[PATCH v2 3/9] migrate: Remove call to ->writepage

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

The writepage callback is going away; filesystems must implement
migrate_folio or else dirty folios will not be migratable.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/migrate.c | 60 ++++++----------------------------------------------
 1 file changed, 7 insertions(+), 53 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index f3ee6d8d5e2e..6e2488e5dbe4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -944,67 +944,21 @@ int filemap_migrate_folio(struct address_space *mapping,
 }
 EXPORT_SYMBOL_GPL(filemap_migrate_folio);
 
-/*
- * Writeback a folio to clean the dirty state
- */
-static int writeout(struct address_space *mapping, struct folio *folio)
-{
-	struct writeback_control wbc = {
-		.sync_mode = WB_SYNC_NONE,
-		.nr_to_write = 1,
-		.range_start = 0,
-		.range_end = LLONG_MAX,
-		.for_reclaim = 1
-	};
-	int rc;
-
-	if (!mapping->a_ops->writepage)
-		/* No write method for the address space */
-		return -EINVAL;
-
-	if (!folio_clear_dirty_for_io(folio))
-		/* Someone else already triggered a write */
-		return -EAGAIN;
-
-	/*
-	 * A dirty folio may imply that the underlying filesystem has
-	 * the folio on some queue. So the folio must be clean for
-	 * migration. Writeout may mean we lose the lock and the
-	 * folio state is no longer what we checked for earlier.
-	 * At this point we know that the migration attempt cannot
-	 * be successful.
-	 */
-	remove_migration_ptes(folio, folio, 0);
-
-	rc = mapping->a_ops->writepage(&folio->page, &wbc);
-
-	if (rc != AOP_WRITEPAGE_ACTIVATE)
-		/* unlocked. Relock */
-		folio_lock(folio);
-
-	return (rc < 0) ? -EIO : -EAGAIN;
-}
-
 /*
  * Default handling if a filesystem does not provide a migration function.
  */
 static int fallback_migrate_folio(struct address_space *mapping,
 		struct folio *dst, struct folio *src, enum migrate_mode mode)
 {
-	if (folio_test_dirty(src)) {
-		/* Only writeback folios in full synchronous migration */
-		switch (mode) {
-		case MIGRATE_SYNC:
-			break;
-		default:
-			return -EBUSY;
-		}
-		return writeout(mapping, src);
-	}
+	WARN_ONCE(mapping->a_ops->writepages,
+			"%ps does not implement migrate_folio\n",
+			mapping->a_ops);
+	if (folio_test_dirty(src))
+		return -EBUSY;
 
 	/*
-	 * Buffers may be managed in a filesystem specific way.
-	 * We must have no buffers or drop them.
+	 * Filesystem may have private data at folio->private that we
+	 * can't migrate automatically.
 	 */
 	if (!filemap_release_folio(src, GFP_KERNEL))
 		return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY;
-- 
2.47.2