linux-kernel - Re: lift the xfs writepage code into iomap v3

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Date:   Sat, 27 Jul 2019 15:33:14 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Christoph Hellwig <hch@....de>,
        Damien Le Moal <Damien.LeMoal@....com>,
        linux-xfs@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: lift the xfs writepage code into iomap v3

On Sat, 27 Jul 2019 at 01:38, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> On Mon, Jul 23, 2019 at 11:50:12AM +0200, Christoph Hellwig wrote:
> > Hi all,
> >
> > this series cleans up the xfs writepage code and then lifts it to
> > fs/iomap.c so that it could be use by other file system.  I've been
> > wanting to this for a while so that I could eventually convert gfs2
> > over to it, but I never got to it.  Now Damien has a new zonefs
> > file system for semi-raw access to zoned block devices that would
> > like to use the iomap code instead of reinventing it, so I finally
> > had to do the work.
>
> Hmm... I don't like how there are xfs changes mixed in with the iomap
> changes, because were I to take this series as-is then I'd have to
> commit both to adding iomap writeback code /and/ converting xfs at the
> same time.
>
> I think I'd be more comfortable creating a branch to merge the changes
> to list.h and fs/iomap/, and then gfs2/zonefs/xfs can sprout their own
> branches from there to do whatever conversions are necessary.
>
> To me what that means is splitting patch 7 into 7a which does the iomap
> changes and 7b which does the xfs changes.  To get there, I'd create a
> iomap-writeback branch containing:
>
> 1 7a 8 9 10 11 12
>
> and then a new xfs-iomap-writeback branch containing:
>
> 2 4 7b
>
> This eliminates the need for patches 3, 5, and 6, though the cost is
> that it's less clear from the history that we did some reorganizing of
> the xfs writeback code and then moved it over to iomap.  OTOH, I also
> see this as a way to lower risk because if some patch in the
> xfs-iomap-writeback branch shakes loose a bug that doesn't affect gfs2
> or zonedfs we don't have to hold them up.
>
> I'll try to restructure this series along those lines and report back
> how it went.

Keeping the infrastructure changes in separate commits would certainly
make the patches easier to work with for me. Keeping the commits
interleaved should be fine though: patch "iomap: zero newly allocated
mapped blocks" depends on "xfs: set IOMAP_F_NEW more carefully", so a
pure infrastructure branch without "xfs: set IOMAP_F_NEW more
carefully" probably wouldn't be correct.

Thanks,
Andreas