erts: Remove hashmap probabilistic heap overestimation

by adding a dynamic heap factory.

"binary_to_term" is now a hybrid solution with both
a call to decoded_size() to calculate needed heap space
AND possible dynamic allocation of more heap space
if needed for big maps.

The heap size returned from decoded_size() is guaranteed
to be sufficient for all term heap data except for hashmap
nodes. All hashmap nodes are created at the end of dec_term()
by invoking the heap factory interface that may allocate more
heap space on process heap or in fragments.

With this commit it is no longer guaranteed that a message
is confined to only one heap fragment.

1 files changed, 13 insertions, 1 deletions

diff --git a/erts/emulator/beam/erl_map.h b/erts/emulator/beam/erl_map.h
index 2cc6768bfc..b5941c5c9a 100644
--- a/erts/emulator/beam/erl_map.h
+++ b/erts/emulator/beam/erl_map.h
@@ -91,7 +91,6 @@ Eterm  erts_hashmap_insert_up(Eterm *hp, Eterm key, Eterm value,
 			      Uint *upsz, struct ErtsEStack_ *sp);
 
 int    erts_validate_and_sort_flatmap(flatmap_t* map);
-Uint   hashmap_over_estimated_heap_size(Uint n);
 void   hashmap_iterator_init(struct ErtsWStack_* s, Eterm node, int reverse);
 Eterm* hashmap_iterator_next(struct ErtsWStack_* s);
 Eterm* hashmap_iterator_prev(struct ErtsWStack_* s);
@@ -191,5 +190,18 @@ typedef struct hashmap_head_s {
 
 #define hashmap_index(hash)      (((Uint32)hash) & 0xf)
 
+/* hashmap heap size:
+   [one cons cell + one list term in parent node] per key
+   [one header + one boxed term in parent node] per inner node
+   [one header + one size word] for root node
+*/
+#define HASHMAP_HEAP_SIZE(KEYS,NODES) ((KEYS)*3 + (NODES)*2)
+#ifdef DEBUG
+#  define HASHMAP_ESTIMATED_NODE_COUNT(KEYS) (KEYS)
+#else
+#  define HASHMAP_ESTIMATED_NODE_COUNT(KEYS) (2*(KEYS)/5)
+#endif
+#define HASHMAP_ESTIMATED_HEAP_SIZE(KEYS) \
+        HASHMAP_HEAP_SIZE(KEYS,HASHMAP_ESTIMATED_NODE_COUNT(KEYS))
 
 #endif