On Fri, 14 Jun 2013 17:39:12 +0530 Sandeep Joshi <sanjos100@xxxxxxxxx> wrote: > On Wed, Jun 12, 2013 at 10:16 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > > > On Wed, Jun 12, 2013 at 09:51:09PM +0530, Sandeep Joshi wrote: > > > 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<http://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.. > > > > Right, the thing is, nfsd reads the rpc request from the socket into its > > own buffers before it parses it. If you want to move the data directly > > out of the network buffers into the page cache, then you have to know at > > what point the write data starts in the request--which I believe will > > mean doing the xdr parsing (and gss decryption if necessary) as the > > request comes in off the wire. > > > > That sounds like a lot of work and even if you have someone willing to > > do the work they'd also need to justify that it's worth it. > > > > RDMA may have some protocol support that simplifies this, I don't know. > > > > --b. > > Hi Bruce, > > > nfsd reads the rpc request from the socket into its own buffers before it parses it. > > I am not intimate with the gss code but do you think the > svc_rqst->rq_pages[] can be spliced ? > Probably not in its current form. The problem is one of alignment. You need to know where the write data actually starts before doing the receive off the socket, so you can make sure that it ends up in the correct spot in the pages you're going to splice in. There's also the problem of what to do about WRITE requests that contain data that isn't page aligned or that's shorter than a page... -- Jeff Layton <jlayton@xxxxxxxxxx> -- 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
