linux-ext4 - Re: [Cluster-devel] iomap preparations for GFS2 v2

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Message-ID: <5a1e303b-e96e-7faf-1bcd-36d63a237514@redhat.com>
Date:   Fri, 15 Jun 2018 09:31:26 +0100
From:   Steven Whitehouse <swhiteho@...hat.com>
To:     Christoph Hellwig <hch@....de>,
        Andreas Gruenbacher <agruenba@...hat.com>
Cc:     cluster-devel <cluster-devel@...hat.com>,
        linux-xfs@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [Cluster-devel] iomap preparations for GFS2 v2

Hi,


On 15/06/18 09:03, Christoph Hellwig wrote:
> 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.
>

Yes, for block size == page size, it should not be an issue to drop the 
use of buffer heads on reads in GFS2. I was fairly sure that we already 
did that in ->readpages() anyway, but it is a while since I looked at 
the code and my memory may be playing tricks on me,

Steve.