diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index d8676dda7fa6..46c7e1085efc 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -289,8 +289,7 @@ tcp_ecn_fallback - BOOLEAN
 	Default: 1 (fallback enabled)
 
 tcp_fack - BOOLEAN
-	Enable FACK congestion avoidance and fast retransmission.
-	The value is not used, if tcp_sack is not enabled.
+	This is a legacy option, it has no effect anymore.
 
 tcp_fin_timeout - INTEGER
 	The length of time an orphaned (no longer referenced by any
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 22f40c96a15b..df5d97a85e1a 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -85,7 +85,6 @@ struct tcp_sack_block {
 
 /*These are used to set the sack_ok field in struct tcp_options_received */
 #define TCP_SACK_SEEN     (1 << 0)   /*1 = peer is SACK capable, */
-#define TCP_FACK_ENABLED  (1 << 1)   /*1 = FACK is enabled locally*/
 #define TCP_DSACK_SEEN    (1 << 2)   /*1 = DSACK was received from peer*/
 
 struct tcp_options_received {
@@ -294,7 +293,6 @@ struct tcp_sock {
 	u32	pushed_seq;	/* Last pushed seq, required to talk to windows */
 	u32	lost_out;	/* Lost packets			*/
 	u32	sacked_out;	/* SACK'd packets			*/
-	u32	fackets_out;	/* FACK'd packets			*/
 
 	struct hrtimer	pacing_timer;
 
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 2f2c69ad31b2..ed71511e67a6 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -384,7 +384,6 @@ void tcp_update_metrics(struct sock *sk);
 void tcp_init_metrics(struct sock *sk);
 void tcp_metrics_init(void);
 bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst);
-void tcp_disable_fack(struct tcp_sock *tp);
 void tcp_close(struct sock *sk, long timeout);
 void tcp_init_sock(struct sock *sk);
 void tcp_init_transfer(struct sock *sk, int bpf_op);
@@ -776,7 +775,7 @@ struct tcp_skb_cb {
 	};
 	__u8		tcp_flags;	/* TCP header flags. (tcp[13])	*/
 
-	__u8		sacked;		/* State flags for SACK/FACK.	*/
+	__u8		sacked;		/* State flags for SACK.	*/
 #define TCPCB_SACKED_ACKED	0x01	/* SKB ACK'd by a SACK block	*/
 #define TCPCB_SACKED_RETRANS	0x02	/* SKB retransmitted		*/
 #define TCPCB_LOST		0x04	/* SKB is lost			*/
@@ -1066,7 +1065,6 @@ void tcp_rate_check_app_limited(struct sock *sk);
  *
  * tcp_is_sack - SACK enabled
  * tcp_is_reno - No SACK
- * tcp_is_fack - FACK enabled, implies SACK enabled
  */
 static inline int tcp_is_sack(const struct tcp_sock *tp)
 {
@@ -1078,16 +1076,6 @@ static inline bool tcp_is_reno(const struct tcp_sock *tp)
 	return !tcp_is_sack(tp);
 }
 
