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net: pskb_expand_head() optimization 

pskb_expand_head() blindly takes references on fragments before calling
skb_release_data(), potentially releasing these references.

We can add a fast path, avoiding these atomic operations, if we own the
last reference on skb->head.

Based on a previous patch from David

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2010-09-02 23:09:32 +00:00 committed by David S. Miller
parent 9d348af476
commit 1fd63041c4
1 changed files with 20 additions and 5 deletions
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25
net/core/skbuff.c
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@ -779,6 +779,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
u8 *data;
int size = nhead + (skb_end_pointer(skb) - skb->head) + ntail;
long off;
bool fastpath;
BUG_ON(nhead < 0);
@ -800,14 +801,28 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
skb_shinfo(skb),
offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
get_page(skb_shinfo(skb)->frags[i].page);
/* Check if we can avoid taking references on fragments if we own
* the last reference on skb->head. (see skb_release_data())
*/
if (!skb->cloned)
fastpath = true;
else {
int delta = skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1;
if (skb_has_frag_list(skb))
skb_clone_fraglist(skb);
fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
}
skb_release_data(skb);
if (fastpath) {
kfree(skb->head);
} else {
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
get_page(skb_shinfo(skb)->frags[i].page);
if (skb_has_frag_list(skb))
skb_clone_fraglist(skb);
skb_release_data(skb);
}
off = (data + nhead) - skb->head;
skb->head = data;