* space faster than objects are added to the old space.
*
* Each young or incremental collection adds a number of
- * objects, S (for survivors) to the old space, and
- * incremental collectors scan I objects from the old space.
- * I > S must be true. We also want I > S * N to be where
- * N > 1. Higher values of N mean that the old space is
+ * new objects (N) to the heap, and incremental collectors
+ * scan I objects from the old space.
+ * I > N must be true. We also want I > N * K to be where
+ * K > 2. Higher values of K mean that the old space is
* scanned more rapidly.
- * The default incremental threshold of 10 translates to
- * N == 1.4 (1 + 4/threshold)
*/
-
-/* Divide by 10, so that the default incremental threshold of 10
- * scans objects at 1% of the heap size */
-#define SCAN_RATE_DIVISOR 10
+#define SCAN_RATE_DIVISOR 5
static void
add_stats(GCState *gcstate, int gen, struct gc_collection_stats *stats)
validate_spaces(gcstate);
}
-#ifndef NDEBUG
-static inline int
-IS_IN_VISITED(PyGC_Head *gc, int visited_space)
+typedef struct work_stack {
+ PyGC_Head *top;
+ int visited_space;
+} WorkStack;
+
+/* Remove gc from the list it is currently in and push it to the stack */
+static inline void
+push_to_stack(PyGC_Head *gc, WorkStack *stack)
{
- assert(visited_space == 0 || other_space(visited_space) == 0);
- return gc_old_space(gc) == visited_space;
+ PyGC_Head *prev = GC_PREV(gc);
+ PyGC_Head *next = GC_NEXT(gc);
+ _PyGCHead_SET_NEXT(prev, next);
+ _PyGCHead_SET_PREV(next, prev);
+ _PyGCHead_SET_PREV(gc, stack->top);
+ stack->top = gc;
}
-#endif
-struct container_and_flag {
- PyGC_Head *container;
- int visited_space;
- intptr_t size;
-};
+static inline PyGC_Head *
+pop_from_stack(WorkStack *stack)
+{
+ PyGC_Head *gc = stack->top;
+ stack->top = _PyGCHead_PREV(gc);
+ return gc;
+}
-/* A traversal callback for adding to container) */
-static int
-visit_add_to_container(PyObject *op, void *arg)
+/* append list `from` to `stack`; `from` becomes an empty list */
+static void
+move_list_to_stack(PyGC_Head *from, WorkStack *stack)
{
- OBJECT_STAT_INC(object_visits);
- struct container_and_flag *cf = (struct container_and_flag *)arg;
- int visited = cf->visited_space;
- assert(visited == get_gc_state()->visited_space);
- if (!_Py_IsImmortal(op) && _PyObject_IS_GC(op)) {
+ if (!gc_list_is_empty(from)) {
+ PyGC_Head *from_head = GC_NEXT(from);
+ PyGC_Head *from_tail = GC_PREV(from);
+ _PyGCHead_SET_PREV(from_head, stack->top);
+ stack->top = from_tail;
+ gc_list_init(from);
+ }
+}
+
+static inline void
+move_to_stack(PyObject *op, WorkStack *stack, int visited_space)
+{
+ assert(op != NULL);
+ if (_PyObject_IS_GC(op)) {
PyGC_Head *gc = AS_GC(op);
if (_PyObject_GC_IS_TRACKED(op) &&
- gc_old_space(gc) != visited) {
+ gc_old_space(gc) != visited_space) {
+ assert(!_Py_IsImmortal(op));
gc_flip_old_space(gc);
- gc_list_move(gc, cf->container);
- cf->size++;
+ push_to_stack(gc, stack);
}
}
- return 0;
}
-static intptr_t
-expand_region_transitively_reachable(PyGC_Head *container, PyGC_Head *gc, GCState *gcstate)
-{
- struct container_and_flag arg = {
- .container = container,
- .visited_space = gcstate->visited_space,
- .size = 0
- };
- assert(GC_NEXT(gc) == container);
- while (gc != container) {
- /* Survivors will be moved to visited space, so they should
- * have been marked as visited */
- assert(IS_IN_VISITED(gc, gcstate->visited_space));
- PyObject *op = FROM_GC(gc);
- assert(_PyObject_GC_IS_TRACKED(op));
- if (_Py_IsImmortal(op)) {
- PyGC_Head *next = GC_NEXT(gc);
- gc_list_move(gc, &get_gc_state()->permanent_generation.head);
- gc = next;
- continue;
- }
- traverseproc traverse = Py_TYPE(op)->tp_traverse;
- (void) traverse(op,
- visit_add_to_container,
- &arg);
- gc = GC_NEXT(gc);
- }
- return arg.size;
