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

David Hildenbrand (Arm)
2026-04-12T19:00:49Z

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