linux-kernel - Re: [PATCH] mm/hugetlb: remove duplicate codes of setting compound

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Date:   Tue, 2 Feb 2021 21:24:03 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     yanfei.xu@...driver.com, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: remove duplicate codes of setting compound_nr

On 2/2/21 8:40 PM, yanfei.xu@...driver.com wrote:
> From: Yanfei Xu <yanfei.xu@...driver.com>
> 
> set_compound_order() set both of page's compound_order and
> compound_nr. It's no need to assign to compound_nr again, so
> remove it.
> 
> Signed-off-by: Yanfei Xu <yanfei.xu@...driver.com>
> ---
>  mm/hugetlb.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index a3e4fa2c5e94..ac249b1583de 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1228,7 +1228,6 @@ static void destroy_compound_gigantic_page(struct page *page,
>  	}
>  
>  	set_compound_order(page, 0);
> -	page[1].compound_nr = 0;

I may be reading the code wrong, but set_compound_order(page, 0) will
set page[1].compound_nr to the value of 1.  That is different than the
explicit setting to 0 in the existing code.

If that is correct, then you should say why the explicit assignment
is not necessary.
-- 
Mike Kravetz

>  	__ClearPageHead(page);
>  }
>  
>