mm: vmscan.c: fix OOM on swap stress test

commit 0885ef4705607936fc36a38fd74356e1c465b023 upstream.

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/
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch")
Signed-off-by: Chris Li <[email protected]>
Suggested-by: Yu Zhao <[email protected]>
Suggested-by: Hugh Dickins <[email protected]>
Closes: https://lore.kernel.org/all/CAF8kJuNP5iTj2p07QgHSGOJsiUfYpJ2f4R1Q5-3BN9JiD9W_KA@mail.gmail.com/
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: hanliyang <[email protected]>

mm/vmscan.c

@@ -4951,7 +4951,7 @@ 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;