diff options
| -rw-r--r-- | Misc/NEWS.d/next/Core and Builtins/2020-03-11-12-28-16.bpo-38373.FE9S21.rst | 2 | ||||
| -rw-r--r-- | Objects/listobject.c | 14 |
2 files changed, 10 insertions, 6 deletions
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-03-11-12-28-16.bpo-38373.FE9S21.rst b/Misc/NEWS.d/next/Core and Builtins/2020-03-11-12-28-16.bpo-38373.FE9S21.rst new file mode 100644 index 0000000..83d60e0 --- /dev/null +++ b/Misc/NEWS.d/next/Core and Builtins/2020-03-11-12-28-16.bpo-38373.FE9S21.rst @@ -0,0 +1,2 @@ +Chaged list overallocation strategy. It no longer overallocates if the new +size is closer to overalocated size than to the old size and adds padding. diff --git a/Objects/listobject.c b/Objects/listobject.c index 46bc777..4e2b6a9 100644 --- a/Objects/listobject.c +++ b/Objects/listobject.c @@ -54,15 +54,17 @@ list_resize(PyListObject *self, Py_ssize_t newsize) * enough to give linear-time amortized behavior over a long * sequence of appends() in the presence of a poorly-performing * system realloc(). - * The growth pattern is: 0, 4, 8, 16, 25, 35, 46, 58, 72, 88, ... + * Add padding to make the allocated size multiple of 4. + * The growth pattern is: 0, 4, 8, 16, 24, 32, 40, 52, 64, 76, ... * Note: new_allocated won't overflow because the largest possible value * is PY_SSIZE_T_MAX * (9 / 8) + 6 which always fits in a size_t. */ - new_allocated = (size_t)newsize + (newsize >> 3) + (newsize < 9 ? 3 : 6); - if (new_allocated > (size_t)PY_SSIZE_T_MAX / sizeof(PyObject *)) { - PyErr_NoMemory(); - return -1; - } + new_allocated = ((size_t)newsize + (newsize >> 3) + 6) & ~(size_t)3; + /* Do not overallocate if the new size is closer to overalocated size + * than to the old size. + */ + if (newsize - Py_SIZE(self) > (Py_ssize_t)(new_allocated - newsize)) + new_allocated = ((size_t)newsize + 3) & ~(size_t)3; if (newsize == 0) new_allocated = 0; |