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GH-126491: GC: Mark objects reachable from roots before doing cycle collection (GH-127110)

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* Mark almost all reachable objects before doing collection phase

* Add stats for objects marked

* Visit new frames before each increment

* Update docs

* Clearer calculation of work to do.
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Mark Shannon 2024-12-02 10:12:17 +00:00 • committed by GitHub
parent 2a373da770
commit a8dd821d5b
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GPG key ID: B5690EEEBB952194
14 changed files with 365 additions and 113 deletions
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2
Include/cpython/pystats.h
View file

@ -99,6 +99,8 @@ typedef struct _gc_stats {
uint64_t collections;
uint64_t object_visits;
uint64_t objects_collected;
uint64_t objects_transitively_reachable;
uint64_t objects_not_transitively_reachable;
} GCStats;
typedef struct _uop_stats {

3
Include/internal/pycore_frame.h
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@ -75,6 +75,7 @@ typedef struct _PyInterpreterFrame {
_PyStackRef *stackpointer;
uint16_t return_offset; /* Only relevant during a function call */
char owner;
char visited;
/* Locals and stack */
_PyStackRef localsplus[1];
} _PyInterpreterFrame;
@ -207,6 +208,7 @@ _PyFrame_Initialize(
#endif
frame->return_offset = 0;
frame->owner = FRAME_OWNED_BY_THREAD;
frame->visited = 0;
for (int i = null_locals_from; i < code->co_nlocalsplus; i++) {
frame->localsplus[i] = PyStackRef_NULL;
@ -389,6 +391,7 @@ _PyFrame_PushTrampolineUnchecked(PyThreadState *tstate, PyCodeObject *code, int
frame->instr_ptr = _PyCode_CODE(code);
#endif
frame->owner = FRAME_OWNED_BY_THREAD;
frame->visited = 0;
frame->return_offset = 0;
#ifdef Py_GIL_DISABLED

10
Include/internal/pycore_gc.h
View file

@ -10,11 +10,11 @@ extern "C" {
/* GC information is stored BEFORE the object structure. */
typedef struct {
// Pointer to next object in the list.
// Tagged pointer to next object in the list.
// 0 means the object is not tracked
uintptr_t _gc_next;
// Pointer to previous object in the list.
// Tagged pointer to previous object in the list.
// Lowest two bits are used for flags documented later.
uintptr_t _gc_prev;
} PyGC_Head;
@ -284,6 +284,11 @@ struct gc_generation_stats {
Py_ssize_t uncollectable;
};
enum _GCPhase {
GC_PHASE_MARK = 0,
GC_PHASE_COLLECT = 1
};
struct _gc_runtime_state {
/* List of objects that still need to be cleaned up, singly linked
* via their gc headers' gc_prev pointers. */
@ -311,6 +316,7 @@ struct _gc_runtime_state {
Py_ssize_t work_to_do;
/* Which of the old spaces is the visited space */
int visited_space;
int phase;
#ifdef Py_GIL_DISABLED
/* This is the number of objects that survived the last full

4
Include/internal/pycore_object.h
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@ -471,8 +471,8 @@ static inline void _PyObject_GC_TRACK(
PyGC_Head *last = (PyGC_Head*)(generation0->_gc_prev);
_PyGCHead_SET_NEXT(last, gc);
_PyGCHead_SET_PREV(gc, last);
/* Young objects will be moved into the visited space during GC, so set the bit here */
gc->_gc_next = ((uintptr_t)generation0) | (uintptr_t)interp->gc.visited_space;
uintptr_t not_visited = 1 ^ interp->gc.visited_space;
gc->_gc_next = ((uintptr_t)generation0) | not_visited;
generation0->_gc_prev = (uintptr_t)gc;
#endif
}

1
Include/internal/pycore_runtime_init.h
View file

@ -137,6 +137,7 @@ extern PyTypeObject _PyExc_MemoryError;
{ .threshold = 0, }, \
}, \
.work_to_do = -5000, \
.phase = GC_PHASE_MARK, \
}, \
.qsbr = { \
.wr_seq = QSBR_INITIAL, \