net: set net.core.rmem_max and net.core.wmem_max to 4 MB

SO_RCVBUF and SO_SNDBUF have limited range today, unless
distros or system admins change rmem_max and wmem_max.

Even iproute2 uses 1 MB SO_RCVBUF which is capped by
the kernel.

Decouple [rw]mem_max and [rw]mem_default and increase
[rw]mem_max to 4 MB.

Before:

$ sysctl net.core.rmem_default net.core.rmem_max net.core.wmem_default net.core.wmem_max
net.core.rmem_default = 212992
net.core.rmem_max = 212992
net.core.wmem_default = 212992
net.core.wmem_max = 212992

After:

$ sysctl net.core.rmem_default net.core.rmem_max net.core.wmem_default net.core.wmem_max
net.core.rmem_default = 212992
net.core.rmem_max = 4194304
net.core.wmem_default = 212992
net.core.wmem_max = 4194304

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Link: https://patch.msgid.link/20250819174030.1986278-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

6 files changed, 15 insertions, 11 deletions

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index 7b0c4291c686..2ef50828aff1 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -222,6 +222,8 @@ rmem_max
 
 The maximum receive socket buffer size in bytes.
 
+Default: 4194304
+
 rps_default_mask
 ----------------
 
@@ -247,6 +249,8 @@ wmem_max
 
 The maximum send socket buffer size in bytes.
 
+Default: 4194304
+
 message_burst and message_cost
 ------------------------------
 
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 43badb338d22..9f5891c9b07b 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -209,7 +209,7 @@ neigh/default/unres_qlen_bytes - INTEGER
 
 	Setting negative value is meaningless and will return error.
 
-	Default: SK_WMEM_MAX, (same as net.core.wmem_default).
+	Default: SK_WMEM_DEFAULT, (same as net.core.wmem_default).
 
 		Exact value depends on architecture and kernel options,
 		but should be enough to allow queuing 256 packets
@@ -805,8 +805,8 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max
 	This value results in initial window of 65535.
 
 	max: maximal size of receive buffer allowed for automatically
-	selected receiver buffers for TCP socket. This value does not override
-	net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
+	selected receiver buffers for TCP socket.
+	Calling setsockopt() with SO_RCVBUF disables
 	automatic tuning of that socket's receive buffer size, in which
 	case this value is ignored.
 	Default: between 131072 and 32MB, depending on RAM size.
diff --git a/include/net/sock.h b/include/net/sock.h
index 1c49ea13af4a..63a6a48afb48 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2970,8 +2970,8 @@ void sk_get_meminfo(const struct sock *sk, u32 *meminfo);
  */
 #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)
+#define SK_WMEM_DEFAULT		(_SK_MEM_OVERHEAD * _SK_MEM_PACKETS)
+#define SK_RMEM_DEFAULT		(_SK_MEM_OVERHEAD * _SK_MEM_PACKETS)
 
 extern __u32 sysctl_wmem_max;
 extern __u32 sysctl_rmem_max;
diff --git a/net/core/sock.c b/net/core/sock.c
index ab6953d295df..8002ac6293dc 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -281,12 +281,12 @@ static struct lock_class_key af_elock_keys[AF_MAX];
 static struct lock_class_key af_kern_callback_keys[AF_MAX];
 
 /* Run time adjustable parameters. */
-__u32 sysctl_wmem_max __read_mostly = SK_WMEM_MAX;
+__u32 sysctl_wmem_max __read_mostly = 4 << 20;
 EXPORT_SYMBOL(sysctl_wmem_max);
-__u32 sysctl_rmem_max __read_mostly = SK_RMEM_MAX;
+__u32 sysctl_rmem_max __read_mostly = 4 << 20;
 EXPORT_SYMBOL(sysctl_rmem_max);
-__u32 sysctl_wmem_default __read_mostly = SK_WMEM_MAX;
-__u32 sysctl_rmem_default __read_mostly = SK_RMEM_MAX;
+__u32 sysctl_wmem_default __read_mostly = SK_WMEM_DEFAULT;
+__u32 sysctl_rmem_default __read_mostly = SK_RMEM_DEFAULT;
 
 DEFINE_STATIC_KEY_FALSE(memalloc_socks_key);
 EXPORT_SYMBOL_GPL(memalloc_socks_key);
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 5cfc1c939673..833f2cf97178 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -170,7 +170,7 @@ struct neigh_table arp_tbl = {
 			[NEIGH_VAR_DELAY_PROBE_TIME] = 5 * HZ,
 			[NEIGH_VAR_INTERVAL_PROBE_TIME_MS] = 5 * HZ,
 			[NEIGH_VAR_GC_STALETIME] = 60 * HZ,
-			[NEIGH_VAR_QUEUE_LEN_BYTES] = SK_WMEM_MAX,
+			[NEIGH_VAR_QUEUE_LEN_BYTES] = SK_WMEM_DEFAULT,
 			[NEIGH_VAR_PROXY_QLEN] = 64,
 			[NEIGH_VAR_ANYCAST_DELAY] = 1 * HZ,
 			[NEIGH_VAR_PROXY_DELAY]	= (8 * HZ) / 10,
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 7d5abb3158ec..57aaa7ae8ac3 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -130,7 +130,7 @@ struct neigh_table nd_tbl = {
 			[NEIGH_VAR_DELAY_PROBE_TIME] = 5 * HZ,
 			[NEIGH_VAR_INTERVAL_PROBE_TIME_MS] = 5 * HZ,
 			[NEIGH_VAR_GC_STALETIME] = 60 * HZ,
-			[NEIGH_VAR_QUEUE_LEN_BYTES] = SK_WMEM_MAX,
+			[NEIGH_VAR_QUEUE_LEN_BYTES] = SK_WMEM_DEFAULT,
 			[NEIGH_VAR_PROXY_QLEN] = 64,
 			[NEIGH_VAR_ANYCAST_DELAY] = 1 * HZ,
 			[NEIGH_VAR_PROXY_DELAY] = (8 * HZ) / 10,