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bpo-45522: Allow to disable freelists on build time (GH-29056)
Freelists for object structs can now be disabled. A new ``configure`` option ``--without-freelists`` can be used to disable all freelists except empty tuple singleton. Internal Py*_MAXFREELIST macros can now be defined as 0 without causing compiler warnings and segfaults. Signed-off-by: Christian Heimes <[email protected]>
1 parent 5a14f71 commit 9942f42

15 files changed

Lines changed: 218 additions & 35 deletions

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‎Doc/whatsnew/3.11.rst‎

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Original file line numberDiff line numberDiff line change
@@ -481,6 +481,11 @@ Build Changes
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``isinf()``, ``isnan()``, ``round()``.
482482
(Contributed by Victor Stinner in :issue:`45440`.)
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484+
* Freelists for object structs can now be disabled. A new :program:`configure`
485+
option :option:`!--without-freelists` can be used to disable all freelists
486+
except empty tuple singleton.
487+
(Contributed by Christian Heimes in :issue:`45522`)
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C API Changes
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=============
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‎Include/internal/pycore_interp.h‎

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Original file line numberDiff line numberDiff line change
@@ -85,12 +85,31 @@ struct _Py_unicode_state {
8585
struct _Py_unicode_ids ids;
8686
};
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88+
#ifndef WITH_FREELISTS
89+
// without freelists
90+
# define PyFloat_MAXFREELIST 0
91+
// for tuples only store empty tuple singleton
92+
# define PyTuple_MAXSAVESIZE 1
93+
# define PyTuple_MAXFREELIST 1
94+
# define PyList_MAXFREELIST 0
95+
# define PyDict_MAXFREELIST 0
96+
# define PyFrame_MAXFREELIST 0
97+
# define _PyAsyncGen_MAXFREELIST 0
98+
# define PyContext_MAXFREELIST 0
99+
#endif
100+
101+
#ifndef PyFloat_MAXFREELIST
102+
# define PyFloat_MAXFREELIST 100
103+
#endif
104+
88105
struct _Py_float_state {
106+
#if PyFloat_MAXFREELIST > 0
89107
/* Special free list
90108
free_list is a singly-linked list of available PyFloatObjects,
91109
linked via abuse of their ob_type members. */
92110
int numfree;
93111
PyFloatObject *free_list;
112+
#endif
94113
};
95114

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/* Speed optimization to avoid frequent malloc/free of small tuples */
@@ -119,33 +138,44 @@ struct _Py_tuple_state {
119138
#endif
120139

121140
struct _Py_list_state {
141+
#if PyList_MAXFREELIST > 0
122142
PyListObject *free_list[PyList_MAXFREELIST];
123143
int numfree;
144+
#endif
124145
};
125146

126147
#ifndef PyDict_MAXFREELIST
127148
# define PyDict_MAXFREELIST 80
128149
#endif
129150

130151
struct _Py_dict_state {
152+
#if PyDict_MAXFREELIST > 0
131153
/* Dictionary reuse scheme to save calls to malloc and free */
132154
PyDictObject *free_list[PyDict_MAXFREELIST];
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int numfree;
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PyDictKeysObject *keys_free_list[PyDict_MAXFREELIST];
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int keys_numfree;
158+
#endif
136159
};
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161+
#ifndef PyFrame_MAXFREELIST
162+
# define PyFrame_MAXFREELIST 200
163+
#endif
164+
138165
struct _Py_frame_state {
166+
#if PyFrame_MAXFREELIST > 0
139167
PyFrameObject *free_list;
140168
/* number of frames currently in free_list */
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int numfree;
170+
#endif
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};
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144173
#ifndef _PyAsyncGen_MAXFREELIST
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# define _PyAsyncGen_MAXFREELIST 80
146175
#endif
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148177
struct _Py_async_gen_state {
178+
#if _PyAsyncGen_MAXFREELIST > 0
149179
/* Freelists boost performance 6-10%; they also reduce memory
150180
fragmentation, as _PyAsyncGenWrappedValue and PyAsyncGenASend
151181
are short-living objects that are instantiated for every
@@ -155,12 +185,19 @@ struct _Py_async_gen_state {
155185

