[PATCH 2/4] mm: Introduce page_mapcount_is_type()

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Resolve the awkward "and add one to this opaque constant" test into a
self-documenting inline function.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/proc/internal.h         |  3 +--
 include/linux/mm.h         |  3 +--
 include/linux/page-flags.h | 12 +++++++++---
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index a8a8576d8592..cc520168f8b6 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -166,8 +166,7 @@ static inline int folio_precise_page_mapcount(struct folio *folio,
 {
 	int mapcount = atomic_read(&page->_mapcount) + 1;
 
-	/* Handle page_has_type() pages */
-	if (mapcount < PAGE_MAPCOUNT_RESERVE + 1)
+	if (page_mapcount_is_type(mapcount))
 		mapcount = 0;
 	if (folio_test_large(folio))
 		mapcount += folio_entire_mapcount(folio);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 00501f85f45f..47aa932075a8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1232,8 +1232,7 @@ static inline int folio_mapcount(const struct folio *folio)
 
 	if (likely(!folio_test_large(folio))) {
 		mapcount = atomic_read(&folio->_mapcount) + 1;
-		/* Handle page_has_type() pages */
-		if (mapcount < PAGE_MAPCOUNT_RESERVE + 1)
+		if (page_mapcount_is_type(mapcount))
 			mapcount = 0;
 		return mapcount;
 	}
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 17175a328e6b..998a99441e4f 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -956,12 +956,18 @@ enum pagetype {
 #define folio_test_type(folio, flag)					\
 	((READ_ONCE(folio->page.page_type) & (PAGE_TYPE_BASE | flag))  == PAGE_TYPE_BASE)
 
-static inline int page_type_has_type(unsigned int page_type)
+static inline bool page_type_has_type(int page_type)
 {
-	return (int)page_type < PAGE_MAPCOUNT_RESERVE;
+	return page_type < PAGE_MAPCOUNT_RESERVE;
 }
 
-static inline int page_has_type(const struct page *page)
+/* This takes a mapcount which is one more than page->_mapcount */
+static inline bool page_mapcount_is_type(unsigned int mapcount)
+{
+	return page_type_has_type(mapcount - 1);
+}
+
+static inline bool page_has_type(const struct page *page)
 {
 	return page_type_has_type(READ_ONCE(page->page_type));
 }
-- 
2.43.0