tcp: remove RFC3517/RFC6675 hint state: lost_skb_hint, lost_cnt_hint

Now that obsolete RFC3517/RFC6675 TCP loss detection has been removed,
we can remove the somewhat complex and intrusive code to maintain its
hint state: lost_skb_hint and lost_cnt_hint.

This commit makes tcp_clear_retrans_hints_partial() empty. We will
remove tcp_clear_retrans_hints_partial() and its call sites in the
next commit.

Suggested-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250615001435.2390793-3-ncardwell.sw@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 1 insertions, 26 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f64f8276a73c..27d3ef83ce7b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -5053,9 +5053,8 @@ static void __init tcp_struct_check(void)
 	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, reordering);
 	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, notsent_lowat);
 	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, gso_segs);
-	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, lost_skb_hint);
 	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, retransmit_skb_hint);
-	CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_read_tx, 40);
+	CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_read_tx, 32);
 
 	/* TXRX read-mostly hotpath cache lines */
 	CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_txrx, tsoffset);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index dc234d3854aa..e8e130e946f1 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1451,11 +1451,6 @@ static u8 tcp_sacktag_one(struct sock *sk,
 		tp->sacked_out += pcount;
 		/* Out-of-order packets delivered */
 		state->sack_delivered += pcount;
-
-		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
-		if (tp->lost_skb_hint &&
-		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
-			tp->lost_cnt_hint += pcount;
 	}
 
 	/* D-SACK. We can detect redundant retransmission in S|R and plain R
@@ -1496,9 +1491,6 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
 			tcp_skb_timestamp_us(skb));
 	tcp_rate_skb_delivered(sk, skb, state->rate);
 
-	if (skb == tp->lost_skb_hint)
-		tp->lost_cnt_hint += pcount;
-
 	TCP_SKB_CB(prev)->end_seq += shifted;
 	TCP_SKB_CB(skb)->seq += shifted;
 
@@ -1531,10 +1523,6 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
 
 	if (skb == tp->retransmit_skb_hint)
 		tp->retransmit_skb_hint = prev;
-	if (skb == tp->lost_skb_hint) {
-		tp->lost_skb_hint = prev;
-		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
-	}
 
 	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
 	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
@@ -3318,8 +3306,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
 		next = skb_rb_next(skb);
 		if (unlikely(skb == tp->retransmit_skb_hint))
 			tp->retransmit_skb_hint = NULL;
-		if (unlikely(skb == tp->lost_skb_hint))
-			tp->lost_skb_hint = NULL;
 		tcp_highest_sack_replace(sk, skb, next);
 		tcp_rtx_queue_unlink_and_free(skb, sk);
 	}
@@ -3377,14 +3363,9 @@ static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
 			if (flag & FLAG_RETRANS_DATA_ACKED)
 				flag &= ~FLAG_ORIG_SACK_ACKED;
 		} else {
-			int delta;
-
 			/* Non-retransmitted hole got filled? That's reordering */
 			if (before(reord, prior_fack))
 				tcp_check_sack_reordering(sk, reord, 0);
-
-			delta = prior_sacked - tp->sacked_out;
-			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
 		}
 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
 		   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3ac8d2d17e1f..b0ffefe604b4 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1554,11 +1554,6 @@ 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);
 
-	if (tp->lost_skb_hint &&
-	    before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
-	    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
-		tp->lost_cnt_hint -= decr;
-
 	tcp_verify_left_out(tp);
 }