On Wed, Jun 08, 2016 at 09:11:30AM +0200, Christoph Hellwig wrote:
> On Fri, Jun 03, 2016 at 08:54:15AM +1000, Dave Chinner wrote:
> > On Thu, Jun 02, 2016 at 04:19:07PM +0200, Christoph Hellwig wrote:
> > > I've had some vocal user requests to allow enabling reflinks at run time,
> > > which happens to be a mostly trivial feature. The only caveat is that we
> > > need a large enough log size to support the reflink requirements, but for
> > > typical large file systems that's not an issue.
> >
> > Hmmm - how does this interact with all the rmap code? I was not
> > planning on enabling reflink without rmap and vice versa simply
> > because it makes the validation and testing matrix vastly more
> > complex.
>
> Uh. So far I've only been testing pure reflink code, mostly because
> rmap really doesn't buy much for the use case I'm working on.
So far I've mostly been testing with mkfs.xfs -i sparse=1 -m rmapbt=1,reflink=1
on the assumption that sparse will get turned on soon and that it
might help a lot in the post-COW fragmentation world.
(Hoping that the cowextsize defaults avoid most of the horrifying
fragmentation that we see on the second- and last-letter filesystems.)
> Enabling rmap post-mkfs is defintively a different ballpark, and probably
> not worth it even if it would be doable.
Hughflgrgh. I wasn't even going to consider /that/ possibility. :)
(I guess you could flip on the feature bit and run xfs_repair...)
--D
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