net: pskb_expand_head() optimization

Move frags[] at the end of struct skb_shared_info, and make
pskb_expand_head() copy only the used part of it instead of whole array.

This should avoid kmemcheck warnings and speedup pskb_expand_head() as
well, avoiding a lot of cache misses.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f5aa87e..d89876b 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -202,10 +202,11 @@ struct skb_shared_info {
         */
        atomic_t        dataref;
 
-       skb_frag_t      frags[MAX_SKB_FRAGS];
        /* Intermediate layers must ensure that destructor_arg
         * remains valid until skb destructor */
        void *          destructor_arg;
+       /* must be last field, see pskb_expand_head() */
+       skb_frag_t      frags[MAX_SKB_FRAGS];
 };
 
 /* We divide dataref into two halves.  The higher 16 bits hold references

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 76d33ca..7da58a2 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -817,7 +817,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
        memcpy(data + nhead, skb->head, skb->tail - skb->head);
 #endif
        memcpy(data + size, skb_end_pointer(skb),
-              sizeof(struct skb_shared_info));
+              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);