-static inline bool tcp_is_fack(const struct tcp_sock *tp)
-{
-	return tp->rx_opt.sack_ok & TCP_FACK_ENABLED;
-}
-
-static inline void tcp_enable_fack(struct tcp_sock *tp)
-{
-	tp->rx_opt.sack_ok |= TCP_FACK_ENABLED;
-}
-
 static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
 {
 	return tp->sacked_out + tp->lost_out;
diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index 0d941cdd8e8c..33a70ece462f 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -191,7 +191,6 @@ enum
 	LINUX_MIB_TCPRENORECOVERY,		/* TCPRenoRecovery */
 	LINUX_MIB_TCPSACKRECOVERY,		/* TCPSackRecovery */
 	LINUX_MIB_TCPSACKRENEGING,		/* TCPSACKReneging */
-	LINUX_MIB_TCPFACKREORDER,		/* TCPFACKReorder */
 	LINUX_MIB_TCPSACKREORDER,		/* TCPSACKReorder */
 	LINUX_MIB_TCPRENOREORDER,		/* TCPRenoReorder */
 	LINUX_MIB_TCPTSREORDER,			/* TCPTSReorder */
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 127153f1ed8a..9f37c4727861 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -212,7 +212,6 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("TCPRenoRecovery", LINUX_MIB_TCPRENORECOVERY),
 	SNMP_MIB_ITEM("TCPSackRecovery", LINUX_MIB_TCPSACKRECOVERY),
 	SNMP_MIB_ITEM("TCPSACKReneging", LINUX_MIB_TCPSACKRENEGING),
-	SNMP_MIB_ITEM("TCPFACKReorder", LINUX_MIB_TCPFACKREORDER),
 	SNMP_MIB_ITEM("TCPSACKReorder", LINUX_MIB_TCPSACKREORDER),
 	SNMP_MIB_ITEM("TCPRenoReorder", LINUX_MIB_TCPRENOREORDER),
 	SNMP_MIB_ITEM("TCPTSReorder", LINUX_MIB_TCPTSREORDER),
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index bc71a27d5ad9..bf97317e6c97 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2509,8 +2509,6 @@ static int tcp_repair_options_est(struct sock *sk,
 				return -EINVAL;
 
 			tp->rx_opt.sack_ok |= TCP_SACK_SEEN;
-			if (sock_net(sk)->ipv4.sysctl_tcp_fack)
-				tcp_enable_fack(tp);
 			break;
 		case TCPOPT_TIMESTAMP:
 			if (opt.opt_val != 0)
@@ -2979,7 +2977,6 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 
 	info->tcpi_lost = tp->lost_out;
 	info->tcpi_retrans = tp->retrans_out;
-	info->tcpi_fackets = tp->fackets_out;
 
 	now = tcp_jiffies32;
 	info->tcpi_last_data_sent = jiffies_to_msecs(now - tp->lsndtime);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 9ceaa1fdc3ab..94d729be42a9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -842,18 +842,6 @@ __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
 	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 }
 
-/*
- * Packet counting of FACK is based on in-order assumptions, therefore TCP
- * disables it when reordering is detected
- */
-void tcp_disable_fack(struct tcp_sock *tp)
-{
-	/* RFC3517 uses different metric in lost marker => reset on change */
-	if (tcp_is_fack(tp))
-		tp->lost_skb_hint = NULL;
-	tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
-}
-
 /* Take a notice that peer is sending D-SACKs */
 static void tcp_dsack_seen(struct tcp_sock *tp)
 {
@@ -861,42 +849,39 @@ static void tcp_dsack_seen(struct tcp_sock *tp)
 	tp->rack.dsack_seen = 1;
 }
 
-static void tcp_update_reordering(struct sock *sk, const int metric,
-				  const int ts)
+/* It's reordering when higher sequence was delivered (i.e. sacked) before
+ * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
+ * distance is approximated in full-mss packet distance ("reordering").
+ */
+static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
+				      const int ts)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
-	int mib_idx;
+	const u32 mss = tp->mss_cache;
+	u32 fack, metric;
 
-	if (WARN_ON_ONCE(metric < 0))
+	fack = tcp_highest_sack_seq(tp);
+	if (!before(low_seq, fack))
 		return;
 
-	if (metric > tp->reordering) {
-		tp->reordering = min(sock_net(sk)->ipv4.sysctl_tcp_max_reordering, metric);
-
+	metric = fack - low_seq;
+	if ((metric > tp->reordering * mss) && mss) {
 #if FASTRETRANS_DEBUG > 1
 		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
 			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
 			 tp->reordering,
-			 tp->fackets_out,
+			 0,
 			 tp->sacked_out,
 			 tp->undo_marker ? tp->undo_retrans : 0);
 #endif
-		tcp_disable_fack(tp);
+		tp->reordering = min_t(u32, (metric + mss - 1) / mss,
+				       sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
 	}
 
 	tp->rack.reord = 1;
-
 	/* This exciting event is worth to be remembered. 8) */
-	if (ts)
-		mib_idx = LINUX_MIB_TCPTSREORDER;
-	else if (tcp_is_reno(tp))
-		mib_idx = LINUX_MIB_TCPRENOREORDER;
-	else if (tcp_is_fack(tp))
-		mib_idx = LINUX_MIB_TCPFACKREORDER;
-	else
-		mib_idx = LINUX_MIB_TCPSACKREORDER;
-
-	NET_INC_STATS(sock_net(sk), mib_idx);
+	NET_INC_STATS(sock_net(sk),
+		      ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
 }
 
 /* This must be called before lost_out is incremented */
@@ -970,7 +955,6 @@ void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
  * 3. Loss detection event of two flavors:
  *	A. Scoreboard estimator decided the packet is lost.
  *	   A'. Reno "three dupacks" marks head of queue lost.
- *	   A''. Its FACK modification, head until snd.fack is lost.
  *	B. SACK arrives sacking SND.NXT at the moment, when the
  *	   segment was retransmitted.
  * 4. D-SACK added new rule: D-SACK changes any tag to S.
@@ -1113,8 +1097,7 @@ static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
 }
 
 struct tcp_sacktag_state {
-	int	reord;
-	int	fack_count;
+	u32	reord;
 	/* Timestamps for earliest and latest never-retransmitted segment
 	 * that was SACKed. RTO needs the earliest RTT to stay conservative,
 	 * but congestion control should still get an accurate delay signal.
@@ -1190,15 +1173,15 @@ static u8 tcp_sacktag_one(struct sock *sk,
 			  u64 xmit_time)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
-	int fack_count = state->fack_count;
 
 	/* Account D-SACK for retransmitted packet. */
 	if (dup_sack && (sacked & TCPCB_RETRANS)) {
 		if (tp->undo_marker && tp->undo_retrans > 0 &&
 		    after(end_seq, tp->undo_marker))
 			tp->undo_retrans--;
-		if (sacked & TCPCB_SACKED_ACKED)
-			state->reord = min(fack_count, state->reord);
+		if ((sacked & TCPCB_SACKED_ACKED) &&
+		    before(start_seq, state->reord))
+				state->reord = start_seq;
 	}
 
 	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
@@ -1224,9 +1207,10 @@ static u8 tcp_sacktag_one(struct sock *sk,
 				 * which was in hole. It is reordering.
 				 */
 				if (before(start_seq,
-					   tcp_highest_sack_seq(tp)))
-					state->reord = min(fack_count,
-							   state->reord);
+					   tcp_highest_sack_seq(tp)) &&
+				    before(start_seq, state->reord))
+					state->reord = start_seq;
+
 				if (!after(end_seq, tp->high_seq))
 					state->flag |= FLAG_ORIG_SACK_ACKED;
 				if (state->first_sackt == 0)
@@ -1245,15 +1229,10 @@ static u8 tcp_sacktag_one(struct sock *sk,
 		tp->sacked_out += pcount;
 		tp->delivered += pcount;  /* Out-of-order packets delivered */
 
-		fack_count += pcount;
-
 		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
-		if (!tcp_is_fack(tp) && tp->lost_skb_hint &&
+		if (tp->lost_skb_hint &&
 		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
 			tp->lost_cnt_hint += pcount;
-
-		if (fack_count > tp->fackets_out)
-			tp->fackets_out = fack_count;
 	}
 
 	/* D-SACK. We can detect redundant retransmission in S|R and plain R
@@ -1500,7 +1479,6 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
 	}
 
 out:
-	state->fack_count += pcount;
 	return prev;
 
 noop:
@@ -1579,8 +1557,6 @@ static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
 				    tcp_highest_sack_seq(tp)))
 				tcp_advance_highest_sack(sk, skb);
 		}
-
-		state->fack_count += tcp_skb_pcount(skb);
 	}
 	return skb;
 }
@@ -1591,7 +1567,6 @@ static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk,
 {
 	struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
 	struct sk_buff *skb;
-	int unack_bytes;
 
 	while (*p) {
 		parent = *p;
@@ -1604,12 +1579,6 @@ static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk,
 			p = &parent->rb_right;
 			continue;
 		}
-
-		state->fack_count = 0;
-		unack_bytes = TCP_SKB_CB(skb)->seq - tcp_sk(sk)->snd_una;
-		if (state->mss_now && unack_bytes > 0)
-			state->fack_count = unack_bytes / state->mss_now;
-
 		return skb;
 	}
 	return NULL;
@@ -1667,13 +1636,10 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
 	int first_sack_index;
 
 	state->flag = 0;
-	state->reord = tp->packets_out;
+	state->reord = tp->snd_nxt;
 
