gro: Do not merge paged packets into frag_list

gro: Do not merge paged packets into frag_list

Bigger is not always better :)

It was easy to continue to merged packets into frag_list after the
page array is full.  However, this turns out to be worse than LRO
because frag_list is a much less efficient form of storage than the
page array.  So we're better off stopping the merge and starting
a new entry with an empty page array.

In future we can optimise this further by doing frag_list merging
but making sure that we continue to fill in the page array.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -2591,9 +2591,11 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 
 	if (skb_shinfo(p)->frag_list)
 		goto merge;
-	else if (skb_headlen(skb) <= skb_gro_offset(skb) &&
-		 skb_shinfo(p)->nr_frags + skb_shinfo(skb)->nr_frags <=
-		 MAX_SKB_FRAGS) {
+	else if (skb_headlen(skb) <= skb_gro_offset(skb)) {
+		if (skb_shinfo(p)->nr_frags + skb_shinfo(skb)->nr_frags >
+		    MAX_SKB_FRAGS)
+			return -E2BIG;
+
 		skb_shinfo(skb)->frags[0].page_offset +=
 			skb_gro_offset(skb) - skb_headlen(skb);
 		skb_shinfo(skb)->frags[0].size -=