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. > Enabling rmap post-mkfs is defintively a different ballpark, and probably > not worth it even if it would be doable. Wasn't expecting rmap to ever be dynamically enabled ;) So ignoring the testing side of things, and looking more at the implementation of the enabling, I'm not sure I really like the idea of doing this via a mount option. Because we've got to make significant additions to the on disk format in each AG, this seems more like a "growfs style" operation than anything. i.e. lock out allocation, add all the structures to the AG headers and allocate all the blocks needed, re-initialise the per-ag structures with all the necessary info, then switch on the feature bit and commit the change. It's probably a little more intricate than doing it at mount time, but it gets around the fact that users have to add a mount option and bounce the filesystem to turn on reflinks. I can see this being much easier than a mount option in some situations, (e.g. for the root filesystem), and I don't think it's much harder to test than the mount option (e.g. the way growfs is tested under stress by xfs/104)... Your thoughts, Christoph? Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
