Bruce, Splice can be implemented independent of RDMA. It is supposed to transfer pages between two file descriptors. I found some postings on lkml from 2006 where Linus says it is quite possible to splice from a socket to a file. See the paragraph: " For filesystems, splice support tends to be really easy (both read and write). For other things, it depends a bit. But unlike sendfile(), it really is quite possible to splice _from_ a socket too, not just _to_ a socket. But no, that case hasn't been written yet." http://yarchive.net/comp/linux/splice.html Larry McVoy's 1997 proposal for adding splice support to the kernel can be read at ftp.tux.org/pub/sites/ftp.bitmover.com/pub/splice.ps.gz Perhaps I should have opened this thread on lkml to determine if splice from socket to file is still feasible.. -Sandeep On Wed, Jun 12, 2013 at 9:09 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > On Tue, Jun 11, 2013 at 10:36:12PM -0400, Tom Talpey wrote: > > On 6/11/2013 3:51 PM, J. Bruce Fields wrote: > > >On Sun, Jun 09, 2013 at 01:05:16PM +0530, Sandeep Joshi wrote: > > >>Is there a reason as to why the nfsd server does not use splice in the > > >>write calls - nfsd_vfs_write() ? Is there some structural limitation > > >>or is it just something nobody got around to implementing ? > > >> > > >>I have looked at the source back to the 2.6.x kernels and it seems > > >>only nfsd_vfs_read() has ever used splice/sendfile. > > >>http://lxr.linux.no/linux+v3.9.5/fs/nfsd/vfs.c > > > > > >I don't actually know how splice_write works.... I assume to avoid a > > >copy we'd have to place the incoming write data into pages already > > >correctly aligned. That would be an interesting trick. > > > > NFS-RDMA does that, by design. ;-) > > So teaching nfsd to take advantage of splice in the rdma case could be > a doable project for someone? > > I was thinking about NFSv4/tcp, in which case I guess we'd need to start > parsing the xdr in the tcp receive code. > > --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
