@ -555,6 +557,9 @@ struct lru_gen_mm_walk {
 	/* total batched items */
 	int batched;
 	int swappiness;
+	/* for the pmd under scanning */
+	int nr_young_pte;
+	int nr_total_pte;
 	bool force_scan;
 };
 
diff --git a/mm/internal.h b/mm/internal.h
index 1561fc2ff5b8..531104a96c51 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -538,6 +538,10 @@ extern unsigned long highest_memmap_pfn;
 bool folio_isolate_lru(struct folio *folio);
 void folio_putback_lru(struct folio *folio);
 extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason);
+void set_task_reclaim_state(struct task_struct *task,
+				   struct reclaim_state *rs);
+void lru_gen_scan_lruvec(struct lruvec *lruvec, unsigned long seq,
+			 bool (*accessed_cb)(unsigned long), void (*flush_cb)(void));
 #ifdef CONFIG_NUMA
 int user_proactive_reclaim(char *buf,
 			   struct mem_cgroup *memcg, pg_data_t *pgdat);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b2fc8b626d3d..1bb637fd6e5e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -289,7 +289,7 @@ static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
 			continue;				\
 		else
 
-static void set_task_reclaim_state(struct task_struct *task,
+void set_task_reclaim_state(struct task_struct *task,
 				   struct reclaim_state *rs)
 {
 	/* Check for an overwrite */
@@ -3093,7 +3093,7 @@ static bool iterate_mm_list(struct lru_gen_mm_walk *walk, struct mm_struct **ite
 
 	VM_WARN_ON_ONCE(mm_state->seq + 1 < walk->seq);
 
-	if (walk->seq <= mm_state->seq)
+	if (!walk->accessed_cb && walk->seq <= mm_state->seq)
 		goto done;
 
 	if (!mm_state->head)
@@ -3519,16 +3519,14 @@ static void walk_update_folio(struct lru_gen_mm_walk *walk, struct folio *folio,
 	}
 }
 
-static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
-			   struct mm_walk *args)
+static int walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
+			   struct mm_walk *args, bool *suitable)
 {
 	int i;
 	bool dirty;
 	pte_t *pte;
 	spinlock_t *ptl;
 	unsigned long addr;
-	int total = 0;
-	int young = 0;
 	struct folio *last = NULL;
 	struct lru_gen_mm_walk *walk = args->private;
 	struct mem_cgroup *memcg = lruvec_memcg(walk->lruvec);
@@ -3536,19 +3534,24 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 	DEFINE_MAX_SEQ(walk->lruvec);
 	int gen = lru_gen_from_seq(max_seq);
 	pmd_t pmdval;
+	int err = 0;
 
 	pte = pte_offset_map_rw_nolock(args->mm, pmd, start & PMD_MASK, &pmdval, &ptl);
-	if (!pte)
-		return false;
+	if (!pte) {
+		*suitable = false;
+		return err;
+	}
 
 	if (!spin_trylock(ptl)) {
 		pte_unmap(pte);
-		return true;
+		*suitable = true;
+		return err;
 	}
 
 	if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
 		pte_unmap_unlock(pte, ptl);
-		return false;
+		*suitable = false;
+		return err;
 	}
 
 	arch_enter_lazy_mmu_mode();
@@ -3557,8 +3560,9 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 		unsigned long pfn;
 		struct folio *folio;
 		pte_t ptent = ptep_get(pte + i);
+		bool do_flush;
 
-		total++;
+		walk->nr_total_pte++;
 		walk->mm_stats[MM_LEAF_TOTAL]++;
 
 		pfn = get_pte_pfn(ptent, args->vma, addr, pgdat);
@@ -3582,23 +3586,36 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 		if (pte_dirty(ptent))
 			dirty = true;
 
-		young++;
+		walk->nr_young_pte++;
 		walk->mm_stats[MM_LEAF_YOUNG]++;
+
+		if (!walk->accessed_cb)
+			continue;
+
+		do_flush = walk->accessed_cb(pfn);
+		if (do_flush) {
+			walk->next_addr = addr + PAGE_SIZE;
+
+			err = -EAGAIN;
+			break;
+		}
 	}
 
 	walk_update_folio(walk, last, gen, dirty);
 	last = NULL;
 
-	if (i < PTRS_PER_PTE && get_next_vma(PMD_MASK, PAGE_SIZE, args, &start, &end))
+	if (!err && i < PTRS_PER_PTE &&
+	    get_next_vma(PMD_MASK, PAGE_SIZE, args, &start, &end))
 		goto restart;
 
 	arch_leave_lazy_mmu_mode();
 	pte_unmap_unlock(pte, ptl);
 
-	return suitable_to_scan(total, young);
+	*suitable = suitable_to_scan(walk->nr_total_pte, walk->nr_young_pte);
+	return err;
 }
 
-static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area_struct *vma,
+static int walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area_struct *vma,
 				  struct mm_walk *args, unsigned long *bitmap, unsigned long *first)
 {
 	int i;
@@ -3611,6 +3628,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 	struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec);
 	DEFINE_MAX_SEQ(walk->lruvec);
 	int gen = lru_gen_from_seq(max_seq);
+	int err = 0;
 
 	VM_WARN_ON_ONCE(pud_leaf(*pud));
 
@@ -3618,13 +3636,13 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 	if (*first == -1) {
 		*first = addr;
 		bitmap_zero(bitmap, MIN_LRU_BATCH);
-		return;
+		return err;
 	}
 
 	i = addr == -1 ? 0 : pmd_index(addr) - pmd_index(*first);
 	if (i && i <= MIN_LRU_BATCH) {
 		__set_bit(i - 1, bitmap);
-		return;
+		return err;
 	}
 
 	pmd = pmd_offset(pud, *first);
@@ -3638,6 +3656,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 	do {
 		unsigned long pfn;
 		struct folio *folio;
+		bool do_flush;
 
