On Wed, Sep 25, 2013 at 12:06:20PM -0700, Zach Brown wrote: > On Wed, Sep 25, 2013 at 03:02:29PM -0400, Anna Schumaker wrote: > > On Wed, Sep 25, 2013 at 2:38 PM, Zach Brown <zab@xxxxxxxxxx> wrote: > > > > > > Hrmph. I had composed a reply to you during Plumbers but.. something > > > happened to it :). Here's another try now that I'm back. > > > > > >> > Some things to talk about: > > >> > - I really don't care about the naming here. If you do, holler. > > >> > - We might want different flags for file-to-file splicing and acceleration > > >> > > >> Yes, I think "copy" and "reflink" needs to be differentiated. > > > > > > I initially agreed but I'm not so sure now. The problem is that we > > > can't know whether the acceleration is copying or not. XCOPY on some > > > array may well do some shared referencing tricks. The nfs COPY op can > > > have a server use btrfs reflink, or ext* and XCOPY, or .. who knows. At > > > some point we have to admit that we have no way to determine the > > > relative durability of writes. Storage can do a lot to make writes more > > > or less fragile that we have no visibility of. SSD FTLs can log a bunch > > > of unrelated sectors on to one flash failure domain. > > > > > > And if such a flag couldn't *actually* guarantee anything for a bunch of > > > storage topologies, well, let's not bother with it. > > > > > > The only flag I'm in favour of now is one that has splice return rather > > > than falling back to manual page cache reads and writes. It's more like > > > O_NONBLOCK than any kind of data durability hint. > > > > For reference, I'm planning to have the NFS server do the fallback > > when it copies since any local copy will be faster than a read and > > write over the network. > > Agreed, this is definitely the reasonable thing to do. A client-side copy will be slower, but I guess it does have the advantage that the application can track progress to some degree, and abort it fairly quickly without leaving the file in a totally undefined state--and both might be useful if the copy's not a simple constant-time operation. So maybe a way to pass your NONBLOCKy flag to the server would be useful? FWIW the protocol doesn't seem frozen yet, so I assume we could still add an extra flag field if you think it would be worthwhile. --b. -- 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
