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gh-100240: Use a consistent implementation for freelists (#121934)

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This combines and updates our freelist handling to use a consistent
implementation. Objects in the freelist are linked together using the
first word of memory block.

If configured with freelists disabled, these operations are essentially
no-ops.
This commit is contained in:
Sam Gross 2024-07-22 12:08:27 -04:00 • committed by GitHub
parent 2408a8a22b
commit 5716cc3529
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GPG key ID: B5690EEEBB952194
27 changed files with 295 additions and 705 deletions
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48
Python/object_stack.c
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@ -8,24 +8,11 @@
extern _PyObjectStackChunk *_PyObjectStackChunk_New(void);
extern void _PyObjectStackChunk_Free(_PyObjectStackChunk *);
static struct _Py_object_stack_freelist *
get_object_stack_freelist(void)
{
struct _Py_object_freelists *freelists = _Py_object_freelists_GET();
return &freelists->object_stacks;
}
_PyObjectStackChunk *
_PyObjectStackChunk_New(void)
{
_PyObjectStackChunk *buf;
struct _Py_object_stack_freelist *obj_stack_freelist = get_object_stack_freelist();
if (obj_stack_freelist->numfree > 0) {
buf = obj_stack_freelist->items;
obj_stack_freelist->items = buf->prev;
obj_stack_freelist->numfree--;
}
else {
_PyObjectStackChunk *buf = _Py_FREELIST_POP_MEM(object_stack_chunks);
if (buf == NULL) {
// NOTE: we use PyMem_RawMalloc() here because this is used by the GC
// during mimalloc heap traversal. In that context, it is not safe to
// allocate mimalloc memory, such as via PyMem_Malloc().
@ -43,17 +30,7 @@ void
_PyObjectStackChunk_Free(_PyObjectStackChunk *buf)
{
assert(buf->n == 0);
struct _Py_object_stack_freelist *obj_stack_freelist = get_object_stack_freelist();
if (obj_stack_freelist->numfree >= 0 &&
obj_stack_freelist->numfree < _PyObjectStackChunk_MAXFREELIST)
{
buf->prev = obj_stack_freelist->items;
obj_stack_freelist->items = buf;
obj_stack_freelist->numfree++;
}
else {
PyMem_RawFree(buf);
}
_Py_FREELIST_FREE(object_stack_chunks, buf, PyMem_RawFree);
}
void
@ -87,22 +64,3 @@ _PyObjectStack_Merge(_PyObjectStack *dst, _PyObjectStack *src)
dst->head = src->head;
src->head = NULL;
}
void
_PyObjectStackChunk_ClearFreeList(struct _Py_object_freelists *freelists, int is_finalization)
{
if (!is_finalization) {
// Ignore requests to clear the free list during GC. We use object
// stacks during GC, so emptying the free-list is counterproductive.
return;
}
struct _Py_object_stack_freelist *freelist = &freelists->object_stacks;
while (freelist->numfree > 0) {
_PyObjectStackChunk *buf = freelist->items;
freelist->items = buf->prev;
freelist->numfree--;
PyMem_RawFree(buf);
}
freelist->numfree = -1;
}