-	if (!tp->sacked_out) {
-		if (WARN_ON(tp->fackets_out))
-			tp->fackets_out = 0;
+	if (!tp->sacked_out)
 		tcp_highest_sack_reset(sk);
-	}
 
 	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
 					 num_sacks, prior_snd_una);
@@ -1745,7 +1711,6 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
 	}
 
 	state->mss_now = tcp_current_mss(sk);
-	state->fack_count = 0;
 	skb = NULL;
 	i = 0;
 
@@ -1803,7 +1768,6 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
 				skb = tcp_highest_sack(sk);
 				if (!skb)
 					break;
-				state->fack_count = tp->fackets_out;
 				cache++;
 				goto walk;
 			}
@@ -1818,7 +1782,6 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
 			skb = tcp_highest_sack(sk);
 			if (!skb)
 				break;
-			state->fack_count = tp->fackets_out;
 		}
 		skb = tcp_sacktag_skip(skb, sk, state, start_seq);
 
@@ -1838,9 +1801,8 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
 	for (j = 0; j < used_sacks; j++)
 		tp->recv_sack_cache[i++] = sp[j];
 
-	if ((state->reord < tp->fackets_out) &&
-	    ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
-		tcp_update_reordering(sk, tp->fackets_out - state->reord, 0);
+	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
+		tcp_check_sack_reordering(sk, state->reord, 0);
 
 	tcp_verify_left_out(tp);
 out:
@@ -1878,8 +1840,13 @@ static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
-	if (tcp_limit_reno_sacked(tp))
-		tcp_update_reordering(sk, tp->packets_out + addend, 0);
+
+	if (!tcp_limit_reno_sacked(tp))
+		return;
+
+	tp->reordering = min_t(u32, tp->packets_out + addend,
+			       sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
 }
 
 /* Emulate SACKs for SACKless connection: account for a new dupack. */
@@ -1925,7 +1892,6 @@ void tcp_clear_retrans(struct tcp_sock *tp)
 	tp->lost_out = 0;
 	tp->undo_marker = 0;
 	tp->undo_retrans = -1;
-	tp->fackets_out = 0;
 	tp->sacked_out = 0;
 }
 
@@ -1975,7 +1941,6 @@ void tcp_enter_loss(struct sock *sk)
 	if (is_reneg) {
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
 		tp->sacked_out = 0;
-		tp->fackets_out = 0;
 	}
 	tcp_clear_all_retrans_hints(tp);
 
@@ -2042,19 +2007,10 @@ static bool tcp_check_sack_reneging(struct sock *sk, int flag)
 	return false;
 }
 
-static inline int tcp_fackets_out(const struct tcp_sock *tp)
-{
-	return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
-}
-
 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
  * counter when SACK is enabled (without SACK, sacked_out is used for
  * that purpose).
  *
- * Instead, with FACK TCP uses fackets_out that includes both SACKed
- * segments up to the highest received SACK block so far and holes in
- * between them.
- *
  * With reordering, holes may still be in flight, so RFC3517 recovery
  * uses pure sacked_out (total number of SACKed segments) even though
  * it violates the RFC that uses duplicate ACKs, often these are equal
@@ -2064,10 +2020,10 @@ static inline int tcp_fackets_out(const struct tcp_sock *tp)
  */
 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
 {
-	return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
+	return tp->sacked_out + 1;
 }
 