 		/* don't round down the first address */
 		addr = i ? (*first & PMD_MASK) + i * PMD_SIZE : *first;
@@ -3674,6 +3693,17 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 			dirty = true;
 
 		walk->mm_stats[MM_LEAF_YOUNG]++;
+		if (!walk->accessed_cb)
+			goto next;
+
+		do_flush = walk->accessed_cb(pfn);
+		if (do_flush) {
+			i = find_next_bit(bitmap, MIN_LRU_BATCH, i) + 1;
+
+			walk->next_addr = (*first & PMD_MASK) + i * PMD_SIZE;
+			err = -EAGAIN;
+			break;
+		}
 next:
 		i = i > MIN_LRU_BATCH ? 0 : find_next_bit(bitmap, MIN_LRU_BATCH, i) + 1;
 	} while (i <= MIN_LRU_BATCH);
@@ -3684,9 +3714,10 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 	spin_unlock(ptl);
 done:
 	*first = -1;
+	return err;
 }
 
-static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
+static int walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 			   struct mm_walk *args)
 {
 	int i;
@@ -3698,6 +3729,7 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 	unsigned long first = -1;
 	struct lru_gen_mm_walk *walk = args->private;
 	struct lru_gen_mm_state *mm_state = get_mm_state(walk->lruvec);
+	int err = 0;
 
 	VM_WARN_ON_ONCE(pud_leaf(*pud));
 
@@ -3711,6 +3743,7 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 	/* walk_pte_range() may call get_next_vma() */
 	vma = args->vma;
 	for (i = pmd_index(start), addr = start; addr != end; i++, addr = next) {
+		bool suitable;
 		pmd_t val = pmdp_get_lockless(pmd + i);
 
 		next = pmd_addr_end(addr, end);
@@ -3727,7 +3760,10 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 			walk->mm_stats[MM_LEAF_TOTAL]++;
 
 			if (pfn != -1)
-				walk_pmd_range_locked(pud, addr, vma, args, bitmap, &first);
+				err = walk_pmd_range_locked(pud, addr, vma, args,
+						bitmap, &first);
+			if (err)
+				return err;
 			continue;
 		}
 
@@ -3736,33 +3772,51 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 			if (!pmd_young(val))
 				continue;
 
-			walk_pmd_range_locked(pud, addr, vma, args, bitmap, &first);
+			err = walk_pmd_range_locked(pud, addr, vma, args,
+						bitmap, &first);
+			if (err)
+				return err;
 		}
 
 		if (!walk->force_scan && !test_bloom_filter(mm_state, walk->seq, pmd + i))
 			continue;
 
+		err = walk_pte_range(&val, addr, next, args, &suitable);
+		if (err && walk->next_addr < next && first == -1)
+			return err;
+
+		walk->nr_total_pte = 0;
+		walk->nr_young_pte = 0;
+
 		walk->mm_stats[MM_NONLEAF_FOUND]++;
 
-		if (!walk_pte_range(&val, addr, next, args))
-			continue;
+		if (!suitable)
+			goto next;
 
 		walk->mm_stats[MM_NONLEAF_ADDED]++;
 
 		/* carry over to the next generation */
 		update_bloom_filter(mm_state, walk->seq + 1, pmd + i);
+next:
+		if (err) {
+			walk->next_addr = first;
+			return err;
+		}
 	}
 
-	walk_pmd_range_locked(pud, -1, vma, args, bitmap, &first);
+	err = walk_pmd_range_locked(pud, -1, vma, args, bitmap, &first);
 
-	if (i < PTRS_PER_PMD && get_next_vma(PUD_MASK, PMD_SIZE, args, &start, &end))
+	if (!err && i < PTRS_PER_PMD &&
+	    get_next_vma(PUD_MASK, PMD_SIZE, args, &start, &end))
 		goto restart;
+
+	return err;
 }
 
 static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end,
 			  struct mm_walk *args)
 {
-	int i;
+	int i, err;
 	pud_t *pud;
 	unsigned long addr;
 	unsigned long next;
@@ -3780,7 +3834,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end,
 		if (!pud_present(val) || WARN_ON_ONCE(pud_leaf(val)))
 			continue;
 
-		walk_pmd_range(&val, addr, next, args);
+		err = walk_pmd_range(&val, addr, next, args);
+		if (err)
+			return err;
 
 		if (need_resched() || walk->batched >= MAX_LRU_BATCH) {
 			end = (addr | ~PUD_MASK) + 1;
@@ -3801,40 +3857,48 @@ static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end,
 	return -EAGAIN;
 }
 
-static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
+static int try_walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
 {
+	int err;
 	static const struct mm_walk_ops mm_walk_ops = {
 		.test_walk = should_skip_vma,
 		.p4d_entry = walk_pud_range,
 		.walk_lock = PGWALK_RDLOCK,
 	};
-	int err;
 	struct lruvec *lruvec = walk->lruvec;
 
-	walk->next_addr = FIRST_USER_ADDRESS;
+	DEFINE_MAX_SEQ(lruvec);
 
-	do {
-		DEFINE_MAX_SEQ(lruvec);
+	err = -EBUSY;
 
-		err = -EBUSY;
+	/* another thread might have called inc_max_seq() */
+	if (walk->seq != max_seq)
+		return err;
 
-		/* another thread might have called inc_max_seq() */
-		if (walk->seq != max_seq)
-			break;
+	/* the caller might be holding the lock for write */
+	if (mmap_read_trylock(mm)) {
+		err = walk_page_range(mm, walk->next_addr, ULONG_MAX,
+				      &mm_walk_ops, walk);
 
-		/* the caller might be holding the lock for write */
-		if (mmap_read_trylock(mm)) {
-			err = walk_page_range(mm, walk->next_addr, ULONG_MAX, &mm_walk_ops, walk);
+		mmap_read_unlock(mm);
+	}
 
-			mmap_read_unlock(mm);
-		}
+	if (walk->batched) {
+		spin_lock_irq(&lruvec->lru_lock);
+		reset_batch_size(walk);
+		spin_unlock_irq(&lruvec->lru_lock);
+	}
 
-		if (walk->batched) {
-			spin_lock_irq(&lruvec->lru_lock);
-			reset_batch_size(walk);
-			spin_unlock_irq(&lruvec->lru_lock);
-		}
+	return err;
+}
+
+static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
+{
+	int err;
 
