fragment: add fast path for in-order fragments

add fast path for in-order fragments

As the fragments are sent in order in most of OSes, such as Windows, Darwin and
FreeBSD, it is likely the new fragments are at the end of the inet_frag_queue.
In the fast path, we check if the skb at the end of the inet_frag_queue is the
prev we expect.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
----
 include/net/inet_frag.h |    1 +
 net/ipv4/ip_fragment.c  |   12 ++++++++++++
 net/ipv6/reassembly.c   |   11 +++++++++++
 3 files changed, 24 insertions(+)
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 0 deletions

diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 0b97230a3251..545c4141b755 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -333,6 +333,11 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
          * in the chain of fragments so far.  We must know where to put
          * this fragment, right?
          */
+        prev = fq->q.fragments_tail;
+        if (!prev || FRAG6_CB(prev)->offset < offset) {
+                next = NULL;
+                goto found;
+        }
         prev = NULL;
         for(next = fq->q.fragments; next != NULL; next = next->next) {
                 if (FRAG6_CB(next)->offset >= offset)
@@ -340,6 +345,7 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
                 prev = next;
         }
 
+found:
         /* We found where to put this one.  Check for overlap with
          * preceding fragment, and, if needed, align things so that
          * any overlaps are eliminated.
@@ -397,6 +403,8 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
 
         /* Insert this fragment in the chain of fragments. */
         skb->next = next;
+        if (!next)
+                fq->q.fragments_tail = skb;
         if (prev)
                 prev->next = skb;
         else
@@ -463,6 +471,8 @@ static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
                         goto out_oom;
 
                 fp->next = head->next;
+                if (!fp->next)
+                        fq->q.fragments_tail = fp;
                 prev->next = fp;
 
                 skb_morph(head, fq->q.fragments);
@@ -549,6 +559,7 @@ static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
         IP6_INC_STATS_BH(net, __in6_dev_get(dev), IPSTATS_MIB_REASMOKS);
         rcu_read_unlock();
         fq->q.fragments = NULL;
+        fq->q.fragments_tail = NULL;
         return 1;
 
 out_oversize: