NFS over RMDA

[Josh Boyer]

On Tue, Nov 25, 2014 at 02:12:08PM +0100, Paul Bolle wrote:
> On Tue, 2014-11-25 at 13:40 +0100, poma wrote:
> > On 25.11.2014 11:14, Ian Chapman wrote:
> > > Hi,
> > > 
> > > Is anyone successfully running NFS over RDMA on Fedora 20+?
> > > 
> > > I've edited /etc/sysconfig/nfs and set the the following config paramter.
> > > 
> > > RDMA_PORT=20049
> > > 
> > > Upon restarting the nfs server I get the following:
> > > 
> > > modprobe: FATAL: Module svcrdma not found
> > > /usr/libexec/nfs-utils/scripts/nfs-server.postconfig: line 12: echo: 
> > > write error: Protocol not supported
> > > 
> > > So it looks like the kernel module svcrdma is missing and the last 
> > > kernel to have it was 3.11.10-301.fc20. The postconfig script belongs to 
> > > nfs-utils.
> > > 
> > > Is svcrdma intentionally not built in the current kernels or has it been 
> > > replaced by something else?
> > > 
> >
> > [snip unedited copy from someone's terminal]
> 
> 0) In mainline kernel v3.15 the config option SUNRPC_XPRT_RDMA was split
> in two options: SUNRPC_XPRT_RDMA_CLIENT and SUNRPC_XPRT_RDMA_SERVER. See
> commit 2e8c12e1b765 ("xprtrdma: add separate Kconfig options for
> NFSoRDMA client and server support").
> 
> 1) Fedora 20 first shipped v3.15 in last July (kernel-3.15.3-200.fc20).
> Looking at the git history of the Fedora kernel package I found commit
> commit fd469c7db4e6 ("Linux v3.15.2"). It dropped
> CONFIG_SUNRPC_XPRT_RDMA=m from the config files (as it was useless). It
> set CONFIG_SUNRPC_XPRT_RDMA_CLIENT to 'm' but did not set
> CONFIG_SUNRPC_XPRT_RDMA_SERVER. The commit offers no explanation of this
> choice. Perhaps it was discusses somewhere else.
> 
> 2) A similar commit for Rawhide was 700baa35a69e ("Linux
> v3.14-12042-g69cd9eba3886"), but it doesn't comment on this choice
> either.
> 
> 3) Perhaps Justin or Josh, authors of those commits, might recall why
> only CONFIG_SUNRPC_XPRT_RDMA_CLIENT was set.

At the time, server support for NFSoRDMA wasn't in the greatest shape
and we disabled it at the request of the NFS developers.  I believe this
also matches what wound up in RHEL7.

The NFS developers haven't asked us to turn it back on, so it has stayed
off since.

josh