[PATCH RFC 1/1] mm/swap: queue reclaimable folio to local rotate batch when !folio_test_lru()

[chengming.zhou@linux.dev]

From: Chengming Zhou <zhouchengming@bytedance.com>

All LRU move interfaces have a problem that it has no effect if the
folio is isolated from LRU (in cpu batch or isolated by shrinker).
Since it can't move/change folio LRU status when it's isolated, mostly
just clear the folio flag and do nothing in this case.

In our case, a written back and reclaimable folio won't be rotated to
the tail of inactive list, since it's still in cpu lru_add batch. It
may cause the delayed reclaim of this folio and evict other folios.

This patch changes to queue the reclaimable folio to cpu rotate batch
even when !folio_test_lru(), hoping it will likely be handled after
the lru_add batch which will put folio on the LRU list first, so
will be rotated to the tail successfully when handle rotate batch.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 mm/swap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index cd8f0150ba3a..d304731e47cf 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -236,7 +236,8 @@ static void folio_batch_add_and_move(struct folio_batch *fbatch,
 
 static void lru_move_tail_fn(struct lruvec *lruvec, struct folio *folio)
 {
-	if (!folio_test_unevictable(folio)) {
+	if (!folio_test_locked(folio) && !folio_test_dirty(folio) &&
+	    !folio_test_unevictable(folio) && !folio_test_active(folio)) {
 		lruvec_del_folio(lruvec, folio);
 		folio_clear_active(folio);
 		lruvec_add_folio_tail(lruvec, folio);
@@ -254,7 +255,7 @@ static void lru_move_tail_fn(struct lruvec *lruvec, struct folio *folio)
 void folio_rotate_reclaimable(struct folio *folio)
 {
 	if (!folio_test_locked(folio) && !folio_test_dirty(folio) &&
-	    !folio_test_unevictable(folio) && folio_test_lru(folio)) {
+	    !folio_test_unevictable(folio) && !folio_test_active(folio)) {
 		struct folio_batch *fbatch;
 		unsigned long flags;
 
-- 
2.40.1