From: Chen Ridong <redacted>

Currently, flush_reclaim_state is placed differently between
shrink_node_memcgs and shrink_many. shrink_many (only used for gen-LRU)
calls it after each lruvec is shrunk, while shrink_node_memcgs calls it
only after all lruvecs have been shrunk.

This patch moves flush_reclaim_state into shrink_node_memcgs and calls it
after each lruvec. This unifies the behavior and is reasonable because:

1. flush_reclaim_state adds current->reclaim_state->reclaimed to
   sc->nr_reclaimed.
2. For non-MGLRU root reclaim, this can help stop the iteration earlier
   when nr_to_reclaim is reached.
3. For non-root reclaim, the effect is negligible since flush_reclaim_state
   does nothing in that case.

After moving flush_reclaim_state into shrink_node_memcgs, shrink_one can be
extended to support both lrugen and non-lrugen paths. It will call
try_to_shrink_lruvec for lrugen root reclaim and shrink_lruvec otherwise.

Signed-off-by: Chen Ridong <redacted>
---
 mm/vmscan.c | 57 +++++++++++++++++++++--------------------------------
 1 file changed, 23 insertions(+), 34 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 584f41eb4c14..795f5ebd9341 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -4758,23 +4758,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 	return nr_to_scan < 0;
 }
 
-static void shrink_one(struct lruvec *lruvec, struct scan_control *sc)
-{
-	unsigned long scanned = sc->nr_scanned;
-	unsigned long reclaimed = sc->nr_reclaimed;
-	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
-	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
-
-	try_to_shrink_lruvec(lruvec, sc);
-
-	shrink_slab(sc->gfp_mask, pgdat->node_id, memcg, sc->priority);
-
-	if (!sc->proactive)
-		vmpressure(sc->gfp_mask, memcg, false, sc->nr_scanned - scanned,
-			   sc->nr_reclaimed - reclaimed);
-
-	flush_reclaim_state(sc);
-}
+static void shrink_one(struct lruvec *lruvec, struct scan_control *sc);
 
 static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc)
 {

@@ -5760,6 +5744,27 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
 	return inactive_lru_pages > pages_for_compaction;
 }
 
+static void shrink_one(struct lruvec *lruvec, struct scan_control *sc)
+{
+	unsigned long scanned = sc->nr_scanned;
+	unsigned long reclaimed = sc->nr_reclaimed;
+	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+
+	if (lru_gen_enabled() && root_reclaim(sc))
+		try_to_shrink_lruvec(lruvec, sc);
+	else
+		shrink_lruvec(lruvec, sc);