> On Jan 12, 2017, at 12:38 PM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote: > > On Fri, 2016-12-16 at 11:48 -0500, Chuck Lever wrote: >> Current NFS clients rely on connection loss to determine when to >> retransmit. In particular, for protocols like NFSv4, clients no >> longer rely on RPC timeouts to drive retransmission: NFSv4 servers >> are required to terminate a connection when they need a client to >> retransmit pending RPCs. >> >> When a server is no longer reachable, either because it has crashed >> or because the network path has broken, the server cannot actively >> terminate a connection. Thus NFS clients depend on transport-level >> keepalive to determine when a connection must be replaced and >> pending RPCs retransmitted. >> >> However, RDMA RC connections do not have a native keepalive >> mechanism. If an NFS/RDMA server crashes after a client has sent >> RPCs successfully (an RC ACK has been received for all OTW RDMA >> requests), there is no way for the client to know the connection is >> moribund. >> >> In addition, new RDMA requests are subject to the RPC-over-RDMA >> credit limit. If the client has consumed all granted credits with >> NFS traffic, it is not allowed to send another RDMA request until >> the server replies. Thus it has no way to send a true keepalive when >> the workload has already consumed all credits with pending RPCs. >> >> To address this, we reserve one RPC-over-RDMA credit that may be >> used only for an NFS NULL. A periodic RPC ping is done on transports >> whenever there are outstanding RPCs. >> >> The purpose of this ping is to drive traffic regularly on each >> connection to force the transport layer to disconnect it if it is no >> longer viable. Some RDMA operations are fully offloaded to the HCA, >> and can be successful even if the remote host has crashed. Thus an >> operation that requires that the server is responsive is used for >> the ping. >> >> This implementation re-uses existing generic RPC infrastructure to >> form each NULL Call. An rpc_clnt context must be available to start >> an RPC. Thus a generic keepalive mechanism is introduced so that >> both an rpc_clnt and an rpc_xprt is available to perform the ping. >> >> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> >> --- >> >> Before sending this for internal testing, I'd like to hear comments >> on this approach. It's a little more churn than I had hoped for. >> >> >> fs/nfs/nfs4client.c | 1 >> include/linux/sunrpc/clnt.h | 2 + >> include/linux/sunrpc/sched.h | 3 + >> include/linux/sunrpc/xprt.h | 1 >> net/sunrpc/clnt.c | 101 >> +++++++++++++++++++++++++++++++++++++++ >> net/sunrpc/sched.c | 19 +++++++ >> net/sunrpc/xprt.c | 5 ++ >> net/sunrpc/xprtrdma/rpc_rdma.c | 4 +- >> net/sunrpc/xprtrdma/transport.c | 13 +++++ >> 9 files changed, 148 insertions(+), 1 deletion(-) >> >> diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c >> index 074ac71..c5f5ce8 100644 >> --- a/fs/nfs/nfs4client.c >> +++ b/fs/nfs/nfs4client.c >> @@ -378,6 +378,7 @@ struct nfs_client *nfs4_init_client(struct >> nfs_client *clp, >> error = nfs_create_rpc_client(clp, cl_init, >> RPC_AUTH_UNIX); >> if (error < 0) >> goto error; >> + rpc_schedule_keepalive(clp->cl_rpcclient); > > Why do we want to enable this for non-RDMA transports? Shouldn't this > functionality be hidden in the RDMA client code, in the same way that > the TCP keepalive is hidden in the socket code. Sending a NULL request by re-using the normal RPC infrastructure requires a struct rpc_clnt. Thus it has to be driven by an upper layer context. I'm open to suggestions. -- Chuck Lever -- 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
