freelist optimization by youknowone · Pull Request #7337 · RustPython/RustPython

Add freelist_push/freelist_pop hooks to PyPayload trait with default
no-op implementations. Modify default_dealloc to offer dead objects
to the freelist before freeing memory. Modify PyRef::new_ref to try
popping from the freelist before allocating.

Implement thread-local freelist for PyFloat (max 100 entries).
Float objects are ideal candidates: fixed-size payload (f64),
no GC tracking, no instance dict, trivial Drop.

Benchmark improvement on float-heavy workloads:
  float_arith: ~12% faster
  float_list:  ~17% faster

Add HAS_FREELIST const to PyPayload trait. For freelist types, GC
untracking is done immediately (not deferred) during dealloc to
prevent race conditions when the object is reused.

Restructure new_ref so freelist-popped objects also get GC tracked,
enabling freelist support for GC-tracked types like PyList.

Add drop_in_place for old payload before writing new one, required
for types with non-trivial Drop (e.g. PyList's RwLock<Vec>).

Implement thread-local freelist for PyList (max 80 entries).

Add thread-local freelist for PyDict (max 80 entries).

Add heaptype check in default_dealloc to prevent subclass instances
from entering the freelist. Subclass objects have a different Python
type than the base type, so reusing them would return objects with
the wrong __class__.

Skip PyTuple freelist: structseq types (stat_result, struct_time)
are static subtypes sharing the same Rust payload, making type-safe
reuse impractical with heaptype check alone.

* Add object freelist infrastructure and PyFloat freelist

Add freelist_push/freelist_pop hooks to PyPayload trait with default
no-op implementations. Modify default_dealloc to offer dead objects
to the freelist before freeing memory. Modify PyRef::new_ref to try
popping from the freelist before allocating.

Implement thread-local freelist for PyFloat (max 100 entries).
Float objects are ideal candidates: fixed-size payload (f64),
no GC tracking, no instance dict, trivial Drop.

Benchmark improvement on float-heavy workloads:
  float_arith: ~12% faster
  float_list:  ~17% faster

* Add PyList freelist and GC-safe freelist infrastructure

Add HAS_FREELIST const to PyPayload trait. For freelist types, GC
untracking is done immediately (not deferred) during dealloc to
prevent race conditions when the object is reused.

Restructure new_ref so freelist-popped objects also get GC tracked,
enabling freelist support for GC-tracked types like PyList.

Add drop_in_place for old payload before writing new one, required
for types with non-trivial Drop (e.g. PyList's RwLock<Vec>).

Implement thread-local freelist for PyList (max 80 entries).

* Add PyDict freelist and exact-type guard for freelist push

Add thread-local freelist for PyDict (max 80 entries).

Add heaptype check in default_dealloc to prevent subclass instances
from entering the freelist. Subclass objects have a different Python
type than the base type, so reusing them would return objects with
the wrong __class__.

Skip PyTuple freelist: structseq types (stat_result, struct_time)
are static subtypes sharing the same Rust payload, making type-safe
reuse impractical with heaptype check alone.

* Add PySlice freelist (max 1, matching PySlice_MAXFREELIST)

* Add FreeList<T> wrapper to drain cached objects on thread teardown

Replace Cell<Vec<*mut PyObject>> with Cell<FreeList<T>> which implements
Drop to properly deallocate PyInner<T> when threads exit.
Also fix freelist_pop safety doc to match actual contract.

* Add manual Traverse impl for PySlice with clear() and fix comment

* Deduplicate allocation fallback in PyRef::new_ref