linux-kernel - Re: [PATCH 0/4] eliminate SECTOR related magic numbers and duplicated conversions

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Date:   Tue, 5 May 2020 11:01:13 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     antlists <antlists@...ngman.org.uk>
Cc:     Zhen Lei <thunder.leizhen@...wei.com>,
        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 0/4] eliminate SECTOR related magic numbers and
 duplicated conversions

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.