+	walk->next_addr = FIRST_USER_ADDRESS;
+	do {
+		err = try_walk_mm(mm, walk);
 		cond_resched();
 	} while (err == -EAGAIN);
 }
@@ -4046,6 +4110,33 @@ static bool inc_max_seq(struct lruvec *lruvec, unsigned long seq, int swappiness
 	return success;
 }
 
+void lru_gen_scan_lruvec(struct lruvec *lruvec, unsigned long seq,
+			 bool (*accessed_cb)(unsigned long), void (*flush_cb)(void))
+{
+	struct lru_gen_mm_walk *walk = current->reclaim_state->mm_walk;
+	struct mm_struct *mm = NULL;
+
+	walk->lruvec = lruvec;
+	walk->seq = seq;
+	walk->accessed_cb = accessed_cb;
+	walk->swappiness = MAX_SWAPPINESS;
+
+	do {
+		int err = -EBUSY;
+
+		iterate_mm_list(walk, &mm);
+		if (!mm)
+			break;
+
+		walk->next_addr = FIRST_USER_ADDRESS;
+		do {
+			err = try_walk_mm(mm, walk);
+			cond_resched();
+			flush_cb();
+		} while (err == -EAGAIN);
+	} while (mm);
+}
+
 static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long seq,
 			       int swappiness, bool force_scan)
 {
-- 
2.34.1

[RFC PATCH v4 7/9] mm: klruscand: use mglru scanning for page promotion

[Bharata B Rao]

From: Kinsey Ho <kinseyho@google.com>

Introduce a new kernel daemon, klruscand, that periodically invokes the
MGLRU page table walk. It leverages the new callbacks to gather access
information and forwards it to pghot sub-system for promotion decisions.

This benefits from reusing the existing MGLRU page table walk
infrastructure, which is optimized with features such as hierarchical
scanning and bloom filters to reduce CPU overhead.

As an additional optimization to be added in the future, we can tune
the scan intervals for each memcg.

Signed-off-by: Kinsey Ho <kinseyho@google.com>
Signed-off-by: Yuanchu Xie <yuanchu@google.com>
[Reduced the scan interval to 500ms, KLRUSCAND to default n in config]
Signed-off-by: Bharata B Rao <bharata@amd.com>
---
 mm/Kconfig     |   8 ++++
 mm/Makefile    |   1 +
 mm/klruscand.c | 110 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 119 insertions(+)
 create mode 100644 mm/klruscand.c

diff --git a/mm/Kconfig b/mm/Kconfig
index 6057c96b9cd3..80221594413d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1403,6 +1403,14 @@ config HWMEM_PROFILER
 	  rolled up to PGHOT sub-system for further action like hot page
 	  promotion or NUMA Balancing
 
+config KLRUSCAND
+	bool "Kernel lower tier access scan daemon"
+	default n
+	depends on PGHOT && LRU_GEN_WALKS_MMU
+	help
+	  Scan for accesses from lower tiers by invoking MGLRU to perform
+	  page table walks.
+
 source "mm/damon/Kconfig"
 
 endmenu
diff --git a/mm/Makefile b/mm/Makefile
index a6fac171c36e..1c0c79fec106 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -147,3 +147,4 @@ obj-$(CONFIG_EXECMEM) += execmem.o
 obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o
 obj-$(CONFIG_PT_RECLAIM) += pt_reclaim.o
 obj-$(CONFIG_PGHOT) += pghot.o
+obj-$(CONFIG_KLRUSCAND) += klruscand.o
diff --git a/mm/klruscand.c b/mm/klruscand.c
new file mode 100644
index 000000000000..13a41b38d67d
--- /dev/null
+++ b/mm/klruscand.c
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/memcontrol.h>
+#include <linux/kthread.h>
+#include <linux/module.h>
+#include <linux/vmalloc.h>
+#include <linux/memory-tiers.h>
+#include <linux/pghot.h>
+
+#include "internal.h"
+
+#define KLRUSCAND_INTERVAL 500
+#define BATCH_SIZE (2 << 16)
+
+static struct task_struct *scan_thread;
+static unsigned long pfn_batch[BATCH_SIZE];
+static int batch_index;
+
+static void flush_cb(void)
+{
+	int i;
+
+	for (i = 0; i < batch_index; i++) {
+		unsigned long pfn = pfn_batch[i];
+
+		pghot_record_access(pfn, NUMA_NO_NODE, PGHOT_PGTABLE_SCAN, jiffies);
+
+		if (i % 16 == 0)
+			cond_resched();
+	}
+	batch_index = 0;
+}
+
+static bool accessed_cb(unsigned long pfn)
+{
+	WARN_ON_ONCE(batch_index == BATCH_SIZE);
+
+	if (batch_index < BATCH_SIZE)
+		pfn_batch[batch_index++] = pfn;
+
+	return batch_index == BATCH_SIZE;
+}
+
+static int klruscand_run(void *unused)
+{
+	struct lru_gen_mm_walk *walk;
+
+	walk = kzalloc(sizeof(*walk),
+		       __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN);
+	if (!walk)
+		return -ENOMEM;
+
+	while (!kthread_should_stop()) {
+		unsigned long next_wake_time;
+		long sleep_time;
+		struct mem_cgroup *memcg;
+		int flags;
+		int nid;
+
+		next_wake_time = jiffies + msecs_to_jiffies(KLRUSCAND_INTERVAL);
+
+		for_each_node_state(nid, N_MEMORY) {
+			pg_data_t *pgdat = NODE_DATA(nid);
+			struct reclaim_state rs = { 0 };
+
+			if (node_is_toptier(nid))
+				continue;
+
+			rs.mm_walk = walk;
+			set_task_reclaim_state(current, &rs);
+			flags = memalloc_noreclaim_save();
+
+			memcg = mem_cgroup_iter(NULL, NULL, NULL);
+			do {
+				struct lruvec *lruvec =
+					mem_cgroup_lruvec(memcg, pgdat);
+				unsigned long max_seq =
+					READ_ONCE((lruvec)->lrugen.max_seq);
+
+				lru_gen_scan_lruvec(lruvec, max_seq, accessed_cb, flush_cb);
+				cond_resched();
+			} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
+
+			memalloc_noreclaim_restore(flags);
+			set_task_reclaim_state(current, NULL);
+			memset(walk, 0, sizeof(*walk));
+		}
+
+		sleep_time = next_wake_time - jiffies;
+		if (sleep_time > 0 && sleep_time != MAX_SCHEDULE_TIMEOUT)
+			schedule_timeout_idle(sleep_time);
+	}
+	kfree(walk);
+	return 0;
+}
+
+static int __init klruscand_init(void)
+{
+	struct task_struct *task;
+
+	task = kthread_run(klruscand_run, NULL, "klruscand");
+
+	if (IS_ERR(task)) {
+		pr_err("Failed to create klruscand kthread\n");
+		return PTR_ERR(task);
+	}
+
+	scan_thread = task;
+	return 0;
+}
+module_init(klruscand_init);
-- 
2.34.1

