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

Michal Hocko
2017-08-30T12:36:55Z

On Tue 29-08-17 11:01:50, Roman Gushchin wrote:
[...]
> 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);
> }

Why do we need this? In other words, why cannot we rely on draining we
already do?

>
> @@ -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);
> }

This makes sense to me.
--
Michal Hocko
SUSE Labs