From: Felix Fietkau <nbd@openwrt.org>
Date: Tue, 29 May 2012 03:35:08 +0000 (+0000)
Subject: skb: avoid unnecessary reallocations in __skb_cow
X-Git-Tag: v3.5-rc1~35^2~9
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=617c8c11236716dcbda877e764b7bf37c6fd8063;p=pandora-kernel.git

skb: avoid unnecessary reallocations in __skb_cow

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 <nbd@openwrt.org>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

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