From patchwork Sun May 27 15:26:10 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Felix Fietkau X-Patchwork-Id: 161552 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id AEF14B6F62 for ; Mon, 28 May 2012 01:26:52 +1000 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751406Ab2E0P0R (ORCPT ); Sun, 27 May 2012 11:26:17 -0400 Received: from nbd.name ([46.4.11.11]:33211 "EHLO nbd.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750926Ab2E0P0Q (ORCPT ); Sun, 27 May 2012 11:26:16 -0400 Received: by nf.local (Postfix, from userid 501) id E15D8656082B; Sun, 27 May 2012 17:26:10 +0200 (CEST) From: Felix Fietkau To: netdev@vger.kernel.org Subject: [RFC] skb: avoid unnecessary reallocations in __skb_cow Date: Sun, 27 May 2012 17:26:10 +0200 Message-Id: <1338132370-88299-1-git-send-email-nbd@openwrt.org> X-Mailer: git-send-email 1.7.3.2 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org At the beginning of __skb_cow, headroom gets set to a minimum of NET_SKB_PAD. This causes unnecessary reallocations if the buffer was not cloned and the headroom is just below NET_SKB_PAD, but still more than the amount requested by the caller. This was showing up frequently in my tests on VLAN tx, where vlan_insert_tag calls skb_cow_head(skb, VLAN_HLEN). Fix this by only setting the headroom delta if either there is less headroom than specified by the caller, or if reallocation has to be done anyway because the skb was cloned. Signed-off-by: Felix Fietkau --- include/linux/skbuff.h | 9 ++++++--- 1 files changed, 6 insertions(+), 3 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 0e50171..1898471 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1894,12 +1894,15 @@ static inline int skb_clone_writable(const struct sk_buff *skb, unsigned int len static inline int __skb_cow(struct sk_buff *skb, unsigned int headroom, int cloned) { + unsigned int alloc_headroom = headroom; int delta = 0; if (headroom < NET_SKB_PAD) - headroom = NET_SKB_PAD; - if (headroom > skb_headroom(skb)) - delta = headroom - skb_headroom(skb); + alloc_headroom = NET_SKB_PAD; + if (headroom > skb_headroom(skb) || + (cloned && alloc_headroom > skb_headroom(skb))) { + delta = alloc_headroom - skb_headroom(skb); + } if (delta || cloned) return pskb_expand_head(skb, ALIGN(delta, NET_SKB_PAD), 0,