From 16a5d1e4727db5c27a03d57d477512e07abe4988 Mon Sep 17 00:00:00 2001
From: Ethan Jackson <ethan@nicira.com>
Date: Fri, 22 Jul 2011 12:00:46 -0700
Subject: [PATCH] mac-learning: Simplify memory management.

The mac-learning implementation used a free list to keep track of
statically allocated table entries.  This made the code slightly
more difficult to understand than the more straightforward heap
based strategy implemented by this patch.
---
 lib/mac-learning.c | 31 ++++++++++++++++---------------
 lib/mac-learning.h |  4 +---
 2 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/lib/mac-learning.c b/lib/mac-learning.c
index 5e05885e..bb84cfcc 100644
--- a/lib/mac-learning.c
+++ b/lib/mac-learning.c
@@ -103,16 +103,10 @@ struct mac_learning *
 mac_learning_create(void)
 {
     struct mac_learning *ml;
-    int i;
 
     ml = xmalloc(sizeof *ml);
     list_init(&ml->lrus);
-    list_init(&ml->free);
     hmap_init(&ml->table);
-    for (i = 0; i < MAC_MAX; i++) {
-        struct mac_entry *s = &ml->entries[i];
-        list_push_front(&ml->free, &s->lru_node);
-    }
     ml->secret = random_uint32();
     ml->flood_vlans = NULL;
     return ml;
@@ -123,7 +117,14 @@ void
 mac_learning_destroy(struct mac_learning *ml)
 {
     if (ml) {
+        struct mac_entry *e, *next;
+
+        HMAP_FOR_EACH_SAFE (e, next, hmap_node, &ml->table) {
+            hmap_remove(&ml->table, &e->hmap_node);
+            free(e);
+        }
         hmap_destroy(&ml->table);
+
         bitmap_free(ml->flood_vlans);
         free(ml);
     }
@@ -181,22 +182,22 @@ mac_learning_insert(struct mac_learning *ml,
     if (!e) {
         uint32_t hash = mac_table_hash(ml, src_mac, vlan);
 
-        if (!list_is_empty(&ml->free)) {
-            e = mac_entry_from_lru_node(ml->free.next);
-        } else {
-            e = mac_entry_from_lru_node(ml->lrus.next);
-            hmap_remove(&ml->table, &e->hmap_node);
+        if (hmap_count(&ml->table) >= MAC_MAX) {
+            get_lru(ml, &e);
+            mac_learning_expire(ml, e);
         }
 
+        e = xmalloc(sizeof *e);
         hmap_insert(&ml->table, &e->hmap_node, hash);
         memcpy(e->mac, src_mac, ETH_ADDR_LEN);
         e->vlan = vlan;
         e->tag = 0;
         e->grat_arp_lock = TIME_MIN;
+    } else {
+        list_remove(&e->lru_node);
     }
 
     /* Mark 'e' as recently used. */
-    list_remove(&e->lru_node);
     list_push_back(&ml->lrus, &e->lru_node);
     e->expires = time_now() + MAC_ENTRY_IDLE_TIME;
 
@@ -250,14 +251,13 @@ mac_learning_lookup(const struct mac_learning *ml,
     }
 }
 
-/* Expires 'e' from the 'ml' hash table.  'e' must not already be on the free
- * list. */
+/* Expires 'e' from the 'ml' hash table. */
 void
 mac_learning_expire(struct mac_learning *ml, struct mac_entry *e)
 {
     hmap_remove(&ml->table, &e->hmap_node);
     list_remove(&e->lru_node);
-    list_push_front(&ml->free, &e->lru_node);
+    free(e);
 }
 
 /* Expires all the mac-learning entries in 'ml'.  The tags in 'ml' are
@@ -270,6 +270,7 @@ mac_learning_flush(struct mac_learning *ml)
     while (get_lru(ml, &e)){
         mac_learning_expire(ml, e);
     }
+    hmap_shrink(&ml->table);
 }
 
 void
diff --git a/lib/mac-learning.h b/lib/mac-learning.h
index d2f28744..0263e498 100644
--- a/lib/mac-learning.h
+++ b/lib/mac-learning.h
@@ -36,7 +36,7 @@
 /* A MAC learning table entry. */
 struct mac_entry {
     struct hmap_node hmap_node; /* Node in a mac_learning hmap. */
-    struct list lru_node;       /* Element in 'lrus' or 'free' list. */
+    struct list lru_node;       /* Element in 'lrus' list. */
     time_t expires;             /* Expiration time. */
     time_t grat_arp_lock;       /* Gratuitous ARP lock expiration time. */
     uint8_t mac[ETH_ADDR_LEN];  /* Known MAC address. */
@@ -76,10 +76,8 @@ static inline bool mac_entry_is_grat_arp_locked(const struct mac_entry *mac)
 /* MAC learning table. */
 struct mac_learning {
     struct hmap table;          /* Learning table. */
-    struct list free;           /* Not-in-use entries. */
     struct list lrus;           /* In-use entries, least recently used at the
                                    front, most recently used at the back. */
-    struct mac_entry entries[MAC_MAX]; /* All entries. */
     uint32_t secret;            /* Secret for randomizing hash table. */
     unsigned long *flood_vlans; /* Bitmap of learning disabled VLANs. */
 };
-- 
2.30.2