https://github.com/python/cpython/commit/21fb9dc71d2dd4ea9faf966385c102be20ce99e8
commit: 21fb9dc71d2dd4ea9faf966385c102be20ce99e8
branch: main
author: Pablo Galindo Salgado <[email protected]>
committer: pablogsal <[email protected]>
date: 2026-04-04T18:42:30+01:00
summary:
gh-146527: Heap-allocate gc_stats to avoid bloating PyInterpreterState (#148057)
The gc_stats struct contains ring buffers of gc_generation_stats
entries (11 young + 3×2 old on default builds). Embedding it inline
in _gc_runtime_state, which is itself inline in PyInterpreterState,
pushed fields like _gil.locked and threads.head to offsets beyond
what out-of-process profilers and debuggers can reasonably read in
a single buffer (e.g. offset 9384 for _gil.locked vs an 8 KiB read
buffer).
Heap-allocate generation_stats via PyMem_RawCalloc in _PyGC_Init and
free it in _PyGC_Fini. This shrinks PyInterpreterState by ~1.6 KiB
and keeps the GIL, thread-list, and other frequently-inspected fields
at stable, low offsets.
files:
M Include/internal/pycore_interp_structs.h
M Modules/gcmodule.c
M Python/gc.c
M Python/gc_free_threading.c
diff --git a/Include/internal/pycore_interp_structs.h
b/Include/internal/pycore_interp_structs.h
index f76d4f41c55119..c4b084642668a9 100644
--- a/Include/internal/pycore_interp_structs.h
+++ b/Include/internal/pycore_interp_structs.h
@@ -248,7 +248,7 @@ struct _gc_runtime_state {
struct gc_generation old[2];
/* a permanent generation which won't be collected */
struct gc_generation permanent_generation;
- struct gc_stats generation_stats;
+ struct gc_stats *generation_stats;
/* true if we are currently running the collector */
int collecting;
// The frame that started the current collection. It might be NULL even
when
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index c21b61589bd261..8da28130e9da9a 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -347,9 +347,9 @@ gc_get_stats_impl(PyObject *module)
/* To get consistent values despite allocations while constructing
the result list, we use a snapshot of the running stats. */
GCState *gcstate = get_gc_state();
- stats[0] =
gcstate->generation_stats.young.items[gcstate->generation_stats.young.index];
- stats[1] =
gcstate->generation_stats.old[0].items[gcstate->generation_stats.old[0].index];
- stats[2] =
gcstate->generation_stats.old[1].items[gcstate->generation_stats.old[1].index];
+ stats[0] =
gcstate->generation_stats->young.items[gcstate->generation_stats->young.index];
+ stats[1] =
gcstate->generation_stats->old[0].items[gcstate->generation_stats->old[0].index];
+ stats[2] =
gcstate->generation_stats->old[1].items[gcstate->generation_stats->old[1].index];
PyObject *result = PyList_New(0);
if (result == NULL)
diff --git a/Python/gc.c b/Python/gc.c
index 7bca40f6e3f58e..284ac725d37ac6 100644
--- a/Python/gc.c
+++ b/Python/gc.c
@@ -177,6 +177,11 @@ _PyGC_Init(PyInterpreterState *interp)
{
GCState *gcstate = &interp->gc;
+ gcstate->generation_stats = PyMem_RawCalloc(1, sizeof(struct gc_stats));
+ if (gcstate->generation_stats == NULL) {
+ return _PyStatus_NO_MEMORY();
+ }
+
gcstate->garbage = PyList_New(0);
if (gcstate->garbage == NULL) {
return _PyStatus_NO_MEMORY();
@@ -1398,13 +1403,13 @@ static struct gc_generation_stats *
gc_get_stats(GCState *gcstate, int gen)
{
if (gen == 0) {
- struct gc_young_stats_buffer *buffer =
&gcstate->generation_stats.young;
+ struct gc_young_stats_buffer *buffer =
&gcstate->generation_stats->young;
buffer->index = (buffer->index + 1) % GC_YOUNG_STATS_SIZE;
struct gc_generation_stats *stats = &buffer->items[buffer->index];
return stats;
}
else {
- struct gc_old_stats_buffer *buffer =
&gcstate->generation_stats.old[gen - 1];
+ struct gc_old_stats_buffer *buffer =
&gcstate->generation_stats->old[gen - 1];
buffer->index = (buffer->index + 1) % GC_OLD_STATS_SIZE;
struct gc_generation_stats *stats = &buffer->items[buffer->index];
return stats;
@@ -1415,12 +1420,12 @@ static struct gc_generation_stats *
gc_get_prev_stats(GCState *gcstate, int gen)
{
if (gen == 0) {
- struct gc_young_stats_buffer *buffer =
&gcstate->generation_stats.young;
+ struct gc_young_stats_buffer *buffer =
&gcstate->generation_stats->young;
struct gc_generation_stats *stats = &buffer->items[buffer->index];
return stats;
}
else {
- struct gc_old_stats_buffer *buffer =
&gcstate->generation_stats.old[gen - 1];
+ struct gc_old_stats_buffer *buffer =
&gcstate->generation_stats->old[gen - 1];
struct gc_generation_stats *stats = &buffer->items[buffer->index];
return stats;
}
@@ -2299,6 +2304,8 @@ _PyGC_Fini(PyInterpreterState *interp)
GCState *gcstate = &interp->gc;
Py_CLEAR(gcstate->garbage);
Py_CLEAR(gcstate->callbacks);
+ PyMem_RawFree(gcstate->generation_stats);
+ gcstate->generation_stats = NULL;
/* Prevent a subtle bug that affects sub-interpreters that use basic
* single-phase init extensions (m_size == -1). Those extensions cause
objects
diff --git a/Python/gc_free_threading.c b/Python/gc_free_threading.c
index 7ad60a73a56a69..4b46ca04f56b20 100644
--- a/Python/gc_free_threading.c
+++ b/Python/gc_free_threading.c
@@ -1698,6 +1698,11 @@ _PyGC_Init(PyInterpreterState *interp)
{
GCState *gcstate = &interp->gc;
+ gcstate->generation_stats = PyMem_RawCalloc(1, sizeof(struct gc_stats));
+ if (gcstate->generation_stats == NULL) {
+ return _PyStatus_NO_MEMORY();
+ }
+
gcstate->garbage = PyList_New(0);
if (gcstate->garbage == NULL) {
return _PyStatus_NO_MEMORY();
@@ -2387,12 +2392,12 @@ static struct gc_generation_stats *
get_stats(GCState *gcstate, int gen)
{
if (gen == 0) {
- struct gc_young_stats_buffer *buffer =
&gcstate->generation_stats.young;
+ struct gc_young_stats_buffer *buffer =
&gcstate->generation_stats->young;
struct gc_generation_stats *stats = &buffer->items[buffer->index];
return stats;
}
else {
- struct gc_old_stats_buffer *buffer =
&gcstate->generation_stats.old[gen - 1];
+ struct gc_old_stats_buffer *buffer =
&gcstate->generation_stats->old[gen - 1];
struct gc_generation_stats *stats = &buffer->items[buffer->index];
return stats;
}
@@ -2831,6 +2836,8 @@ _PyGC_Fini(PyInterpreterState *interp)
GCState *gcstate = &interp->gc;
Py_CLEAR(gcstate->garbage);
Py_CLEAR(gcstate->callbacks);
+ PyMem_RawFree(gcstate->generation_stats);
+ gcstate->generation_stats = NULL;
/* We expect that none of this interpreters objects are shared
with other interpreters.
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