skb: avoid unnecessary reallocations in __skb_cow
authorFelix Fietkau <nbd@openwrt.org>
Tue, 29 May 2012 03:35:08 +0000 (03:35 +0000)
committerDavid S. Miller <davem@davemloft.net>
Tue, 29 May 2012 21:30:08 +0000 (17:30 -0400)
commit617c8c11236716dcbda877e764b7bf37c6fd8063
tree78211c03e4e80eb1ea448c45139ce07534ccd238
parent79fba9f51755c704c0a7d7b7f0df10874dc0a744
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>
include/linux/skbuff.h