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>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index c030cf8..2d1bc76 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -779,6 +779,7 @@
u8 *data;
int size = nhead + (skb_end_pointer(skb) - skb->head) + ntail;
long off;
+ bool fastpath;
BUG_ON(nhead < 0);
@@ -800,14 +801,28 @@
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;