From: Joe Perches <joe@perches.com>
To: David Miller <davem@davemloft.net>
Cc: eric.dumazet@gmail.com, netdev@vger.kernel.org
Subject: Re: [PATCH net-next] tcp: tcp_make_synack() minor changes
Date: Wed, 26 Mar 2014 11:52:48 -0700 [thread overview]
Message-ID: <1395859968.3726.32.camel@joe-AO722> (raw)
In-Reply-To: <20140326.142551.19958322633174107.davem@davemloft.net>
On Wed, 2014-03-26 at 14:25 -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Wed, 26 Mar 2014 09:57:19 -0700
>
> > From: Eric Dumazet <edumazet@google.com>
> >
> > There is no need to allocate 15 bytes in excess for a SYNACK packet,
> > as it contains no data, only headers.
> >
> > SYNACK are always generated in softirq context, and contain a single
> > segment, we can use TCP_INC_STATS_BH()
> >
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> ...
> > - skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, GFP_ATOMIC);
> > + skb = sock_wmalloc(sk, MAX_TCP_HEADER, 1, GFP_ATOMIC);
>
> Do you know where this "+ 15" comes from? :-)
> It is a kind of Linux networking trivia question.
It's really old, pre v1 days.
I presume it was some kind of ethernet minimum packet size padding.
next prev parent reply other threads:[~2014-03-26 18:52 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-26 16:57 [PATCH net-next] tcp: tcp_make_synack() minor changes Eric Dumazet
2014-03-26 18:25 ` David Miller
2014-03-26 18:52 ` Joe Perches [this message]
2014-03-26 19:11 ` David Miller
2014-03-26 19:08 ` Eric Dumazet
2014-03-26 19:12 ` David Miller
2014-03-27 19:10 ` David Miller
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