+static void
+move_unvisited(PyObject *op, WorkStack *stack, int visited_space)
+{
+ move_to_stack(op, stack, visited_space);
+}
+
+#define MOVE_UNVISITED(O, T, V) if ((O) != NULL) move_unvisited((O), (T), (V))
+
+/* A traversal callback for adding to container */
+static int
+visit_add_to_container(PyObject *op, void *arg)
+{
+ OBJECT_STAT_INC(object_visits);
+ WorkStack *stack = (WorkStack *)arg;
+ assert(stack->visited_space == get_gc_state()->visited_space);
+ move_to_stack(op, stack, stack->visited_space);
+ return 0;
}
/* Do bookkeeping for a completed GC cycle */
gc_list_set_space(&gcstate->old[not_visited].head, not_visited);
}
assert(gc_list_is_empty(&gcstate->old[visited].head));
- gcstate->work_to_do = 0;
gcstate->phase = GC_PHASE_MARK;
}
-static intptr_t
-move_to_reachable(PyObject *op, PyGC_Head *reachable, int visited_space)
-{
- if (op != NULL && !_Py_IsImmortal(op) && _PyObject_IS_GC(op)) {
- PyGC_Head *gc = AS_GC(op);
- if (_PyObject_GC_IS_TRACKED(op) &&
- gc_old_space(gc) != visited_space) {
- gc_flip_old_space(gc);
- gc_list_move(gc, reachable);
- return 1;
+static void
+frame_move_unvisited(_PyInterpreterFrame *frame, WorkStack *stack, int visited_space)
+{
+ _PyStackRef *locals = frame->localsplus;
+ _PyStackRef *sp = frame->stackpointer;
+ if (frame->f_locals != NULL) {
+ move_unvisited(frame->f_locals, stack, visited_space);
+ }
+ PyObject *func = PyStackRef_AsPyObjectBorrow(frame->f_funcobj);
+ move_unvisited(func, stack, visited_space);
+ while (sp > locals) {
+ sp--;
+ _PyStackRef ref = *sp;
+ if (!PyStackRef_IsNull(ref)) {
+ PyObject *op = PyStackRef_AsPyObjectBorrow(ref);
+ if (!_Py_IsImmortal(op)) {
+ move_unvisited(op, stack, visited_space);
+ }
}
}
- return 0;
}
-static intptr_t
-mark_all_reachable(PyGC_Head *reachable, PyGC_Head *visited, int visited_space)
+static Py_ssize_t
+move_all_transitively_reachable(WorkStack *stack, PyGC_Head *visited, int visited_space)
{
// Transitively traverse all objects from reachable, until empty
- struct container_and_flag arg = {
- .container = reachable,
- .visited_space = visited_space,
- .size = 0
- };
- while (!gc_list_is_empty(reachable)) {
- PyGC_Head *gc = _PyGCHead_NEXT(reachable);
+ Py_ssize_t objects_marked = 0;
+ while (stack->top != NULL) {
+ PyGC_Head *gc = pop_from_stack(stack);
assert(gc_old_space(gc) == visited_space);
- gc_list_move(gc, visited);
+ gc_list_append(gc, visited);
+ objects_marked++;
PyObject *op = FROM_GC(gc);
- traverseproc traverse = Py_TYPE(op)->tp_traverse;
- (void) traverse(op,
- visit_add_to_container,
- &arg);
+ assert(PyObject_IS_GC(op));
+ assert(_PyObject_GC_IS_TRACKED(op));
+ if (_Py_IsImmortal(op)) {
+ _PyObject_GC_UNTRACK(op);
+ }
+ else {
+ traverseproc traverse = Py_TYPE(op)->tp_traverse;
+ (void) traverse(op, visit_add_to_container, stack);
+ }
}
gc_list_validate_space(visited, visited_space);
- return arg.size;
+ return objects_marked;
}
static intptr_t
mark_stacks(PyInterpreterState *interp, PyGC_Head *visited, int visited_space, bool start)
{
- PyGC_Head reachable;
- gc_list_init(&reachable);
- Py_ssize_t objects_marked = 0;
+ WorkStack stack;
+ stack.top = NULL;
+ stack.visited_space = visited_space;
// Move all objects on stacks to reachable
_PyRuntimeState *runtime = &_PyRuntime;
HEAD_LOCK(runtime);
frame = frame->previous;
continue;
}
- _PyStackRef *locals = frame->localsplus;
- _PyStackRef *sp = frame->stackpointer;
- objects_marked += move_to_reachable(frame->f_locals, &reachable, visited_space);
- PyObject *func = PyStackRef_AsPyObjectBorrow(frame->f_funcobj);
- objects_marked += move_to_reachable(func, &reachable, visited_space);
- while (sp > locals) {
- sp--;
- if (PyStackRef_IsNull(*sp)) {
- continue;
- }
- PyObject *op = PyStackRef_AsPyObjectBorrow(*sp);
