linux-kernel - [RFC PATCH 1/9] mm: introduce PAGE_TYPE

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Message-Id: <20250724084441.380404-2-link@vivo.com>
Date: Thu, 24 Jul 2025 16:44:29 +0800
From: Huan Yang <link@...o.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Rik van Riel <riel@...riel.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Harry Yoo <harry.yoo@...cle.com>,
	Xu Xin <xu.xin16@....com.cn>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Zi Yan <ziy@...dia.com>,
	Matthew Brost <matthew.brost@...el.com>,
	Joshua Hahn <joshua.hahnjy@...il.com>,
	Rakie Kim <rakie.kim@...com>,
	Byungchul Park <byungchul@...com>,
	Gregory Price <gourry@...rry.net>,
	Ying Huang <ying.huang@...ux.alibaba.com>,
	Alistair Popple <apopple@...dia.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Huan Yang <link@...o.com>,
	Christian Brauner <brauner@...nel.org>,
	Usama Arif <usamaarif642@...il.com>,
	Yu Zhao <yuzhao@...gle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [RFC PATCH 1/9] mm: introduce PAGE_TYPE_SHIFT

The current shift value for page_type is 24. To avoid hardcode, define
a macro called PAGE_TYPE_SHIFT and PAGE_TYPE_MASK.

No functional change.

Signed-off-by: Huan Yang <link@...o.com>
---
 include/linux/page-flags.h | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 4fe5ee67535b..3c7103c2eee4 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -961,9 +961,12 @@ enum pagetype {
 	PGTY_mapcount_underflow = 0xff
 };
 
+#define PAGE_TYPE_SHIFT		24
+#define PAGE_TYPE_MASK		((1 << PAGE_TYPE_SHIFT) - 1)
+
 static inline bool page_type_has_type(int page_type)
 {
-	return page_type < (PGTY_mapcount_underflow << 24);
+	return page_type < (PGTY_mapcount_underflow << PAGE_TYPE_SHIFT);
 }
 
 /* This takes a mapcount which is one more than page->_mapcount */
@@ -980,7 +983,8 @@ static inline bool page_has_type(const struct page *page)
 #define FOLIO_TYPE_OPS(lname, fname)					\
 static __always_inline bool folio_test_##fname(const struct folio *folio) \
 {									\
-	return data_race(folio->page.page_type >> 24) == PGTY_##lname;	\
+	return data_race(folio->page.page_type >> PAGE_TYPE_SHIFT)      \
+	       == PGTY_##lname;						\
 }									\
 static __always_inline void __folio_set_##fname(struct folio *folio)	\
 {									\
@@ -988,7 +992,8 @@ static __always_inline void __folio_set_##fname(struct folio *folio)	\
 		return;							\
 	VM_BUG_ON_FOLIO(data_race(folio->page.page_type) != UINT_MAX,	\
 			folio);						\
-	folio->page.page_type = (unsigned int)PGTY_##lname << 24;	\
+	folio->page.page_type = (unsigned int)PGTY_##lname		\
+					      << PAGE_TYPE_SHIFT;	\
 }									\
 static __always_inline void __folio_clear_##fname(struct folio *folio)	\
 {									\
@@ -1002,14 +1007,16 @@ static __always_inline void __folio_clear_##fname(struct folio *folio)	\
 FOLIO_TYPE_OPS(lname, fname)						\
 static __always_inline int Page##uname(const struct page *page)		\
 {									\
-	return data_race(page->page_type >> 24) == PGTY_##lname;	\
+	return data_race(page->page_type >> PAGE_TYPE_SHIFT)		\
+	       == PGTY_##lname;						\
 }									\
 static __always_inline void __SetPage##uname(struct page *page)		\
 {									\
 	if (Page##uname(page))						\
 		return;							\
 	VM_BUG_ON_PAGE(data_race(page->page_type) != UINT_MAX, page);	\
-	page->page_type = (unsigned int)PGTY_##lname << 24;		\
+	page->page_type = (unsigned int)PGTY_##lname			\
+					<< PAGE_TYPE_SHIFT;		\
 }									\
 static __always_inline void __ClearPage##uname(struct page *page)	\
 {									\
-- 
2.34.1