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Commit 623d0c2d authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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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: default avatarEric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Yue Cao <ycao009@ucr.edu>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 19f92a03

Documentation/networking/ip-sysctl.txt

+5 −2
Original line number Diff line number Diff line
@@ -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.

net/ipv4/tcp_ipv4.c

+1 −1
Original line number Diff line number Diff line
@@ -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;