Author: Laurence Tratt <[email protected]>
Branch:
Changeset: r74945:22ee57670e0d
Date: 2014-12-15 16:37 +0000
http://bitbucket.org/pypy/pypy/changeset/22ee57670e0d/
Log: Compact dictionaries that have very few live items left in them.
For some reason, we copied CPython's hard-to-defend behaviour here.
Replace it with a (very) conservative check that will only shrink
the memory allocated for a dictionary if it has very few items left.
diff --git a/rpython/rtyper/lltypesystem/rordereddict.py
b/rpython/rtyper/lltypesystem/rordereddict.py
--- a/rpython/rtyper/lltypesystem/rordereddict.py
+++ b/rpython/rtyper/lltypesystem/rordereddict.py
@@ -661,19 +661,11 @@
entry.key = lltype.nullptr(ENTRY.key.TO)
if ENTRIES.must_clear_value:
entry.value = lltype.nullptr(ENTRY.value.TO)
- #
- # The rest is commented out: like CPython we no longer shrink the
- # dictionary here. It may shrink later if we try to append a number
- # of new items to it. Unsure if this behavior was designed in
- # CPython or is accidental. A design reason would be that if you
- # delete all items in a dictionary (e.g. with a series of
- # popitem()), then CPython avoids shrinking the table several times.
- #num_entries = len(d.entries)
- #if num_entries > DICT_INITSIZE and d.num_items <= num_entries / 4:
- # ll_dict_resize(d)
- # A previous xxx: move the size checking and resize into a single
- # call which is opaque to the JIT when the dict isn't virtual, to
- # avoid extra branches.
+
+ # If the dictionary is at least 87.5% dead items, then consider shrinking
+ # it.
+ if d.num_live_items + DICT_INITSIZE <= len(d.entries) / 8:
+ ll_dict_resize(d)
def ll_dict_resize(d):
# make a 'new_size' estimate and shrink it if there are many
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