linux-kernel - Re: [PATCH v2 06/10] mm/swap: use npage_to_sectors() and PAGE

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Date:   Fri, 15 May 2020 14:42:44 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
        "Sergey Senozhatsky" <sergey.senozhatsky.work@...il.com>,
        Jens Axboe <axboe@...nel.dk>, Coly Li <colyli@...e.de>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        linux-block <linux-block@...r.kernel.org>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>, 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 v2 06/10] mm/swap: use npage_to_sectors() and PAGE_SECTORS
 to clean up code



On 2020/5/15 12:14, Matthew Wilcox wrote:
> On Thu, May 07, 2020 at 03:50:56PM +0800, Zhen Lei wrote:
>> +++ b/mm/page_io.c
>> @@ -38,7 +38,7 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
>>  
>>  		bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
>>  		bio_set_dev(bio, bdev);
>> -		bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
>> +		bio->bi_iter.bi_sector *= PAGE_SECTORS;
>>  		bio->bi_end_io = end_io;
> 
> This just doesn't look right.  Why is map_swap_page() returning a sector_t
> which isn't actually a sector_t?

I try to understand map_swap_page(). Here maybe a bug. Otherwise, it would be
better to add a temporary variable to cache the return value of map_swap_page(page, &bdev).

> 
> 
> .
>