[RFC PATCH v4 8/9] mm: sched: Move hot page promotion from NUMAB=2 to pghot tracking

[Bharata B Rao]

Currently hot page promotion (NUMA_BALANCING_MEMORY_TIERING
mode of NUMA Balancing) does hot page detection (via hint faults),
hot page classification and eventual promotion, all by itself and
sits within the scheduler.

With the new hot page tracking and promotion mechanism being
available, NUMA Balancing can limit itself to detection of
hot pages (via hint faults) and off-load rest of the
functionality to the common hot page tracking system.

pghot_record_access(PGHOT_HINT_FAULT) API is used to feed the
hot page info. In addition, the migration rate limiting and
dynamic threshold logic are moved to kmigrated so that the same
can be used for hot pages reported by other sources too.

Signed-off-by: Bharata B Rao <bharata@amd.com>
---
 include/linux/pghot.h |   3 +
 kernel/sched/debug.c  |   1 -
 kernel/sched/fair.c   | 152 ++----------------------------------------
 mm/huge_memory.c      |  26 ++------
 mm/memory.c           |  31 ++-------
 mm/pghot.c            | 129 ++++++++++++++++++++++++++++++++++-
 6 files changed, 147 insertions(+), 195 deletions(-)

diff --git a/include/linux/pghot.h b/include/linux/pghot.h
index 00f450f79c86..615009a39348 100644
--- a/include/linux/pghot.h
+++ b/include/linux/pghot.h
@@ -71,6 +71,9 @@ enum pghot_src_enabed {
 #define PGHOT_SECTION_HOT_BIT	BIT(0)
 #define PGHOT_SECTION_HOT_MASK	GENMASK(PGHOT_SECTION_HOT_BIT - 1, 0)
 
+#define KMIGRATED_MIGRATION_ADJUST_STEPS	16
+#define KMIGRATED_PROMOTION_THRESHOLD_WINDOW	60000
+
 int pghot_record_access(unsigned long pfn, int nid, int src, unsigned long now);
 #else
 static inline int pghot_record_access(unsigned long pfn, int nid, int src, unsigned long now)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 02e16b70a790..10dc3c996806 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -520,7 +520,6 @@ static __init int sched_init_debug(void)
 	debugfs_create_u32("scan_period_min_ms", 0644, numa, &sysctl_numa_balancing_scan_period_min);
 	debugfs_create_u32("scan_period_max_ms", 0644, numa, &sysctl_numa_balancing_scan_period_max);
 	debugfs_create_u32("scan_size_mb", 0644, numa, &sysctl_numa_balancing_scan_size);
-	debugfs_create_u32("hot_threshold_ms", 0644, numa, &sysctl_numa_balancing_hot_threshold);
 #endif /* CONFIG_NUMA_BALANCING */
 
 	debugfs_create_file("debug", 0444, debugfs_sched, NULL, &sched_debug_fops);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5b752324270b..32f0de52ecd2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -125,11 +125,6 @@ int __weak arch_asym_cpu_priority(int cpu)
 static unsigned int sysctl_sched_cfs_bandwidth_slice		= 5000UL;
 #endif
 
-#ifdef CONFIG_NUMA_BALANCING
-/* Restrict the NUMA promotion throughput (MB/s) for each target node. */
-static unsigned int sysctl_numa_balancing_promote_rate_limit = 65536;
-#endif
-
 #ifdef CONFIG_SYSCTL
 static const struct ctl_table sched_fair_sysctls[] = {
 #ifdef CONFIG_CFS_BANDWIDTH
@@ -142,16 +137,6 @@ static const struct ctl_table sched_fair_sysctls[] = {
 		.extra1         = SYSCTL_ONE,
 	},
 #endif
-#ifdef CONFIG_NUMA_BALANCING
-	{
-		.procname	= "numa_balancing_promote_rate_limit_MBps",
-		.data		= &sysctl_numa_balancing_promote_rate_limit,
-		.maxlen		= sizeof(unsigned int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= SYSCTL_ZERO,
-	},
-#endif /* CONFIG_NUMA_BALANCING */
 };
 
 static int __init sched_fair_sysctl_init(void)
@@ -1443,9 +1428,6 @@ unsigned int sysctl_numa_balancing_scan_size = 256;
 /* Scan @scan_size MB every @scan_period after an initial @scan_delay in ms */
 unsigned int sysctl_numa_balancing_scan_delay = 1000;
 
-/* The page with hint page fault latency < threshold in ms is considered hot */
-unsigned int sysctl_numa_balancing_hot_threshold = MSEC_PER_SEC;
-
 struct numa_group {
 	refcount_t refcount;
 
@@ -1800,108 +1782,6 @@ static inline bool cpupid_valid(int cpupid)
 	return cpupid_to_cpu(cpupid) < nr_cpu_ids;
 }
 
