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authorEric Dumazet <eric.dumazet@gmail.com>2010-09-02 23:09:32 +0000
committerDavid S. Miller <davem@davemloft.net>2010-09-06 18:24:59 -0700
commit1fd63041c49c5c6ed1fe58b7bccc2de462d51e2b (patch)
treeaac2e108e2c8c545669bd9fe655f04ac026f5e15 /net/core/skbuff.c
parent9d348af47656a65a697ff55a53daf294ea4d5662 (diff)
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>
Diffstat (limited to 'net/core/skbuff.c')
-rw-r--r--net/core/skbuff.c25
1 files changed, 20 insertions, 5 deletions
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index c030cf894f57..2d1bc761fe4b 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -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;