sunrpc: allow SOMAXCONN backlogged TCP connections

The connection backlog passed to listen() denotes the number of
connections that are fully established, but that have not yet been
accept()ed. If the amount goes above that level, new connection requests
will be dropped on the floor until the value goes down. If all the knfsd
threads are bogged down in (e.g.) disk I/O, new connection attempts can
stall because of this.

For the same rationale that Trond points out in the userland patch [1],
ensure that svc_xprt sockets created by the kernel allow SOMAXCONN
(4096) backlogged connections instead of the 64 that they do today.

[1]: https://lore.kernel.org/linux-nfs/20240308180223.2965601-1-trond.myklebust@hammerspace.com/

Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 72e5a01df3d352582a5c25e0b8081a041e3792ee..60f2883268faf15b8e01a5d12d67a5d01b278a5e 100644 (file)
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -1542,7 +1542,7 @@ static struct svc_xprt *svc_create_socket(struct svc_serv *serv,
 
        if (protocol == IPPROTO_TCP) {
                sk_net_refcnt_upgrade(sock->sk);
-               if ((error = kernel_listen(sock, 64)) < 0)
+               if ((error = kernel_listen(sock, SOMAXCONN)) < 0)
                        goto bummer;
        }