-/*
- * For memory tiering mode, if there are enough free pages (more than
- * enough watermark defined here) in fast memory node, to take full
- * advantage of fast memory capacity, all recently accessed slow
- * memory pages will be migrated to fast memory node without
- * considering hot threshold.
- */
-static bool pgdat_free_space_enough(struct pglist_data *pgdat)
-{
-	int z;
-	unsigned long enough_wmark;
-
-	enough_wmark = max(1UL * 1024 * 1024 * 1024 >> PAGE_SHIFT,
-			   pgdat->node_present_pages >> 4);
-	for (z = pgdat->nr_zones - 1; z >= 0; z--) {
-		struct zone *zone = pgdat->node_zones + z;
-
-		if (!populated_zone(zone))
-			continue;
-
-		if (zone_watermark_ok(zone, 0,
-				      promo_wmark_pages(zone) + enough_wmark,
-				      ZONE_MOVABLE, 0))
-			return true;
-	}
-	return false;
-}
-
-/*
- * For memory tiering mode, when page tables are scanned, the scan
- * time will be recorded in struct page in addition to make page
- * PROT_NONE for slow memory page.  So when the page is accessed, in
- * hint page fault handler, the hint page fault latency is calculated
- * via,
- *
- *	hint page fault latency = hint page fault time - scan time
- *
- * The smaller the hint page fault latency, the higher the possibility
- * for the page to be hot.
- */
-static int numa_hint_fault_latency(struct folio *folio)
-{
-	int last_time, time;
-
-	time = jiffies_to_msecs(jiffies);
-	last_time = folio_xchg_access_time(folio, time);
-
-	return (time - last_time) & PAGE_ACCESS_TIME_MASK;
-}
-
-/*
- * For memory tiering mode, too high promotion/demotion throughput may
- * hurt application latency.  So we provide a mechanism to rate limit
- * the number of pages that are tried to be promoted.
- */
-static bool numa_promotion_rate_limit(struct pglist_data *pgdat,
-				      unsigned long rate_limit, int nr)
-{
-	unsigned long nr_cand;
-	unsigned int now, start;
-
-	now = jiffies_to_msecs(jiffies);
-	mod_node_page_state(pgdat, PGPROMOTE_CANDIDATE, nr);
-	nr_cand = node_page_state(pgdat, PGPROMOTE_CANDIDATE);
-	start = pgdat->nbp_rl_start;
-	if (now - start > MSEC_PER_SEC &&
-	    cmpxchg(&pgdat->nbp_rl_start, start, now) == start)
-		pgdat->nbp_rl_nr_cand = nr_cand;
-	if (nr_cand - pgdat->nbp_rl_nr_cand >= rate_limit)
-		return true;
-	return false;
-}
-
-#define NUMA_MIGRATION_ADJUST_STEPS	16
-
-static void numa_promotion_adjust_threshold(struct pglist_data *pgdat,
-					    unsigned long rate_limit,
-					    unsigned int ref_th)
-{
-	unsigned int now, start, th_period, unit_th, th;
-	unsigned long nr_cand, ref_cand, diff_cand;
-
-	now = jiffies_to_msecs(jiffies);
-	th_period = sysctl_numa_balancing_scan_period_max;
-	start = pgdat->nbp_th_start;
-	if (now - start > th_period &&
-	    cmpxchg(&pgdat->nbp_th_start, start, now) == start) {
-		ref_cand = rate_limit *
-			sysctl_numa_balancing_scan_period_max / MSEC_PER_SEC;
-		nr_cand = node_page_state(pgdat, PGPROMOTE_CANDIDATE);
-		diff_cand = nr_cand - pgdat->nbp_th_nr_cand;
-		unit_th = ref_th * 2 / NUMA_MIGRATION_ADJUST_STEPS;
-		th = pgdat->nbp_threshold ? : ref_th;
-		if (diff_cand > ref_cand * 11 / 10)
-			th = max(th - unit_th, unit_th);
-		else if (diff_cand < ref_cand * 9 / 10)
-			th = min(th + unit_th, ref_th * 2);
-		pgdat->nbp_th_nr_cand = nr_cand;
-		pgdat->nbp_threshold = th;
-	}
-}
-
 bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
 				int src_nid, int dst_cpu)
 {
@@ -1917,33 +1797,11 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
 
 	/*
 	 * The pages in slow memory node should be migrated according
-	 * to hot/cold instead of private/shared.
-	 */
-	if (folio_use_access_time(folio)) {
-		struct pglist_data *pgdat;
-		unsigned long rate_limit;
-		unsigned int latency, th, def_th;
-		long nr = folio_nr_pages(folio);
-
-		pgdat = NODE_DATA(dst_nid);
-		if (pgdat_free_space_enough(pgdat)) {
-			/* workload changed, reset hot threshold */
-			pgdat->nbp_threshold = 0;
-			mod_node_page_state(pgdat, PGPROMOTE_CANDIDATE_NRL, nr);
-			return true;
-		}
-
-		def_th = sysctl_numa_balancing_hot_threshold;
-		rate_limit = MB_TO_PAGES(sysctl_numa_balancing_promote_rate_limit);
-		numa_promotion_adjust_threshold(pgdat, rate_limit, def_th);
-
-		th = pgdat->nbp_threshold ? : def_th;
-		latency = numa_hint_fault_latency(folio);
-		if (latency >= th)
-			return false;
-
-		return !numa_promotion_rate_limit(pgdat, rate_limit, nr);
-	}
+	 * to hot/cold instead of private/shared. Also the migration
+	 * of such pages are handled by kmigrated.
+	 */
+	if (folio_use_access_time(folio))
+		return true;
 
 	this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid);
 	last_cpupid = folio_xchg_last_cpupid(folio, this_cpupid);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6cba1cb14b23..314395e67685 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -39,6 +39,7 @@
 #include <linux/compat.h>
 #include <linux/pgalloc_tag.h>
 #include <linux/pagewalk.h>
+#include <linux/pghot.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -2051,29 +2052,12 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
 
 	target_nid = numa_migrate_check(folio, vmf, haddr, &flags, writable,
 					&last_cpupid);
+	nid = target_nid;
 	if (target_nid == NUMA_NO_NODE)
 		goto out_map;
-	if (migrate_misplaced_folio_prepare(folio, vma, target_nid)) {
-		flags |= TNF_MIGRATE_FAIL;
-		goto out_map;
-	}
-	/* The folio is isolated and isolation code holds a folio reference. */
-	spin_unlock(vmf->ptl);
-	writable = false;
 
-	if (!migrate_misplaced_folio(folio, target_nid)) {
-		flags |= TNF_MIGRATED;
-		nid = target_nid;
-		task_numa_fault(last_cpupid, nid, HPAGE_PMD_NR, flags);
-		return 0;
-	}
+	writable = false;
 
