From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751256AbdAYDtH (ORCPT ); Tue, 24 Jan 2017 22:49:07 -0500 Received: from mail-pf0-f193.google.com ([209.85.192.193]:36176 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751174AbdAYDtF (ORCPT ); Tue, 24 Jan 2017 22:49:05 -0500 Subject: Re: [PATCH v2] virtio_net: fix PAGE_SIZE > 64k To: "Michael S. Tsirkin" , David Miller References: <20170124221114-mutt-send-email-mst@kernel.org> <20170124.155331.1409241818867862249.davem@davemloft.net> <20170124225502-mutt-send-email-mst@kernel.org> <20170124.161046.824400071485171478.davem@davemloft.net> <20170124235101-mutt-send-email-mst@kernel.org> Cc: linux-kernel@vger.kernel.org, jasowang@redhat.com, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org From: John Fastabend Message-ID: <58882023.8060801@gmail.com> Date: Tue, 24 Jan 2017 19:48:51 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20170124235101-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17-01-24 01:56 PM, Michael S. Tsirkin wrote: > On Tue, Jan 24, 2017 at 04:10:46PM -0500, David Miller wrote: >> This works in the regimen that XDP packets always live in exactly one >> page. That will be needed to mmap the RX ring into userspace, and it >> helps make adjust_header trivial as well. I still don't see why this is a hard requirement for mmap let me post some patches later tonight to show how we do this with af_packet. > > I think the point was to avoid resets across xdp attach/detach. If we > are doing resets now, we could do whatever buffering we want. We could > also just disable mergeable buffers for that matter. > >> MTU 1500, PAGESIZE >= 4096, so a headroom of 256 is no problem, and >> we still have enough tailroom for skb_shared_info should we wrap >> the buffer into a real SKB and push it into the stack. >> >> If you are trying to do buffering differently for virtio_net, well... >> that's a self inflicted wound as far as I can tell. > > Right but I was wondering about the fact that this makes XDP_PASS > much slower than processing skbs without XDP, as truesize is huge > so we'll quickly run out of rmem space. > > When XDP is used to fight DOS attacks, why isn't this a concern? > It is a concern on my side. I want XDP and Linux stack to work reasonably well together. .John