Commit bd1e75ab authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: add coalescing attempt in tcp_ofo_queue() 



In order to make TCP more resilient in presence of reorders, we need
to allow coalescing to happen when skbs from out of order queue are
transferred into receive queue. LRO/GRO can be completely canceled
in some pathological cases, like per packet load balancing on aggregated
links.

I had to move tcp_try_coalesce() up in the file above tcp_ofo_queue()

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4cdf507d

net/ipv4/tcp_input.c

+47 −42
Original line number Diff line number Diff line
@@ -4061,6 +4061,44 @@ static void tcp_sack_remove(struct tcp_sock *tp) 
	tp->rx_opt.num_sacks = num_sacks;

}



/**

 * tcp_try_coalesce - try to merge skb to prior one

 * @sk: socket

 * @to: prior buffer

 * @from: buffer to add in queue

 * @fragstolen: pointer to boolean

 *

 * Before queueing skb @from after @to, try to merge them

 * to reduce overall memory use and queue lengths, if cost is small.

 * Packets in ofo or receive queues can stay a long time.

 * Better try to coalesce them right now to avoid future collapses.

 * Returns true if caller should free @from instead of queueing it

 */

static bool tcp_try_coalesce(struct sock *sk,

			     struct sk_buff *to,

			     struct sk_buff *from,

			     bool *fragstolen)

{

	int delta;



	*fragstolen = false;



	/* Its possible this segment overlaps with prior segment in queue */

	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)

		return false;



	if (!skb_try_coalesce(to, from, fragstolen, &delta))

		return false;



	atomic_add(delta, &sk->sk_rmem_alloc);

	sk_mem_charge(sk, delta);

	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);

	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;

	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;

	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;

	return true;

}



/* This one checks to see if we can put data from the

 * out_of_order queue into the receive_queue.

 */
@@ -4068,7 +4106,8 @@ static void tcp_ofo_queue(struct sock *sk) 
{

	struct tcp_sock *tp = tcp_sk(sk);

	__u32 dsack_high = tp->rcv_nxt;

	struct sk_buff *skb;

	struct sk_buff *skb, *tail;

	bool fragstolen, eaten;



	while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {

		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
@@ -4081,9 +4120,9 @@ static void tcp_ofo_queue(struct sock *sk) 
			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);

		}



		__skb_unlink(skb, &tp->out_of_order_queue);

		if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {

			SOCK_DEBUG(sk, "ofo packet was already received\n");

			__skb_unlink(skb, &tp->out_of_order_queue);

			__kfree_skb(skb);

			continue;

		}
@@ -4091,11 +4130,15 @@ static void tcp_ofo_queue(struct sock *sk) 
			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,

			   TCP_SKB_CB(skb)->end_seq);



		__skb_unlink(skb, &tp->out_of_order_queue);

		__skb_queue_tail(&sk->sk_receive_queue, skb);

		tail = skb_peek_tail(&sk->sk_receive_queue);

		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);

		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;

		if (!eaten)

			__skb_queue_tail(&sk->sk_receive_queue, skb);

		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)

			tcp_fin(sk);

		if (eaten)

			kfree_skb_partial(skb, fragstolen);

	}

}
@@ -4122,44 +4165,6 @@ static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb, 
	return 0;

}



/**

 * tcp_try_coalesce - try to merge skb to prior one

 * @sk: socket

 * @to: prior buffer

 * @from: buffer to add in queue

 * @fragstolen: pointer to boolean

 *

 * Before queueing skb @from after @to, try to merge them

 * to reduce overall memory use and queue lengths, if cost is small.

 * Packets in ofo or receive queues can stay a long time.

 * Better try to coalesce them right now to avoid future collapses.

 * Returns true if caller should free @from instead of queueing it

 */

static bool tcp_try_coalesce(struct sock *sk,

			     struct sk_buff *to,

			     struct sk_buff *from,

			     bool *fragstolen)

{

	int delta;



	*fragstolen = false;



	/* Its possible this segment overlaps with prior segment in queue */

	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)

		return false;



	if (!skb_try_coalesce(to, from, fragstolen, &delta))

		return false;



	atomic_add(delta, &sk->sk_rmem_alloc);

	sk_mem_charge(sk, delta);

	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);

	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;

	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;

	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;

	return true;

}



static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)

{

	struct tcp_sock *tp = tcp_sk(sk);

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