netdev - Re: [PATCH net-next] tcp: use TCP_DEFAULT_INIT_RCVWND in tcp_fixup

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Message-ID: <1319140954.2854.12.camel@edumazet-laptop>
Date:	Thu, 20 Oct 2011 22:02:34 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tcp: use TCP_DEFAULT_INIT_RCVWND in
 tcp_fixup_rcvbuf()

Le jeudi 20 octobre 2011 à 15:50 -0400, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Thu, 20 Oct 2011 21:16:26 +0200
> 
> > Since commit 356f039822b (TCP: increase default initial receive
> > window.), we allow sender to send 10 (TCP_DEFAULT_INIT_RCVWND) segments.
> > 
> > Change tcp_fixup_rcvbuf() to reflect this change, even if no real change 
> > is expected, since sysctl_tcp_rmem[1] = 87380 and this value
> > is bigger than tcp_fixup_rcvbuf() computed rcvmem (~23720)
> > 
> > Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
>  ...
> > +	unsigned int mss = min_t(unsigned int, tp->advmss, 1460);
> 
> I don't understand where this calculation comes from, and even if it
> should be obvious it isn't to me and deserves a mention in the commit
> message at a minimum.

This is the calculation done in commit 356f039822b as well.

The window is 10*MSS, but no more than 14600

On loopback, this matters, because we could end with rcvmem=219680



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