From: Eric Dumazet <edumazet@google.com>
Date: Wed, 30 Oct 2019 10:05:46 -0700
Subject: tcp: increase tcp_max_syn_backlog max value
Patch-mainline: v5.4-rc6
Git-commit: 623d0c2db02043e43b698fdd8de1bd398b8e7b37
References: bsc#1154353
tcp_max_syn_backlog default value depends on memory size
and TCP ehash size. Before this patch, the max value
was 2048 [1], which is considered too small nowadays.
Increase it to 4096 to match the recent SOMAXCONN change.
[1] This is with TCP ehash size being capped to 524288 buckets.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Yue Cao <ycao009@ucr.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
Documentation/networking/ip-sysctl.txt | 7 +++++--
net/ipv4/tcp_ipv4.c | 2 +-
2 files changed, 6 insertions(+), 3 deletions(-)
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -402,11 +402,14 @@ tcp_max_orphans - INTEGER
up to ~64K of unswappable memory.
tcp_max_syn_backlog - INTEGER
- Maximal number of remembered connection requests, which have not
- received an acknowledgment from connecting client.
+ Maximal number of remembered connection requests (SYN_RECV),
+ which have not received an acknowledgment from connecting client.
+ This is a per-listener limit.
The minimal value is 128 for low memory machines, and it will
increase in proportion to the memory of machine.
If server suffers from overload, try increasing this number.
+ Remember to also check /proc/sys/net/core/somaxconn
+ A SYN_RECV request socket consumes about 304 bytes of memory.
tcp_max_tw_buckets - INTEGER
Maximal number of timewait sockets held by system simultaneously.
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2676,7 +2676,7 @@ static int __net_init tcp_sk_init(struct
net->ipv4.tcp_death_row.sysctl_max_tw_buckets = cnt / 2;
net->ipv4.tcp_death_row.hashinfo = &tcp_hashinfo;
- net->ipv4.sysctl_max_syn_backlog = max(128, cnt / 256);
+ net->ipv4.sysctl_max_syn_backlog = max(128, cnt / 128);
net->ipv4.sysctl_tcp_sack = 1;
net->ipv4.sysctl_tcp_window_scaling = 1;
net->ipv4.sysctl_tcp_timestamps = 1;