[PATCH] dbg mapping_ptr

[Huang Ying]

---
 mm/rmap.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 8632e02661ac..50ee208baff9 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -466,6 +466,13 @@ void __init anon_vma_init(void)
 			SLAB_PANIC|SLAB_ACCOUNT);
 }
=20
+union mapping_ptr {
+	struct address_space *mapping;
+	unsigned long tag;
+	struct anon_vma *anon_vma;
+	struct movable_operations *mops;
+};
+
 /*
  * Getting a lock on a stable anon_vma from a page off the LRU is tricky!
  *
@@ -493,16 +500,17 @@ void __init anon_vma_init(void)
 struct anon_vma *folio_get_anon_vma(struct folio *folio)
 {
 	struct anon_vma *anon_vma =3D NULL;
-	unsigned long anon_mapping;
+	union mapping_ptr mptr;
=20
 	rcu_read_lock();
-	anon_mapping =3D (unsigned long)READ_ONCE(folio->mapping);
-	if ((anon_mapping & PAGE_MAPPING_FLAGS) !=3D PAGE_MAPPING_ANON)
+	mptr.mapping =3D READ_ONCE(folio->mapping);
+	if ((mptr.tag & PAGE_MAPPING_FLAGS) !=3D PAGE_MAPPING_ANON)
 		goto out;
 	if (!folio_mapped(folio))
 		goto out;
=20
-	anon_vma =3D (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
+	mptr.tag &=3D ~PAGE_MAPPING_FLAGS;
+	anon_vma =3D mptr.anon_vma;
 	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
 		anon_vma =3D NULL;
 		goto out;
@@ -1115,18 +1123,20 @@ int folio_total_mapcount(struct folio *folio)
 void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)
 {
 	void *anon_vma =3D vma->anon_vma;
+	union mapping_ptr mptr;
 	struct folio *folio =3D page_folio(page);
=20
 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 	VM_BUG_ON_VMA(!anon_vma, vma);
=20
-	anon_vma +=3D PAGE_MAPPING_ANON;
+	mptr.anon_vma =3D anon_vma;
+	mptr.tag |=3D PAGE_MAPPING_ANON;
 	/*
 	 * Ensure that anon_vma and the PAGE_MAPPING_ANON bit are written
 	 * simultaneously, so a concurrent reader (eg folio_referenced()'s
 	 * folio_test_anon()) will not see one without the other.
 	 */
-	WRITE_ONCE(folio->mapping, anon_vma);
+	WRITE_ONCE(folio->mapping, mptr.mapping);
 	SetPageAnonExclusive(page);
 }
=20
@@ -1142,6 +1152,7 @@ static void __page_set_anon_rmap(struct folio *folio,=
 struct page *page,
 	struct vm_area_struct *vma, unsigned long address, int exclusive)
 {
 	struct anon_vma *anon_vma =3D vma->anon_vma;
+	union mapping_ptr mptr;
=20
 	BUG_ON(!anon_vma);
=20
@@ -1162,8 +1173,9 @@ static void __page_set_anon_rmap(struct folio *folio,=
 struct page *page,
 	 * the PAGE_MAPPING_ANON type identifier, otherwise the rmap code
 	 * could mistake the mapping for a struct address_space and crash.
 	 */
-	anon_vma =3D (void *) anon_vma + PAGE_MAPPING_ANON;
-	WRITE_ONCE(folio->mapping, (struct address_space *) anon_vma);
+	mptr.anon_vma =3D anon_vma;
+	mptr.tag |=3D PAGE_MAPPING_ANON;
+	WRITE_ONCE(folio->mapping, mptr.mapping);
 	folio->index =3D linear_page_index(vma, address);
 out:
 	if (exclusive)
--=20
2.39.2