[PATCH 17/22] mm: Reimplement compound_nr()

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

Turn compound_nr() into a wrapper around folio_nr_pages().  Similarly
to compound_order(), casting the struct page directly to struct folio
preserves the existing behaviour, while calling page_folio() would change
the behaviour.  Move thp_nr_pages() down in the file so that compound_nr()
can be after folio_nr_pages().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/mm.h | 38 ++++++++++++++++----------------------
 1 file changed, 16 insertions(+), 22 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 19bdb4b0e00a..75054fce8ec6 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1016,18 +1016,6 @@ static inline void folio_set_compound_order(struct folio *folio,
 #endif
 }
 
-/* Returns the number of pages in this potentially compound page. */
-static inline unsigned long compound_nr(struct page *page)
-{
-	if (!PageHead(page))
-		return 1;
-#ifdef CONFIG_64BIT
-	return page[1].compound_nr;
-#else
-	return 1UL << compound_order(page);
-#endif
-}
-
 /* Returns the number of bytes in this potentially compound page. */
 static inline unsigned long page_size(struct page *page)
 {
@@ -1050,16 +1038,6 @@ static inline unsigned int thp_order(struct page *page)
 	return compound_order(page);
 }
 
-/**
- * thp_nr_pages - The number of regular pages in this huge page.
- * @page: The head page of a huge page.
- */
-static inline int thp_nr_pages(struct page *page)
-{
-	VM_BUG_ON_PGFLAGS(PageTail(page), page);
-	return compound_nr(page);
-}
-
 /**
  * thp_size - Size of a transparent huge page.
  * @page: Head page of a transparent huge page.
@@ -1754,6 +1732,22 @@ static inline long folio_nr_pages(struct folio *folio)
 #endif
 }
 
+/* Returns the number of pages in this potentially compound page. */
+static inline unsigned long compound_nr(struct page *page)
+{
+	return folio_nr_pages((struct folio *)page);
+}
+
+/**
+ * thp_nr_pages - The number of regular pages in this huge page.
+ * @page: The head page of a huge page.
+ */
+static inline int thp_nr_pages(struct page *page)
+{
+	VM_BUG_ON_PGFLAGS(PageTail(page), page);
+	return compound_nr(page);
+}
+
 /**
  * folio_next - Move to the next physical folio.
  * @folio: The folio we're currently operating on.
-- 
2.35.1