156186
struct PyAsyncGenASend* asend_freelist[_PyAsyncGen_MAXFREELIST];
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int asend_numfree;
188+
#endif
158189
};
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191+
#ifndef PyContext_MAXFREELIST
192+
# define PyContext_MAXFREELIST 255
193+
#endif
194+
160195
struct _Py_context_state {
196+
#if PyContext_MAXFREELIST > 0
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// List of free PyContext objects
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PyContext *freelist;
163199
int numfree;
200+
#endif
164201
};
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166203
struct _Py_exc_state {

‎Lib/test/test_sys.py‎

Lines changed: 12 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -825,7 +825,18 @@ def test_debugmallocstats(self):
825825
from test.support.script_helper import assert_python_ok
826826
args = ['-c', 'import sys; sys._debugmallocstats()']
827827
ret, out, err = assert_python_ok(*args)
828-
self.assertIn(b"free PyDictObjects", err)
828+
829+
# Output of sys._debugmallocstats() depends on configure flags.
830+
# The sysconfig vars are not available on Windows.
831+
if sys.platform != "win32":
832+
with_freelists = sysconfig.get_config_var("WITH_FREELISTS")
833+
with_pymalloc = sysconfig.get_config_var("WITH_PYMALLOC")
834+
if with_freelists:
835+
self.assertIn(b"free PyDictObjects", err)
836+
if with_pymalloc:
837+
self.assertIn(b'Small block threshold', err)
838+
if not with_freelists and not with_pymalloc:
839+
self.assertFalse(err)
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830841
# The function has no parameter
831842
self.assertRaises(TypeError, sys._debugmallocstats, True)

‎Misc/NEWS.d/next/C API/2021-10-19-13-07-46.bpo-45522.kGAwmZ.rst‎

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@@ -0,0 +1,2 @@
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The internal freelists for frame, float, list, dict, async generators, and
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context objects can now be disabled.

‎Objects/dictobject.c‎

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Original file line numberDiff line numberDiff line change
@@ -240,17 +240,20 @@ uint64_t _pydict_global_version = 0;
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#include "clinic/dictobject.c.h"
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243+
#if PyDict_MAXFREELIST > 0
243244
static struct _Py_dict_state *
244245
get_dict_state(void)
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{
246247
PyInterpreterState *interp = _PyInterpreterState_GET();
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return &interp->dict_state;
248249
}
250+
#endif
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250252

251253
void
252254
_PyDict_ClearFreeList(PyInterpreterState *interp)
253255
{
256+
#if PyDict_MAXFREELIST > 0
254257
struct _Py_dict_state *state = &interp->dict_state;
255258
while (state->numfree) {
256259
PyDictObject *op = state->free_list[--state->numfree];
@@ -260,14 +263,15 @@ _PyDict_ClearFreeList(PyInterpreterState *interp)
260263
while (state->keys_numfree) {
261264
PyObject_Free(state->keys_free_list[--state->keys_numfree]);
262265
}
266+
#endif
263267
}
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266270
void
267271
_PyDict_Fini(PyInterpreterState *interp)
268272
{
269273
_PyDict_ClearFreeList(interp);
270-
#ifdef Py_DEBUG
274+
#if defined(Py_DEBUG) && PyDict_MAXFREELIST > 0
271275
struct _Py_dict_state *state = &interp->dict_state;
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state->numfree = -1;
273277
state->keys_numfree = -1;
@@ -279,9 +283,11 @@ _PyDict_Fini(PyInterpreterState *interp)
279283
void
280284
_PyDict_DebugMallocStats(FILE *out)
281285
{
286+
#if PyDict_MAXFREELIST > 0
282287
struct _Py_dict_state *state = get_dict_state();
283288
_PyDebugAllocatorStats(out, "free PyDictObject",
284289
state->numfree, sizeof(PyDictObject));
290+
#endif
285291
}
286292

