rculfhash test: -A option for auto resize

[urcu.git] / rculfhash.c

diff --git a/rculfhash.c b/rculfhash.c
index 4a001cf328298d43f16862ece4251ac7e2c43648..0c153982a1aac87cf0b785ecc8fe93fcec27fafa 100644 (file)
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -120,11 +120,11 @@
  * order              bits       reverse
  * 0               0  000        000
  *                 |
- * 1               |  1  001        100             <-
- *                 |  |                              |
- * 2               |  |  2  010        010           |
- *                 |  |  |  3  011        110    <-  |
- *                 |  |  |  |                     |  |
+ * 1               |  1  001        100       <-    <-
+ *                 |  |                        |     |
+ * 2               |  |  2  010        010     |     |
+ *                 |  |  |  3  011        110  | <-  |
+ *                 |  |  |  |                  |  |  |
  * 3               -> |  |  |  4  100        001  |  |
  *                    -> |  |     5  101        101  |
  *                       -> |        6  110        011
@@ -166,6 +166,16 @@
 #define CHAIN_LEN_TARGET               1
 #define CHAIN_LEN_RESIZE_THRESHOLD     3
 
+/*
+ * Define the minimum table size. Protects against hash table resize overload
+ * when too many entries are added quickly before the resize can complete.
+ * This is especially the case if the table could be shrinked to a size of 1.
+ * TODO: we might want to make the add/remove operations help the resize to
+ * add or remove dummy nodes when a resize is ongoing to ensure upper-bound on
+ * chain length.
+ */
+#define MIN_TABLE_SIZE                 128
+
 #ifndef max
 #define max(a, b)      ((a) > (b) ? (a) : (b))
 #endif
@@ -201,6 +211,7 @@ struct cds_lfht {
        cds_lfht_hash_fct hash_fct;
        cds_lfht_compare_fct compare_fct;
        unsigned long hash_seed;
+       int flags;
        pthread_mutex_t resize_mutex;   /* resize mutex: add/del mutex */
        unsigned int in_progress_resize, in_progress_destroy;
        void (*cds_lfht_call_rcu)(struct rcu_head *head,
@@ -567,6 +578,8 @@ void check_resize(struct cds_lfht *ht, struct rcu_table *t,
 {
        unsigned long count;
 
+       if (!(ht->flags & CDS_LFHT_AUTO_RESIZE))
+               return;
        count = uatomic_read(&ht->count);
        /*
         * Use bucket-local length for small table expand and for
@@ -897,6 +910,7 @@ struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
                        cds_lfht_compare_fct compare_fct,
                        unsigned long hash_seed,
                        unsigned long init_size,
+                       int flags,
                        void (*cds_lfht_call_rcu)(struct rcu_head *head,
                                        void (*func)(struct rcu_head *head)),
                        void (*cds_lfht_synchronize_rcu)(void))
@@ -917,10 +931,11 @@ struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
        ht->percpu_count = alloc_per_cpu_items_count();
        /* this mutex should not nest in read-side C.S. */
        pthread_mutex_init(&ht->resize_mutex, NULL);
-       order = get_count_order_ulong(max(init_size, 1)) + 1;
+       order = get_count_order_ulong(max(init_size, MIN_TABLE_SIZE)) + 1;
        ht->t = calloc(1, sizeof(struct cds_lfht)
                       + (order * sizeof(struct rcu_level *)));
        ht->t->size = 0;
+       ht->flags = flags;
        pthread_mutex_lock(&ht->resize_mutex);
        init_table(ht, ht->t, 0, order);
        pthread_mutex_unlock(&ht->resize_mutex);
@@ -1154,7 +1169,7 @@ void _do_cds_lfht_shrink(struct cds_lfht *ht, struct rcu_table *old_t,
        unsigned long old_order, new_order;
        struct rcu_table *new_t;
 
-       new_size = max(new_size, 1);
+       new_size = max(new_size, MIN_TABLE_SIZE);
        old_order = get_count_order_ulong(old_size) + 1;
        new_order = get_count_order_ulong(new_size) + 1;
        printf("resize from %lu (order %lu) to %lu (order %lu) buckets\n",
@@ -1211,19 +1226,18 @@ unsigned long resize_target_update(struct rcu_table *t,
 }
 
 static
-unsigned long resize_target_update_count(struct rcu_table *t,
-                                  unsigned long count)
+void resize_target_update_count(struct rcu_table *t,
+                               unsigned long count)
 {
-       count = max(count, 1);
-       return uatomic_set(&t->resize_target, count);
+       count = max(count, MIN_TABLE_SIZE);
+       uatomic_set(&t->resize_target, count);
 }
 
 void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size)
 {
        struct rcu_table *t = rcu_dereference(ht->t);
-       unsigned long target_size;
 
-       target_size = resize_target_update_count(t, new_size);
+       resize_target_update_count(t, new_size);
        CMM_STORE_SHARED(t->resize_initiated, 1);
        pthread_mutex_lock(&ht->resize_mutex);
        _do_cds_lfht_resize(ht);
@@ -1269,9 +1283,10 @@ void cds_lfht_resize_lazy_count(struct cds_lfht *ht, struct rcu_table *t,
                                unsigned long count)
 {
        struct rcu_resize_work *work;
-       unsigned long target_size;
 
-       target_size = resize_target_update_count(t, count);
+       if (!(ht->flags & CDS_LFHT_AUTO_RESIZE))
+               return;
+       resize_target_update_count(t, count);
        if (!CMM_LOAD_SHARED(t->resize_initiated)) {
                uatomic_inc(&ht->in_progress_resize);
                cmm_smp_mb();   /* increment resize count before calling it */