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Date:   Mon, 18 Sep 2023 17:36:29 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Hannes Reinecke <hare@suse.de>
Cc:     Luis Chamberlain <mcgrof@kernel.org>,
        Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Pankaj Raghav <p.raghav@samsung.com>,
        linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 03/18] block/buffer_head: introduce
 block_{index_to_sector,sector_to_index}
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On Mon, Sep 18, 2023 at 01:04:55PM +0200, Hannes Reinecke wrote:
> @@ -449,6 +450,22 @@ __bread(struct block_device *bdev, sector_t block, unsigned size)
>  
>  bool block_dirty_folio(struct address_space *mapping, struct folio *folio);
>  
> +static inline sector_t block_index_to_sector(pgoff_t index, unsigned int blkbits)
> +{
> +	if (PAGE_SHIFT < blkbits)
> +		return (sector_t)index >> (blkbits - PAGE_SHIFT);
> +	else
> +		return (sector_t)index << (PAGE_SHIFT - blkbits);
> +}

Is this actually more efficient than ...

	loff_t pos = (loff_t)index * PAGE_SIZE;
	return pos >> blkbits;

It feels like we're going to be doing this a lot, so we should find out
what's actually faster.