mm/mglru: respect min_ttl_ms with memcgs
While investigating kswapd "consuming 100% CPU" [1] (also see "mm/mglru:
try to stop at high watermarks"), it was discovered that the memcg LRU can
breach the thrashing protection imposed by min_ttl_ms.
Before the memcg LRU:
kswapd()
shrink_node_memcgs()
mem_cgroup_iter()
inc_max_seq() // always hit a different memcg
lru_gen_age_node()
mem_cgroup_iter()
check the timestamp of the oldest generation
After the memcg LRU:
kswapd()
shrink_many()
restart:
iterate the memcg LRU:
inc_max_seq() // occasionally hit the same memcg
if raced with lru_gen_rotate_memcg():
goto restart
lru_gen_age_node()
mem_cgroup_iter()
check the timestamp of the oldest generation
Specifically, when the restart happens in shrink_many(), it needs to stick
with the (memcg LRU) generation it began with. In other words, it should
neither re-read memcg_lru->seq nor age an lruvec of a different
generation. Otherwise it can hit the same memcg multiple times without
giving lru_gen_age_node() a chance to check the timestamp of that memcg's
oldest generation (against min_ttl_ms).
[1] https://lore.kernel.org/CAK8fFZ4DY+GtBA40Pm7Nn5xCHy+51w3sfxPqkqpqakSXYyX+Wg@mail.gmail.com/
Link: https://lkml.kernel.org/r/20231208061407.2125867-3-yuzhao@google.com
Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: T.J. Mercier <tjmercier@google.com>
Cc: Charan Teja Kalla <quic_charante@quicinc.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Jaroslav Pulchart <jaroslav.pulchart@gooddata.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bb7dacd..e5fe4a9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4089,6 +4089,9 @@ static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
else
VM_WARN_ON_ONCE(true);
+ 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)
@@ -4099,9 +4102,6 @@ static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
pgdat->memcg_lru.nr_memcgs[old]--;
pgdat->memcg_lru.nr_memcgs[new]++;
- lruvec->lrugen.gen = new;
- WRITE_ONCE(lruvec->lrugen.seg, seg);
-
if (!pgdat->memcg_lru.nr_memcgs[old] && old == get_memcg_gen(pgdat->memcg_lru.seq))
WRITE_ONCE(pgdat->memcg_lru.seq, pgdat->memcg_lru.seq + 1);
@@ -4124,11 +4124,11 @@ void lru_gen_online_memcg(struct mem_cgroup *memcg)
gen = get_memcg_gen(pgdat->memcg_lru.seq);
+ lruvec->lrugen.gen = gen;
+
hlist_nulls_add_tail_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[gen][bin]);
pgdat->memcg_lru.nr_memcgs[gen]++;
- lruvec->lrugen.gen = gen;
-
spin_unlock_irq(&pgdat->memcg_lru.lock);
}
}
@@ -4635,7 +4635,7 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, bool
DEFINE_MAX_SEQ(lruvec);
if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg))
- return 0;
+ return -1;
if (!should_run_aging(lruvec, max_seq, sc, can_swap, &nr_to_scan))
return nr_to_scan;
@@ -4710,7 +4710,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
cond_resched();
}
- /* whether try_to_inc_max_seq() was successful */
+ /* whether this lruvec should be rotated */
return nr_to_scan < 0;
}
@@ -4764,13 +4764,13 @@ static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc)
struct lruvec *lruvec;
struct lru_gen_folio *lrugen;
struct mem_cgroup *memcg;
- const struct hlist_nulls_node *pos;
+ struct hlist_nulls_node *pos;
+ gen = get_memcg_gen(READ_ONCE(pgdat->memcg_lru.seq));
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();
@@ -4781,6 +4781,10 @@ static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc)
}
mem_cgroup_put(memcg);
+ memcg = NULL;
+
+ if (gen != READ_ONCE(lrugen->gen))
+ continue;
lruvec = container_of(lrugen, struct lruvec, lrugen);
memcg = lruvec_memcg(lruvec);
@@ -4865,16 +4869,14 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
if (sc->priority != DEF_PRIORITY || sc->nr_to_reclaim < MIN_LRU_BATCH)
return;
/*
- * Determine the initial priority based on ((total / MEMCG_NR_GENS) >>
- * priority) * reclaimed_to_scanned_ratio = nr_to_reclaim, where the
- * estimated reclaimed_to_scanned_ratio = inactive / total.
+ * Determine the initial priority based on
+ * (total >> priority) * reclaimed_to_scanned_ratio = nr_to_reclaim,
+ * where reclaimed_to_scanned_ratio = inactive / total.
*/
reclaimable = node_page_state(pgdat, NR_INACTIVE_FILE);
if (get_swappiness(lruvec, sc))
reclaimable += node_page_state(pgdat, NR_INACTIVE_ANON);
- reclaimable /= MEMCG_NR_GENS;
-
/* round down reclaimable and round up sc->nr_to_reclaim */
priority = fls_long(reclaimable) - 1 - fls_long(sc->nr_to_reclaim - 1);
