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gh-92914: Round the allocated size for lists up to the even number #92915

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Merged
merged 5 commits into from
May 19, 2022
Merged

gh-92914: Round the allocated size for lists up to the even number #92915

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9a2ed09
gh-92914: Always round up the size allocated for lists up to 16 bytes
serhiy-storchaka May 18, 2022
a6b1a79
Round up to the even number.
serhiy-storchaka May 18, 2022
8599f81
Fix tests.
serhiy-storchaka May 18, 2022
67779ed
Update 2022-05-18-08-32-33.gh-issue-92914.tJUeTD.rst
serhiy-storchaka May 18, 2022
7025f22
Update 2022-05-18-08-32-33.gh-issue-92914.tJUeTD.rst
serhiy-storchaka May 18, 2022
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7 changes: 4 additions & 3 deletions Lib/test/test_sys.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1432,9 +1432,10 @@ def get_gen(): yield 1
import re
check(re.finditer('',''), size('2P'))
# list
samples = [[], [1,2,3], ['1', '2', '3']]
for sample in samples:
check(list(sample), vsize('Pn') + len(sample)*self.P)
check(list([]), vsize('Pn'))
check(list([1]), vsize('Pn') + 2*self.P)
check(list([1, 2]), vsize('Pn') + 2*self.P)
check(list([1, 2, 3]), vsize('Pn') + 4*self.P)
# sortwrapper (list)
# XXX
# cmpwrapper (list)
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2022-05-18-08-32-33.gh-issue-92914.tJUeTD.rst
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@@ -0,0 +1 @@
Always round the allocated size for lists up to the nearest even number.
6 changes: 6 additions & 0 deletions Objects/listobject.c
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Expand Up @@ -94,6 +94,12 @@ list_preallocate_exact(PyListObject *self, Py_ssize_t size)
assert(self->ob_item == NULL);
assert(size > 0);

/* Since the Python memory allocator has granularity of 16 bytes on 64-bit
* platforms (8 on 32-bit), there is no benefit of allocating space for
* the odd number of items, and there is no drawback of rounding the
* allocated size up to the nearest even number.
*/
size = (size + 1) & ~(size_t)1;
PyObject **items = PyMem_New(PyObject*, size);
if (items == NULL) {
PyErr_NoMemory();
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