From mboxrd@z Thu Jan  1 00:00:00 1970
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH 0/4] eliminate SECTOR related magic numbers and
 duplicated conversions
Date: Tue, 5 May 2020 11:01:13 -0700
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References: <20200505115543.1660-1-thunder.leizhen@huawei.com>
 <ea522f15-991d-6f67-ba8b-9cb4954a1064@youngman.org.uk>
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Cc: Zhen Lei <thunder.leizhen@huawei.com>, Minchan Kim <minchan@kernel.org>, Nitin Gupta <ngupta@vflare.org>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Jens Axboe <axboe@kernel.dk>, linux-block <linux-block@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm <linux-mm@kvack.org>, Alasdair Kergon <agk@redhat.com>, Mike Snitzer <snitzer@redhat.com>, dm-devel <dm-devel@redhat.com>, Song Liu <song@kernel.org>, linux-raid <linux-raid@vger.kernel.org>, linux-kernel <linux-kernel@vger.kernel.org>
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On Tue, May 05, 2020 at 06:32:36PM +0100, antlists wrote:
> On 05/05/2020 12:55, Zhen Lei wrote:
> > When I studied the code of mm/swap, I found "1 << (PAGE_SHIFT - 9)" appears
> > many times. So I try to clean up it.
> > 
> > 1. Replace "1 << (PAGE_SHIFT - 9)" or similar with SECTORS_PER_PAGE
> > 2. Replace "PAGE_SHIFT - 9" with SECTORS_PER_PAGE_SHIFT
> > 3. Replace "9" with SECTOR_SHIFT
> > 4. Replace "512" with SECTOR_SIZE
> 
> Naive question - what is happening about 4096-byte sectors? Do we need to
> forward-plan?

They're fully supported already, but Linux defines a sector to be 512
bytes.  So we multiply by 8 and divide by 8 a few times unnecessarily,
but it's not worth making sector size be a per-device property.

Good thought, though.