mm/migrate: Convert expected_page_refs() to folio_expected_refs()

Now that both callers have a folio, convert this function to
take a folio & rename it.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

mm/migrate.c

@@ -336,13 +336,18 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
 }
 #endif
 
-static int expected_page_refs(struct address_space *mapping, struct page *page)
+static int folio_expected_refs(struct address_space *mapping,
+		struct folio *folio)
 {
-	int expected_count = 1;
+	int refs = 1;
+	if (!mapping)
+		return refs;
 
-	if (mapping)
-		expected_count += compound_nr(page) + page_has_private(page);
-	return expected_count;
+	refs += folio_nr_pages(folio);
+	if (folio_test_private(folio))
+		refs++;
+
+	return refs;
 }
 
 /*
@@ -359,7 +364,7 @@ int folio_migrate_mapping(struct address_space *mapping,
 	XA_STATE(xas, &mapping->i_pages, folio_index(folio));
 	struct zone *oldzone, *newzone;
 	int dirty;
-	int expected_count = expected_page_refs(mapping, &folio->page) + extra_count;
+	int expected_count = folio_expected_refs(mapping, folio) + extra_count;
 	long nr = folio_nr_pages(folio);
 
 	if (!mapping) {
@@ -669,7 +674,7 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 		return migrate_page(mapping, &dst->page, &src->page, mode);
 
 	/* Check whether page does not have extra refs before we do more work */
-	expected_count = expected_page_refs(mapping, &src->page);
+	expected_count = folio_expected_refs(mapping, src);
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;