From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next] net: increase LL_MAX_HEADER if HYPERV_NET is enabled Date: Sun, 01 Nov 2015 15:58:59 -0500 (EST) Message-ID: <20151101.155859.1206189858863918018.davem@davemloft.net> References: <1446249142.6254.47.camel@edumazet-glaptop2.roam.corp.google.com> <1446398459.6254.90.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: haiyangz@microsoft.com, edumazet@google.com, netdev@vger.kernel.org, kys@microsoft.com To: eric.dumazet@gmail.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:55110 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752573AbbKAU7C (ORCPT ); Sun, 1 Nov 2015 15:59:02 -0500 In-Reply-To: <1446398459.6254.90.camel@edumazet-glaptop2.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Date: Sun, 01 Nov 2015 09:20:59 -0800 > From: Eric Dumazet > > My recent commit, attaching SYNACK messages to request sockets > exposed a too small LL_MAX_HEADER when netvsc_drv.c is in use, > because this driver sets a needed_headroom of 220 bytes. > > Increase LL_MAX_HEADER in this case, to avoid a realloc of all > TCP frames. > > In another patch, I'll make skb_set_owner_w() more robust. > > Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener") > Signed-off-by: Eric Dumazet > Bisected-by: Haiyang Zhang Using a value of 256 just because HYPER-V is crazy imposes a huge unnecessary burdon upon the rest of the stack. I rejected a previous attempt to use such a huge value for LL_MAX_HEADER, and I will do so again here. We need a different fix for this issue, one that doesn't hurt everyone. Every distribution is going to turn all the options on, so you might as well consider the largest LL_MAX_HEADER value the one %99.999 users end up paying the price for.