On Wed, Jan 15, 2014 at 10:03:12AM +0100, Jan Kara wrote: > Hello, > > On Tue 14-01-14 23:16:20, mingming cao wrote: > > I'd like to attend Linux storage and filesystem summit. I am > > interested in discussion of general lockless direct io and more > > interested in discussion of reflink support for filesystem. Btrfs > > and OCFS2 has this support, My goal is explore what's best to way > > this support for ext4. If there is any crossover work between > > filesystem and vfs people, or filesystem and dm layer I am more than > > happy to discuss about it too. > There was a project for implementing COW for ext4 but it was a really > major surgery and in the end didn't get to an upstreamable state. Reflink > is somewhat simpler than general COW because it's only about fs data. In > particular implementing reflink with a file granularity (i.e., a type of > hardlink which is automatically converted to a copy when first opened for > writing) is relatively simple to do but I'm not sure how useful it is. > Doing reflink properly with block granularity is harder with block > refcounting etc. > > Do you have any particular usecase in mind? The use case I keep hearing for reflink in XFS is optimising distributed filesystem snapshot implementations, which tend to require file block level COW semantics on a per-file basis... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
