From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C904CC4321E for ; Mon, 10 Sep 2018 03:44:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E57E20833 for ; Mon, 10 Sep 2018 03:44:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7E57E20833 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727046AbeIJIg3 (ORCPT ); Mon, 10 Sep 2018 04:36:29 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:38590 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726024AbeIJIg3 (ORCPT ); Mon, 10 Sep 2018 04:36:29 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9077540201BC; Mon, 10 Sep 2018 03:44:33 +0000 (UTC) Received: from [10.72.12.30] (ovpn-12-30.pek2.redhat.com [10.72.12.30]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5695310075FE; Mon, 10 Sep 2018 03:44:28 +0000 (UTC) Subject: Re: [PATCH net-next 04/11] tuntap: simplify error handling in tun_build_skb() To: "Michael S. Tsirkin" Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org References: <20180906040526.22518-1-jasowang@redhat.com> <20180906040526.22518-5-jasowang@redhat.com> <20180906130425-mutt-send-email-mst@kernel.org> <20180907101645-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <372ec320-83cf-add5-acf7-27d876c3d604@redhat.com> Date: Mon, 10 Sep 2018 11:44:26 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180907101645-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Mon, 10 Sep 2018 03:44:33 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Mon, 10 Sep 2018 03:44:33 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'jasowang@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018年09月07日 22:17, Michael S. Tsirkin wrote: > On Fri, Sep 07, 2018 at 11:22:00AM +0800, Jason Wang wrote: >>>> @@ -1668,6 +1668,9 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun, >>>> if (copied != len) >>>> return ERR_PTR(-EFAULT); >>>> + get_page(alloc_frag->page); >>>> + alloc_frag->offset += buflen; >>>> + >>> This adds an atomic op on XDP_DROP which is a data path >>> operation for some workloads. >> Yes, I have patch on top to amortize this, the idea is to have a very big >> refcount once after the frag was allocated and maintain a bias and decrease >> them all when allocating new frags.' > Why bother with refcounting for a drop though? It should be simple. > Right, let me fix this. Thanks