[core] fix group offloading when using torchao (#13276)

* fix group offloading when using torchao

* switch to swap_tensors.

* up

* address feedback.

* error out for the offload to disk option.

Author: sayakpaul

src/diffusers/hooks/group_offloading.py

@@ -22,7 +22,7 @@
 import safetensors.torch
 import torch
 
-from ..utils import get_logger, is_accelerate_available
+from ..utils import get_logger, is_accelerate_available, is_torchao_available
 from ._common import _GO_LC_SUPPORTED_PYTORCH_LAYERS
 from .hooks import HookRegistry, ModelHook
 
@@ -35,6 +35,54 @@
 logger = get_logger(__name__)  # pylint: disable=invalid-name
 
 
+def _is_torchao_tensor(tensor: torch.Tensor) -> bool:
+    if not is_torchao_available():
+        return False
+    from torchao.utils import TorchAOBaseTensor
+
+    return isinstance(tensor, TorchAOBaseTensor)
+
+
+def _get_torchao_inner_tensor_names(tensor: torch.Tensor) -> list[str]:
+    """Get names of all internal tensor data attributes from a TorchAO tensor."""
+    cls = type(tensor)
+    names = list(getattr(cls, "tensor_data_names", []))
+    for attr_name in getattr(cls, "optional_tensor_data_names", []):
+        if getattr(tensor, attr_name, None) is not None:
+            names.append(attr_name)
+    return names
+
+
+def _swap_torchao_tensor(param: torch.Tensor, source: torch.Tensor) -> None:
+    """Move a TorchAO parameter to the device of `source` via `swap_tensors`.
+
+    `param.data = source` does not work for `_make_wrapper_subclass` tensors because the `.data` setter only replaces
+    the outer wrapper storage while leaving the subclass's internal attributes (e.g. `.qdata`, `.scale`) on the
+    original device. `swap_tensors` swaps the full tensor contents in-place, preserving the parameter's identity so
+    that any dict keyed by `id(param)` remains valid.
+
+    Refer to https://github.com/huggingface/diffusers/pull/13276#discussion_r2944471548 for the full discussion.
+    """
+    torch.utils.swap_tensors(param, source)
+
+
+def _restore_torchao_tensor(param: torch.Tensor, source: torch.Tensor) -> None:
+    """Restore internal tensor data of a TorchAO parameter from `source` without mutating `source`.
+
+    Unlike `_swap_torchao_tensor` this copies attribute references one-by-one via `setattr` so that `source` is **not**
+    modified. Use this when `source` is a cached tensor that must remain unchanged (e.g. a pinned CPU copy in
+    `cpu_param_dict`).
+    """
+    for attr_name in _get_torchao_inner_tensor_names(source):
+        setattr(param, attr_name, getattr(source, attr_name))
+
+
+def _record_stream_torchao_tensor(param: torch.Tensor, stream) -> None:
+    """Record stream for all internal tensors of a TorchAO parameter."""
+    for attr_name in _get_torchao_inner_tensor_names(param):
+        getattr(param, attr_name).record_stream(stream)
+
+
 # fmt: off
 _GROUP_OFFLOADING = "group_offloading"
 _LAYER_EXECUTION_TRACKER = "layer_execution_tracker"
@@ -124,24 +172,29 @@ def __init__(
             else torch.cuda
         )
 
+    @staticmethod
+    def _to_cpu(tensor, low_cpu_mem_usage):
+        # For TorchAO tensors, `.data` returns an incomplete wrapper without internal attributes
+        # (e.g. `.qdata`, `.scale`), so we must call `.cpu()` on the tensor directly.
+        t = tensor.cpu() if _is_torchao_tensor(tensor) else tensor.data.cpu()
+        return t if low_cpu_mem_usage else t.pin_memory()
+
     def _init_cpu_param_dict(self):
         cpu_param_dict = {}
         if self.stream is None:
             return cpu_param_dict
 
         for module in self.modules:
             for param in module.parameters():
-                cpu_param_dict[param] = param.data.cpu() if self.low_cpu_mem_usage else param.data.cpu().pin_memory()
+                cpu_param_dict[param] = self._to_cpu(param, self.low_cpu_mem_usage)
             for buffer in module.buffers():
-                cpu_param_dict[buffer] = (
-                    buffer.data.cpu() if self.low_cpu_mem_usage else buffer.data.cpu().pin_memory()
-                )
+                cpu_param_dict[buffer] = self._to_cpu(buffer, self.low_cpu_mem_usage)
 
         for param in self.parameters:
-            cpu_param_dict[param] = param.data.cpu() if self.low_cpu_mem_usage else param.data.cpu().pin_memory()
+            cpu_param_dict[param] = self._to_cpu(param, self.low_cpu_mem_usage)
 
         for buffer in self.buffers:
-            cpu_param_dict[buffer] = buffer.data.cpu() if self.low_cpu_mem_usage else buffer.data.cpu().pin_memory()
+            cpu_param_dict[buffer] = self._to_cpu(buffer, self.low_cpu_mem_usage)
 
         return cpu_param_dict
 
@@ -157,9 +210,16 @@ def _pinned_memory_tensors(self):
             pinned_dict = None
 
     def _transfer_tensor_to_device(self, tensor, source_tensor, default_stream):
-        tensor.data = source_tensor.to(self.onload_device, non_blocking=self.non_blocking)
+        moved = source_tensor.to(self.onload_device, non_blocking=self.non_blocking)
+        if _is_torchao_tensor(tensor):
+            _swap_torchao_tensor(tensor, moved)
+        else:
+            tensor.data = moved
         if self.record_stream:
-            tensor.data.record_stream(default_stream)
+            if _is_torchao_tensor(tensor):
+                _record_stream_torchao_tensor(tensor, default_stream)
+            else:
+                tensor.data.record_stream(default_stream)
 
     def _process_tensors_from_modules(self, pinned_memory=None, default_stream=None):
         for group_module in self.modules:
@@ -178,7 +238,19 @@ def _process_tensors_from_modules(self, pinned_memory=None, default_stream=None)
             source = pinned_memory[buffer] if pinned_memory else buffer.data
             self._transfer_tensor_to_device(buffer, source, default_stream)
 
+    def _check_disk_offload_torchao(self):
+        all_tensors = list(self.tensor_to_key.keys())
+        has_torchao = any(_is_torchao_tensor(t) for t in all_tensors)
+        if has_torchao:
+            raise ValueError(
+                "Disk offloading is not supported for TorchAO quantized tensors because safetensors "
+                "cannot serialize TorchAO subclass tensors. Use memory offloading instead by not "
+                "setting `offload_to_disk_path`."
+            )
+
     def _onload_from_disk(self):
+        self._check_disk_offload_torchao()
+
         if self.stream is not None:
             # Wait for previous Host->Device transfer to complete
             self.stream.synchronize()
@@ -221,6 +293,8 @@ def _onload_from_memory(self):
                 self._process_tensors_from_modules(None)
 
     def _offload_to_disk(self):
+        self._check_disk_offload_torchao()
+
         # TODO: we can potentially optimize this code path by checking if the _all_ the desired
         # safetensor files exist on the disk and if so, skip this step entirely, reducing IO
         # overhead. