Re: [PATCH v3 3/3] NFSD: Add support for encoding multiple segments

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Mar 17, 2015 at 03:56:33PM -0400, J. Bruce Fields wrote:
> On Mon, Mar 16, 2015 at 05:18:08PM -0400, Anna Schumaker wrote:
> > This patch implements sending an array of segments back to the client.
> > Clients should be prepared to handle multiple segment reads to make this
> > useful.  We try to splice the first data segment into the XDR result,
> > and remaining segments are encoded directly.
> 
> I'm still interested in what would happen if we started with an
> implementation like:
> 
> 	- if the entire requested range falls within a hole, return that
> 	  single hole.
> 	- otherwise, just treat the thing as one big data segment.
> 
> That would provide a benefit in the case there are large-ish holes
> with minimal impact otherwise.
> 
> (Though patches for full support are still useful even if only for
> client-testing purposes.)

Also, looks like

	xvs_io -c "fiemap -v" <file>

will give hole sizes for a given <file>.  (Thanks, esandeen.)  Running
that on a few of my test vm images shows a fair number of large
(hundreds of megs) files, which suggests identifying only >=rwsize holes
might still be useful.

--b.