- if (!_Py_IsImmortal(op) && _PyObject_IS_GC(op)) {
- PyGC_Head *gc = AS_GC(op);
- if (_PyObject_GC_IS_TRACKED(op) &&
- gc_old_space(gc) != visited_space) {
- gc_flip_old_space(gc);
- objects_marked++;
- gc_list_move(gc, &reachable);
- }
- }
- }
+ frame_move_unvisited(frame, &stack, visited_space);
if (!start && frame->visited) {
// If this frame has already been visited, then the lower frames
// will have already been visited and will not have changed
ts = PyThreadState_Next(ts);
HEAD_UNLOCK(runtime);
}
- objects_marked += mark_all_reachable(&reachable, visited, visited_space);
- assert(gc_list_is_empty(&reachable));
+ Py_ssize_t objects_marked = move_all_transitively_reachable(&stack, visited, visited_space);
+ assert(stack.top == NULL);
return objects_marked;
}
static intptr_t
mark_global_roots(PyInterpreterState *interp, PyGC_Head *visited, int visited_space)
{
- PyGC_Head reachable;
- gc_list_init(&reachable);
- Py_ssize_t objects_marked = 0;
- objects_marked += move_to_reachable(interp->sysdict, &reachable, visited_space);
- objects_marked += move_to_reachable(interp->builtins, &reachable, visited_space);
- objects_marked += move_to_reachable(interp->dict, &reachable, visited_space);
+ WorkStack stack;
+ stack.top = NULL;
+ stack.visited_space = visited_space;
+ MOVE_UNVISITED(interp->sysdict, &stack, visited_space);
+ MOVE_UNVISITED(interp->builtins, &stack, visited_space);
+ MOVE_UNVISITED(interp->dict, &stack, visited_space);
struct types_state *types = &interp->types;
for (int i = 0; i < _Py_MAX_MANAGED_STATIC_BUILTIN_TYPES; i++) {
- objects_marked += move_to_reachable(types->builtins.initialized[i].tp_dict, &reachable, visited_space);
- objects_marked += move_to_reachable(types->builtins.initialized[i].tp_subclasses, &reachable, visited_space);
+ MOVE_UNVISITED(types->builtins.initialized[i].tp_dict, &stack, visited_space);
+ MOVE_UNVISITED(types->builtins.initialized[i].tp_subclasses, &stack, visited_space);
}
for (int i = 0; i < _Py_MAX_MANAGED_STATIC_EXT_TYPES; i++) {
- objects_marked += move_to_reachable(types->for_extensions.initialized[i].tp_dict, &reachable, visited_space);
- objects_marked += move_to_reachable(types->for_extensions.initialized[i].tp_subclasses, &reachable, visited_space);
+ MOVE_UNVISITED(types->for_extensions.initialized[i].tp_dict, &stack, visited_space);
+ MOVE_UNVISITED(types->for_extensions.initialized[i].tp_subclasses, &stack, visited_space);
}
- objects_marked += mark_all_reachable(&reachable, visited, visited_space);
- assert(gc_list_is_empty(&reachable));
+ Py_ssize_t objects_marked = move_all_transitively_reachable(&stack, visited, visited_space);
+ assert(stack.top == NULL);
return objects_marked;
}
PyGC_Head *visited = &gcstate->old[gcstate->visited_space].head;
Py_ssize_t objects_marked = mark_global_roots(tstate->interp, visited, gcstate->visited_space);
objects_marked += mark_stacks(tstate->interp, visited, gcstate->visited_space, true);
- gcstate->work_to_do -= objects_marked;
gcstate->phase = GC_PHASE_COLLECT;
validate_spaces(gcstate);
return objects_marked;
}
+
+/* See InternalDocs/garbage_collector.md for more details. */
+#define MAX_HEAP_PORTION_MULTIPLIER 5
+#define MARKING_PROGRESS_MULTIPLIER 2
+
static intptr_t
assess_work_to_do(GCState *gcstate)
{
- /* The amount of work we want to do depends on three things.
+ /* The amount of work we want to do depends on two things.
* 1. The number of new objects created
- * 2. The growth in heap size since the last collection
- * 3. The heap size (up to the number of new objects, to avoid quadratic effects)
- *
- * For a steady state heap, the amount of work to do is three times the number
- * of new objects added to the heap. This ensures that we stay ahead in the
- * worst case of all new objects being garbage.
