gro: Nasty optimisations for page frags in skb_gro_receive

This patch reverses the direction of the frags array copy in
skb_gro_receive in order simplify the loop conditional.  It
also avoids touching the first element of the original frags
array.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 168e949..19afb18 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2676,21 +2676,26 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
                goto merge;
        else if (headlen <= offset) {
                skb_frag_t *frag;
-               int i;
+               skb_frag_t *frag2;
+               int i = skb_shinfo(skb)->nr_frags;
+               int nr_frags = skb_shinfo(p)->nr_frags + i;
+
+               offset -= headlen;
 
-               if (skb_shinfo(p)->nr_frags + skb_shinfo(skb)->nr_frags >
-                   MAX_SKB_FRAGS)
+               if (nr_frags > MAX_SKB_FRAGS)
                        return -E2BIG;
 
-               skb_shinfo(skb)->frags[0].page_offset += offset - headlen;
-               skb_shinfo(skb)->frags[0].size -= offset - headlen;
+               skb_shinfo(p)->nr_frags = nr_frags;
+               skb_shinfo(skb)->nr_frags = 0;
 
-               frag = skb_shinfo(p)->frags + skb_shinfo(p)->nr_frags;
-               for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
-                       *frag++ = skb_shinfo(skb)->frags[i];
+               frag = skb_shinfo(p)->frags + nr_frags;
+               frag2 = skb_shinfo(skb)->frags + i;
+               do {
+                       *--frag = *--frag2;
+               } while (--i);
 
-               skb_shinfo(p)->nr_frags += skb_shinfo(skb)->nr_frags;
-               skb_shinfo(skb)->nr_frags = 0;
+               frag->page_offset += offset;
+               frag->size -= offset;
 
                skb->truesize -= skb->data_len;
                skb->len -= skb->data_len;