tcp_mtu_probe implementation details

Hi all,

Looking on TCP implementation in Linux I see that there are some things that I don't understand in tcp_mtu_probe() implementation. Could someone clear them for me or share the link to Linux PMTUD documentation, please?
The first thing I don't understand is tp->snd_cwnd < 11 in if (!icsk->icsk_mtup.enabled ||

            icsk->icsk_mtup.probe_size ||
            inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
            tp->snd_cwnd < 11 ||
            tp->rx_opt.num_sacks || tp->rx_opt.dsack)
                return -1;

What is magic number "11" here?
The other question is about size_needed variable.
It is assigned to value probe_size + (tp->reordering + 1) * tp->mss_cache And that is not clear for me.
What is this "(tp->reordering + 1) * tp->mss_cache" addition?

Thanks.
--
To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.linux-learn.org/faqs