netdev - Re: [net-next 3/3] tcp: keep tcp_collapse controllable even after processing starts

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Date:   Sun, 15 Oct 2017 11:45:49 +0900
From:   Koichiro Den <den@...ipeden.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuznet@....inr.ac.ru,
        yoshfuji@...ux-ipv6.org
Subject: Re: [net-next 3/3] tcp: keep tcp_collapse controllable even after
 processing starts

On Sat, 2017-10-14 at 08:46 -0700, Eric Dumazet wrote:
> On Sat, 2017-10-14 at 16:27 +0900, Koichiro Den wrote:
> > Combining actual collapsing with reasoning for deciding the starting
> > point, we can apply its logic in a consistent manner such that we can
> > avoid costly yet not much useful collapsing. When collapsing to be
> > triggered, it's not rare that most of the skbs in the receive or ooo
> > queue are large ones without much metadata overhead. This also
> > simplifies code and makes it easier to apply logic in a fair manner.
> > 
> > Subtle subsidiary changes included:
> > - When the end_seq of the skb we are trying to collapse was larger than
> >   the 'end' argument provided, we would end up copying to the 'end'
> >   even though we couldn't collapse the original one. Current users of
> >   tcp_collapse does not require such reserves so redefines it as the
> >   point over which skbs whose seq passes guranteed not to be collapsed.
> > - Naturally tcp_collapse_ofo_queue shapes up and we no longer need
> >   'tail' argument.
> 
> 
> I am not inclined to review such a large change, without you providing
> actual numbers.
> 
> We have a problem in TCP right now, that receiver announces a too big
> window, and that is the main reason we trigger collapsing.
> 
> I would rather fix the root cause.
> 
> 
Ok I got it, thank you.