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Date:   Thu, 17 Jan 2019 00:18:47 -0800
From:   yupeng <yupeng0921@...il.com>
To:     netdev@...r.kernel.org, davem@...emloft.net, kuznet@....inr.ac.ru,
        yoshfuji@...ux-ipv6.org
Subject: [PATCH net-next] remove TWKilled counter

The most possible way to trigger TWKilled is using tcp_tw_recycle, but
tcp_tw_recycle was removed. The TWKilled could still be triggered if
below conditions are satisfied:
1 the tw_timer expires in fin_wait_2 status
2 the timeout value of tw_timer is changed to less than 4 seconds
  (via net.ipv4.tcp_fin_timeout or TCP_LINGER2 option)
But the 4 seconds threshold makes no sense in this scenario. So remove
this counter.

Signed-off-by: yupeng <yupeng0921@...il.com>
---
 include/net/inet_timewait_sock.h |  3 +--
 include/uapi/linux/snmp.h        |  1 -
 net/ipv4/inet_timewait_sock.c    | 31 +------------------------------
 net/ipv4/proc.c                  |  1 -
 4 files changed, 2 insertions(+), 34 deletions(-)

diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h
index 78775038f011..b042c0baa2ca 100644
--- a/include/net/inet_timewait_sock.h
+++ b/include/net/inet_timewait_sock.h
@@ -69,8 +69,7 @@ struct inet_timewait_sock {
 	/* these three are in inet_sock */
 	__be16			tw_sport;
 	/* And these are ours. */
-	unsigned int		tw_kill		: 1,
-				tw_transparent  : 1,
+	unsigned int		tw_transparent  : 1,
 				tw_flowlabel	: 20,
 				tw_pad		: 2,	/* 2 bits hole */
 				tw_tos		: 8;
diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index 86dc24a96c90..fb0a17337bf2 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -178,7 +178,6 @@ enum
 	LINUX_MIB_ARPFILTER,			/* ArpFilter */
 	LINUX_MIB_TIMEWAITED,			/* TimeWaited */
 	LINUX_MIB_TIMEWAITRECYCLED,		/* TimeWaitRecycled */
-	LINUX_MIB_TIMEWAITKILLED,		/* TimeWaitKilled */
 	LINUX_MIB_PAWSACTIVEREJECTED,		/* PAWSActiveRejected */
 	LINUX_MIB_PAWSESTABREJECTED,		/* PAWSEstabRejected */
 	LINUX_MIB_DELAYEDACKS,			/* DelayedACKs */
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 88c5069b5d20..f0c4fe21909d 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -144,10 +144,7 @@ static void tw_timer_handler(struct timer_list *t)
 {
 	struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);
 
-	if (tw->tw_kill)
-		__NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITKILLED);
-	else
-		__NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITED);
+	__NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITED);
 	inet_twsk_kill(tw);
 }
 
@@ -218,32 +215,6 @@ EXPORT_SYMBOL(inet_twsk_deschedule_put);
 
 void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
 {
-	/* timeout := RTO * 3.5
-	 *
-	 * 3.5 = 1+2+0.5 to wait for two retransmits.
-	 *
-	 * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
-	 * our ACK acking that FIN can be lost. If N subsequent retransmitted
-	 * FINs (or previous seqments) are lost (probability of such event
-	 * is p^(N+1), where p is probability to lose single packet and
-	 * time to detect the loss is about RTO*(2^N - 1) with exponential
-	 * backoff). Normal timewait length is calculated so, that we
-	 * waited at least for one retransmitted FIN (maximal RTO is 120sec).
-	 * [ BTW Linux. following BSD, violates this requirement waiting
-	 *   only for 60sec, we should wait at least for 240 secs.
-	 *   Well, 240 consumes too much of resources 8)
-	 * ]
-	 * This interval is not reduced to catch old duplicate and
-	 * responces to our wandering segments living for two MSLs.
-	 * However, if we use PAWS to detect
-	 * old duplicates, we can reduce the interval to bounds required
-	 * by RTO, rather than MSL. So, if peer understands PAWS, we
-	 * kill tw bucket after 3.5*RTO (it is important that this number
-	 * is greater than TS tick!) and detect old duplicates with help
-	 * of PAWS.
-	 */
-
-	tw->tw_kill = timeo <= 4*HZ;
 	if (!rearm) {
 		BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
 		atomic_inc(&tw->tw_dr->tw_count);
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index c3610b37bb4c..20a29736d07e 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -186,7 +186,6 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("ArpFilter", LINUX_MIB_ARPFILTER),
 	SNMP_MIB_ITEM("TW", LINUX_MIB_TIMEWAITED),
 	SNMP_MIB_ITEM("TWRecycled", LINUX_MIB_TIMEWAITRECYCLED),
-	SNMP_MIB_ITEM("TWKilled", LINUX_MIB_TIMEWAITKILLED),
 	SNMP_MIB_ITEM("PAWSActive", LINUX_MIB_PAWSACTIVEREJECTED),
 	SNMP_MIB_ITEM("PAWSEstab", LINUX_MIB_PAWSESTABREJECTED),
 	SNMP_MIB_ITEM("DelayedACKs", LINUX_MIB_DELAYEDACKS),
-- 
2.17.1

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