linux-kernel - Re: [PATCH 3/5] iomap: simplify iomap_init() with PAGE

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Message-ID: <47688c1d-9cf1-3e08-1f1d-a051b25d010e@kernel.dk>
Date:   Fri, 21 Apr 2023 16:24:57 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Matthew Wilcox <willy@...radead.org>
Cc:     agk@...hat.com, snitzer@...nel.org, philipp.reisner@...bit.com,
        lars.ellenberg@...bit.com, christoph.boehmwalder@...bit.com,
        hch@...radead.org, djwong@...nel.org, minchan@...nel.org,
        senozhatsky@...omium.org, patches@...ts.linux.dev,
        linux-block@...r.kernel.org, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        dm-devel@...hat.com, drbd-dev@...ts.linbit.com,
        linux-kernel@...r.kernel.org, hare@...e.de, p.raghav@...sung.com,
        da.gomez@...sung.com, kbusch@...nel.org
Subject: Re: [PATCH 3/5] iomap: simplify iomap_init() with PAGE_SECTORS

On 4/21/23 4:02 PM, Luis Chamberlain wrote:
> On Fri, Apr 21, 2023 at 09:14:00PM +0100, Matthew Wilcox wrote:
>> On Fri, Apr 21, 2023 at 12:58:05PM -0700, Luis Chamberlain wrote:
>>> Just use the PAGE_SECTORS generic define. This produces no functional
>>> changes. While at it use left shift to simplify this even further.
>>
>> How is FOO << 2 simpler than FOO * 4?
>>
>>> -	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
>>> +	return bioset_init(&iomap_ioend_bioset, PAGE_SECTORS << 2,
> 
> We could just do:
> 
> 
> -	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
> +	return bioset_init(&iomap_ioend_bioset, 4 * PAGE_SECTORS,
> 
> The shift just seemed optimal if we're just going to change it.

It's going to generate the same code, but the multiplication is arguably
easier to read (or harder to misread).

-- 
Jens Axboe