linux-ext4 - Re: iomap preparations for GFS2 v2

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Date:   Fri, 15 Jun 2018 10:03:27 +0200
From:   Christoph Hellwig <hch@....de>
To:     Andreas Gruenbacher <agruenba@...hat.com>
Cc:     Christoph Hellwig <hch@....de>, linux-xfs@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        cluster-devel <cluster-devel@...hat.com>,
        linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: iomap preparations for GFS2 v2

On Thu, Jun 14, 2018 at 03:04:38PM +0200, Andreas Gruenbacher wrote:
> I saw that you've pushed this onto the gfs2-iomap branch in your xfs
> repository. I've rebased the gfs2 iomap-write branch onto that;
> there's a trivial patch for adding a private pointer to struct iomap
> at the head of that branch that would sense to move to the shared
> branch as well now.

Please send that patch out ASAP.

> The next step would probably be to start using iomap_readpage /
> iomap_readpages in gfs2 for block size == page size. This requires
> adding inline data support to iomap_readpage which is trivial, but
> because of gfs2's reliance on buffer heads, that alone isn't enough.

Is it?  At least for block size == page size we will only call
readpage on a pristine, newly allocated page.  So buffer heads won't
be in the game at that point, and the iomap buffered write code will
just allocate them for you once we start a write operation, or take
a page fault that makes the page writable.