-	flags |= TNF_MIGRATE_FAIL;
-	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
-	if (unlikely(!pmd_same(pmdp_get(vmf->pmd), vmf->orig_pmd))) {
-		spin_unlock(vmf->ptl);
-		return 0;
-	}
 out_map:
 	/* Restore the PMD */
 	pmd = pmd_modify(pmdp_get(vmf->pmd), vma->vm_page_prot);
@@ -2084,8 +2068,10 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
 	update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
 	spin_unlock(vmf->ptl);
 
-	if (nid != NUMA_NO_NODE)
+	if (nid != NUMA_NO_NODE) {
+		pghot_record_access(folio_pfn(folio), nid, PGHOT_HINT_FAULT, jiffies);
 		task_numa_fault(last_cpupid, nid, HPAGE_PMD_NR, flags);
+	}
 	return 0;
 }
 
diff --git a/mm/memory.c b/mm/memory.c
index b59ae7ce42eb..ff3d75f7360c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -75,6 +75,7 @@
 #include <linux/perf_event.h>
 #include <linux/ptrace.h>
 #include <linux/vmalloc.h>
+#include <linux/pghot.h>
 #include <linux/sched/sysctl.h>
 
 #include <trace/events/kmem.h>
@@ -6007,34 +6008,12 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
 
 	target_nid = numa_migrate_check(folio, vmf, vmf->address, &flags,
 					writable, &last_cpupid);
+	nid = target_nid;
 	if (target_nid == NUMA_NO_NODE)
 		goto out_map;
-	if (migrate_misplaced_folio_prepare(folio, vma, target_nid)) {
-		flags |= TNF_MIGRATE_FAIL;
-		goto out_map;
-	}
-	/* The folio is isolated and isolation code holds a folio reference. */
-	pte_unmap_unlock(vmf->pte, vmf->ptl);
+
 	writable = false;
 	ignore_writable = true;
-
-	/* Migrate to the requested node */
-	if (!migrate_misplaced_folio(folio, target_nid)) {
-		nid = target_nid;
-		flags |= TNF_MIGRATED;
-		task_numa_fault(last_cpupid, nid, nr_pages, flags);
-		return 0;
-	}
-
-	flags |= TNF_MIGRATE_FAIL;
-	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
-				       vmf->address, &vmf->ptl);
-	if (unlikely(!vmf->pte))
-		return 0;
-	if (unlikely(!pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
-		pte_unmap_unlock(vmf->pte, vmf->ptl);
-		return 0;
-	}
 out_map:
 	/*
 	 * Make it present again, depending on how arch implements
@@ -6048,8 +6027,10 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
 					    writable);
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
 
-	if (nid != NUMA_NO_NODE)
+	if (nid != NUMA_NO_NODE) {
+		pghot_record_access(folio_pfn(folio), nid, PGHOT_HINT_FAULT, jiffies);
 		task_numa_fault(last_cpupid, nid, nr_pages, flags);
+	}
 	return 0;
 }
 
diff --git a/mm/pghot.c b/mm/pghot.c
index a3f52d4e8750..b28d11bf4c9f 100644
--- a/mm/pghot.c
+++ b/mm/pghot.c
@@ -12,6 +12,9 @@
  * the hot pages. kmigrated runs for each lower tier node. It iterates
  * over the node's PFNs and  migrates pages marked for migration into
  * their targeted nodes.
+ *
+ * Migration rate-limiting and dynamic threshold logic implementations
+ * were moved from NUMA Balancing mode 2.
  */
 #include <linux/mm.h>
 #include <linux/migrate.h>
@@ -25,6 +28,8 @@ static unsigned int pghot_freq_threshold = PGHOT_DEFAULT_FREQ_THRESHOLD;
 static unsigned int kmigrated_sleep_ms = KMIGRATED_DEFAULT_SLEEP_MS;
 static unsigned int kmigrated_batch_nr = KMIGRATED_DEFAULT_BATCH_NR;
 
+/* Restrict the NUMA promotion throughput (MB/s) for each target node. */
+static unsigned int sysctl_pghot_promote_rate_limit = 65536;
 static unsigned int sysctl_pghot_freq_window = PGHOT_DEFAULT_FREQ_WINDOW;
 
 static DEFINE_STATIC_KEY_FALSE(pghot_src_hwhints);
@@ -43,6 +48,14 @@ static const struct ctl_table pghot_sysctls[] = {
 		.proc_handler   = proc_dointvec_minmax,
 		.extra1         = SYSCTL_ZERO,
 	},
+	{
+		.procname	= "pghot_promote_rate_limit_MBps",
+		.data		= &sysctl_pghot_promote_rate_limit,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+	},
 };
 #endif
 
@@ -137,8 +150,13 @@ int pghot_record_access(unsigned long pfn, int nid, int src, unsigned long now)
 		old_freq = (hotness >> PGHOT_FREQ_SHIFT) & PGHOT_FREQ_MASK;
 		old_time = (hotness >> PGHOT_TIME_SHIFT) & PGHOT_TIME_MASK;
 
-		if (((time - old_time) > msecs_to_jiffies(sysctl_pghot_freq_window))
-		    || (nid != NUMA_NO_NODE && old_nid != nid))
+		/*
+		 * Bypass the new window logic for NUMA hint fault source
+		 * as it is too slow in reporting accesses.
+		 * TODO: Fix this.
+		 */
+		if ((((time - old_time) > msecs_to_jiffies(sysctl_pghot_freq_window))
+		    && (src != PGHOT_HINT_FAULT)) || (nid != NUMA_NO_NODE && old_nid != nid))
 			new_window = true;
 
 		if (new_window)
@@ -166,6 +184,110 @@ int pghot_record_access(unsigned long pfn, int nid, int src, unsigned long now)
 	return 0;
 }
 
