mm: convert total_compound_mapcount() to folio_total_mapcount()

Instead of enforcing that the argument must be a head page by naming,
enforce it with the compiler by making it a folio.  Also rename the
counter in struct folio from _compound_mapcount to _entire_mapcount.

Link: https://lkml.kernel.org/r/20230111142915.1001531-5-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -871,7 +871,7 @@ static inline int page_mapcount(struct page *page)
 	return head_compound_mapcount(page) + mapcount;
 }
 
-int total_compound_mapcount(struct page *head);
+int folio_total_mapcount(struct folio *folio);
 
 /**
  * folio_mapcount() - Calculate the number of mappings of this folio.
@@ -888,14 +888,14 @@ static inline int folio_mapcount(struct folio *folio)
 {
 	if (likely(!folio_test_large(folio)))
 		return atomic_read(&folio->_mapcount) + 1;
-	return total_compound_mapcount(&folio->page);
+	return folio_total_mapcount(folio);
 }
 
 static inline int total_mapcount(struct page *page)
 {
 	if (likely(!PageCompound(page)))
 		return atomic_read(&page->_mapcount) + 1;
-	return total_compound_mapcount(compound_head(page));
+	return folio_total_mapcount(page_folio(page));
 }
 
 static inline bool folio_large_is_mapped(struct folio *folio)

include/linux/mm_types.h

@@ -306,7 +306,7 @@ static inline struct page *encoded_page_ptr(struct encoded_page *page)
  * @_head_1: Points to the folio.  Do not use.
  * @_folio_dtor: Which destructor to use for this folio.
  * @_folio_order: Do not use directly, call folio_order().
- * @_compound_mapcount: Do not use directly, call folio_entire_mapcount().
+ * @_entire_mapcount: Do not use directly, call folio_entire_mapcount().
  * @_nr_pages_mapped: Do not use directly, call folio_mapcount().
  * @_pincount: Do not use directly, call folio_maybe_dma_pinned().
  * @_folio_nr_pages: Do not use directly, call folio_nr_pages().
@@ -360,7 +360,7 @@ struct folio {
 			unsigned long _head_1;
 			unsigned char _folio_dtor;
 			unsigned char _folio_order;
-			atomic_t _compound_mapcount;
+			atomic_t _entire_mapcount;
 			atomic_t _nr_pages_mapped;
 			atomic_t _pincount;
 #ifdef CONFIG_64BIT
@@ -403,7 +403,7 @@ FOLIO_MATCH(flags, _flags_1);
 FOLIO_MATCH(compound_head, _head_1);
 FOLIO_MATCH(compound_dtor, _folio_dtor);
 FOLIO_MATCH(compound_order, _folio_order);
-FOLIO_MATCH(compound_mapcount, _compound_mapcount);
+FOLIO_MATCH(compound_mapcount, _entire_mapcount);
 FOLIO_MATCH(subpages_mapcount, _nr_pages_mapped);
 FOLIO_MATCH(compound_pincount, _pincount);
 #ifdef CONFIG_64BIT

mm/rmap.c

@@ -1078,27 +1078,26 @@ int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
 	return page_vma_mkclean_one(&pvmw);
 }
 
-int total_compound_mapcount(struct page *head)
+int folio_total_mapcount(struct folio *folio)
 {
-	struct folio *folio = (struct folio *)head;
-	int mapcount = head_compound_mapcount(head);
-	int nr_subpages;
+	int mapcount = folio_entire_mapcount(folio);
+	int nr_pages;
 	int i;
 
-	/* In the common case, avoid the loop when no subpages mapped by PTE */
+	/* In the common case, avoid the loop when no pages mapped by PTE */
 	if (folio_nr_pages_mapped(folio) == 0)
 		return mapcount;
 	/*
-	 * Add all the PTE mappings of those subpages mapped by PTE.
-	 * Limit the loop, knowing that only subpages_mapcount are mapped?
+	 * Add all the PTE mappings of those pages mapped by PTE.
+	 * Limit the loop to folio_nr_pages_mapped()?
 	 * Perhaps: given all the raciness, that may be a good or a bad idea.
 	 */
-	nr_subpages = thp_nr_pages(head);
-	for (i = 0; i < nr_subpages; i++)
-		mapcount += atomic_read(&head[i]._mapcount);
+	nr_pages = folio_nr_pages(folio);
+	for (i = 0; i < nr_pages; i++)
+		mapcount += atomic_read(&folio_page(folio, i)->_mapcount);
 
 	/* But each of those _mapcounts was based on -1 */
-	mapcount += nr_subpages;
+	mapcount += nr_pages;
 	return mapcount;
 }