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

[Steven Whitehouse <swhiteho@redhat.com>]

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.