Do fewer probes when growing stack limit

markshannon · markshannon · commit afac1e635be2 · 2025-02-12T11:07:59.000Z
diff --git a/Include/internal/pycore_ceval.h b/Include/internal/pycore_ceval.h
@@ -223,6 +223,7 @@ static inline void _Py_LeaveRecursiveCallTstate(PyThreadState *tstate) {
 }
 
 static inline int _Py_ReachedRecursionLimit(PyThreadState *tstate, int margin_count)  {
+    assert(tstate->c_stack_soft_limit != UINTPTR_MAX);
     char here;
     uintptr_t here_addr = (uintptr_t)&here;
     return here_addr <= tstate->c_stack_soft_limit + margin_count * PYOS_STACK_MARGIN_BYTES;
diff --git a/Python/ceval.c b/Python/ceval.c
@@ -332,10 +332,15 @@ _Py_CheckRecursiveCall(PyThreadState *tstate, const char *where)
             tstate->c_stack_soft_limit = here_addr - PYOS_STACK_MARGIN_BYTES;
             return 0;
         }
+        int margin = PYOS_STACK_MARGIN;
         assert(tstate->c_stack_soft_limit != UINTPTR_MAX);
-        int margin = PYOS_STACK_MARGIN*3/2;
-        while (margin > 0 && _PyOS_CheckStack(margin)) {
-            margin -= PYOS_STACK_MARGIN/2;
+        if (_PyOS_CheckStack(margin)) {
+            margin = PYOS_STACK_MARGIN/2;
+        }
+        else {
+            if (_PyOS_CheckStack(PYOS_STACK_MARGIN*3/2) == 0) {
+                margin = PYOS_STACK_MARGIN*3/2;
+            }
         }
         tstate->c_stack_hard_limit = here_addr - margin * sizeof(void *);
         tstate->c_stack_soft_limit = tstate->c_stack_hard_limit + PYOS_STACK_MARGIN_BYTES;

Original file line number	Diff line number	Diff line change
`@@ -223,6 +223,7 @@ static inline void _Py_LeaveRecursiveCallTstate(PyThreadState *tstate) {`
`223`	`223`	`}`
`224`	`224`
`225`	`225`	`static inline int _Py_ReachedRecursionLimit(PyThreadState *tstate, int margin_count) {`
	`226`	`+ assert(tstate->c_stack_soft_limit != UINTPTR_MAX);`
`226`	`227`	`char here;`
`227`	`228`	`uintptr_t here_addr = (uintptr_t)&here;`
`228`	`229`	`return here_addr <= tstate->c_stack_soft_limit + margin_count * PYOS_STACK_MARGIN_BYTES;`