287293
#define DK_MASK(dk) (DK_SIZE(dk)-1)
@@ -570,6 +576,7 @@ new_keys_object(uint8_t log2_size)
570576
es = sizeof(Py_ssize_t);
571577
}
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579+
#if PyDict_MAXFREELIST > 0
573580
struct _Py_dict_state *state = get_dict_state();
574581
#ifdef Py_DEBUG
575582
// new_keys_object() must not be called after _PyDict_Fini()
@@ -579,6 +586,7 @@ new_keys_object(uint8_t log2_size)
579586
dk = state->keys_free_list[--state->keys_numfree];
580587
}
581588
else
589+
#endif
582590
{
583591
dk = PyObject_Malloc(sizeof(PyDictKeysObject)
584592
+ (es<<log2_size)
@@ -611,6 +619,7 @@ free_keys_object(PyDictKeysObject *keys)
611619
Py_XDECREF(entries[i].me_key);
612620
Py_XDECREF(entries[i].me_value);
613621
}
622+
#if PyDict_MAXFREELIST > 0
614623
struct _Py_dict_state *state = get_dict_state();
615624
#ifdef Py_DEBUG
616625
// free_keys_object() must not be called after _PyDict_Fini()
@@ -620,6 +629,7 @@ free_keys_object(PyDictKeysObject *keys)
620629
state->keys_free_list[state->keys_numfree++] = keys;
621630
return;
622631
}
632+
#endif
623633
PyObject_Free(keys);
624634
}
625635

@@ -638,6 +648,7 @@ new_dict(PyDictKeysObject *keys, PyDictValues *values, Py_ssize_t used, int free
638648
{
639649
PyDictObject *mp;
640650
assert(keys != NULL);
651+
#if PyDict_MAXFREELIST > 0
641652
struct _Py_dict_state *state = get_dict_state();
642653
#ifdef Py_DEBUG
643654
// new_dict() must not be called after _PyDict_Fini()
@@ -649,7 +660,9 @@ new_dict(PyDictKeysObject *keys, PyDictValues *values, Py_ssize_t used, int free
649660
assert (Py_IS_TYPE(mp, &PyDict_Type));
650661
_Py_NewReference((PyObject *)mp);
651662
}
652-
else {
663+
else
664+
#endif
665+
{
653666
mp = PyObject_GC_New(PyDictObject, &PyDict_Type);
654667
if (mp == NULL) {
655668
dictkeys_decref(keys);
@@ -1259,6 +1272,7 @@ dictresize(PyDictObject *mp, uint8_t log2_newsize)
12591272
#ifdef Py_REF_DEBUG
12601273
_Py_RefTotal--;
12611274
#endif
1275+
#if PyDict_MAXFREELIST > 0
12621276
struct _Py_dict_state *state = get_dict_state();
12631277
#ifdef Py_DEBUG
12641278
// dictresize() must not be called after _PyDict_Fini()
@@ -1269,7 +1283,9 @@ dictresize(PyDictObject *mp, uint8_t log2_newsize)
12691283
{
12701284
state->keys_free_list[state->keys_numfree++] = oldkeys;
12711285
}
1272-
else {
1286+
else
1287+
#endif
1288+
{
12731289
PyObject_Free(oldkeys);
12741290
}
12751291
}
@@ -1987,6 +2003,7 @@ dict_dealloc(PyDictObject *mp)
19872003
assert(keys->dk_refcnt == 1);
19882004
dictkeys_decref(keys);
19892005
}
2006+
#if PyDict_MAXFREELIST > 0
19902007
struct _Py_dict_state *state = get_dict_state();
19912008
#ifdef Py_DEBUG
19922009
// new_dict() must not be called after _PyDict_Fini()
@@ -1995,7 +2012,9 @@ dict_dealloc(PyDictObject *mp)
19952012
if (state->numfree < PyDict_MAXFREELIST && Py_IS_TYPE(mp, &PyDict_Type)) {
19962013
state->free_list[state->numfree++] = mp;
19972014
}
1998-
else {
2015+
else
2016+
#endif
2017+
{
19992018
Py_TYPE(mp)->tp_free((PyObject *)mp);
20002019
}
20012020
Py_TRASHCAN_END

