[PATCH RFC 08/13] mm: re-consolidate folio->_entire_mapcount

["David Hildenbrand (Arm)" <david@kernel.org>]

Now that we have some space left in page[1] of a large folio on 32bit,
we can re-consolidate folio->_entire_mapcount.

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 include/linux/mm.h       |  4 +---
 include/linux/mm_types.h |  5 ++---
 mm/internal.h            |  5 ++---
 mm/page_alloc.c          | 12 ++++--------
 4 files changed, 9 insertions(+), 17 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 633bbf9a184a..1715c6ed14d4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1832,9 +1832,7 @@ static inline int is_vmalloc_or_module_addr(const void *x)
  */
 static inline int folio_entire_mapcount(const struct folio *folio)
 {
-	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
-	if (!IS_ENABLED(CONFIG_64BIT) && unlikely(folio_large_order(folio) == 1))
-		return 0;
+	VM_WARN_ON_FOLIO(!folio_test_large(folio), folio);
 	return atomic_read(&folio->_entire_mapcount) + 1;
 }
 
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 47b2c3d05f41..1e1befe7d418 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -452,9 +452,9 @@ struct folio {
 				struct {
 	/* public: */
 					atomic_t _large_mapcount;
-					unsigned int _unused_1;
-#ifdef CONFIG_64BIT
 					atomic_t _entire_mapcount;
+#ifdef CONFIG_64BIT
+					unsigned int _unused_1;
 					atomic_t _pincount;
 #endif /* CONFIG_64BIT */
 					mm_id_mapcount_t _mm_id_mapcount[2];
@@ -483,7 +483,6 @@ struct folio {
 	/* public: */
 			struct list_head _deferred_list;
 #ifndef CONFIG_64BIT
-			atomic_t _entire_mapcount;
 			atomic_t _pincount;
 #endif /* !CONFIG_64BIT */
 	/* private: the union with struct page is transitional */
diff --git a/mm/internal.h b/mm/internal.h
index 30e48f39d2de..53b20de141b9 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -868,10 +868,9 @@ static inline void prep_compound_head(struct page *page, unsigned int order)
 		folio->_mm_id_mapcount[0] = -1;
 		folio->_mm_id_mapcount[1] = -1;
 	}
-	if (IS_ENABLED(CONFIG_64BIT) || order > 1) {
+	atomic_set(&folio->_entire_mapcount, -1);
+	if (IS_ENABLED(CONFIG_64BIT) || order > 1)
 		atomic_set(&folio->_pincount, 0);
-		atomic_set(&folio->_entire_mapcount, -1);
-	}
 	if (order > 1)
 		INIT_LIST_HEAD(&folio->_deferred_list);
 }
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8888f31aca49..1c09d79cade3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1121,11 +1121,11 @@ static int free_tail_page_prepare(struct page *head_page, struct page *page)
 				goto out;
 			}
 		}
+		if (folio_entire_mapcount(folio)) {
+			bad_page(page, "nonzero entire_mapcount");
+			goto out;
+		}
 		if (IS_ENABLED(CONFIG_64BIT)) {
-			if (unlikely(atomic_read(&folio->_entire_mapcount) + 1)) {
-				bad_page(page, "nonzero entire_mapcount");
-				goto out;
-			}
 			if (unlikely(atomic_read(&folio->_pincount))) {
 				bad_page(page, "nonzero pincount");
 				goto out;
@@ -1139,10 +1139,6 @@ static int free_tail_page_prepare(struct page *head_page, struct page *page)
 			goto out;
 		}
 		if (!IS_ENABLED(CONFIG_64BIT)) {
-			if (unlikely(atomic_read(&folio->_entire_mapcount) + 1)) {
-				bad_page(page, "nonzero entire_mapcount");
-				goto out;
-			}
 			if (unlikely(atomic_read(&folio->_pincount))) {
 				bad_page(page, "nonzero pincount");
 				goto out;

-- 
2.43.0