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

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Date:   Fri, 15 May 2020 14:28:53 +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 12:06, Matthew Wilcox wrote:
> On Thu, May 07, 2020 at 03:50:56PM +0800, Zhen Lei wrote:
>> @@ -266,7 +266,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
>>  
>>  static sector_t swap_page_sector(struct page *page)
>>  {
>> -	return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
>> +	return npage_to_sectors((sector_t)__page_file_index(page));
> 
> If you make npage_to_sectors() a proper function instead of a macro,
> you can do the casting inside the function instead of in the callers
> (which is prone to bugs).

Oh, yes. __page_file_index(page) maybe called many times in marco, althouth currently
it is not. So that, not all are suitable for page_to_sector(). And for this example,
still need to use "<< PAGE_SECTORS_SHIFT".

> 
> Also, this is a great example of why page_to_sector() was a better name
> than npage_to_sectors().  This function doesn't return a count of sectors,
> it returns a sector number within the swap device.
OK, so I will change to page_to_sector()/sector_to_page().

> 
> 
> .
>