neigh: increase queue_len_bytes to match wmem_default

Florian reported UDP xmit drops that could be root caused to the
too small neigh limit.

Current limit is 64 KB, meaning that even a single UDP socket would hit
it, since its default sk_sndbuf comes from net.core.wmem_default
(~212992 bytes on 64bit arches).

Once ARP/ND resolution is in progress, we should allow a little more
packets to be queued, at least for one producer.

Once neigh arp_queue is filled, a rogue socket should hit its sk_sndbuf
limit and either block in sendmsg() or return -EAGAIN.

Signed-off-by: Eric Dumazet <[e-mail]>
Reported-by: Florian Fainelli <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/ip-sysctl.txt

···
 	queued for each	unresolved address by other network layers.
 	(added in linux 3.3)
 	Setting negative value is meaningless and will return error.
-	Default: 65536 Bytes(64KB)
+	Default: SK_WMEM_MAX, (same as net.core.wmem_default).
+		Exact value depends on architecture and kernel options,
+		but should be enough to allow queuing 256 packets
+		of medium size.
 
 neigh/default/unres_qlen - INTEGER
 	The maximum number of packets which may be queued for each
···
 	unexpected packet loss. The current default value is calculated
 	according to default value of unres_qlen_bytes and true size of
 	packet.
-	Default: 31
+	Default: 101
 
 mtu_expires - INTEGER
 	Time, in seconds, that cached PMTU information is kept.

include/net/sock.h

···
 
 void sk_get_meminfo(const struct sock *sk, u32 *meminfo);
 
+/* Take into consideration the size of the struct sk_buff overhead in the
+ * determination of these values, since that is non-constant across
+ * platforms.  This makes socket queueing behavior and performance
+ * not depend upon such differences.
+ */
+#define _SK_MEM_PACKETS		256
+#define _SK_MEM_OVERHEAD	SKB_TRUESIZE(256)
+#define SK_WMEM_MAX		(_SK_MEM_OVERHEAD * _SK_MEM_PACKETS)
+#define SK_RMEM_MAX		(_SK_MEM_OVERHEAD * _SK_MEM_PACKETS)
+
 extern __u32 sysctl_wmem_max;
 extern __u32 sysctl_rmem_max;
 

net/core/sock.c

···
 static struct lock_class_key af_elock_keys[AF_MAX];
 static struct lock_class_key af_kern_callback_keys[AF_MAX];
 
-/* Take into consideration the size of the struct sk_buff overhead in the
- * determination of these values, since that is non-constant across
- * platforms.  This makes socket queueing behavior and performance
- * not depend upon such differences.
- */
-#define _SK_MEM_PACKETS		256
-#define _SK_MEM_OVERHEAD	SKB_TRUESIZE(256)
-#define SK_WMEM_MAX		(_SK_MEM_OVERHEAD * _SK_MEM_PACKETS)
-#define SK_RMEM_MAX		(_SK_MEM_OVERHEAD * _SK_MEM_PACKETS)
-
 /* Run time adjustable parameters. */
 __u32 sysctl_wmem_max __read_mostly = SK_WMEM_MAX;
 EXPORT_SYMBOL(sysctl_wmem_max);

net/decnet/dn_neigh.c

···
 			[NEIGH_VAR_BASE_REACHABLE_TIME] = 30 * HZ,
 			[NEIGH_VAR_DELAY_PROBE_TIME] = 5 * HZ,
 			[NEIGH_VAR_GC_STALETIME] = 60 * HZ,
-			[NEIGH_VAR_QUEUE_LEN_BYTES] = 64*1024,
+			[NEIGH_VAR_QUEUE_LEN_BYTES] = SK_WMEM_MAX,
 			[NEIGH_VAR_PROXY_QLEN] = 0,
 			[NEIGH_VAR_ANYCAST_DELAY] = 0,
 			[NEIGH_VAR_PROXY_DELAY] = 0,

net/ipv4/arp.c

···
 			[NEIGH_VAR_BASE_REACHABLE_TIME] = 30 * HZ,
 			[NEIGH_VAR_DELAY_PROBE_TIME] = 5 * HZ,
 			[NEIGH_VAR_GC_STALETIME] = 60 * HZ,
-			[NEIGH_VAR_QUEUE_LEN_BYTES] = 64 * 1024,
+			[NEIGH_VAR_QUEUE_LEN_BYTES] = SK_WMEM_MAX,
 			[NEIGH_VAR_PROXY_QLEN] = 64,
 			[NEIGH_VAR_ANYCAST_DELAY] = 1 * HZ,
 			[NEIGH_VAR_PROXY_DELAY]	= (8 * HZ) / 10,

net/ipv4/tcp_input.c

···
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct net *net = sock_net(sk);
 	struct sock *fastopen_sk = NULL;
-	struct dst_entry *dst = NULL;
 	struct request_sock *req;
 	bool want_cookie = false;
+	struct dst_entry *dst;
 	struct flowi fl;
 
 	/* TW buckets are converted to open requests without

net/ipv6/ndisc.c

···
 			[NEIGH_VAR_BASE_REACHABLE_TIME] = ND_REACHABLE_TIME,
 			[NEIGH_VAR_DELAY_PROBE_TIME] = 5 * HZ,
 			[NEIGH_VAR_GC_STALETIME] = 60 * HZ,
-			[NEIGH_VAR_QUEUE_LEN_BYTES] = 64 * 1024,
+			[NEIGH_VAR_QUEUE_LEN_BYTES] = SK_WMEM_MAX,
 			[NEIGH_VAR_PROXY_QLEN] = 64,
 			[NEIGH_VAR_ANYCAST_DELAY] = 1 * HZ,
 			[NEIGH_VAR_PROXY_DELAY] = (8 * HZ) / 10,