linux-kernel - Re: [PATCH 2/5] mm, memcg: narrow the scope of percpu_charge

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Date:   Fri, 30 Jul 2021 08:46:45 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     hannes@...xchg.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, shakeelb@...gle.com, guro@...com,
        willy@...radead.org, alexs@...nel.org, richard.weiyang@...il.com,
        songmuchun@...edance.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH 2/5] mm, memcg: narrow the scope of percpu_charge_mutex

On Thu 29-07-21 20:57:52, Miaohe Lin wrote:
> Since percpu_charge_mutex is only used inside drain_all_stock(), we can
> narrow the scope of percpu_charge_mutex by moving it here.

Makes sense and this is usually my preference as well. We used to have
other caller back then so I couldn't.

> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

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

Thanks!

> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6580c2381a3e..a03e24e57cd9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2050,7 +2050,6 @@ struct memcg_stock_pcp {
>  #define FLUSHING_CACHED_CHARGE	0
>  };
>  static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
> -static DEFINE_MUTEX(percpu_charge_mutex);
>  
>  #ifdef CONFIG_MEMCG_KMEM
>  static void drain_obj_stock(struct obj_stock *stock);
> @@ -2209,6 +2208,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
>   */
>  static void drain_all_stock(struct mem_cgroup *root_memcg)
>  {
> +	static DEFINE_MUTEX(percpu_charge_mutex);
>  	int cpu, curcpu;
>  
>  	/* If someone's already draining, avoid adding running more workers. */
> -- 
> 2.23.0

-- 
Michal Hocko
SUSE Labs