Re: [PATCH 1/1] NFSv4.1+ add trunking when server trunking detected

On Tue, 2021-06-08 at 21:19 +0000, Trond Myklebust wrote:

On Tue, 2021-06-08 at 21:06 +0000, Chuck Lever III wrote:

quoted

quoted

On Jun 8, 2021, at 4:56 PM, Olga Kornievskaia < 
olga.kornievskaia@gmail.com> wrote:

On Tue, Jun 8, 2021 at 4:41 PM Chuck Lever III < 
chuck.lever@oracle.com> wrote:

quoted

quoted

On Jun 8, 2021, at 2:45 PM, Olga Kornievskaia < 
olga.kornievskaia@gmail.com> wrote:

From: Olga Kornievskaia <redacted>

After trunking is discovered in
nfs4_discover_server_trunking(),
add the transport to the old client structure before
destroying
the new client structure (along with its transport).

Signed-off-by: Olga Kornievskaia <redacted>
---
fs/nfs/nfs4client.c | 40
++++++++++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)

diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index 42719384e25f..984c851844d8 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c

@@ -361,6 +361,44 @@ static int

nfs4_init_client_minor_version(struct nfs_client *clp)
     return nfs4_init_callback(clp);
}

+static void nfs4_add_trunk(struct nfs_client *clp, struct
nfs_client *old)
+{
+     struct sockaddr_storage clp_addr, old_addr;
+     struct sockaddr *clp_sap = (struct sockaddr
*)&clp_addr;
+     struct sockaddr *old_sap = (struct sockaddr
*)&old_addr;
+     size_t clp_salen, old_salen;
+     struct xprt_create xprt_args = {
+             .ident = old->cl_proto,
+             .net = old->cl_net,
+             .servername = old->cl_hostname,
+     };
+     struct nfs4_add_xprt_data xprtdata = {
+             .clp = old,
+     };
+     struct rpc_add_xprt_test rpcdata = {
+             .add_xprt_test = old->cl_mvops->session_trunk,
+             .data = &xprtdata,
+     };
+
+     if (clp->cl_proto != old->cl_proto)
+             return;
+     clp_salen = rpc_peeraddr(clp->cl_rpcclient, clp_sap,
sizeof(clp_addr));
+     old_salen = rpc_peeraddr(old->cl_rpcclient, old_sap,
sizeof(old_addr));
+
+     if (clp_addr.ss_family != old_addr.ss_family)
+             return;
+
+     xprt_args.dstaddr = clp_sap;
+     xprt_args.addrlen = clp_salen;
+
+     xprtdata.cred = nfs4_get_clid_cred(old);
+     rpc_clnt_add_xprt(old->cl_rpcclient, &xprt_args,
+                       rpc_clnt_setup_test_and_add_xprt,
&rpcdata);

Is there an upper bound on the number of transports that
are added to the NFS client's switch?

I don't believe any limits exist right now. Why should there be a
limit? Are you saying that the client should limit trunking?
While
this is not what's happening here, but say FS_LOCATION returned
100
ips for the server. Are you saying the client should be limiting
how
many trunkable connections it would be establishing and picking
just a
few addresses to try? What's happening with this patch is that
say
there are 100mounts to 100 ips (each representing the same server
or
trunkable server(s)), without this patch a single connection is
kept,
with this patch we'll have 100 connections.

The patch description needs to make this behavior more clear. It
needs to explain "why" -- the body of the patch already explains
"what". Can you include your last sentence in the description as
a use case?

As for the behavior... Seems to me that there are going to be only
infinitesimal gains after the first few connections, and after
that, it's going to be a lot for both sides to manage for no real
gain. I think you do want to cap the total number of connections
at a reasonable number, even in the FS_LOCATIONS case.

I'd tend to agree. If you want to scale I/O then pNFS is the way to
go,
not vast numbers of connections to a single server.

BTW: AFAICS this patch will end up adding another connection every time
we mount a new filesystem, whether or not a connection already exists
to that IP address. That's unacceptable.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com