linux-kernel - Re: [PATCH 2/4] mm/swap: use SECTORS_PER_PAGE

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Date:   Tue, 5 May 2020 10:25:20 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>, Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        dm-devel <dm-devel@...hat.com>, Song Liu <song@...nel.org>,
        linux-raid <linux-raid@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] mm/swap: use SECTORS_PER_PAGE_SHIFT to clean up code

On Tue, May 05, 2020 at 07:55:41PM +0800, Zhen Lei wrote:
> +++ b/mm/swapfile.c
> @@ -177,8 +177,8 @@ static int discard_swap(struct swap_info_struct *si)
>  
>  	/* Do not discard the swap header page! */
>  	se = first_se(si);
> -	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
> -	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
> +	start_block = (se->start_block + 1) << SECTORS_PER_PAGE_SHIFT;
> +	nr_blocks = ((sector_t)se->nr_pages - 1) << SECTORS_PER_PAGE_SHIFT;

Thinking about this some more, wouldn't this look better?

	start_block = page_sectors(se->start_block + 1);
	nr_block = page_sectors(se->nr_pages - 1);