[PATCH RFC 11/29] mm/migrate: move movable_ops page handling out of move_to_new_folio()

[David Hildenbrand]

Let's move that handling directly into migrate_folio_move(), so we can
simplify move_to_new_folio(). While at it, fixup the documentation a
bit.

Note that unmap_and_move_huge_page() does not care, because it only
deals with actual folios. (we only support migration of
individual movable_ops pages)

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 mm/migrate.c | 61 ++++++++++++++++++++++++----------------------------
 1 file changed, 28 insertions(+), 33 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 456e41dad83a2..db807f9bbf975 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1024,11 +1024,12 @@ static int fallback_migrate_folio(struct address_space *mapping,
 }
 
 /*
- * Move a page to a newly allocated page
- * The page is locked and all ptes have been successfully removed.
+ * Move a src folio to a newly allocated dst folio.
  *
- * The new page will have replaced the old page if this function
- * is successful.
+ * The src and dst folios are locked and the src folios was unmapped from
+ * the page tables.
+ *
+ * On success, the src folio was replaced by the dst folio.
  *
  * Return value:
  *   < 0 - error code
@@ -1037,34 +1038,30 @@ static int fallback_migrate_folio(struct address_space *mapping,
 static int move_to_new_folio(struct folio *dst, struct folio *src,
 				enum migrate_mode mode)
 {
+	struct address_space *mapping = folio_mapping(src);
 	int rc = -EAGAIN;
-	bool is_lru = !__folio_test_movable(src);
 
 	VM_BUG_ON_FOLIO(!folio_test_locked(src), src);
 	VM_BUG_ON_FOLIO(!folio_test_locked(dst), dst);
 
-	if (likely(is_lru)) {
-		struct address_space *mapping = folio_mapping(src);
-
-		if (!mapping)
-			rc = migrate_folio(mapping, dst, src, mode);
-		else if (mapping_inaccessible(mapping))
-			rc = -EOPNOTSUPP;
-		else if (mapping->a_ops->migrate_folio)
-			/*
-			 * Most folios have a mapping and most filesystems
-			 * provide a migrate_folio callback. Anonymous folios
-			 * are part of swap space which also has its own
-			 * migrate_folio callback. This is the most common path
-			 * for page migration.
-			 */
-			rc = mapping->a_ops->migrate_folio(mapping, dst, src,
-								mode);
-		else
-			rc = fallback_migrate_folio(mapping, dst, src, mode);
+	if (!mapping)
+		rc = migrate_folio(mapping, dst, src, mode);
+	else if (mapping_inaccessible(mapping))
+		rc = -EOPNOTSUPP;
+	else if (mapping->a_ops->migrate_folio)
+		/*
+		 * Most folios have a mapping and most filesystems
+		 * provide a migrate_folio callback. Anonymous folios
+		 * are part of swap space which also has its own
+		 * migrate_folio callback. This is the most common path
+		 * for page migration.
+		 */
+		rc = mapping->a_ops->migrate_folio(mapping, dst, src,
+							mode);
+	else
+		rc = fallback_migrate_folio(mapping, dst, src, mode);
 
-		if (rc != MIGRATEPAGE_SUCCESS)
-			goto out;
+	if (rc == MIGRATEPAGE_SUCCESS) {
 		/*
 		 * For pagecache folios, src->mapping must be cleared before src
 		 * is freed. Anonymous folios must stay anonymous until freed.
@@ -1074,10 +1071,7 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
 
 		if (likely(!folio_is_zone_device(dst)))
 			flush_dcache_folio(dst);
-	} else {
-		rc = migrate_movable_ops_page(&dst->page, &src->page, mode);
 	}
-out:
 	return rc;
 }
 
@@ -1328,20 +1322,21 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,
 	int rc;
 	int old_page_state = 0;
 	struct anon_vma *anon_vma = NULL;
-	bool is_lru = !__folio_test_movable(src);
 	struct list_head *prev;
 
 	__migrate_folio_extract(dst, &old_page_state, &anon_vma);
 	prev = dst->lru.prev;
 	list_del(&dst->lru);
 
+	if (unlikely(__folio_test_movable(src))) {
+		rc = migrate_movable_ops_page(&dst->page, &src->page, mode);
+		goto out_unlock_both;
+	}
+
 	rc = move_to_new_folio(dst, src, mode);
 	if (rc)
 		goto out;
 
-	if (unlikely(!is_lru))
-		goto out_unlock_both;
-
 	/*
 	 * When successful, push dst to LRU immediately: so that if it
 	 * turns out to be an mlocked page, remove_migration_ptes() will
-- 
2.49.0