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Date:   Tue, 25 Aug 2020 10:09:02 +1000
From:   Dave Chinner <david@fromorbit.com>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc:     linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        "Darrick J . Wong" <darrick.wong@oracle.com>,
        linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/9] iomap: Convert read_count to byte count
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 <20200824145511.10500-7-willy@infradead.org>
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On Mon, Aug 24, 2020 at 03:55:07PM +0100, Matthew Wilcox (Oracle) wrote:
> Instead of counting bio segments, count the number of bytes submitted.
> This insulates us from the block layer's definition of what a 'same page'
> is, which is not necessarily clear once THPs are involved.

I'd like to see a comment on the definition of struct iomap_page to
indicate that read_count (and write count) reflect the byte count of
IO currently in flight on the page, not an IO count, because THP
makes tracking this via bio state hard. Otherwise it is not at all
obvious why it is done and why it is intentional...

Otherwise the code looks OK.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com