From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH v2 net-next] tcp: avoid expensive pskb_expand_head()
 calls
Date: Thu, 19 Apr 2012 14:44:50 +0200
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Cc: Neal Cardwell <ncardwell@google.com>,
	David Miller <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	Tom Herbert <therbert@google.com>,
	Maciej =?UTF-8?Q?=C5=BBenczykowski?= <maze@google.com>,
	Yuchung Cheng <ycheng@google.com>
To: Ilpo =?ISO-8859-1?Q?J=E4rvinen?= <ilpo.jarvinen@helsinki.fi>
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On Thu, 2012-04-19 at 14:57 +0300, Ilpo J=C3=A4rvinen wrote:

> I'm not concerned of the output side, that seems to work because=20
> of the in tcp_retransmit_skb getting rid of the extra first.
>=20
> The ACK input stuff is more interesting, e.g., this one in=20
> tcp_mark_head_lost:
>=20
> 	err =3D tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
>=20
> It splits from TCP_SKB_CB(skb)->seq + (packets - oldcnt) * mss wherea=
s
> I think the desired point would be: TCP_SKB_CB(skb)->seq + offset_ack=
 +=20
> (packets - oldcnt) * mss?
>=20
> ...There is similar case in sacktag code too while it's aligning to m=
ss=20
> boundaries in tcp_match_skb_to_sack.

Hmm yes, so maybe its safer to update TCP_SKB_CB(skb)->seq in
tcp_tso_acked() (as well as offset_ack) and make needed adjustements in
tcp_fragment() if we find offset_ack being not null.