+/*
+ * For memory tiering mode, if there are enough free pages (more than
+ * enough watermark defined here) in fast memory node, to take full
+ * advantage of fast memory capacity, all recently accessed slow
+ * memory pages will be migrated to fast memory node without
+ * considering hot threshold.
+ */
+static bool pgdat_free_space_enough(struct pglist_data *pgdat)
+{
+	int z;
+	unsigned long enough_wmark;
+
+	enough_wmark = max(1UL * 1024 * 1024 * 1024 >> PAGE_SHIFT,
+			   pgdat->node_present_pages >> 4);
+	for (z = pgdat->nr_zones - 1; z >= 0; z--) {
+		struct zone *zone = pgdat->node_zones + z;
+
+		if (!populated_zone(zone))
+			continue;
+
+		if (zone_watermark_ok(zone, 0,
+				      promo_wmark_pages(zone) + enough_wmark,
+				      ZONE_MOVABLE, 0))
+			return true;
+	}
+	return false;
+}
+
+/*
+ * For memory tiering mode, too high promotion/demotion throughput may
+ * hurt application latency.  So we provide a mechanism to rate limit
+ * the number of pages that are tried to be promoted.
+ */
+static bool kmigrated_promotion_rate_limit(struct pglist_data *pgdat, unsigned long rate_limit,
+					   int nr, unsigned long now_ms)
+{
+	unsigned long nr_cand;
+	unsigned int start;
+
+	mod_node_page_state(pgdat, PGPROMOTE_CANDIDATE, nr);
+	nr_cand = node_page_state(pgdat, PGPROMOTE_CANDIDATE);
+	start = pgdat->nbp_rl_start;
+	if (now_ms - start > MSEC_PER_SEC &&
+	    cmpxchg(&pgdat->nbp_rl_start, start, now_ms) == start)
+		pgdat->nbp_rl_nr_cand = nr_cand;
+	if (nr_cand - pgdat->nbp_rl_nr_cand >= rate_limit)
+		return true;
+	return false;
+}
+
+static void kmigrated_promotion_adjust_threshold(struct pglist_data *pgdat,
+						 unsigned long rate_limit, unsigned int ref_th,
+						 unsigned long now_ms)
+{
+	unsigned int start, th_period, unit_th, th;
+	unsigned long nr_cand, ref_cand, diff_cand;
+
+	th_period = KMIGRATED_PROMOTION_THRESHOLD_WINDOW;
+	start = pgdat->nbp_th_start;
+	if (now_ms - start > th_period &&
+	    cmpxchg(&pgdat->nbp_th_start, start, now_ms) == start) {
+		ref_cand = rate_limit *
+			KMIGRATED_PROMOTION_THRESHOLD_WINDOW / MSEC_PER_SEC;
+		nr_cand = node_page_state(pgdat, PGPROMOTE_CANDIDATE);
+		diff_cand = nr_cand - pgdat->nbp_th_nr_cand;
+		unit_th = ref_th * 2 / KMIGRATED_MIGRATION_ADJUST_STEPS;
+		th = pgdat->nbp_threshold ? : ref_th;
+		if (diff_cand > ref_cand * 11 / 10)
+			th = max(th - unit_th, unit_th);
+		else if (diff_cand < ref_cand * 9 / 10)
+			th = min(th + unit_th, ref_th * 2);
+		pgdat->nbp_th_nr_cand = nr_cand;
+		pgdat->nbp_threshold = th;
+	}
+}
+
+static bool kmigrated_should_migrate_memory(unsigned long nr_pages, unsigned long nid,
+					    unsigned long time)
+{
+	struct pglist_data *pgdat;
+	unsigned long rate_limit;
+	unsigned int th, def_th;
+	unsigned long now = jiffies;
+	unsigned long now_ms = jiffies_to_msecs(now);
+
+	pgdat = NODE_DATA(nid);
+	if (pgdat_free_space_enough(pgdat)) {
+		/* workload changed, reset hot threshold */
+		pgdat->nbp_threshold = 0;
+		mod_node_page_state(pgdat, PGPROMOTE_CANDIDATE_NRL, nr_pages);
+		return true;
+	}
+
+	def_th = sysctl_pghot_freq_window;
+	rate_limit = MB_TO_PAGES(sysctl_pghot_promote_rate_limit);
+	kmigrated_promotion_adjust_threshold(pgdat, rate_limit, def_th, now_ms);
+
+	th = pgdat->nbp_threshold ? : def_th;
+	if (jiffies_to_msecs(now - time) >= th)
+		return false;
+
+	return !kmigrated_promotion_rate_limit(pgdat, rate_limit, nr_pages, now_ms);
+}
+
 static int pghot_get_hotness(unsigned long pfn, unsigned long *nid, unsigned long *freq,
 				    unsigned long *time)
 {
@@ -233,6 +355,9 @@ static void kmigrated_walk_zone(unsigned long start_pfn, unsigned long end_pfn,
 		if (folio_nid(folio) == nid)
 			goto out_next;
 
+		if (!kmigrated_should_migrate_memory(nr, nid, time))
+			goto out_next;
+
 		if (migrate_misplaced_folio_prepare(folio, NULL, nid))
 			goto out_next;
 
-- 
2.34.1

[RFC PATCH v4 9/9] mm: pghot: Add folio_mark_accessed() as hotness source

[Bharata B Rao]

Unmapped page cache pages that end up in lower tiers don't get
promoted easily. There were attempts to identify such pages and
get them promoted as part of NUMA Balancing earlier [1]. The
same idea is taken forward here by using folio_mark_accessed()
as a source of hotness.

Lower tier accesses from folio_mark_accessed() are reported to
pghot sub-system for hotness tracking and subsequent promotion.

TODO: Need a better naming for this hotness source. Need to
better understand/evaluate the overhead of hotness info
collection from this path.

[1] https://lore.kernel.org/linux-mm/20250411221111.493193-1-gourry@gourry.net/

Signed-off-by: Bharata B Rao <bharata@amd.com>
---
 Documentation/admin-guide/mm/pghot.txt | 3 ++-
 include/linux/pghot.h                  | 3 +++
 include/linux/vm_event_item.h          | 1 +
 mm/pghot-debug.c                       | 7 +++++++
 mm/pghot.c                             | 6 ++++++
 mm/swap.c                              | 8 ++++++++
 mm/vmstat.c                            | 1 +
 7 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/mm/pghot.txt b/Documentation/admin-guide/mm/pghot.txt
index 13b87bcfa6a4..485407f2b288 100644
--- a/Documentation/admin-guide/mm/pghot.txt
+++ b/Documentation/admin-guide/mm/pghot.txt
@@ -23,9 +23,10 @@ Path: /sys/kernel/debug/pghot/
      - 0: Hardware hints (value 0x1)
      - 1: Page table scan (value 0x2)
      - 2: Hint faults (value 0x4)
+     - 2: folio_mark_accessed (value 0x8)
    - Default: 0 (disabled)
    - Example:
-     # echo 0x7 > /sys/kernel/debug/pghot/enabled_sources
+     # echo 0xf > /sys/kernel/debug/pghot/enabled_sources
      Enables all sources.
 
