tcp: refine tcp_prune_ofo_queue() to not drop all packets (36a6503f) · Commits · 戴 / test

Over the years, TCP BDP has increased a lot, and is typically in the order of ~10 Mbytes with help of clever Congestion Control modules. In presence of packet losses, TCP stores incoming packets into an out of order queue, and number of skbs sitting there waiting for the missing packets to be received can match the BDP (~10 Mbytes) In some cases, TCP needs to make room for incoming skbs, and current strategy can simply remove all skbs in the out of order queue as a last resort, incurring a huge penalty, both for receiver and sender. Unfortunately these 'last resort events' are quite frequent, forcing sender to send all packets again, stalling the flow and wasting a lot of resources. This patch cleans only a part of the out of order queue in order to meet the memory constraints. Signed-off-by:

Eric Dumazet <edumazet@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Soheil Hassas Yeganeh <soheil@google.com> Cc: C. Stephen Gun <csg@google.com> Cc: Van Jacobson <vanj@google.com> Acked-by:

Soheil Hassas Yeganeh <soheil@google.com> Acked-by:

Yuchung Cheng <ycheng@google.com> Acked-by:

Neal Cardwell <ncardwell@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

+28 −19

Original line number	Diff line number	Diff line
		@@ -4392,12 +4392,9 @@ static int tcp_try_rmem_schedule(struct sock sk, struct sk_buff skb,
		if (tcp_prune_queue(sk) < 0)
		return -1;

		if (!sk_rmem_schedule(sk, skb, size)) {
		while (!sk_rmem_schedule(sk, skb, size)) {
		if (!tcp_prune_ofo_queue(sk))
		return -1;

		if (!sk_rmem_schedule(sk, skb, size))
		return -1;
		}
		}
		return 0;
		@@ -4874,17 +4871,32 @@ static void tcp_collapse_ofo_queue(struct sock *sk)
		}

		/*
		* Purge the out-of-order queue.
		* Return true if queue was pruned.
		* Clean the out-of-order queue to make room.
		* We drop high sequences packets to :
		* 1) Let a chance for holes to be filled.
		* 2) not add too big latencies if thousands of packets sit there.
		* (But if application shrinks SO_RCVBUF, we could still end up
		* freeing whole queue here)
		*
		* Return true if queue has shrunk.
		*/
		static bool tcp_prune_ofo_queue(struct sock *sk)
		{
		struct tcp_sock *tp = tcp_sk(sk);
		bool res = false;
		struct sk_buff *skb;

		if (skb_queue_empty(&tp->out_of_order_queue))
		return false;

		if (!skb_queue_empty(&tp->out_of_order_queue)) {
		NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
		__skb_queue_purge(&tp->out_of_order_queue);

		while ((skb = __skb_dequeue_tail(&tp->out_of_order_queue)) != NULL) {
		tcp_drop(sk, skb);
		sk_mem_reclaim(sk);
		if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
		!tcp_under_memory_pressure(sk))
		break;
		}

		/* Reset SACK state. A conforming SACK implementation will
		* do the same at a timeout based retransmit. When a connection
		@@ -4893,10 +4905,7 @@ static bool tcp_prune_ofo_queue(struct sock *sk)
		*/
		if (tp->rx_opt.sack_ok)
		tcp_sack_reset(&tp->rx_opt);
		sk_mem_reclaim(sk);
		res = true;
		}
		return res;
		return true;
		}

		/* Reduce allocated memory if we can, trying to get

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