ipv6: frags: get rid of ip6frag_skb_cb/FRAG6_CB

ip6_frag_queue uses skb->cb[] to store the fragment offset, meaning that
we could use two cache lines per skb when finding the insertion point,
if for some reason inet6_skb_parm size is increased in the future.

By using skb->ip_defrag_offset instead of skb->cb[], we pack all
the fields in a single cache line, matching what we did for IPv4.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 2127da130dc2cee677059247d5e079a8afbca13d..7b52efc63f6adad2c242ae1171e5b7b27b40f0bf 100644 (file)
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -62,13 +62,6 @@
 
 static const char ip6_frag_cache_name[] = "ip6-frags";
 
-struct ip6frag_skb_cb {
-       struct inet6_skb_parm   h;
-       int                     offset;
-};
-
-#define FRAG6_CB(skb)  ((struct ip6frag_skb_cb *)((skb)->cb))
-
 static u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
 {
        return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
@@ -250,13 +243,13 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
         * this fragment, right?
         */
        prev = fq->q.fragments_tail;
-       if (!prev || FRAG6_CB(prev)->offset < offset) {
+       if (!prev || prev->ip_defrag_offset < offset) {
                next = NULL;
                goto found;
        }
        prev = NULL;
        for (next = fq->q.fragments; next != NULL; next = next->next) {
-               if (FRAG6_CB(next)->offset >= offset)
+               if (next->ip_defrag_offset >= offset)
                        break;  /* bingo! */
                prev = next;
        }
@@ -271,14 +264,20 @@ found:
 
        /* Check for overlap with preceding fragment. */
        if (prev &&
-           (FRAG6_CB(prev)->offset + prev->len) > offset)
+           (prev->ip_defrag_offset + prev->len) > offset)
                goto discard_fq;
 
        /* Look for overlap with succeeding segment. */
-       if (next && FRAG6_CB(next)->offset < end)
+       if (next && next->ip_defrag_offset < end)
                goto discard_fq;
 
-       FRAG6_CB(skb)->offset = offset;
+       /* Note : skb->ip_defrag_offset and skb->dev share the same location */
+       dev = skb->dev;
+       if (dev)
+               fq->iif = dev->ifindex;
+       /* Makes sure compiler wont do silly aliasing games */
+       barrier();
+       skb->ip_defrag_offset = offset;
 
        /* Insert this fragment in the chain of fragments. */
        skb->next = next;
@@ -289,11 +288,6 @@ found:
        else
                fq->q.fragments = skb;
 
-       dev = skb->dev;
-       if (dev) {
-               fq->iif = dev->ifindex;
-               skb->dev = NULL;
-       }
        fq->q.stamp = skb->tstamp;
        fq->q.meat += skb->len;
        fq->ecn |= ecn;
@@ -380,7 +374,7 @@ static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
        }
 
        WARN_ON(head == NULL);
-       WARN_ON(FRAG6_CB(head)->offset != 0);
+       WARN_ON(head->ip_defrag_offset != 0);
 
        /* Unfragmented part is taken from the first segment. */
        payload_len = ((head->data - skb_network_header(head)) -