 2. **target_nid**
diff --git a/include/linux/pghot.h b/include/linux/pghot.h
index 615009a39348..c0919baf69e4 100644
--- a/include/linux/pghot.h
+++ b/include/linux/pghot.h
@@ -17,6 +17,7 @@ enum pghot_src {
 	PGHOT_HW_HINTS,
 	PGHOT_PGTABLE_SCAN,
 	PGHOT_HINT_FAULT,
+	PGHOT_FMA,
 };
 
 #ifdef CONFIG_PGHOT
@@ -28,12 +29,14 @@ enum pghot_src_enabed {
 	PGHOT_HWHINTS_BIT	= 0,
 	PGHOT_PGTSCAN_BIT,
 	PGHOT_HINTFAULT_BIT,
+	PGHOT_FMA_BIT,
 	PGHOT_MAX_BIT
 };
 
 #define PGHOT_HWHINTS_ENABLED	BIT(PGHOT_HWHINTS_BIT)
 #define PGHOT_PGTSCAN_ENABLED	BIT(PGHOT_PGTSCAN_BIT)
 #define PGHOT_HINTFAULT_ENABLED	BIT(PGHOT_HINTFAULT_BIT)
+#define PGHOT_FMA_ENABLED	BIT(PGHOT_FMA_BIT)
 #define PGHOT_SRC_ENABLED_MASK	GENMASK(PGHOT_MAX_BIT - 1, 0)
 
 #define PGHOT_DEFAULT_FREQ_WINDOW	(5 * MSEC_PER_SEC)
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 67efbca9051c..ac1f28646b9c 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -193,6 +193,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		PGHOT_RECORD_HWHINTS,
 		PGHOT_RECORD_PGTSCANS,
 		PGHOT_RECORD_HINTFAULTS,
+		PGHOT_RECORD_FMA,
 #ifdef CONFIG_HWMEM_PROFILER
 		HWHINT_NR_EVENTS,
 		HWHINT_KERNEL,
diff --git a/mm/pghot-debug.c b/mm/pghot-debug.c
index b6bee0f32389..fc1506c3134c 100644
--- a/mm/pghot-debug.c
+++ b/mm/pghot-debug.c
@@ -117,6 +117,13 @@ static void pghot_src_enabled_update(unsigned int enabled)
 		else
 			static_branch_disable(&pghot_src_hintfaults);
 	}
+
+	if (changed & PGHOT_FMA_ENABLED) {
+		if (enabled & PGHOT_FMA_ENABLED)
+			static_branch_enable(&pghot_src_fma);
+		else
+			static_branch_disable(&pghot_src_fma);
+	}
 }
 
 static ssize_t pghot_src_enabled_write(struct file *filp, const char __user *ubuf,
diff --git a/mm/pghot.c b/mm/pghot.c
index b28d11bf4c9f..b5780ae08522 100644
--- a/mm/pghot.c
+++ b/mm/pghot.c
@@ -35,6 +35,7 @@ static unsigned int sysctl_pghot_freq_window = PGHOT_DEFAULT_FREQ_WINDOW;
 static DEFINE_STATIC_KEY_FALSE(pghot_src_hwhints);
 static DEFINE_STATIC_KEY_FALSE(pghot_src_pghtscans);
 static DEFINE_STATIC_KEY_FALSE(pghot_src_hintfaults);
+static DEFINE_STATIC_KEY_FALSE(pghot_src_fma);
 
 #include "pghot-debug.c"
 
@@ -110,6 +111,11 @@ int pghot_record_access(unsigned long pfn, int nid, int src, unsigned long now)
 			return -EINVAL;
 		count_vm_event(PGHOT_RECORD_HINTFAULTS);
 		break;
+	case PGHOT_FMA:
+		if (!static_branch_likely(&pghot_src_fma))
+			return -EINVAL;
+		count_vm_event(PGHOT_RECORD_FMA);
+		break;
 	default:
 		return -EINVAL;
 	}
diff --git a/mm/swap.c b/mm/swap.c
index 2260dcd2775e..31a654b19844 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -37,6 +37,8 @@
 #include <linux/page_idle.h>
 #include <linux/local_lock.h>
 #include <linux/buffer_head.h>
+#include <linux/pghot.h>
+#include <linux/memory-tiers.h>
 
 #include "internal.h"
 
@@ -454,8 +456,14 @@ static bool lru_gen_clear_refs(struct folio *folio)
  */
 void folio_mark_accessed(struct folio *folio)
 {
+	unsigned long pfn = folio_pfn(folio);
+
 	if (folio_test_dropbehind(folio))
 		return;
+
+	if (!node_is_toptier(pfn_to_nid(pfn)))
+		pghot_record_access(pfn, NUMA_NO_NODE, PGHOT_FMA, jiffies);
+
 	if (lru_gen_enabled()) {
 		lru_gen_inc_refs(folio);
 		return;
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 4160476c4ee5..5085ff248ccc 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1501,6 +1501,7 @@ const char * const vmstat_text[] = {
 	[I(PGHOT_RECORD_HWHINTS)]		= "pghot_recorded_hwhints",
 	[I(PGHOT_RECORD_PGTSCANS)]		= "pghot_recorded_pgtscans",
 	[I(PGHOT_RECORD_HINTFAULTS)]		= "pghot_recorded_hintfaults",
+	[I(PGHOT_RECORD_FMA)]			= "pghot_recorded_fma",
 #ifdef CONFIG_HWMEM_PROFILER
 	[I(HWHINT_NR_EVENTS)]			= "hwhint_nr_events",
 	[I(HWHINT_KERNEL)]			= "hwhint_kernel",
-- 
2.34.1