[PATCH] mm: vmscan.c: fix OOM on swap stress test

[Chris Li <chrisl@kernel.org>]

I found a regression on mm-unstable during my swap stress test,
using tmpfs to compile linux. The test OOM very soon after
the make spawns many cc processes.

It bisects down to this change: 33dfe9204f29b415bbc0abb1a50642d1ba94f5e9
(mm/gup: clear the LRU flag of a page before adding to LRU batch)

Yu Zhao propose the fix: "I think this is one of the potential side
effects -- Huge mentioned earlier about isolate_lru_folios():"

I test that with it the swap stress test no longer OOM.

Link: https://lore.kernel.org/r/CAOUHufYi9h0kz5uW3LHHS3ZrVwEq-kKp8S6N-MZUmErNAXoXmw@mail.gmail.com/
Fixes: 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch")
Suggested-by: Yu Zhao <yuzhao@google.com>
Suggested-by: Hugh Dickins <hughd@google.com>
Tested-by: Chris Li <chrisl@kernel.org>
Signed-off-by: Chris Li <chrisl@kernel.org>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a9b6a8196f95..96abf4a52382 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4323,7 +4323,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 	}
 
 	/* ineligible */
-	if (zone > sc->reclaim_idx) {
+	if (!folio_test_lru(folio) || zone > sc->reclaim_idx) {
 		gen = folio_inc_gen(lruvec, folio, false);
 		list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
 		return true;

---
base-commit: 756ca36d643324d028b325a170e73e392b9590cd
change-id: 20240904-lru-flag-2af2f955740e

Best regards,
-- 
Chris Li <chrisl@kernel.org>