mm/migrate: putback split folios when numa hint migration fails

This issue is not from any report yet, but by code observation only.

This is yet another fix besides Hugh's patch [1] but on relevant code
path, where eager split of folio can happen if the folio is already on
deferred list during a folio migration.

Here the issue is NUMA path (migrate_misplaced_folio()) may start to
encounter such folio split now even with MR_NUMA_MISPLACED hint applied. 
Then when migrate_pages() didn't migrate all the folios, it's possible the
split small folios be put onto the list instead of the original folio. 
Then putting back only the head page won't be enough.

Fix it by putting back all the folios on the list.

[1] https://lore.kernel.org/all/[email protected]/

[[email protected]: remove now unused local `nr_pages']
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 7262f20 ("mm/migrate: split source folio if it is on deferred split list")
Signed-off-by: Peter Xu <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: xzpeter

mm/migrate.c

@@ -2621,20 +2621,13 @@ int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
 	int nr_remaining;
 	unsigned int nr_succeeded;
 	LIST_HEAD(migratepages);
-	int nr_pages = folio_nr_pages(folio);
 
 	list_add(&folio->lru, &migratepages);
 	nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_folio,
 				     NULL, node, MIGRATE_ASYNC,
 				     MR_NUMA_MISPLACED, &nr_succeeded);
-	if (nr_remaining) {
-		if (!list_empty(&migratepages)) {
-			list_del(&folio->lru);
-			node_stat_mod_folio(folio, NR_ISOLATED_ANON +
-					folio_is_file_lru(folio), -nr_pages);
-			folio_putback_lru(folio);
-		}
-	}
+	if (nr_remaining && !list_empty(&migratepages))
+		putback_movable_pages(&migratepages);
 	if (nr_succeeded) {
 		count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
 		if (!node_is_toptier(folio_nid(folio)) && node_is_toptier(node))