Config options for hobject resize controls

config/config-options/DUK_USE_HOBJECT_ARRAY_ABANDON_LIMIT.yaml

@@ -0,0 +1,14 @@
+define: DUK_USE_HOBJECT_ARRAY_ABANDON_LIMIT
+introduced: 2.1.0
+default: 2
+tags:
+  - performance
+  - lowmemory
+description: >
+  Abandon array part if its density is below L.  The limit L is expressed as
+  a .3 fixed point point, e.g. 2 means 2/8 = 25%.
+
+  The default limit is quite low: one array entry with packed duk_tval is 8
+  bytes whereas one normal entry is 4+1+8 = 13 bytes without a hash entry,
+  and 17-21 bytes with a hash entry (load factor 0.5-1.0).  So the array part
+  shouldn't be abandoned very easily from a footprint point of view.

config/config-options/DUK_USE_HOBJECT_ARRAY_FAST_RESIZE_LIMIT.yaml

@@ -0,0 +1,13 @@
+define: DUK_USE_HOBJECT_ARRAY_FAST_RESIZE_LIMIT
+introduced: 2.1.0
+default: 9
+tags:
+  - performance
+  - lowmemory
+description: >
+  Skip abandon check in object array part resize if new_size < L * old_size.
+  The limit L is expressed as a .3 fixed point value, e.g. 9 means 9/8 =
+  112.5% of current size.
+
+  This is rather technical and you should only change the parameter if you've
+  looked at the internals.

config/config-options/DUK_USE_HOBJECT_ARRAY_MINGROW_ADD.yaml

@@ -0,0 +1,8 @@
+define: DUK_USE_HOBJECT_ARRAY_MINGROW_ADD
+introduced: 2.1.0
+default: 16
+tags:
+  - performance
+description: >
+  Technical internal parameter, see sources for details.  Only adjust if
+  you've looked at the internals.

config/config-options/DUK_USE_HOBJECT_ARRAY_MINGROW_DIVISOR.yaml

@@ -0,0 +1,8 @@
+define: DUK_USE_HOBJECT_ARRAY_MINGROW_DIVISOR
+introduced: 2.1.0
+default: 8
+tags:
+  - performance
+description: >
+  Technical internal parameter, see sources for details.  Only adjust if
+  you've looked at the internals.

config/config-options/DUK_USE_HOBJECT_ENTRY_MINGROW_ADD.yaml

@@ -0,0 +1,8 @@
+define: DUK_USE_HOBJECT_ENTRY_MINGROW_DIVISOR
+introduced: 2.1.0
+default: 8
+tags:
+  - performance
+description: >
+  Technical internal parameter, see sources for details.  Only adjust if
+  you've looked at the internals.

config/config-options/DUK_USE_HOBJECT_ENTRY_MINGROW_DIVISOR.yaml

@@ -0,0 +1,8 @@
+define: DUK_USE_HOBJECT_ENTRY_MINGROW_ADD
+introduced: 2.1.0
+default: 16
+tags:
+  - performance
+description: >
+  Technical internal parameter, see sources for details.  Only adjust if
+  you've looked at the internals.

config/config-options/DUK_USE_HOBJECT_HASH_PART.yaml

@@ -9,5 +9,3 @@ description: >
   enabled unless the target is very low on memory.
 
   If DUK_USE_OBJSIZES16 is defined, this option must not be defined.
-
-# FIXME: expose property limit for hash table as a DUK_USE_xxx flag?

config/config-options/DUK_USE_HOBJECT_HASH_PROP_LIMIT.yaml

@@ -0,0 +1,20 @@
+define: DUK_USE_HOBJECT_HASH_PROP_LIMIT
+introduced: 2.1.0
+default: 8
+tags:
+  - performance
+  - lowmemory
+description: >
+  Minimum number of properties needed for a hash part to be included in the
+  object property table.  This limit is checked whenever an object is resized.
+
+  A hash part improves property lookup performance even for small objects,
+  starting from roughly 4 properties.  However, this ignores the cost of
+  setting up and managing the hash part, which is offset only if property
+  lookups made through the hash part can offset the setup cost.  A hash part
+  is worth it for heavily accessed small objects or large objects (even those
+  accessed quite infrequently).  The limit doesn't take into account property
+  access frequency, so it is necessarily a compromise.
+
+  A lower value improves performance (a value as low a 4-8 can be useful)
+  while a higher value conserves memory.

config/examples/low_memory.yaml

@@ -55,6 +55,10 @@ DUK_USE_STRTAB_RESIZE_CHECK_MASK: 255  # -""-
 
 DUK_USE_HSTRING_ARRIDX: false
 
+# Only add a hash table for quite large objects to conserve memory.  Even
+# lower memory targets usually drop hash part support entirely.
+DUK_USE_HOBJECT_HASH_PROP_LIMIT: 64
+
 # Consider using pointer compression, see doc/low-memory.rst.
 #DUK_USE_REFCOUNT16: true
 #DUK_USE_STRHASH16: true