- *
- * This could be improved by tracking survival rates, but it is still a
- * large improvement on the non-marking approach.
+ * 2. The heap size (up to a multiple of the number of new objects, to avoid quadratic effects)
*/
intptr_t scale_factor = gcstate->old[0].threshold;
if (scale_factor < 2) {
scale_factor = 2;
}
intptr_t new_objects = gcstate->young.count;
- intptr_t max_heap_fraction = new_objects*3/2;
- intptr_t heap_fraction = gcstate->heap_size / SCAN_RATE_DIVISOR / scale_factor;
- if (heap_fraction > max_heap_fraction) {
- heap_fraction = max_heap_fraction;
+ intptr_t max_heap_portion = new_objects * MAX_HEAP_PORTION_MULTIPLIER;
+ intptr_t heap_portion = gcstate->heap_size / SCAN_RATE_DIVISOR / scale_factor;
+ if (heap_portion > max_heap_portion) {
+ heap_portion = max_heap_portion;
}
gcstate->young.count = 0;
- return new_objects + heap_fraction;
+ return new_objects + heap_portion;
}
static void
if (gcstate->phase == GC_PHASE_MARK) {
Py_ssize_t objects_marked = mark_at_start(tstate);
GC_STAT_ADD(1, objects_transitively_reachable, objects_marked);
- gcstate->work_to_do -= objects_marked;
+ gcstate->work_to_do -= objects_marked * MARKING_PROGRESS_MULTIPLIER;
validate_spaces(gcstate);
return;
}
PyGC_Head *not_visited = &gcstate->old[gcstate->visited_space^1].head;
PyGC_Head *visited = &gcstate->old[gcstate->visited_space].head;
- PyGC_Head increment;
- gc_list_init(&increment);
- int scale_factor = gcstate->old[0].threshold;
- if (scale_factor < 2) {
- scale_factor = 2;
- }
intptr_t objects_marked = mark_stacks(tstate->interp, visited, gcstate->visited_space, false);
GC_STAT_ADD(1, objects_transitively_reachable, objects_marked);
- gcstate->work_to_do -= objects_marked;
+ gcstate->work_to_do -= objects_marked * MARKING_PROGRESS_MULTIPLIER;
gc_list_set_space(&gcstate->young.head, gcstate->visited_space);
- gc_list_merge(&gcstate->young.head, &increment);
+ PyGC_Head increment;
+ gc_list_init(&increment);
+ WorkStack working;
+ working.top = 0;
+ working.visited_space = gcstate->visited_space;
+ move_list_to_stack(&gcstate->young.head, &working);
+ Py_ssize_t increment_size = move_all_transitively_reachable(&working, &increment, gcstate->visited_space);
gc_list_validate_space(&increment, gcstate->visited_space);
- Py_ssize_t increment_size = gc_list_size(&increment);
+ assert(working.top == NULL);
while (increment_size < gcstate->work_to_do) {
if (gc_list_is_empty(not_visited)) {
break;
}
PyGC_Head *gc = _PyGCHead_NEXT(not_visited);
- gc_list_move(gc, &increment);
- increment_size++;
- assert(!_Py_IsImmortal(FROM_GC(gc)));
gc_set_old_space(gc, gcstate->visited_space);
- increment_size += expand_region_transitively_reachable(&increment, gc, gcstate);
+ push_to_stack(gc, &working);
+ assert(!_Py_IsImmortal(FROM_GC(gc)));
+ increment_size += move_all_transitively_reachable(&working, &increment, gcstate->visited_space);
+ assert(working.top == NULL);
}
+ assert(increment_size == gc_list_size(&increment));
GC_STAT_ADD(1, objects_not_transitively_reachable, increment_size);
validate_list(&increment, collecting_clear_unreachable_clear);
gc_list_validate_space(&increment, gcstate->visited_space);
gc_collect_region(tstate, &increment, &survivors, stats);
gc_list_merge(&survivors, visited);
assert(gc_list_is_empty(&increment));
- gcstate->work_to_do += gcstate->heap_size / SCAN_RATE_DIVISOR / scale_factor;
gcstate->work_to_do -= increment_size;
add_stats(gcstate, 1, stats);
gcstate->old[0].count = 0;
gcstate->old[1].count = 0;
completed_scavenge(gcstate);
+ gcstate->work_to_do = -gcstate->young.threshold;
_PyGC_ClearAllFreeLists(tstate->interp);
validate_spaces(gcstate);
add_stats(gcstate, 2, stats);
projects / thirdparty / Python / cpython.git / commitdiff