‎Objects/floatobject.c‎

Lines changed: 17 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -28,12 +28,14 @@ class float "PyObject *" "&PyFloat_Type"
2828
#endif
2929

3030

31+
#if PyFloat_MAXFREELIST > 0
3132
static struct _Py_float_state *
3233
get_float_state(void)
3334
{
3435
PyInterpreterState *interp = _PyInterpreterState_GET();
3536
return &interp->float_state;
3637
}
38+
#endif
3739

3840

3941
double
@@ -126,8 +128,10 @@ PyFloat_GetInfo(void)
126128
PyObject *
127129
PyFloat_FromDouble(double fval)
128130
{
131+
PyFloatObject *op;
132+
#if PyFloat_MAXFREELIST > 0
129133
struct _Py_float_state *state = get_float_state();
130-
PyFloatObject *op = state->free_list;
134+
op = state->free_list;
131135
if (op != NULL) {
132136
#ifdef Py_DEBUG
133137
// PyFloat_FromDouble() must not be called after _PyFloat_Fini()
@@ -136,7 +140,9 @@ PyFloat_FromDouble(double fval)
136140
state->free_list = (PyFloatObject *) Py_TYPE(op);
137141
state->numfree--;
138142
}
139-
else {
143+
else
144+
#endif
145+
{
140146
op = PyObject_Malloc(sizeof(PyFloatObject));
141147
if (!op) {
142148
return PyErr_NoMemory();
@@ -233,6 +239,7 @@ PyFloat_FromString(PyObject *v)
233239
static void
234240
float_dealloc(PyFloatObject *op)
235241
{
242+
#if PyFloat_MAXFREELIST > 0
236243
if (PyFloat_CheckExact(op)) {
237244
struct _Py_float_state *state = get_float_state();
238245
#ifdef Py_DEBUG
@@ -247,7 +254,9 @@ float_dealloc(PyFloatObject *op)
247254
Py_SET_TYPE(op, (PyTypeObject *)state->free_list);
248255
state->free_list = op;
249256
}
250-
else {
257+
else
258+
#endif
259+
{
251260
Py_TYPE(op)->tp_free((PyObject *)op);
252261
}
253262
}
@@ -2036,6 +2045,7 @@ _PyFloat_InitTypes(void)
20362045
void
20372046
_PyFloat_ClearFreeList(PyInterpreterState *interp)
20382047
{
2048+
#if PyFloat_MAXFREELIST > 0
20392049
struct _Py_float_state *state = &interp->float_state;
20402050
PyFloatObject *f = state->free_list;
20412051
while (f != NULL) {
@@ -2045,13 +2055,14 @@ _PyFloat_ClearFreeList(PyInterpreterState *interp)
20452055
}
20462056
state->free_list = NULL;
20472057
state->numfree = 0;
2058+
#endif
20482059
}
20492060

20502061
void
20512062
_PyFloat_Fini(PyInterpreterState *interp)
20522063
{
20532064
_PyFloat_ClearFreeList(interp);
2054-
#ifdef Py_DEBUG
2065+
#if defined(Py_DEBUG) && PyFloat_MAXFREELIST > 0
20552066
struct _Py_float_state *state = &interp->float_state;
20562067
state->numfree = -1;
20572068
#endif
@@ -2061,10 +2072,12 @@ _PyFloat_Fini(PyInterpreterState *interp)
20612072
void
20622073
_PyFloat_DebugMallocStats(FILE *out)
20632074
{
2075+
#if PyFloat_MAXFREELIST > 0
20642076
struct _Py_float_state *state = get_float_state();
20652077
_PyDebugAllocatorStats(out,
20662078
"free PyFloatObject",
20672079
state->numfree, sizeof(PyFloatObject));
2080+
#endif
20682081
}
20692082

20702083

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