migrate: expand the use of folio in __migrate_device_pages()

Removes a few calls to compound_head() and a call to page_mapping().

Link: https://lkml.kernel.org/r/20240423225552.4113447-5-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/migrate_device.c

@@ -696,6 +696,7 @@ static void __migrate_device_pages(unsigned long *src_pfns,
 		struct page *newpage = migrate_pfn_to_page(dst_pfns[i]);
 		struct page *page = migrate_pfn_to_page(src_pfns[i]);
 		struct address_space *mapping;
+		struct folio *folio;
 		int r;
 
 		if (!newpage) {
@@ -730,15 +731,12 @@ static void __migrate_device_pages(unsigned long *src_pfns,
 			continue;
 		}
 
-		mapping = page_mapping(page);
+		folio = page_folio(page);
+		mapping = folio_mapping(folio);
 
 		if (is_device_private_page(newpage) ||
 		    is_device_coherent_page(newpage)) {
 			if (mapping) {
-				struct folio *folio;
-
-				folio = page_folio(page);
-
 				/*
 				 * For now only support anonymous memory migrating to
 				 * device private or coherent memory.
@@ -761,11 +759,10 @@ static void __migrate_device_pages(unsigned long *src_pfns,
 
 		if (migrate && migrate->fault_page == page)
 			r = migrate_folio_extra(mapping, page_folio(newpage),
-						page_folio(page),
-						MIGRATE_SYNC_NO_COPY, 1);
+						folio, MIGRATE_SYNC_NO_COPY, 1);
 		else
 			r = migrate_folio(mapping, page_folio(newpage),
-					page_folio(page), MIGRATE_SYNC_NO_COPY);
+					folio, MIGRATE_SYNC_NO_COPY);
 		if (r != MIGRATEPAGE_SUCCESS)
 			src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
 	}