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gh-143421: Lazily allocate tracer code and opt buffers #143597

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Merged
Fidget-Spinner merged 2 commits into from
Jan 9, 2026
+34 −5
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gh-143421: Lazily allocate tracer code and opt buffers #143597

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fbbac65
Lazily allocate tracer code and opt buffers
Fidget-Spinner Jan 9, 2026
2354e78
Cut down locals and stack size
Fidget-Spinner Jan 9, 2026
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4 changes: 2 additions & 2 deletions Include/internal/pycore_optimizer_types.h
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Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,8 @@ extern "C" {

#include "pycore_uop.h" // UOP_MAX_TRACE_LENGTH

// Holds locals, stack, locals, stack ... co_consts (in that order)
#define MAX_ABSTRACT_INTERP_SIZE 4096
// Holds locals, stack, locals, stack ... (in that order)
#define MAX_ABSTRACT_INTERP_SIZE 512
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@markshannon markshannon Jan 9, 2026

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Why?

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@Fidget-Spinner Fidget-Spinner Jan 9, 2026

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This number was picked arbitrarily by me back then when I first wrote this. I now realise it's overkill. We don't need 3 pages of memory just to store locals and stack. It's slow and wastes memory.


#define TY_ARENA_SIZE (UOP_MAX_TRACE_LENGTH * 5)

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4 changes: 2 additions & 2 deletions Include/internal/pycore_tstate.h
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Expand Up @@ -56,8 +56,8 @@ typedef struct _PyJitTracerState {
_PyJitTracerInitialState initial_state;
_PyJitTracerPreviousState prev_state;
_PyJitTracerTranslatorState translator_state;
JitOptContext opt_context;
_PyUOpInstruction code_buffer[UOP_MAX_TRACE_LENGTH];
JitOptContext *opt_context;
_PyUOpInstruction *code_buffer;
} _PyJitTracerState;

#endif
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7 changes: 7 additions & 0 deletions Python/optimizer.c
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Expand Up @@ -1025,6 +1025,13 @@ _PyJit_TryInitializeTracing(
if (oparg > 0xFFFF) {
return 0;
}
if (_tstate->jit_tracer_state.code_buffer == NULL) {
_tstate->jit_tracer_state.code_buffer = (_PyUOpInstruction *)_PyObject_VirtualAlloc(UOP_BUFFER_SIZE);
if (_tstate->jit_tracer_state.code_buffer == NULL) {
// Don't error, just go to next instruction.
return 0;
}
}
PyObject *func = PyStackRef_AsPyObjectBorrow(frame->f_funcobj);
if (func == NULL) {
return 0;
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10 changes: 9 additions & 1 deletion Python/optimizer_analysis.c
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Expand Up @@ -345,7 +345,15 @@ optimize_uops(
assert(!PyErr_Occurred());
PyFunctionObject *func = tstate->jit_tracer_state.initial_state.func;

JitOptContext *ctx = &tstate->jit_tracer_state.opt_context;
JitOptContext *ctx = tstate->jit_tracer_state.opt_context;
if (ctx == NULL) {
ctx = (JitOptContext *)_PyObject_VirtualAlloc(sizeof(JitOptContext));
if (ctx == NULL) {
// Don't error, just bail.
return 0;
}
tstate->jit_tracer_state.opt_context = ctx;
}
uint32_t opcode = UINT16_MAX;

// Make sure that watchers are set up
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14 changes: 14 additions & 0 deletions Python/pystate.c
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Expand Up @@ -1553,6 +1553,8 @@ init_threadstate(_PyThreadStateImpl *_tstate,
init_policy(&_tstate->policy.jit.side_exit_initial_backoff,
"PYTHON_JIT_SIDE_EXIT_INITIAL_BACKOFF",
SIDE_EXIT_INITIAL_BACKOFF, 0, MAX_BACKOFF);
_tstate->jit_tracer_state.code_buffer = NULL;
_tstate->jit_tracer_state.opt_context = NULL;
#endif
tstate->delete_later = NULL;

Expand Down Expand Up @@ -1867,6 +1869,18 @@ tstate_delete_common(PyThreadState *tstate, int release_gil)
assert(tstate_impl->refcounts.values == NULL);
#endif

#if _Py_TIER2
_PyThreadStateImpl *_tstate = (_PyThreadStateImpl *)tstate;
if (_tstate->jit_tracer_state.code_buffer != NULL) {
_PyObject_VirtualFree(_tstate->jit_tracer_state.code_buffer, UOP_BUFFER_SIZE);
_tstate->jit_tracer_state.code_buffer = NULL;
}
if (_tstate->jit_tracer_state.opt_context != NULL) {
_PyObject_VirtualFree(_tstate->jit_tracer_state.opt_context, sizeof(JitOptContext));
_tstate->jit_tracer_state.opt_context = NULL;
}
#endif

HEAD_UNLOCK(runtime);

// XXX Unbind in PyThreadState_Clear(), or earlier
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