[PATCH v4 5/6] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_MAY_BLOCK mappings

[Joanne Koong <joannelkoong@xxxxxxxxx>]

For migrations called in MIGRATE_SYNC mode, skip migrating the folio if
it is under writeback and has the AS_WRITEBACK_MAY_BLOCK flag set on its
mapping. If the AS_WRITEBACK_MAY_BLOCK flag is set on the mapping, the
writeback may take an indeterminate amount of time to complete, so we
should not wait.

Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
---
 mm/migrate.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index df91248755e4..1d038a4202ae 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1260,7 +1260,10 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 		 */
 		switch (mode) {
 		case MIGRATE_SYNC:
-			break;
+			if (!src->mapping ||
+			    !mapping_writeback_may_block(src->mapping))
+				break;
+			fallthrough;
 		default:
 			rc = -EBUSY;
 			goto out;
-- 
2.43.5