On Wed, Nov 21, 2018 at 9:52 AM, Eric Dumazet <eduma...@google.com> wrote:
> Under high stress, and if GRO or coalescing does not help,
> we better make room in backlog queue to be able to keep latest
> packet coming.
>
> This generally helps fast recovery, given that we often receive
> packets in order.
I like the benefit of fast recovery but I am a bit leery about head
drop causing HoLB on large read, while tail drops can be repaired by
RACK and TLP already. Hmm -
>
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Tested-by: Jean-Louis Dupond <jean-lo...@dupond.be>
> Cc: Neal Cardwell <ncardw...@google.com>
> Cc: Yuchung Cheng <ych...@google.com>
> ---
> net/ipv4/tcp_ipv4.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index
> 401e1d1cb904a4c7963d8baa419cfbf178593344..36c9d715bf2aa7eb7bf58b045bfeb85a2ec1a696
> 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1693,6 +1693,20 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff
> *skb)
> __skb_push(skb, hdrlen);
> }
>
> + while (sk_rcvqueues_full(sk, limit)) {
> + struct sk_buff *head;
> +
> + head = sk->sk_backlog.head;
> + if (!head)
> + break;
> + sk->sk_backlog.head = head->next;
> + if (!head->next)
> + sk->sk_backlog.tail = NULL;
> + skb_mark_not_on_list(head);
> + sk->sk_backlog.len -= head->truesize;
> + kfree_skb(head);
> + __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPBACKLOGDROP);
> + }
> /* Only socket owner can try to collapse/prune rx queues
> * to reduce memory overhead, so add a little headroom here.
> * Few sockets backlog are possibly concurrently non empty.
> --
> 2.19.1.1215.g8438c0b245-goog
>
