linux-kernel - Re: [PATCH v2 2/3] mm/page_alloc: remove unnecessary check in break_down_buddy

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Message-ID: <20230926113400.GB1539169@ik1-406-35019.vs.sakura.ne.jp>
Date:   Tue, 26 Sep 2023 20:34:00 +0900
From:   Naoya Horiguchi <naoya.horiguchi@...ux.dev>
To:     Kemeng Shi <shikemeng@...weicloud.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, willy@...radead.org,
        naoya.horiguchi@....com, osalvador@...e.de
Subject: Re: [PATCH v2 2/3] mm/page_alloc: remove unnecessary check in
 break_down_buddy_pages

On Sat, Aug 26, 2023 at 11:47:44PM +0800, Kemeng Shi wrote:
> 1. We always have target in range started with next_page and full free
> range started with current_buddy.
> 2. The last splited range size is 1 << low and low should be >= 0, then

s/splited/split/

> size >= 1, then page + size and page will not interleave.

I'm not sure the meaning of "interleave" here, maybe simply meaning
"page + size != page is always true (because size > 0)".

> As summary, current_page will not equal to target page.
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>

But I agree with the summary. So with updating description...

Acked-by: Naoya Horiguchi <naoya.horiguchi@....com>

> ---
>  mm/page_alloc.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 88c5f5aea9b0..bb74b40dc195 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6510,10 +6510,8 @@ static void break_down_buddy_pages(struct zone *zone, struct page *page,
>  		if (set_page_guard(zone, current_buddy, high, migratetype))
>  			continue;
>  
> -		if (current_buddy != target) {
> -			add_to_free_list(current_buddy, zone, high, migratetype);
> -			set_buddy_order(current_buddy, high);
> -		}
> +		add_to_free_list(current_buddy, zone, high, migratetype);
> +		set_buddy_order(current_buddy, high);
>  	}
>  }
>  
> -- 
> 2.30.0
> 
> 
>