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Date: Sat, 11 Nov 2023 22:00:20 -0800
From: Eric Biggers <ebiggers@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Hannes Reinecke <hare@suse.de>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Pankaj Raghav <p.raghav@samsung.com>, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 7/7] buffer: Fix more functions for block size >
 PAGE_SIZE
Message-ID: <20231112060020.GA578127@sol.localdomain>
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In-Reply-To: <ZVBaKPHNM+9Ry7eq@casper.infradead.org>

On Sun, Nov 12, 2023 at 04:52:56AM +0000, Matthew Wilcox wrote:
> On Sat, Nov 11, 2023 at 10:06:13AM -0800, Eric Biggers wrote:
> > On Fri, Nov 10, 2023 at 02:26:43PM +0000, Matthew Wilcox wrote:
> > > Would you want to invest more engineering time in changing it?
> > 
> > It seems logical to just keep the existing approach instead of spending time
> > trying to justify changing it to a less efficient one (divides).
> 
> Except the existing approach doesn't work for block size > PAGE_SIZE

A shift does still work; the block size is still a power of 2, after all.
'(sector_t)folio->index << (PAGE_SHIFT - bbits)' just needs to be changed to
'folio_pos(folio) >> bbits'.

- Eric