tcp: refine tcp_prune_ofo_queue() to not drop all packets
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: NEric 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: NSoheil Hassas Yeganeh <soheil@google.com> Acked-by: NYuchung Cheng <ycheng@google.com> Acked-by: NNeal Cardwell <ncardwell@google.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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