-/* Linux NewReno/SACK/FACK/ECN state machine.
+/* Linux NewReno/SACK/ECN state machine.
  * --------------------------------------
  *
  * "Open"	Normal state, no dubious events, fast path.
@@ -2132,16 +2088,6 @@ static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
  *		dynamically measured and adjusted. This is implemented in
  *		tcp_rack_mark_lost.
  *
- *		FACK (Disabled by default. Subsumbed by RACK):
- *		It is the simplest heuristics. As soon as we decided
- *		that something is lost, we decide that _all_ not SACKed
- *		packets until the most forward SACK are lost. I.e.
- *		lost_out = fackets_out - sacked_out and left_out = fackets_out.
- *		It is absolutely correct estimate, if network does not reorder
- *		packets. And it loses any connection to reality when reordering
- *		takes place. We use FACK by default until reordering
- *		is suspected on the path to this destination.
- *
  *		If the receiver does not support SACK:
  *
  *		NewReno (RFC6582): in Recovery we assume that one segment
@@ -2190,7 +2136,7 @@ static bool tcp_time_to_recover(struct sock *sk, int flag)
 }
 
 /* Detect loss in event "A" above by marking head of queue up as lost.
- * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
+ * For non-SACK(Reno) senders, the first "packets" number of segments
  * are considered lost. For RFC3517 SACK, a segment is considered lost if it
  * has at least tp->reordering SACKed seqments above it; "packets" refers to
  * the maximum SACKed segments to pass before reaching this limit.
@@ -2226,12 +2172,12 @@ static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
 			break;
 
 		oldcnt = cnt;
-		if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
+		if (tcp_is_reno(tp) ||
 		    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
 			cnt += tcp_skb_pcount(skb);
 
 		if (cnt > packets) {
-			if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
+			if (tcp_is_sack(tp) ||
 			    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
 			    (oldcnt >= packets))
 				break;
@@ -2262,11 +2208,6 @@ static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
 
 	if (tcp_is_reno(tp)) {
 		tcp_mark_head_lost(sk, 1, 1);
-	} else if (tcp_is_fack(tp)) {
-		int lost = tp->fackets_out - tp->reordering;
-		if (lost <= 0)
-			lost = 1;
-		tcp_mark_head_lost(sk, lost, 0);
 	} else {
 		int sacked_upto = tp->sacked_out - tp->reordering;
 		if (sacked_upto >= 0)
@@ -2736,15 +2677,15 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
 }
 
 /* Undo during fast recovery after partial ACK. */
-static bool tcp_try_undo_partial(struct sock *sk, const int acked)
+static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
 	if (tp->undo_marker && tcp_packet_delayed(tp)) {
 		/* Plain luck! Hole if filled with delayed
-		 * packet, rather than with a retransmit.
+		 * packet, rather than with a retransmit. Check reordering.
 		 */
-		tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
+		tcp_check_sack_reordering(sk, prior_snd_una, 1);
 
 		/* We are getting evidence that the reordering degree is higher
 		 * than we realized. If there are no retransmits out then we
@@ -2780,6 +2721,14 @@ static void tcp_rack_identify_loss(struct sock *sk, int *ack_flag)
 	}
 }
 
+static bool tcp_force_fast_retransmit(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	return after(tcp_highest_sack_seq(tp),
+		     tp->snd_una + tp->reordering * tp->mss_cache);
+}
+
 /* Process an event, which can update packets-in-flight not trivially.
  * Main goal of this function is to calculate new estimate for left_out,
  * taking into account both packets sitting in receiver's buffer and
@@ -2792,19 +2741,17 @@ static void tcp_rack_identify_loss(struct sock *sk, int *ack_flag)
  * It does _not_ decide what to send, it is made in function
  * tcp_xmit_retransmit_queue().
  */
-static void tcp_fastretrans_alert(struct sock *sk, const int acked,
+static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
 				  bool is_dupack, int *ack_flag, int *rexmit)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 	int fast_rexmit = 0, flag = *ack_flag;
 	bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
-				    (tcp_fackets_out(tp) > tp->reordering));
+				     tcp_force_fast_retransmit(sk));
 
 	if (!tp->packets_out && tp->sacked_out)
 		tp->sacked_out = 0;
-	if (!tp->sacked_out && tp->fackets_out)
-		tp->fackets_out = 0;
 
