linux/Documentation/admin-guide/sysctl
Kuniyuki Iwashima b46ab63181 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@google.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Link: https://patch.msgid.link/20251014235604.3057003-4-kuniyu@google.com
History 2025-10-16 12:04:47 -07:00
..
abi.rst docs: admin-guide: sysctl: avoid using ReST :doc:foo markup 2021-06-17 13:24:36 -06:00
fs.rst docs: admin-guide: update to current minimum pipe size default 2025-08-11 11:10:57 -06:00
index.rst docs: sysctl: add a few more top-level /proc/sys entries 2025-08-21 12:00:10 -06:00
kernel.rst panic: refine the document for 'panic_print' 2025-09-13 17:32:50 -07:00
net.rst net: Introduce net.core.bypass_prot_mem sysctl. 2025-10-16 12:04:47 -07:00
sunrpc.rst docs: admin-guide: move sysctl directory to it 2019-07-15 11:03:01 -03:00
user.rst time/namespace: Add max_time_namespaces ucount 2020-04-07 12:37:21 +02:00
vm.rst docs: Remove colon from ctltable title in vm.rst 2025-07-23 11:57:05 +02:00