From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-Id: <20120607040344.597358152@linuxfoundation.org> Date: Thu, 07 Jun 2012 13:04:33 +0900 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Felix Fietkau , Eric Dumazet , "David S. Miller" Subject: [ 57/82] skb: avoid unnecessary reallocations in __skb_cow In-Reply-To: <20120607041406.GA13233@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Felix Fietkau [ Upstream commit 617c8c11236716dcbda877e764b7bf37c6fd8063 ] 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). Locally generated packets should have enough headroom, and for forward paths, we already have NET_SKB_PAD bytes of headroom, so we don't need to add any extra space here. Signed-off-by: Felix Fietkau Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/linux/skbuff.h | 2 -- 1 file changed, 2 deletions(-) --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1881,8 +1881,6 @@ static inline int __skb_cow(struct sk_bu { int delta = 0; - if (headroom < NET_SKB_PAD) - headroom = NET_SKB_PAD; if (headroom > skb_headroom(skb)) delta = headroom - skb_headroom(skb);