Related: #125583 pointed out that dtype was not being preserved for wrapper subclasses through multiprocessing serialization (or serialization in general).

When implementing the dtype fix, I realized that there are other args not being passed to _make_wrapper_subclass() when rebuilding subclass instances after serialization:

Signature:

_make_wrapper_subclass(
    PyObject* cls,
    SymIntArrayRef size,
    SymIntArrayRef? strides=None,
    SymInt? storage_offset=None,
    MemoryFormat? memory_format=None,  # not preserved
    ScalarType dtype=None,
    Layout layout=torch.strided,
    Device device=None,
    bool pin_memory=False,  # not preserved
    bool requires_grad=False,
    c10::string_view? dispatch_sizes_strides_policy=None,  # not preserved
    bool dispatch_device=False,  # not preserved
    bool dispatch_layout=False,  # not preserved
    DispatchKeySet _extra_dispatch_keys=None  # not preserved
)

Of those not passed, pin_memory() status can be queried by is_pinned(), but the others are not directly queryable to my knowledge. For full correctness, all these args should be preserved through serialization. @albanD has pointed out that this requires tricky changes to the serialization format.

cc @mruberry @mikaylagawarecki @msaroufim @ezyang @albanD