As it is ip_append_data only counts page fragments to the skb that
allocated it.  As such it means that the first skb gets hit with a
4K charge even though it might have only used a fraction of it while
all subsequent skb's that use the same page gets away with no charge
at all.
This bug was exposed by the UDP accounting patch.
[ The wmem_alloc bumping needs to be moved with the truesize,
  noticed by Takahiro Yasui.  -DaveM ]
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
 
                                skb_fill_page_desc(skb, i, page, 0, 0);
                                frag = &skb_shinfo(skb)->frags[i];
-                               skb->truesize += PAGE_SIZE;
-                               atomic_add(PAGE_SIZE, &sk->sk_wmem_alloc);
                        } else {
                                err = -EMSGSIZE;
                                goto error;
                        frag->size += copy;
                        skb->len += copy;
                        skb->data_len += copy;
+                       skb->truesize += copy;
+                       atomic_add(copy, &sk->sk_wmem_alloc);
                }
                offset += copy;
                length -= copy;
 
 
                                skb_fill_page_desc(skb, i, page, 0, 0);
                                frag = &skb_shinfo(skb)->frags[i];
-                               skb->truesize += PAGE_SIZE;
-                               atomic_add(PAGE_SIZE, &sk->sk_wmem_alloc);
                        } else {
                                err = -EMSGSIZE;
                                goto error;
                        frag->size += copy;
                        skb->len += copy;
                        skb->data_len += copy;
+                       skb->truesize += copy;
+                       atomic_add(copy, &sk->sk_wmem_alloc);
                }
                offset += copy;
                length -= copy;