[PATCH] mm: memcontrol: use per-cpu stocks for socket memory uncharging

Roman Gushchin
2017-08-29T10:01:50Z

We've noticed a quite sensible performance overhead on some hosts
with significant network traffic when socket memory accounting
is enabled.

Perf top shows that socket memory uncharging path is hot:
2.13% [kernel] [k] page_counter_cancel
1.14% [kernel] [k] __sk_mem_reduce_allocated
1.14% [kernel] [k] _raw_spin_lock
0.87% [kernel] [k] _raw_spin_lock_irqsave
0.84% [kernel] [k] tcp_ack
0.84% [kernel] [k] ixgbe_poll
0.83% < workload >
0.82% [kernel] [k] enqueue_entity
0.68% [kernel] [k] __fget
0.68% [kernel] [k] tcp_delack_timer_handler
0.67% [kernel] [k] __schedule
0.60% < workload >
0.59% [kernel] [k] __inet6_lookup_established
0.55% [kernel] [k] __switch_to
0.55% [kernel] [k] menu_select
0.54% libc-2.20.so [.] __memcpy_avx_unaligned

To address this issue, the existing per-cpu stock infrastructure
can be used.

refill_stock() can be called from mem_cgroup_uncharge_skmem()
to move charge to a per-cpu stock instead of calling atomic
page_counter_uncharge().

To prevent the uncontrolled growth of per-cpu stocks,
refill_stock() will explicitly drain the cached charge,
if the cached value exceeds CHARGE_BATCH.

This allows significantly optimize the load:
1.21% [kernel] [k] _raw_spin_lock
1.01% [kernel] [k] ixgbe_poll
0.92% [kernel] [k] _raw_spin_lock_irqsave
0.90% [kernel] [k] enqueue_entity
0.86% [kernel] [k] tcp_ack
0.85% < workload >
0.74% perf-11120.map [.] 0x000000000061bf24
0.73% [kernel] [k] __schedule
0.67% [kernel] [k] __fget
0.63% [kernel] [k] __inet6_lookup_established
0.62% [kernel] [k] menu_select
0.59% < workload >
0.59% [kernel] [k] __switch_to
0.57% libc-2.20.so [.] __memcpy_avx_unaligned

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: cgroups@vger.kernel.org
Cc: kernel-team@fb.com
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
mm/memcontrol.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b9cf3cf4a3d0..a69d23082abf 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1792,6 +1792,9 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
}
stock->nr_pages += nr_pages;

+ if (stock->nr_pages > CHARGE_BATCH)
+ drain_stock(stock);
+
local_irq_restore(flags);
}

@@ -5886,8 +5889,7 @@ void mem_cgroup_uncharge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)

this_cpu_sub(memcg->stat->count[MEMCG_SOCK], nr_pages);

- page_counter_uncharge(&memcg->memory, nr_pages);
- css_put_many(&memcg->css, nr_pages);
+ refill_stock(memcg, nr_pages);
}

static int __init cgroup_memory(char *s)
--
2.13.5