[PATCH 6/8] mm: Constify testing page/folio flags

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

Now that dump_page() takes a const argument, we can constify all the
page flag tests.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 include/linux/page-flags.h | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 582ca7400eca..3463cd1baebf 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -237,7 +237,7 @@ static inline const struct page *page_fixed_fake_head(const struct page *page)
 }
 #endif
 
-static __always_inline int page_is_fake_head(struct page *page)
+static __always_inline int page_is_fake_head(const struct page *page)
 {
 	return page_fixed_fake_head(page) != page;
 }
@@ -281,12 +281,12 @@ static inline unsigned long _compound_head(const struct page *page)
  */
 #define folio_page(folio, n)	nth_page(&(folio)->page, n)
 
-static __always_inline int PageTail(struct page *page)
+static __always_inline int PageTail(const struct page *page)
 {
 	return READ_ONCE(page->compound_head) & 1 || page_is_fake_head(page);
 }
 
-static __always_inline int PageCompound(struct page *page)
+static __always_inline int PageCompound(const struct page *page)
 {
 	return test_bit(PG_head, &page->flags) ||
 	       READ_ONCE(page->compound_head) & 1;
@@ -306,6 +306,16 @@ static inline void page_init_poison(struct page *page, size_t size)
 }
 #endif
 
+static const unsigned long *const_folio_flags(const struct folio *folio,
+		unsigned n)
+{
+	const struct page *page = &folio->page;
+
+	VM_BUG_ON_PGFLAGS(PageTail(page), page);
+	VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page);
+	return &page[n].flags;
+}
+
 static unsigned long *folio_flags(struct folio *folio, unsigned n)
 {
 	struct page *page = &folio->page;
@@ -367,8 +377,8 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n)
  * Macros to create function definitions for page flags
  */
 #define FOLIO_TEST_FLAG(name, page)					\
-static __always_inline bool folio_test_##name(struct folio *folio)	\
-{ return test_bit(PG_##name, folio_flags(folio, page)); }
+static __always_inline bool folio_test_##name(const struct folio *folio) \
+{ return test_bit(PG_##name, const_folio_flags(folio, page)); }
 
 #define FOLIO_SET_FLAG(name, page)					\
 static __always_inline void folio_set_##name(struct folio *folio)	\
@@ -401,7 +411,7 @@ FOLIO_CLEAR_FLAG(name, page)
 
 #define TESTPAGEFLAG(uname, lname, policy)				\
 FOLIO_TEST_FLAG(lname, FOLIO_##policy)					\
-static __always_inline int Page##uname(struct page *page)		\
+static __always_inline int Page##uname(const struct page *page)		\
 { return test_bit(PG_##lname, &policy(page, 0)->flags); }
 
 #define SETPAGEFLAG(uname, lname, policy)				\
@@ -801,7 +811,7 @@ static __always_inline bool folio_test_head(struct folio *folio)
 	return test_bit(PG_head, folio_flags(folio, FOLIO_PF_ANY));
 }
 
-static __always_inline int PageHead(struct page *page)
+static __always_inline int PageHead(const struct page *page)
 {
 	PF_POISONED_CHECK(page);
 	return test_bit(PG_head, &page->flags) && !page_is_fake_head(page);
-- 
2.43.0