 	/* Now state machine starts.
 	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
@@ -2851,11 +2798,11 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
 			if (tcp_is_reno(tp) && is_dupack)
 				tcp_add_reno_sack(sk);
 		} else {
-			if (tcp_try_undo_partial(sk, acked))
+			if (tcp_try_undo_partial(sk, prior_snd_una))
 				return;
 			/* Partial ACK arrived. Force fast retransmit. */
 			do_lost = tcp_is_reno(tp) ||
-				  tcp_fackets_out(tp) > tp->reordering;
+				  tcp_force_fast_retransmit(sk);
 		}
 		if (tcp_try_undo_dsack(sk)) {
 			tcp_try_keep_open(sk);
@@ -3065,15 +3012,15 @@ static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
  * is before the ack sequence we can discard it as it's confirmed to have
  * arrived at the other end.
  */
-static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
-			       u32 prior_snd_una, int *acked,
+static int tcp_clean_rtx_queue(struct sock *sk, u32 prior_fack,
+			       u32 prior_snd_una,
 			       struct tcp_sacktag_state *sack)
 {
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 	u64 first_ackt, last_ackt;
 	struct tcp_sock *tp = tcp_sk(sk);
 	u32 prior_sacked = tp->sacked_out;
-	u32 reord = tp->packets_out;
+	u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
 	struct sk_buff *skb, *next;
 	bool fully_acked = true;
 	long sack_rtt_us = -1L;
@@ -3088,6 +3035,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 
 	for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
 		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
+		const u32 start_seq = scb->seq;
 		u8 sacked = scb->sacked;
 		u32 acked_pcount;
 
@@ -3118,7 +3066,8 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 				first_ackt = last_ackt;
 
 			last_in_flight = TCP_SKB_CB(skb)->tx.in_flight;
-			reord = min(pkts_acked, reord);
+			if (before(start_seq, reord))
+				reord = start_seq;
 			if (!after(scb->end_seq, tp->high_seq))
 				flag |= FLAG_ORIG_SACK_ACKED;
 		}
@@ -3196,16 +3145,12 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 			int delta;
 
 			/* Non-retransmitted hole got filled? That's reordering */
-			if (reord < prior_fackets && reord <= tp->fackets_out)
-				tcp_update_reordering(sk, tp->fackets_out - reord, 0);
+			if (before(reord, prior_fack))
+				tcp_check_sack_reordering(sk, reord, 0);
 
-			delta = tcp_is_fack(tp) ? pkts_acked :
-						  prior_sacked - tp->sacked_out;
+			delta = prior_sacked - tp->sacked_out;
 			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
 		}
-
-		tp->fackets_out -= min(pkts_acked, tp->fackets_out);
-
 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
 		   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp, skb->skb_mstamp)) {
 		/* Do not re-arm RTO if the sack RTT is measured from data sent
@@ -3246,7 +3191,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 		}
 	}
 #endif
-	*acked = pkts_acked;
 	return flag;
 }
 
@@ -3555,12 +3499,11 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
 	bool is_dupack = false;
-	u32 prior_fackets;
 	int prior_packets = tp->packets_out;
 	u32 delivered = tp->delivered;
 	u32 lost = tp->lost;
-	int acked = 0; /* Number of packets newly acked */
 	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
+	u32 prior_fack;
 
 	sack_state.first_sackt = 0;
 	sack_state.rate = &rs;
@@ -3592,7 +3535,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 		icsk->icsk_retransmits = 0;
 	}
 
-	prior_fackets = tp->fackets_out;
+	prior_fack = tcp_highest_sack_seq(tp);
 	rs.prior_in_flight = tcp_packets_in_flight(tp);
 
 	/* ts_recent update must be made after we are sure that the packet
@@ -3648,8 +3591,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 		goto no_queue;
 
 	/* See if we can take anything off of the retransmit queue. */
-	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una, &acked,
-				    &sack_state);
+	flag |= tcp_clean_rtx_queue(sk, prior_fack, prior_snd_una, &sack_state);
 
 	tcp_rack_update_reo_wnd(sk, &rs);
 
