list_resize() now has an "exact" option for bypassing the overallocation

scheme in situations that likely won't benefit from it.  This further
improves memory utilization from Py2.3 which always over-allocates
except for PyList_New().

Situations expected to benefit from over-allocation:
    list.insert(), list.pop(), list.append(), and list.extend()

Situations deemed unlikely to benefit:
    list_inplace_repeat, list_ass_slice, list_ass_subscript

The most gray area was for listextend_internal() which only runs
when the argument is a list or a tuple.  This could be viewed as
a one-time fixed length addition or it could be viewed as wrapping
a series of appends.  I left its over-allocation turned on but
could be convinced otherwise.

diff --git a/Objects/listobject.c b/Objects/listobject.c
index 3bda2453038b935572bdf84ad779576e9dd57ac9..c8a819018718354f93530be890d1e6b731b5a552 100644 (file)
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -9,7 +9,7 @@
 #endif
 
 static int
-list_resize(PyListObject *self, int newsize)
+list_resize(PyListObject *self, int newsize, int exact)
 {
        PyObject **items;
        size_t _new_size;
@@ -33,7 +33,10 @@ list_resize(PyListObject *self, int newsize)
         * system realloc().
         * The growth pattern is:  0, 4, 8, 16, 25, 35, 46, 58, 72, 88, ...
         */
-       _new_size = (newsize >> 3) + (self->ob_size < 8 ? 3 : 6) + newsize;
+       if (exact)
+               _new_size = newsize;
+       else
+               _new_size = (newsize>>3) + (self->ob_size < 8 ? 3 : 6) + newsize;
        items = self->ob_item;
        if (_new_size <= ((~(size_t)0) / sizeof(PyObject *)))
                PyMem_RESIZE(items, PyObject *, _new_size);
@@ -152,7 +155,7 @@ ins1(PyListObject *self, int where, PyObject *v)
                return -1;
        }
        
-       if (list_resize(self, n+1) == -1)
+       if (list_resize(self, n+1, 0) == -1)
                return -1;
 
        if (where < 0) {
@@ -518,13 +521,13 @@ list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
                if (d < 0) {
                        memmove(&item[ihigh+d], &item[ihigh], 
                                (a->ob_size - ihigh)*sizeof(PyObject *));
-                       list_resize(a, a->ob_size + d);
+                       list_resize(a, a->ob_size + d, 1);
                        item = a->ob_item;
                }
        }
        else { /* Insert d items; recycle ihigh-ilow items */
                s = a->ob_size;
-               if (list_resize(a, s+d) == -1) {
+               if (list_resize(a, s+d, 1) == -1) {
                        if (recycle != NULL)
                                PyMem_DEL(recycle);
                        return -1;
@@ -588,7 +591,7 @@ list_inplace_repeat(PyListObject *self, int n)
                return (PyObject *)self;
        }
 
-       if (list_resize(self, size*n) == -1) 
+       if (list_resize(self, size*n, 1) == -1) 
                return NULL;
 
        p = size;
@@ -680,7 +683,7 @@ listextend_internal(PyListObject *self, PyObject *b)
                }
        }
 
-       if (list_resize(self, selflen + blen) == -1) {
+       if (list_resize(self, selflen + blen, 0) == -1) {
                Py_DECREF(b);
                return -1;
        }
@@ -733,7 +736,7 @@ listextend(PyListObject *self, PyObject *b)
        }
        m = self->ob_size;
        mn = m + n;
-       if (list_resize(self, mn) == -1)
+       if (list_resize(self, mn, 0) == -1)
                goto error;
        memset(&(self->ob_item[m]), 0, sizeof(*self->ob_item) * n);
 
@@ -818,7 +821,7 @@ listpop(PyListObject *self, PyObject *args)
        }
        v = self->ob_item[i];
        if (i == self->ob_size - 1) {
-               if (list_resize(self, self->ob_size - 1) == -1)
+               if (list_resize(self, self->ob_size - 1, 0) == -1)
                        return NULL;
                return v;
        }
@@ -2517,7 +2520,7 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
                        }
 
                        self->ob_size -= slicelength;
-                       list_resize(self, self->ob_size);
+                       list_resize(self, self->ob_size, 1);
 
                        for (i = 0; i < slicelength; i++) {
                                Py_DECREF(garbage[i]);