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 14725C433F5 for ; Fri, 7 Sep 2018 14:17:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CCE222077C for ; Fri, 7 Sep 2018 14:17:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CCE222077C 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 S1729504AbeIGS6p (ORCPT ); Fri, 7 Sep 2018 14:58:45 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:38764 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727642AbeIGS6p (ORCPT ); Fri, 7 Sep 2018 14:58:45 -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 E0175807689C; Fri, 7 Sep 2018 14:17:35 +0000 (UTC) Received: from redhat.com (ovpn-124-199.rdu2.redhat.com [10.10.124.199]) by smtp.corp.redhat.com (Postfix) with SMTP id 9087710FD2B7; Fri, 7 Sep 2018 14:17:35 +0000 (UTC) Date: Fri, 7 Sep 2018 10:17:35 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH net-next 04/11] tuntap: simplify error handling in tun_build_skb() Message-ID: <20180907101645-mutt-send-email-mst@kernel.org> References: <20180906040526.22518-1-jasowang@redhat.com> <20180906040526.22518-5-jasowang@redhat.com> <20180906130425-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 [10.11.55.8]); Fri, 07 Sep 2018 14:17:35 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 07 Sep 2018 14:17:35 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'mst@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- MST