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>

1 files changed, 15 insertions, 10 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 168e949df6a1..19afb18abae9 100644
--- 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;