From a2b28094081f1b185a31b33e3c1bcb377d6761bb Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Thu, 3 Dec 2015 18:50:20 +0100
Subject: erts: Tweak hashmap heap size estimation
1. Change order between mul and div to not lose too much
in integer divisions.
2. Fix estimation in DEBUG to really be an *under* estimation.
---
erts/emulator/beam/erl_map.h | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
(limited to 'erts')
diff --git a/erts/emulator/beam/erl_map.h b/erts/emulator/beam/erl_map.h
index c391de3f11..4d9d74bc37 100644
--- a/erts/emulator/beam/erl_map.h
+++ b/erts/emulator/beam/erl_map.h
@@ -195,14 +195,17 @@ typedef struct hashmap_head_s {
[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
+ Observed average number of nodes per key is about 0.35.
*/
-#define HASHMAP_HEAP_SIZE(KEYS,NODES) ((KEYS)*3 + (NODES)*2)
+#define HASHMAP_WORDS_PER_KEY 3
+#define HASHMAP_WORDS_PER_NODE 2
#ifdef DEBUG
-# define HASHMAP_ESTIMATED_NODE_COUNT(KEYS) (KEYS)
+# define HASHMAP_ESTIMATED_TOT_NODE_SIZE(KEYS) \
+ (HASHMAP_WORDS_PER_NODE * (KEYS) * 3/10) /* slightly under estimated */
#else
-# define HASHMAP_ESTIMATED_NODE_COUNT(KEYS) (2*(KEYS)/5)
+# define HASHMAP_ESTIMATED_TOT_NODE_SIZE(KEYS) \
+ (HASHMAP_WORDS_PER_NODE * (KEYS) * 4/10) /* slightly over estimated */
#endif
#define HASHMAP_ESTIMATED_HEAP_SIZE(KEYS) \
- HASHMAP_HEAP_SIZE(KEYS,HASHMAP_ESTIMATED_NODE_COUNT(KEYS))
-
+ ((KEYS)*HASHMAP_WORDS_PER_KEY + HASHMAP_ESTIMATED_TOT_NODE_SIZE(KEYS))
#endif
--
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