mm: rename page->index to page->__folio_index

All users of page->index have been converted to not refer to it any more. 
Update a few pieces of documentation that were missed and prevent new
users from appearing (or at least make them easy to grep for).

Link: https://lkml.kernel.org/r/20250514181508.3019795-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/arm/mm/flush.c

@@ -227,9 +227,9 @@ void __flush_dcache_folio(struct address_space *mapping, struct folio *folio)
 	}
 
 	/*
-	 * If this is a page cache page, and we have an aliasing VIPT cache,
+	 * If this is a page cache folio, and we have an aliasing VIPT cache,
 	 * we only need to do one flush - which would be at the relevant
-	 * userspace colour, which is congruent with page->index.
+	 * userspace colour, which is congruent with folio->index.
 	 */
 	if (mapping && cache_is_vipt_aliasing())
 		flush_pfn_alias(folio_pfn(folio), folio_pos(folio));

include/linux/mm.h

@@ -1276,9 +1276,9 @@ vm_fault_t finish_fault(struct vm_fault *vmf);
  * the page's disk buffers. PG_private must be set to tell the VM to call
  * into the filesystem to release these pages.
  *
- * A page may belong to an inode's memory mapping. In this case, page->mapping
- * is the pointer to the inode, and page->index is the file offset of the page,
- * in units of PAGE_SIZE.
+ * A folio may belong to an inode's memory mapping. In this case,
+ * folio->mapping points to the inode, and folio->index is the file
+ * offset of the folio, in units of PAGE_SIZE.
  *
  * If pagecache pages are not associated with an inode, they are said to be
  * anonymous pages. These may become associated with the swapcache, and in that

include/linux/mm_types.h

@@ -107,7 +107,7 @@ struct page {
 			/* See page-flags.h for PAGE_MAPPING_FLAGS */
 			struct address_space *mapping;
 			union {
-				pgoff_t index;		/* Our offset within mapping. */
+				pgoff_t __folio_index;		/* Our offset within mapping. */
 				unsigned long share;	/* share count for fsdax */
 			};
 			/**
@@ -488,7 +488,7 @@ FOLIO_MATCH(flags, flags);
 FOLIO_MATCH(lru, lru);
 FOLIO_MATCH(mapping, mapping);
 FOLIO_MATCH(compound_head, lru);
-FOLIO_MATCH(index, index);
+FOLIO_MATCH(__folio_index, index);
 FOLIO_MATCH(private, private);
 FOLIO_MATCH(_mapcount, _mapcount);
 FOLIO_MATCH(_refcount, _refcount);
@@ -589,7 +589,7 @@ TABLE_MATCH(flags, __page_flags);
 TABLE_MATCH(compound_head, pt_list);
 TABLE_MATCH(compound_head, _pt_pad_1);
 TABLE_MATCH(mapping, __page_mapping);
-TABLE_MATCH(index, pt_index);
+TABLE_MATCH(__folio_index, pt_index);
 TABLE_MATCH(rcu_head, pt_rcu_head);
 TABLE_MATCH(page_type, __page_type);
 TABLE_MATCH(_refcount, __page_refcount);

kernel/futex/core.c

@@ -206,7 +206,7 @@ static u64 get_inode_sequence_number(struct inode *inode)
  *
  * For shared mappings (when @fshared), the key is:
  *
- *   ( inode->i_sequence, page->index, offset_within_page )
+ *   ( inode->i_sequence, page offset within mapping, offset_within_page )
  *
  * [ also see get_inode_sequence_number() ]
  *

mm/filemap.c

@@ -142,7 +142,7 @@ static void page_cache_delete(struct address_space *mapping,
 	xas_init_marks(&xas);
 
 	folio->mapping = NULL;
-	/* Leave page->index set: truncation lookup relies upon it */
+	/* Leave folio->index set: truncation lookup relies upon it */
 	mapping->nrpages -= nr;
 }
 
@@ -949,7 +949,7 @@ unlock:
 	return 0;
 error:
 	folio->mapping = NULL;
-	/* Leave page->index set: truncation relies upon it */
+	/* Leave folio->index set: truncation relies upon it */
 	folio_put_refs(folio, nr);
 	return xas_error(&xas);
 }

mm/memory.c

@@ -4668,8 +4668,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 		/*
 		 * KSM sometimes has to copy on read faults, for example, if
-		 * page->index of !PageKSM() pages would be nonlinear inside the
-		 * anon VMA -- PageKSM() is lost on actual swapout.
+		 * folio->index of non-ksm folios would be nonlinear inside the
+		 * anon VMA -- the ksm flag is lost on actual swapout.
 		 */
 		folio = ksm_might_need_to_copy(folio, vma, vmf->address);
 		if (unlikely(!folio)) {

mm/page-writeback.c

@@ -2565,11 +2565,11 @@ struct folio *writeback_iter(struct address_space *mapping,
 	if (!folio) {
 		/*
 		 * To avoid deadlocks between range_cyclic writeback and callers
-		 * that hold pages in PageWriteback to aggregate I/O until
+		 * that hold folios in writeback to aggregate I/O until
 		 * the writeback iteration finishes, we do not loop back to the
-		 * start of the file.  Doing so causes a page lock/page
+		 * start of the file.  Doing so causes a folio lock/folio
 		 * writeback access order inversion - we should only ever lock
-		 * multiple pages in ascending page->index order, and looping
+		 * multiple folios in ascending folio->index order, and looping
 		 * back to the start of the file violates that rule and causes
 		 * deadlocks.
 		 */

mm/truncate.c

@@ -421,7 +421,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
 		for (i = 0; i < folio_batch_count(&fbatch); i++) {
 			struct folio *folio = fbatch.folios[i];
 
-			/* We rely upon deletion not changing page->index */
+			/* We rely upon deletion not changing folio->index */
 
 			if (xa_is_value(folio))
 				continue;

mm/zpdesc.h

@@ -54,8 +54,8 @@ struct zpdesc {
 ZPDESC_MATCH(flags, flags);
 ZPDESC_MATCH(lru, lru);
 ZPDESC_MATCH(mapping, movable_ops);
-ZPDESC_MATCH(index, next);
-ZPDESC_MATCH(index, handle);
+ZPDESC_MATCH(__folio_index, next);
+ZPDESC_MATCH(__folio_index, handle);
 ZPDESC_MATCH(private, zspage);
 ZPDESC_MATCH(page_type, first_obj_offset);
 ZPDESC_MATCH(_refcount, _refcount);