From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH v2] solos-pci: Increase headroom on received packets Date: Thu, 17 Sep 2015 21:29:21 -0700 (PDT) Message-ID: <20150917.212921.1620012798738986807.davem@davemloft.net> References: <1442399145.131189.56.camel@infradead.org> <1442400813.4116.48.camel@edumazet-glaptop2.roam.corp.google.com> <1442403300.131189.73.camel@infradead.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset=iso-2022-jp Content-Transfer-Encoding: 7bit Cc: eric.dumazet@gmail.com, netdev@vger.kernel.org, simon@fire.lp0.eu, guy@traverse.com.au, linux-atm-general@lists.sourceforge.net To: dwmw2@infradead.org Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:48320 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752351AbbIRE3W (ORCPT ); Fri, 18 Sep 2015 00:29:22 -0400 In-Reply-To: <1442403300.131189.73.camel@infradead.org> Sender: netdev-owner@vger.kernel.org List-ID: From: David Woodhouse Date: Wed, 16 Sep 2015 12:35:00 +0100 > A comment in include/linux/skbuff.h says that: > > * Various parts of the networking layer expect at least 32 bytes of > * headroom, you should not reduce this. > > This was demonstrated by a panic when handling fragmented IPv6 packets: > http://marc.info/?l=linux-netdev&m=144236093519172&w=2 > > It's not entirely clear if that comment is still valid ― and if it is, > perhaps netif_rx() ought to be enforcing it with a warning. > > But either way, it is rather stupid from a performance point of view > for us to be receiving packets into a buffer which doesn't have enough > room to prepend an Ethernet header ― it means that *every* incoming > packet is going to be need to be reallocated. So let's fix that. > > Signed-off-by: David Woodhouse Applied, thanks David.