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

[Bharata B Rao <bharata@amd.com>]

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