[PATCH v2 3/4] mm/migrate: add tracepoint for folios unmapped during migration

[Wandun Chen <chenwandun1@gmail.com>]

From: Wandun Chen <chenwandun@lixiang.com>

Add mm_migrate_unmap_folio tracepoint, fired in try_to_migrate_one()
after a folio's mapping has been replaced by a migration entry.
It records the pfn, address, folio flags and vm_flags, making mlocked
folios under migration easy to observe.

Signed-off-by: Wandun Chen <chenwandun@lixiang.com>
---
 include/trace/events/migrate.h | 29 +++++++++++++++++++++++++++++
 mm/rmap.c                      |  4 ++++
 2 files changed, 33 insertions(+)

diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
index 15ee2ef201b5..1264593ecaee 100644
--- a/include/trace/events/migrate.h
+++ b/include/trace/events/migrate.h
@@ -6,6 +6,7 @@
 #define _TRACE_MIGRATE_H
 
 #include <linux/tracepoint.h>
+#include <trace/events/mmflags.h>
 
 #define MIGRATE_MODE						\
 	EM( MIGRATE_ASYNC,	"MIGRATE_ASYNC")		\
@@ -137,6 +138,34 @@ DEFINE_EVENT(migration_pte, set_migration_pte,
 	TP_ARGS(addr, pte, order)
 );
 
+TRACE_EVENT(mm_migrate_unmap_folio,
+
+	TP_PROTO(unsigned long pfn, unsigned long addr,
+		 unsigned long page_flags, unsigned long vm_flags),
+
+	TP_ARGS(pfn, addr, page_flags, vm_flags),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, pfn)
+		__field(unsigned long, addr)
+		__field(unsigned long, page_flags)
+		__field(unsigned long, vm_flags)
+	),
+
+	TP_fast_assign(
+		__entry->pfn		= pfn;
+		__entry->addr		= addr;
+		__entry->page_flags	= page_flags;
+		__entry->vm_flags	= vm_flags;
+	),
+
+	TP_printk("pfn=0x%lx addr=0x%lx page_flags=%s vm_flags=%s",
+		__entry->pfn,
+		__entry->addr,
+		show_page_flags(__entry->page_flags & PAGEFLAGS_MASK),
+		show_vma_flags(__entry->vm_flags))
+);
+
 DEFINE_EVENT(migration_pte, remove_migration_pte,
 	TP_PROTO(unsigned long addr, unsigned long pte, int order),
 	TP_ARGS(addr, pte, order)
diff --git a/mm/rmap.c b/mm/rmap.c
index 3cb7f6337d38..b110548bebae 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2716,6 +2716,10 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 			hugetlb_remove_rmap(folio);
 		else
 			folio_remove_rmap_pte(folio, subpage, vma);
+
+		trace_mm_migrate_unmap_folio(folio_pfn(folio), address,
+					     folio->flags.f, vma->vm_flags);
+
 		if (vma->vm_flags & VM_LOCKED)
 			mlock_drain_local();
 		folio_put(folio);
-- 
2.43.0