[RFC V3 2/9] mm/migrate: revive MIGRATE_NO_COPY in migrate_mode

[Shivank Garg <shivankg@amd.com>]

From: Zi Yan <ziy@nvidia.com>

It is a preparation patch. The added MIGRATE_NO_COPY will be used by the
following patches to implement batched page copy functions by skipping
folio copy process in __migrate_folio() and copying folios in one shot
at the end.

Signed-off-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 include/linux/migrate_mode.h | 2 ++
 mm/migrate.c                 | 8 +++++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
index 265c4328b36a..9af6c949a057 100644
--- a/include/linux/migrate_mode.h
+++ b/include/linux/migrate_mode.h
@@ -7,11 +7,13 @@
  *	on most operations but not ->writepage as the potential stall time
  *	is too significant
  * MIGRATE_SYNC will block when migrating pages
+ * MIGRATE_NO_COPY will not copy page content
  */
 enum migrate_mode {
 	MIGRATE_ASYNC,
 	MIGRATE_SYNC_LIGHT,
 	MIGRATE_SYNC,
+	MIGRATE_NO_COPY,
 };
 
 enum migrate_reason {
diff --git a/mm/migrate.c b/mm/migrate.c
index ad03e7257847..3fe78ecb146a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -848,9 +848,11 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
 
-	rc = folio_mc_copy(dst, src);
-	if (unlikely(rc))
-		return rc;
+	if (mode != MIGRATE_NO_COPY) {
+		rc = folio_mc_copy(dst, src);
+		if (unlikely(rc))
+			return rc;
+	}
 
 	rc = __folio_migrate_mapping(mapping, dst, src, expected_count);
 	if (rc != MIGRATEPAGE_SUCCESS)
-- 
2.43.0