mm/migrate: Convert fallback_migrate_page() to fallback_migrate_folio()

Use a folio throughout.  migrate_page() will be converted to
migrate_folio() later.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

mm/migrate.c

@@ -805,11 +805,11 @@ static int writeout(struct address_space *mapping, struct page *page)
 /*
  * Default handling if a filesystem does not provide a migration function.
  */
-static int fallback_migrate_page(struct address_space *mapping,
-	struct page *newpage, struct page *page, enum migrate_mode mode)
+static int fallback_migrate_folio(struct address_space *mapping,
+		struct folio *dst, struct folio *src, enum migrate_mode mode)
 {
-	if (PageDirty(page)) {
-		/* Only writeback pages in full synchronous migration */
+	if (folio_test_dirty(src)) {
+		/* Only writeback folios in full synchronous migration */
 		switch (mode) {
 		case MIGRATE_SYNC:
 		case MIGRATE_SYNC_NO_COPY:
@@ -817,18 +817,18 @@ static int fallback_migrate_page(struct address_space *mapping,
 		default:
 			return -EBUSY;
 		}
-		return writeout(mapping, page);
+		return writeout(mapping, &src->page);
 	}
 
 	/*
 	 * Buffers may be managed in a filesystem specific way.
 	 * We must have no buffers or drop them.
 	 */
-	if (page_has_private(page) &&
-	    !try_to_release_page(page, GFP_KERNEL))
+	if (folio_test_private(src) &&
+	    !filemap_release_folio(src, GFP_KERNEL))
 		return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY;
 
-	return migrate_page(mapping, newpage, page, mode);
+	return migrate_page(mapping, &dst->page, &src->page, mode);
 }
 
 /*
@@ -870,8 +870,7 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
 			rc = mapping->a_ops->migratepage(mapping, &dst->page,
 							&src->page, mode);
 		else
-			rc = fallback_migrate_page(mapping, &dst->page,
-							&src->page, mode);
+			rc = fallback_migrate_folio(mapping, dst, src, mode);
 	} else {
 		const struct movable_operations *mops;