linux-kernel - Re: [PATCH 6/7] mm: memcontrol: move obj_cgroup_uncharge_pages() out of css_set

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Message-ID: <YHXa06rdCPih9YAv@carbon.dhcp.thefacebook.com>
Date:   Tue, 13 Apr 2021 10:54:27 -0700
From:   Roman Gushchin <guro@...com>
To:     Muchun Song <songmuchun@...edance.com>
CC:     <hannes@...xchg.org>, <mhocko@...nel.org>,
        <akpm@...ux-foundation.org>, <shakeelb@...gle.com>,
        <vdavydov.dev@...il.com>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <duanxiongchun@...edance.com>,
        <fam.zheng@...edance.com>
Subject: Re: [PATCH 6/7] mm: memcontrol: move obj_cgroup_uncharge_pages() out
 of css_set_lock

On Tue, Apr 13, 2021 at 02:51:52PM +0800, Muchun Song wrote:
> The css_set_lock is used to guard the list of inherited objcgs. So there
> is no need to uncharge kernel memory under css_set_lock. Just move it
> out of the lock.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>

Acked-by: Roman Gushchin <guro@...com>

> ---
>  mm/memcontrol.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 42d8c0f4ab1d..d9c7e44abcd0 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -289,9 +289,10 @@ static void obj_cgroup_release(struct percpu_ref *ref)
>  	WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1));
>  	nr_pages = nr_bytes >> PAGE_SHIFT;
>  
> -	spin_lock_irqsave(&css_set_lock, flags);
>  	if (nr_pages)
>  		obj_cgroup_uncharge_pages(objcg, nr_pages);
> +
> +	spin_lock_irqsave(&css_set_lock, flags);
>  	list_del(&objcg->list);
>  	spin_unlock_irqrestore(&css_set_lock, flags);
>  
> -- 
> 2.11.0
>