mm/migrate_device: try to handle swapcache pages

Migrating file pages and swapcache pages into device memory is not
supported.  Try to get rid of the swap cache, and if successful, go ahead
as with other anonymous pages.

Link: https://lkml.kernel.org/r/20230607172944.11713-1-mpenttil@redhat.comSigned-off-by: Mika Penttilä <mpenttil@redhat.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/migrate_device.c

@@ -727,14 +727,23 @@ static void __migrate_device_pages(unsigned long *src_pfns,
 
 		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.
+				 *
+				 * Try to get rid of swap cache if possible.
 				 */
-			if (mapping) {
+				if (!folio_test_anon(folio) ||
+				    !folio_free_swap(folio)) {
 					src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
 					continue;
 				}
+			}
 		} else if (is_zone_device_page(newpage)) {
 			/*
 			 * Other types of ZONE_DEVICE page are not supported.