inetpeer: get rid of ip_id_count

Ideally, we would need to generate IP ID using a per destination IP
generator.

linux kernels used inet_peer cache for this purpose, but this had a huge
cost on servers disabling MTU discovery.

1) each inet_peer struct consumes 192 bytes

2) inetpeer cache uses a binary tree of inet_peer structs,
   with a nominal size of ~66000 elements under load.

3) lookups in this tree are hitting a lot of cache lines, as tree depth
   is about 20.

4) If server deals with many tcp flows, we have a high probability of
   not finding the inet_peer, allocating a fresh one, inserting it in
   the tree with same initial ip_id_count, (cf secure_ip_id())

5) We garbage collect inet_peer aggressively.

IP ID generation do not have to be 'perfect'

Goal is trying to avoid duplicates in a short period of time,
so that reassembly units have a chance to complete reassembly of
fragments belonging to one message before receiving other fragments
with a recycled ID.

We simply use an array of generators, and a Jenkin hash using the dst IP
as a key.

ipv6_select_ident() is put back into net/ipv6/ip6_output.c where it
belongs (it is only used from this file)

secure_ip_id() and secure_ipv6_id() no longer are needed.

Rename ip_select_ident_more() to ip_select_ident_segs() to avoid
unnecessary decrement/increment of the number of segments.

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

1 files changed, 3 insertions, 20 deletions

diff --git a/include/net/inetpeer.h b/include/net/inetpeer.h
index 6efe73c79c52..823ec7bb9c67 100644
--- a/include/net/inetpeer.h
+++ b/include/net/inetpeer.h
@@ -41,14 +41,13 @@ struct inet_peer {
                 struct rcu_head     gc_rcu;
         };
         /*
-         * Once inet_peer is queued for deletion (refcnt == -1), following fields
-         * are not available: rid, ip_id_count
+         * Once inet_peer is queued for deletion (refcnt == -1), following field
+         * is not available: rid
          * We can share memory with rcu_head to help keep inet_peer small.
          */
         union {
                 struct {
                         atomic_t                        rid;            /* Frag reception counter */
-                        atomic_t                        ip_id_count;    /* IP ID for the next packet */
                 };
                 struct rcu_head         rcu;
                 struct inet_peer        *gc_next;
@@ -165,7 +164,7 @@ bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout);
 void inetpeer_invalidate_tree(struct inet_peer_base *);
 
 /*
- * temporary check to make sure we dont access rid, ip_id_count, tcp_ts,
+ * temporary check to make sure we dont access rid, tcp_ts,
  * tcp_ts_stamp if no refcount is taken on inet_peer
  */
 static inline void inet_peer_refcheck(const struct inet_peer *p)
@@ -173,20 +172,4 @@ static inline void inet_peer_refcheck(const struct inet_peer *p)
         WARN_ON_ONCE(atomic_read(&p->refcnt) <= 0);
 }
 
-
-/* can be called with or without local BH being disabled */
-static inline int inet_getid(struct inet_peer *p, int more)
-{
-        int old, new;
-        more++;
-        inet_peer_refcheck(p);
-        do {
-                old = atomic_read(&p->ip_id_count);
-                new = old + more;
-                if (!new)
-                        new = 1;
-        } while (atomic_cmpxchg(&p->ip_id_count, old, new) != old);
-        return new;
-}
-
 #endif /* _NET_INETPEER_H */