[PATCH] mm/vmscan: fix missing NR_ISOLATED counter update in MGLRU reclaim path

[Hui Zhu]

From: Hui Zhu <zhuhui@xxxxxxxxxx>

The MGLRU evict_folios() isolates folios from the LRU without updating
NR_ISOLATED_ANON/FILE counters, unlike the legacy shrink_inactive_list()
path.
This causes compaction's too_many_isolated() check and the OOMkiller to
under-count isolated pages when MGLRU reclaim is active, potentially
leading to unnecessary compaction attempts or incorrect OOM decisions
under memory pressure.

Add NR_ISOLATED counter updates in evict_folios(): increment after
isolate_folios() and decrement after all retry passes complete, using
the original isolated count saved before retry.

Signed-off-by: Hui Zhu <zhuhui@xxxxxxxxxx>
---
 mm/vmscan.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index bc324e37c5f1..723b513574b3 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4817,6 +4817,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	struct lru_gen_mm_walk *walk;
 	int scanned, reclaimed;
 	int isolated = 0, type, type_scanned;
+	int isolated_orig = 0;
 	bool skip_retry = false;
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
@@ -4829,6 +4830,11 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	scanned = isolate_folios(nr_to_scan, lruvec, sc, swappiness,
 				 &list, &isolated, &type, &type_scanned);
 
+	isolated_orig = isolated;
+	if (isolated)
+		__mod_node_page_state(pgdat, NR_ISOLATED_ANON + type,
+				      isolated);
+
 	/* Scanning may have emptied the oldest gen, flush it */
 	if (scanned)
 		try_to_inc_min_seq(lruvec, swappiness);
@@ -4891,6 +4897,10 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 		goto retry;
 	}
 
+	if (isolated_orig)
+		mod_node_page_state(pgdat, NR_ISOLATED_ANON + type,
+				    -isolated_orig);
+
 	return scanned;
 }
 
-- 
2.53.0