linux-kernel - Re: [PATCH 2/7] migrate_pages(): remove unnecessary list_safe_reset

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Date:   Fri, 24 Jun 2022 17:22:26 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Zi Yan <ziy@...dia.com>, Yang Shi <shy828301@...il.com>
Subject: Re: [PATCH 2/7] migrate_pages(): remove unnecessary
 list_safe_reset_next()



On 6/24/2022 10:53 AM, Huang Ying wrote:
> Before commit b5bade978e9b ("mm: migrate: fix the return value of
> migrate_pages()"), the tail pages of THP will be put in the "from"
> list directly.  So one of the loop cursors (page2) needs to be reset,
> as is done in try_split_thp() via list_safe_reset_next().  But after
> the commit, the tail pages of THP will be put in a dedicated
> list (thp_split_pages).  That is, the "from" list will not be changed
> during splitting.  So, it's unnecessary to call list_safe_reset_next()
> anymore.
> 
> This is a code cleanup, no functionality changes are expected.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Yang Shi <shy828301@...il.com>
> ---

Looks good to me.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>


>   mm/migrate.c | 13 +++++--------
>   1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index a271554be7a1..82444e7df9f1 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1300,16 +1300,13 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
>   	return rc;
>   }
>   
> -static inline int try_split_thp(struct page *page, struct page **page2,
> -				struct list_head *from)
> +static inline int try_split_thp(struct page *page, struct list_head *split_pages)
>   {
> -	int rc = 0;
> +	int rc;
>   
>   	lock_page(page);
> -	rc = split_huge_page_to_list(page, from);
> +	rc = split_huge_page_to_list(page, split_pages);
>   	unlock_page(page);
> -	if (!rc)
> -		list_safe_reset_next(page, *page2, lru);
>   
>   	return rc;
>   }
> @@ -1413,7 +1410,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>   				/* THP migration is unsupported */
>   				if (is_thp) {
>   					nr_thp_failed++;
> -					if (!try_split_thp(page, &page2, &thp_split_pages)) {
> +					if (!try_split_thp(page, &thp_split_pages)) {
>   						nr_thp_split++;
>   						goto retry;
>   					}
> @@ -1432,7 +1429,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>   				 */
>   				if (is_thp && !nosplit) {
>   					nr_thp_failed++;
> -					if (!try_split_thp(page, &page2, &thp_split_pages)) {
> +					if (!try_split_thp(page, &thp_split_pages)) {
>   						nr_thp_split++;
>   						goto retry;
>   					}