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

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Message-ID: <20170830123655.6kce7yfkrhrhwubu@dhcp22.suse.cz>
Date:   Wed, 30 Aug 2017 14:36:55 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Roman Gushchin <guro@...com>
Cc:     linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        cgroups@...r.kernel.org, kernel-team@...com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memcontrol: use per-cpu stocks for socket memory
 uncharging

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