netdev - [PATCH bpf-next/net 3/6] net: Introduce net.core.bypass_prot

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Message-ID: <20251007001120.2661442-4-kuniyu@google.com>
Date: Tue,  7 Oct 2025 00:07:28 +0000
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>
Cc: John Fastabend <john.fastabend@...il.com>, Stanislav Fomichev <sdf@...ichev.me>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Neal Cardwell <ncardwell@...gle.com>, Willem de Bruijn <willemb@...gle.com>, 
	Mina Almasry <almasrymina@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, Kuniyuki Iwashima <kuni1840@...il.com>, bpf@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: [PATCH bpf-next/net 3/6] net: Introduce net.core.bypass_prot_mem sysctl.

If a socket has sk->sk_bypass_prot_mem flagged, the socket opts out
of the global protocol memory accounting.

Let's control the flag by a new sysctl knob.

The flag is written once during socket(2) and is inherited to child
sockets.

Tested with a script that creates local socket pairs and send()s a
bunch of data without recv()ing.

Setup:

  # mkdir /sys/fs/cgroup/test
  # echo $$ >> /sys/fs/cgroup/test/cgroup.procs
  # sysctl -q net.ipv4.tcp_mem="1000 1000 1000"
  # ulimit -n 524288

Without net.core.bypass_prot_mem, charged to tcp_mem & memcg

  # python3 pressure.py &
  # cat /sys/fs/cgroup/test/memory.stat | grep sock
  sock 22642688 <-------------------------------------- charged to memcg
  # cat /proc/net/sockstat| grep TCP
  TCP: inuse 2006 orphan 0 tw 0 alloc 2008 mem 5376 <-- charged to tcp_mem
  # ss -tn | head -n 5
  State Recv-Q Send-Q Local Address:Port  Peer Address:Port
  ESTAB 2000   0          127.0.0.1:34479    127.0.0.1:53188
  ESTAB 2000   0          127.0.0.1:34479    127.0.0.1:49972
  ESTAB 2000   0          127.0.0.1:34479    127.0.0.1:53868
  ESTAB 2000   0          127.0.0.1:34479    127.0.0.1:53554
  # nstat | grep Pressure || echo no pressure
  TcpExtTCPMemoryPressures        1                  0.0

With net.core.bypass_prot_mem=1, charged to memcg only:

  # sysctl -q net.core.bypass_prot_mem=1
  # python3 pressure.py &
  # cat /sys/fs/cgroup/test/memory.stat | grep sock
  sock 2757468160 <------------------------------------ charged to memcg
  # cat /proc/net/sockstat | grep TCP
  TCP: inuse 2006 orphan 0 tw 0 alloc 2008 mem 0 <- NOT charged to tcp_mem
  # ss -tn | head -n 5
  State Recv-Q Send-Q  Local Address:Port  Peer Address:Port
  ESTAB 111000 0           127.0.0.1:36019    127.0.0.1:49026
  ESTAB 110000 0           127.0.0.1:36019    127.0.0.1:45630
  ESTAB 110000 0           127.0.0.1:36019    127.0.0.1:44870
  ESTAB 111000 0           127.0.0.1:36019    127.0.0.1:45274
  # nstat | grep Pressure || echo no pressure
  no pressure

Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
---
 Documentation/admin-guide/sysctl/net.rst | 8 ++++++++
 include/net/netns/core.h                 | 1 +
 net/core/sock.c                          | 5 +++++
 net/core/sysctl_net_core.c               | 9 +++++++++
 4 files changed, 23 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index 2ef50828aff1..3dbe0ea212e8 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -212,6 +212,14 @@ mem_pcpu_rsv
 
 Per-cpu reserved forward alloc cache size in page units. Default 1MB per CPU.
 
+bypass_prot_mem
+---------------
+
+Skip charging socket buffers to the global per-protocol memory
+accounting controlled by net.ipv4.tcp_mem, net.ipv4.udp_mem, etc.
+
+Default: 0 (off)
+
 rmem_default
 ------------
 
diff --git a/include/net/netns/core.h b/include/net/netns/core.h
index 9b36f0ff0c20..e9053d64c8ef 100644
--- a/include/net/netns/core.h
+++ b/include/net/netns/core.h
@@ -16,6 +16,7 @@ struct netns_core {
 	int	sysctl_optmem_max;
 	u8	sysctl_txrehash;
 	u8	sysctl_tstamp_allow_data;
+	u8	sysctl_bypass_prot_mem;
 
 #ifdef CONFIG_PROC_FS
 	struct prot_inuse __percpu *prot_inuse;
diff --git a/net/core/sock.c b/net/core/sock.c
index 7de189ec2556..b28373e20d74 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2306,8 +2306,13 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
 		 * why we need sk_prot_creator -acme
 		 */
 		sk->sk_prot = sk->sk_prot_creator = prot;
+
+		if (READ_ONCE(net->core.sysctl_bypass_prot_mem))
+			sk->sk_bypass_prot_mem = 1;
+
 		sk->sk_kern_sock = kern;
 		sock_lock_init(sk);
+
 		sk->sk_net_refcnt = kern ? 0 : 1;
 		if (likely(sk->sk_net_refcnt)) {
 			get_net_track(net, &sk->ns_tracker, priority);
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 8cf04b57ade1..2e91fe728969 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -676,6 +676,15 @@ static struct ctl_table netns_core_table[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_ONE
 	},
+	{
+		.procname	= "bypass_prot_mem",
+		.data		= &init_net.core.sysctl_bypass_prot_mem,
+		.maxlen		= sizeof(u8),
+		.mode		= 0644,
+		.proc_handler	= proc_dou8vec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE
+	},
 	/* sysctl_core_net_init() will set the values after this
 	 * to readonly in network namespaces
 	 */
-- 
2.51.0.710.ga91ca5db03-goog