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 <[e-mail]>
Signed-off-by: Martin KaFai Lau <[e-mail]>
Reviewed-by: Shakeel Butt <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Acked-by: Roman Gushchin <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

Documentation/admin-guide/sysctl/net.rst

···
 
 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
 ------------
 

include/net/netns/core.h

···
 	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;

net/core/sock.c

···
 		 * 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);

net/core/sysctl_net_core.c

···
 		.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
 	 */