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tcp: increase tcp_max_syn_backlog max value 

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>
This commit is contained in:
Eric Dumazet 2019-10-30 10:05:46 -07:00 committed by David S. Miller
parent 19f92a030c
commit 623d0c2db0
2 changed files with 6 additions and 3 deletions
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7
Documentation/networking/ip-sysctl.txt
View File

@ -408,11 +408,14 @@ 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.

2
net/ipv4/tcp_ipv4.c
View File

@ -2681,7 +2681,7 @@ static int __net_init tcp_sk_init(struct net *net)
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;