diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 44a3aa7..e022f9e2 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1256,6 +1256,8 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
 	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
 
+	printk(KERN_WARNING "[SACK] shifted enter");
+
 	BUG_ON(!pcount);
 
 	/* Adjust counters and hints for the newly sacked sequence
@@ -1274,6 +1276,9 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 	TCP_SKB_CB(prev)->end_seq += shifted;
 	TCP_SKB_CB(skb)->seq += shifted;
 
+	printk(KERN_WARNING "[SACK] shifted: mss %d pcount %u skb_pcount %u",
+		mss, pcount, tcp_skb_pcount(skb));
+
 	tcp_skb_pcount_add(prev, pcount);
 	BUG_ON(tcp_skb_pcount(skb) < pcount);
 	tcp_skb_pcount_add(skb, -pcount);
@@ -1352,6 +1357,8 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
 	int len;
 	int in_sack;
 
+	printk(KERN_WARNING "[SACK] shift enter");
+
 	if (!sk_can_gso(sk))
 		goto fallback;
 
@@ -1450,6 +1457,9 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
 	/* Hole filled allows collapsing with the next as well, this is very
 	 * useful when hole on every nth skb pattern happens
 	 */
+
+	printk(KERN_WARNING "[SACK] shift hole-filling");
+
 	if (prev == tcp_write_queue_tail(sk))
 		goto out;
 	skb = tcp_write_queue_next(sk, prev);
@@ -1468,12 +1478,15 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
 
 out:
 	state->fack_count += pcount;
+	printk(KERN_WARNING "[SACK] shift out");
 	return prev;
 
 noop:
+	printk(KERN_WARNING "[SACK] shift noop");
 	return skb;
 
 fallback:
+	printk(KERN_WARNING "[SACK] shift fallback");
 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
 	return NULL;
 }