[PATCH 2/2] mm: multi-gen lru: fix stat count

[Huan Yang]

For multi-gen lru reclaim in evict_folios, like shrink_inactive_list,
gather folios which isolate to reclaim, and invoke shirnk_folio_list.

But, when complete shrink, it not gather shrink reclaim stat into sc,
we can't get info like nr_dirty\congested in reclaim, and then
control writeback, dirty number and mark as LRUVEC_CONGESTED, or
just bpf trace shrink and get correct sc stat.

This patch fix this by simple copy code from shrink_inactive_list when
end of shrink list.

Signed-off-by: Huan Yang <link@xxxxxxxx>
---
 mm/vmscan.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 21099b9f21e0..88d1d586aea5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4593,6 +4593,41 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap
 	 */
 	nr_taken = sc->nr_scanned - nr_taken;
 
+	/*
+	 * If dirty folios are scanned that are not queued for IO, it
+	 * implies that flushers are not doing their job. This can
+	 * happen when memory pressure pushes dirty folios to the end of
+	 * the LRU before the dirty limits are breached and the dirty
+	 * data has expired. It can also happen when the proportion of
+	 * dirty folios grows not through writes but through memory
+	 * pressure reclaiming all the clean cache. And in some cases,
+	 * the flushers simply cannot keep up with the allocation
+	 * rate. Nudge the flusher threads in case they are asleep.
+	 */
+	if (unlikely(stat.nr_unqueued_dirty == nr_taken)) {
+		wakeup_flusher_threads(WB_REASON_VMSCAN);
+		/*
+		 * For cgroupv1 dirty throttling is achieved by waking up
+		 * the kernel flusher here and later waiting on folios
+		 * which are in writeback to finish (see shrink_folio_list()).
+		 *
+		 * Flusher may not be able to issue writeback quickly
+		 * enough for cgroupv1 writeback throttling to work
+		 * on a large system.
+		 */
+		if (!writeback_throttling_sane(sc))
+			reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
+	}
+
+	sc->nr.dirty += stat.nr_dirty;
+	sc->nr.congested += stat.nr_congested;
+	sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
+	sc->nr.writeback += stat.nr_writeback;
+	sc->nr.immediate += stat.nr_immediate;
+	sc->nr.taken += nr_taken;
+	if (type)
+		sc->nr.file_taken += nr_taken;
+
 	sc->nr_reclaimed += total_reclaimed;
 	trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id, nr_taken,
 					     total_reclaimed, &stat,
-- 
2.34.1