nat: ED: global session LRU list

Maintain a global session LRU allowing reuse of expired session instead
of relying on a scavenging mechanism to periodically walk sessions.
Whenever a new session is being allocated in slow path, also attempt to
free an expired session from global LRU list.

Type: improvement

Signed-off-by: Klement Sekera <ksekera@cisco.com>
Change-Id: I9edde9ec138de67c9a4888e915b0490ec16415fa

1 files changed, 8 insertions, 0 deletions

diff --git a/src/plugins/nat/nat.h b/src/plugins/nat/nat.h
index 46dc040c574..d2b114afbbe 100644
--- a/src/plugins/nat/nat.h
+++ b/src/plugins/nat/nat.h
@@ -320,6 +320,10 @@ typedef CLIB_PACKED(struct
   u32 per_user_index;
   u32 per_user_list_head_index;
 
+  /* index in global LRU list */
+  u32 global_lru_index;
+  f64 last_lru_update;
+
   /* Last heard timer */
   f64 last_heard;
 
@@ -521,6 +525,10 @@ typedef struct
   /* Pool of doubly-linked list elements */
   dlist_elt_t *list_pool;
 
+  /* LRU session list - head is stale, tail is fresh */
+  dlist_elt_t *global_lru_pool;
+  u32 global_lru_head_index;
+
   /* NAT thread index */
   u32 snat_thread_index;