[PATCH RFC 10/13] mm: re-consolidate folio->_pincount

David Hildenbrand (Arm)
2026-04-12T19:01:06Z

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

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
include/linux/mm.h | 4 +---
include/linux/mm_types.h | 7 ++-----
mm/debug.c | 5 +----
mm/internal.h | 3 +--
mm/page_alloc.c | 14 +++-----------
5 files changed, 8 insertions(+), 25 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1715c6ed14d4..6dd906585420 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2593,9 +2593,7 @@ static inline pud_t folio_mk_pud(const struct folio *folio, pgprot_t pgprot)

static inline bool folio_has_pincount(const struct folio *folio)
{
- if (IS_ENABLED(CONFIG_64BIT))
- return folio_test_large(folio);
- return folio_order(folio) > 1;
+ return folio_test_large(folio);
}

/**
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index e59571d2f81d..450f61cad678 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -451,11 +451,11 @@ struct folio {
union {
struct {
/* public: */
- unsigned int _unused_2;
+ atomic_t _pincount;
atomic_t _entire_mapcount;
#ifdef CONFIG_64BIT
unsigned int _unused_1;
- atomic_t _pincount;
+ unsigned int _unused_2;
#endif /* CONFIG_64BIT */
mm_id_mapcount_t _mm_id_mapcount[2];
union {
@@ -482,9 +482,6 @@ struct folio {
unsigned long _head_2;
/* public: */
struct list_head _deferred_list;
-#ifndef CONFIG_64BIT
- atomic_t _pincount;
-#endif /* !CONFIG_64BIT */
/* private: the union with struct page is transitional */
};
struct page __page_2;
diff --git a/mm/debug.c b/mm/debug.c
index bfb41ef17a5e..80e050bf29ba 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -81,10 +81,7 @@ static void __dump_folio(const struct folio *folio, const struct page *page,
folio_ref_count(folio), mapcount, mapping,
folio->index + idx, pfn);
if (folio_test_large(folio)) {
- int pincount = 0;
-
- if (folio_has_pincount(folio))
- pincount = atomic_read(&folio->_pincount);
+ int pincount = atomic_read(&folio->_pincount);

pr_warn("head: order:%u mapcount:%d entire_mapcount:%d pincount:%d\n",
folio_order(folio),
diff --git a/mm/internal.h b/mm/internal.h
index 53b20de141b9..aa1206495bc6 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -869,8 +869,7 @@ static inline void prep_compound_head(struct page *page, unsigned int order)
folio->_mm_id_mapcount[1] = -1;
}
atomic_set(&folio->_entire_mapcount, -1);
- if (IS_ENABLED(CONFIG_64BIT) || order > 1)
- atomic_set(&folio->_pincount, 0);
+ atomic_set(&folio->_pincount, 0);
if (order > 1)
INIT_LIST_HEAD(&folio->_deferred_list);
}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1c09d79cade3..8ed4c73fdba4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1125,11 +1125,9 @@ static int free_tail_page_prepare(struct page *head_page, struct page *page)
bad_page(page, "nonzero entire_mapcount");
goto out;
}
- if (IS_ENABLED(CONFIG_64BIT)) {
- if (unlikely(atomic_read(&folio->_pincount))) {
- bad_page(page, "nonzero pincount");
- goto out;
- }
+ if (unlikely(atomic_read(&folio->_pincount))) {
+ bad_page(page, "nonzero pincount");
+ goto out;
}
break;
case 2:
@@ -1138,12 +1136,6 @@ static int free_tail_page_prepare(struct page *head_page, struct page *page)
bad_page(page, "on deferred list");
goto out;
}
- if (!IS_ENABLED(CONFIG_64BIT)) {
- if (unlikely(atomic_read(&folio->_pincount))) {
- bad_page(page, "nonzero pincount");
- goto out;
- }
- }
break;
case 3:
/* the third tail page: hugetlb specifics overlap ->mappings */

--
2.43.0