@@ -3661,7 +3603,8 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 
 	if (tcp_ack_is_dubious(sk, flag)) {
 		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
-		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
+		tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+				      &rexmit);
 	}
 
 	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
@@ -3677,7 +3620,8 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 no_queue:
 	/* If data was DSACKed, see if we can undo a cwnd reduction. */
 	if (flag & FLAG_DSACKING_ACK)
-		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
+		tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+				      &rexmit);
 	/* If this ack opens up a zero window, clear backoff.  It was
 	 * being used to time the probes, and is probably far higher than
 	 * it needs to be for normal retransmission.
@@ -3699,7 +3643,8 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	if (TCP_SKB_CB(skb)->sacked) {
 		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
 						&sack_state);
-		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
+		tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+				      &rexmit);
 		tcp_xmit_recovery(sk, rexmit);
 	}
 
@@ -5708,9 +5653,6 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 			tp->tcp_header_len = sizeof(struct tcphdr);
 		}
 
-		if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_fack)
-			tcp_enable_fack(tp);
-
 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 		tcp_initialize_rcv_mss(sk);
 
diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index 9d5ddebfd831..7097f92d16e5 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -470,10 +470,8 @@ void tcp_init_metrics(struct sock *sk)
 		tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 	}
 	val = tcp_metric_get(tm, TCP_METRIC_REORDERING);
-	if (val && tp->reordering != val) {
-		tcp_disable_fack(tp);
+	if (val && tp->reordering != val)
 		tp->reordering = val;
-	}
 
 	crtt = tcp_metric_get(tm, TCP_METRIC_RTT);
 	rcu_read_unlock();
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 4bb86580decd..e36eff0403f4 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -475,7 +475,6 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 		newtp->packets_out = 0;
 		newtp->retrans_out = 0;
 		newtp->sacked_out = 0;
-		newtp->fackets_out = 0;
 		newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 		newtp->tlp_high_seq = 0;
 		newtp->lsndtime = tcp_jiffies32;
@@ -509,10 +508,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 						       keepalive_time_when(newtp));
 
 		newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
-		if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
-			if (sock_net(sk)->ipv4.sysctl_tcp_fack)
-				tcp_enable_fack(newtp);
-		}
+		newtp->rx_opt.sack_ok = ireq->sack_ok;
 		newtp->window_clamp = req->rsk_window_clamp;
 		newtp->rcv_ssthresh = req->rsk_rcv_wnd;
 		newtp->rcv_wnd = req->rsk_rcv_wnd;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 9b98d35aa0d8..0256f7a41041 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1218,21 +1218,6 @@ static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
 	}
 }
 
-/* When a modification to fackets out becomes necessary, we need to check
- * skb is counted to fackets_out or not.
- */
-static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
-				   int decr)
-{
-	struct tcp_sock *tp = tcp_sk(sk);
-
-	if (!tp->sacked_out || tcp_is_reno(tp))
-		return;
-
-	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
-		tp->fackets_out -= decr;
-}
-
 /* Pcount in the middle of the write queue got changed, we need to do various
  * tweaks to fix counters
  */
@@ -1253,11 +1238,9 @@ static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int de
 	if (tcp_is_reno(tp) && decr > 0)
 		tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
 
-	tcp_adjust_fackets_out(sk, skb, decr);
-
 	if (tp->lost_skb_hint &&
 	    before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
-	    (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
+	    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
 		tp->lost_cnt_hint -= decr;
 
 	tcp_verify_left_out(tp);
@@ -2961,9 +2944,6 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
  * retransmitted data is acknowledged.  It tries to continue
  * resending the rest of the retransmit queue, until either
  * we've sent it all or the congestion window limit is reached.
- * If doing SACK, the first ACK which comes back for a timeout
- * based retransmit packet might feed us FACK information again.
- * If so, we use it to avoid unnecessarily retransmissions.
  */
 void tcp_xmit_retransmit_queue(struct sock *sk)
 {