linux-kernel - Re: [PATCH 6/9] iomap: Convert read

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Message-ID: <20200825221416.GK6096@magnolia>
Date:   Tue, 25 Aug 2020 15:14:16 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/9] iomap: Convert read_count to byte count

On Tue, Aug 25, 2020 at 10:09:02AM +1000, Dave Chinner wrote:
> 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...

Agreed. :)

--D

> Otherwise the code looks OK.
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com