[PATCH 2/5] mm/vmscan: move code to lru_gen_{add,del}_memcg()

[Max Kellermann]

Preparation for the following patch that adds tail caching.

For simplicity, hlist_nulls_del_init_rcu() is now always used, which
is also valid during rotation, because the entry is immediately
reinserted under `memcg_lru.lock`.

Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
---
 mm/vmscan.c | 36 ++++++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 8 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index f11491ee9ed5..3d4bc12cf18e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4379,6 +4379,29 @@ enum {
 	MEMCG_LRU_YOUNG,
 };
 
+static void lru_gen_add_memcg(struct lru_gen_memcg *memcg_lru,
+			      struct lru_gen_folio *lrugen,
+			      int gen, int bin, bool at_head)
+{
+	struct hlist_nulls_head *head = &memcg_lru->fifo[gen][bin];
+
+	lockdep_assert_held(&memcg_lru->lock);
+
+	if (at_head)
+		hlist_nulls_add_head_rcu(&lrugen->list, head);
+	else
+		hlist_nulls_add_tail_rcu(&lrugen->list, head);
+}
+
+static void lru_gen_del_memcg(struct lru_gen_memcg *memcg_lru,
+			      struct lru_gen_folio *lrugen,
+			      int gen)
+{
+	lockdep_assert_held(&memcg_lru->lock);
+
+	hlist_nulls_del_init_rcu(&lrugen->list);
+}
+
 static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
 {
 	int seg;
@@ -4409,12 +4432,9 @@ static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
 	WRITE_ONCE(lruvec->lrugen.seg, seg);
 	WRITE_ONCE(lruvec->lrugen.gen, new);
 
-	hlist_nulls_del_rcu(&lruvec->lrugen.list);
-
-	if (op == MEMCG_LRU_HEAD || op == MEMCG_LRU_OLD)
-		hlist_nulls_add_head_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[new][bin]);
-	else
-		hlist_nulls_add_tail_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[new][bin]);
+	lru_gen_del_memcg(&pgdat->memcg_lru, &lruvec->lrugen, old);
+	lru_gen_add_memcg(&pgdat->memcg_lru, &lruvec->lrugen, new, bin,
+			  op == MEMCG_LRU_HEAD || op == MEMCG_LRU_OLD);
 
 	pgdat->memcg_lru.nr_memcgs[old]--;
 	pgdat->memcg_lru.nr_memcgs[new]++;
@@ -4445,7 +4465,7 @@ void lru_gen_online_memcg(struct mem_cgroup *memcg)
 
 		lruvec->lrugen.gen = gen;
 
-		hlist_nulls_add_tail_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[gen][bin]);
+		lru_gen_add_memcg(&pgdat->memcg_lru, &lruvec->lrugen, gen, bin, false);
 		pgdat->memcg_lru.nr_memcgs[gen]++;
 
 		spin_unlock_irq(&pgdat->memcg_lru.lock);
@@ -4479,7 +4499,7 @@ void lru_gen_release_memcg(struct mem_cgroup *memcg)
 
 		gen = lruvec->lrugen.gen;
 
-		hlist_nulls_del_init_rcu(&lruvec->lrugen.list);
+		lru_gen_del_memcg(&pgdat->memcg_lru, &lruvec->lrugen, gen);
 		pgdat->memcg_lru.nr_memcgs[gen]--;
 
 		if (!pgdat->memcg_lru.nr_memcgs[gen] && gen == get_memcg_gen(pgdat->memcg_lru.seq))
-- 
2.47.3