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

Michal Hocko
2017-08-30T14:24:18Z

On Tue 29-08-17 11:01:50, Roman Gushchin wrote:
> 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

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> 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

--
Michal Hocko
SUSE Labs