linux-kernel - Re: [PATCH v2] mm: memcontrol: replace the loop with a list_for_each

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Date:   Fri, 5 Feb 2021 16:27:56 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     hannes@...xchg.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: memcontrol: replace the loop with a
 list_for_each_entry()

On Fri 05-02-21 00:30:55, Muchun Song wrote:
> The rule of list walk has gone since:
> 
>  commit a9d5adeeb4b2 ("mm/memcontrol: allow to uncharge page without using page->lru field")
> 
> So remove the strange comment and replace the loop with a
> list_for_each_entry().
> 
> There is only one caller of the uncharge_list(). So just fold it into
> mem_cgroup_uncharge_list() and remove it.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>

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

Thanks!

> ---
> v2:
>  - Fold uncharge_list() to mem_cgroup_uncharge_list().
> 
>  mm/memcontrol.c | 35 ++++++++---------------------------
>  1 file changed, 8 insertions(+), 27 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ed5cc78a8dbf..8c035846c7a4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6862,31 +6862,6 @@ static void uncharge_page(struct page *page, struct uncharge_gather *ug)
>  	css_put(&ug->memcg->css);
>  }
>  
> -static void uncharge_list(struct list_head *page_list)
> -{
> -	struct uncharge_gather ug;
> -	struct list_head *next;
> -
> -	uncharge_gather_clear(&ug);
> -
> -	/*
> -	 * Note that the list can be a single page->lru; hence the
> -	 * do-while loop instead of a simple list_for_each_entry().
> -	 */
> -	next = page_list->next;
> -	do {
> -		struct page *page;
> -
> -		page = list_entry(next, struct page, lru);
> -		next = page->lru.next;
> -
> -		uncharge_page(page, &ug);
> -	} while (next != page_list);
> -
> -	if (ug.memcg)
> -		uncharge_batch(&ug);
> -}
> -
>  /**
>   * mem_cgroup_uncharge - uncharge a page
>   * @page: page to uncharge
> @@ -6918,11 +6893,17 @@ void mem_cgroup_uncharge(struct page *page)
>   */
>  void mem_cgroup_uncharge_list(struct list_head *page_list)
>  {
> +	struct uncharge_gather ug;
> +	struct page *page;
> +
>  	if (mem_cgroup_disabled())
>  		return;
>  
> -	if (!list_empty(page_list))
> -		uncharge_list(page_list);
> +	uncharge_gather_clear(&ug);
> +	list_for_each_entry(page, page_list, lru)
> +		uncharge_page(page, &ug);
> +	if (ug.memcg)
> +		uncharge_batch(&ug);
>  }
>  
>  /**
> -- 
> 2.11.0

-- 
Michal Hocko
SUSE Labs