v4.19.13 snapshot.
diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
new file mode 100644
index 0000000..883c992
--- /dev/null
+++ b/include/linux/migrate_mode.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef MIGRATE_MODE_H_INCLUDED
+#define MIGRATE_MODE_H_INCLUDED
+/*
+ * MIGRATE_ASYNC means never block
+ * MIGRATE_SYNC_LIGHT in the current implementation means to allow blocking
+ * on most operations but not ->writepage as the potential stall time
+ * is too significant
+ * MIGRATE_SYNC will block when migrating pages
+ * MIGRATE_SYNC_NO_COPY will block when migrating pages but will not copy pages
+ * with the CPU. Instead, page copy happens outside the migratepage()
+ * callback and is likely using a DMA engine. See migrate_vma() and HMM
+ * (mm/hmm.c) for users of this mode.
+ */
+enum migrate_mode {
+ MIGRATE_ASYNC,
+ MIGRATE_SYNC_LIGHT,
+ MIGRATE_SYNC,
+ MIGRATE_SYNC_NO_COPY,
+};
+
+#endif /* MIGRATE_MODE_H_INCLUDED */