net/smc: Unbind r/w buffer size from clcsock and make them tunable

Currently, SMC uses smc->sk.sk_{rcv|snd}buf to create buffers for
send buffer and RMB. And the values of buffer size are from tcp_{w|r}mem
in clcsock.

The buffer size from TCP socket doesn't fit SMC well. Generally, buffers
are usually larger than TCP for SMC-R/-D to get higher performance, for
they are different underlay devices and paths.

So this patch unbinds buffer size from TCP, and introduces two sysctl
knobs to tune them independently. Also, these knobs are per net
namespace and work for containers.

Signed-off-by: Tony Lu <tonylu@linux.alibaba.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Documentation/networking/smc-sysctl.rst

@@ -41,3 +41,21 @@ smcr_testlink_time - INTEGER
 	disabling TEST_LINK.
 
 	Default: 30 seconds.
+
+wmem - INTEGER
+	Initial size of send buffer used by SMC sockets.
+	The default value inherits from net.ipv4.tcp_wmem[1].
+
+	The minimum value is 16KiB and there is no hard limit for max value, but
+	only allowed 512KiB for SMC-R and 1MiB for SMC-D.
+
+	Default: 16K
+
+rmem - INTEGER
+	Initial size of receive buffer (RMB) used by SMC sockets.
+	The default value inherits from net.ipv4.tcp_rmem[1].
+
+	The minimum value is 16KiB and there is no hard limit for max value, but
+	only allowed 512KiB for SMC-R and 1MiB for SMC-D.
+
+	Default: 128K

include/net/netns/smc.h

@@ -20,5 +20,7 @@ struct netns_smc {
 	unsigned int			sysctl_autocorking_size;
 	unsigned int			sysctl_smcr_buf_type;
 	int				sysctl_smcr_testlink_time;
+	int				sysctl_wmem;
+	int				sysctl_rmem;
 };
 #endif

net/smc/af_smc.c

@@ -379,6 +379,8 @@ static struct sock *smc_sock_alloc(struct net *net, struct socket *sock,
 	sk->sk_state = SMC_INIT;
 	sk->sk_destruct = smc_destruct;
 	sk->sk_protocol = protocol;
+	WRITE_ONCE(sk->sk_sndbuf, READ_ONCE(net->smc.sysctl_wmem));
+	WRITE_ONCE(sk->sk_rcvbuf, READ_ONCE(net->smc.sysctl_rmem));
 	smc = smc_sk(sk);
 	INIT_WORK(&smc->tcp_listen_work, smc_tcp_listen_work);
 	INIT_WORK(&smc->connect_work, smc_connect_work);
@@ -3253,9 +3255,6 @@ static int __smc_create(struct net *net, struct socket *sock, int protocol,
 		smc->clcsock = clcsock;
 	}
 
-	smc->sk.sk_sndbuf = max(smc->clcsock->sk->sk_sndbuf, SMC_BUF_MIN_SIZE);
-	smc->sk.sk_rcvbuf = max(smc->clcsock->sk->sk_rcvbuf, SMC_BUF_MIN_SIZE);
-
 out:
 	return rc;
 }

net/smc/smc_core.c

@@ -2307,10 +2307,10 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb)
 
 	if (is_rmb)
 		/* use socket recv buffer size (w/o overhead) as start value */
-		sk_buf_size = smc->sk.sk_rcvbuf / 2;
+		sk_buf_size = smc->sk.sk_rcvbuf;
 	else
 		/* use socket send buffer size (w/o overhead) as start value */
-		sk_buf_size = smc->sk.sk_sndbuf / 2;
+		sk_buf_size = smc->sk.sk_sndbuf;
 
 	for (bufsize_short = smc_compress_bufsize(sk_buf_size, is_smcd, is_rmb);
 	     bufsize_short >= 0; bufsize_short--) {
@@ -2369,15 +2369,15 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb)
 	if (is_rmb) {
 		conn->rmb_desc = buf_desc;
 		conn->rmbe_size_short = bufsize_short;
-		smc->sk.sk_rcvbuf = bufsize * 2;
+		smc->sk.sk_rcvbuf = bufsize;
 		atomic_set(&conn->bytes_to_rcv, 0);
 		conn->rmbe_update_limit =
 			smc_rmb_wnd_update_limit(buf_desc->len);
 		if (is_smcd)
 			smc_ism_set_conn(conn); /* map RMB/smcd_dev to conn */
 	} else {
 		conn->sndbuf_desc = buf_desc;
-		smc->sk.sk_sndbuf = bufsize * 2;
+		smc->sk.sk_sndbuf = bufsize;
 		atomic_set(&conn->sndbuf_space, bufsize);
 	}
 	return 0;

net/smc/smc_sysctl.c

@@ -19,6 +19,9 @@
 #include "smc_llc.h"
 #include "smc_sysctl.h"
 
+static int min_sndbuf = SMC_BUF_MIN_SIZE;
+static int min_rcvbuf = SMC_BUF_MIN_SIZE;
+
 static struct ctl_table smc_table[] = {
 	{
 		.procname       = "autocorking_size",
@@ -43,6 +46,22 @@ static struct ctl_table smc_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_jiffies,
 	},
+	{
+		.procname	= "wmem",
+		.data		= &init_net.smc.sysctl_wmem,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &min_sndbuf,
+	},
+	{
+		.procname	= "rmem",
+		.data		= &init_net.smc.sysctl_rmem,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &min_rcvbuf,
+	},
 	{  }
 };
 
@@ -69,6 +88,8 @@ int __net_init smc_sysctl_net_init(struct net *net)
 	net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
 	net->smc.sysctl_smcr_buf_type = SMCR_PHYS_CONT_BUFS;
 	net->smc.sysctl_smcr_testlink_time = SMC_LLC_TESTLINK_DEFAULT_TIME;
+	WRITE_ONCE(net->smc.sysctl_wmem, READ_ONCE(net->ipv4.sysctl_tcp_wmem[1]));
+	WRITE_ONCE(net->smc.sysctl_rmem, READ_ONCE(net->ipv4.sysctl_tcp_rmem[1]));
 
 	return 0;