[PATCH 2/7] mm/migrate: use migrate_info field instead of private

[Shivank Garg]

Add an unsigned long migrate_info member to the struct folio union and
use it to store migration state (anon_vma pointer and FOLIO_WAS_*
flags) instead of using folio->private.

No functional change.

Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Shivank Garg <shivankg@xxxxxxx>
---
 include/linux/mm_types.h |  1 +
 mm/migrate.c             | 14 +++++++-------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index a308e2c23b82..f52818dcf4d2 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -426,6 +426,7 @@ struct folio {
 			union {
 				void *private;
 				swp_entry_t swap;
+				unsigned long migrate_info;
 			};
 			atomic_t _mapcount;
 			atomic_t _refcount;
diff --git a/mm/migrate.c b/mm/migrate.c
index 0c6a0ab6ecce..03c2a6f7e5e4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1130,7 +1130,7 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
 }
 
 /*
- * To record some information during migration, we use unused private
+ * To record some information during migration, we use the migrate_info
  * field of struct folio of the newly allocated destination folio.
  * This is safe because nobody is using it except us.
  */
@@ -1143,17 +1143,17 @@ enum {
 static void __migrate_folio_record(struct folio *dst,
 		int old_folio_state, struct anon_vma *anon_vma)
 {
-	dst->private = (void *)anon_vma + old_folio_state;
+	dst->migrate_info = (unsigned long)anon_vma | old_folio_state;
 }
 
 static void __migrate_folio_extract(struct folio *dst,
 		int *old_folio_state, struct anon_vma **anon_vmap)
 {
-	unsigned long private = (unsigned long)dst->private;
+	unsigned long info = dst->migrate_info;
 
-	*anon_vmap = (struct anon_vma *)(private & ~FOLIO_OLD_STATES);
-	*old_folio_state = private & FOLIO_OLD_STATES;
-	dst->private = NULL;
+	*anon_vmap = (struct anon_vma *)(info & ~FOLIO_OLD_STATES);
+	*old_folio_state = info & FOLIO_OLD_STATES;
+	dst->migrate_info = 0;
 }
 
 /* Restore the source folio to the original state upon failure */
@@ -1217,7 +1217,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 		return -ENOMEM;
 	*dstp = dst;
 
-	dst->private = NULL;
+	dst->migrate_info = 0;
 
 	if (!folio_trylock(src)) {
 		if (mode == MIGRATE_ASYNC)
-- 
2.43.0