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

["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->_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