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gh-142183: Cache one datachunk per tstate to prevent alloc/dealloc thrashing (#145789)

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Cache one datachunk per tstate to prevent alloc/dealloc thrashing when repeatedly hitting the same call depth at exactly the wrong boundary.

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Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
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T. Wouters 2026-03-11 15:46:16 +01:00 • committed by GitHub
parent 4722202a1a
commit 706fd4ec08
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3 changed files with 28 additions and 4 deletions
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30
Python/pystate.c
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@ -1564,6 +1564,7 @@ init_threadstate(_PyThreadStateImpl *_tstate,
tstate->datastack_chunk = NULL;
tstate->datastack_top = NULL;
tstate->datastack_limit = NULL;
tstate->datastack_cached_chunk = NULL;
tstate->what_event = -1;
tstate->current_executor = NULL;
tstate->jit_exit = NULL;
@ -1714,6 +1715,11 @@ clear_datastack(PyThreadState *tstate)
_PyObject_VirtualFree(chunk, chunk->size);
chunk = prev;
}
if (tstate->datastack_cached_chunk != NULL) {
_PyObject_VirtualFree(tstate->datastack_cached_chunk,
tstate->datastack_cached_chunk->size);
tstate->datastack_cached_chunk = NULL;
}
}
void
@ -3045,9 +3051,20 @@ push_chunk(PyThreadState *tstate, int size)
while (allocate_size < (int)sizeof(PyObject*)*(size + MINIMUM_OVERHEAD)) {
allocate_size *= 2;
}
_PyStackChunk *new = allocate_chunk(allocate_size, tstate->datastack_chunk);
if (new == NULL) {
return NULL;
_PyStackChunk *new;
if (tstate->datastack_cached_chunk != NULL
&& (size_t)allocate_size <= tstate->datastack_cached_chunk->size)
{
new = tstate->datastack_cached_chunk;
tstate->datastack_cached_chunk = NULL;
new->previous = tstate->datastack_chunk;
new->top = 0;
}
else {
new = allocate_chunk(allocate_size, tstate->datastack_chunk);
if (new == NULL) {
return NULL;
}
}
if (tstate->datastack_chunk) {
tstate->datastack_chunk->top = tstate->datastack_top -
@ -3083,12 +3100,17 @@ _PyThreadState_PopFrame(PyThreadState *tstate, _PyInterpreterFrame * frame)
if (base == &tstate->datastack_chunk->data[0]) {
_PyStackChunk *chunk = tstate->datastack_chunk;
_PyStackChunk *previous = chunk->previous;
_PyStackChunk *cached = tstate->datastack_cached_chunk;
// push_chunk ensures that the root chunk is never popped:
assert(previous);
tstate->datastack_top = &previous->data[previous->top];
tstate->datastack_chunk = previous;
_PyObject_VirtualFree(chunk, chunk->size);
tstate->datastack_limit = (PyObject **)(((char *)previous) + previous->size);
chunk->previous = NULL;
if (cached != NULL) {
_PyObject_VirtualFree(cached, cached->size);
}
tstate->datastack_cached_chunk = chunk;
}
else {
assert(tstate->datastack_top);