From 620b0ee94455e48d124414cd06d8a53f69fb6453 Mon Sep 17 00:00:00 2001 From: Yu Zhao Date: Mon, 13 Feb 2023 00:53:22 -0700 Subject: [PATCH 09/19] UPSTREAM: mm: multi-gen LRU: avoid futile retries Recall that the per-node memcg LRU has two generations and they alternate when the last memcg (of a given node) is moved from one to the other. Each generation is also sharded into multiple bins to improve scalability. A reclaimer starts with a random bin (in the old generation) and, if it fails, it will retry, i.e., to try the rest of the bins. If a reclaimer fails with the last memcg, it should move this memcg to the young generation first, which causes the generations to alternate, and then retry. Otherwise, the retries will be futile because all other bins are empty. Link: https://lkml.kernel.org/r/20230213075322.1416966-1-yuzhao@google.com Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists") Signed-off-by: Yu Zhao Reported-by: T.J. Mercier Signed-off-by: Andrew Morton Bug: 274865848 (cherry picked from commit 9f550d78b40da21b4da515db4c37d8d7b12aa1a6) Change-Id: Ie92535676b005ec9e7987632b742fdde8d54436f Signed-off-by: T.J. Mercier --- mm/vmscan.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5206,18 +5206,20 @@ static int shrink_one(struct lruvec *lru static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc) { + int op; int gen; int bin; int first_bin; struct lruvec *lruvec; struct lru_gen_folio *lrugen; + struct mem_cgroup *memcg; const struct hlist_nulls_node *pos; - int op = 0; - struct mem_cgroup *memcg = NULL; unsigned long nr_to_reclaim = get_nr_to_reclaim(sc); bin = first_bin = get_random_u32_below(MEMCG_NR_BINS); restart: + op = 0; + memcg = NULL; gen = get_memcg_gen(READ_ONCE(pgdat->memcg_lru.seq)); rcu_read_lock(); @@ -5241,14 +5243,22 @@ restart: op = shrink_one(lruvec, sc); - if (sc->nr_reclaimed >= nr_to_reclaim) - goto success; - rcu_read_lock(); + + if (sc->nr_reclaimed >= nr_to_reclaim) + break; } rcu_read_unlock(); + if (op) + lru_gen_rotate_memcg(lruvec, op); + + mem_cgroup_put(memcg); + + if (sc->nr_reclaimed >= nr_to_reclaim) + return; + /* restart if raced with lru_gen_rotate_memcg() */ if (gen != get_nulls_value(pos)) goto restart; @@ -5257,11 +5267,6 @@ restart: bin = get_memcg_bin(bin + 1); if (bin != first_bin) goto restart; -success: - if (op) - lru_gen_rotate_memcg(lruvec, op); - - mem_cgroup_put(memcg); } static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)