linux-kernel - Re: [PATCH] mm/page_alloc: use nth

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Date:   Fri, 24 Mar 2017 18:43:49 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Geliang Tang <geliangtang@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: use nth_page helper

On 24.3.2017 15:10, Geliang Tang wrote:
> Use nth_page() helper instead of page_to_pfn() and pfn_to_page() to
> simplify the code.

Well I've never heard of this helper so I would have to look it up to see what
it does. Looks like there's not many users.
Anyway it's simpler to use just "page + i" if within MAX_ORDER_NR_PAGES, which
should be the case here. That can also actually save a few cycles. Otherwise it
looks like a pointless churn to me.

> Signed-off-by: Geliang Tang <geliangtang@...il.com>
> ---
>  mm/page_alloc.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f749b7f..3354f56 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2511,9 +2511,8 @@ void mark_free_pages(struct zone *zone)
>  				&zone->free_area[order].free_list[t], lru) {
>  			unsigned long i;
>  
> -			pfn = page_to_pfn(page);
>  			for (i = 0; i < (1UL << order); i++)
> -				swsusp_set_page_free(pfn_to_page(pfn + i));
> +				swsusp_set_page_free(nth_page(page, i));
>  		}
>  	}
>  	spin_unlock_irqrestore(&zone->lock, flags);
>