[PATCH net-next 1/5] tcp: add TCPRcvCollapseSkipped counter

[Eric Dumazet <edumazet@kernel.org>]

Commit c2213d9b61c1 ("tcp: rate limit receive queue collapsing") rate
limits collapsing in tcp_prune_queue(): it is only attempted when at
least 1/8 of sk_rcvbuf of new memory was queued in the receive queues
since the previous collapse.

Add a TcpExtTCPRcvCollapseSkipped counter, incremented when a collapse
is skipped for this reason. A high rate can indicate a peer repeatedly
sending segments that can not be queued.

Signed-off-by: Eric Dumazet <edumazet@kernel.org>
---
 Documentation/networking/snmp_counter.rst | 7 +++++++
 include/uapi/linux/snmp.h                 | 1 +
 net/ipv4/proc.c                           | 1 +
 net/ipv4/tcp_input.c                      | 2 ++
 4 files changed, 11 insertions(+)

diff --git a/Documentation/networking/snmp_counter.rst b/Documentation/networking/snmp_counter.rst
index ff1e6a8ffe21..c8f62bae632f 100644
--- a/Documentation/networking/snmp_counter.rst
+++ b/Documentation/networking/snmp_counter.rst
@@ -1024,6 +1024,13 @@ this counter will be updated. It means the 'prune' fails.
 
 This counter indicates how many skbs are freed during 'collapse'.
 
+* TcpExtTCPRcvCollapseSkipped
+
+'Collapse' was skipped, because less than 1/8 of the receive buffer of
+new memory was queued since the previous 'collapse'.
+A high rate can indicate a peer repeatedly sending segments that can
+not be queued.
+
 examples
 ========
 
diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index 49f5640092a0..ee2900e0d90d 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -306,6 +306,7 @@ enum
 	LINUX_MIB_TCPAOKEYNOTFOUND,		/* TCPAOKeyNotFound */
 	LINUX_MIB_TCPAOGOOD,			/* TCPAOGood */
 	LINUX_MIB_TCPAODROPPEDICMPS,		/* TCPAODroppedIcmps */
+	LINUX_MIB_TCPRCVCOLLAPSESKIPPED,	/* TCPRcvCollapseSkipped */
 	__LINUX_MIB_MAX
 };
 
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index bfc06d1713ec..a4c53a78efc8 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -302,6 +302,7 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("TCPAOKeyNotFound", LINUX_MIB_TCPAOKEYNOTFOUND),
 	SNMP_MIB_ITEM("TCPAOGood", LINUX_MIB_TCPAOGOOD),
 	SNMP_MIB_ITEM("TCPAODroppedIcmps", LINUX_MIB_TCPAODROPPEDICMPS),
+	SNMP_MIB_ITEM("TCPRcvCollapseSkipped", LINUX_MIB_TCPRCVCOLLAPSESKIPPED),
 };
 
 static void icmpmsg_put_line(struct seq_file *seq, unsigned long *vals,
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a2074a1af422..80f8f262bc44 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6100,6 +6100,8 @@ static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb)
 
 		if (tcp_can_ingest(sk, in_skb))
 			return 0;
+	} else {
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSESKIPPED);
 	}
 
 	/* Collapsing did not help (or was not allowed),
-- 
2.53.0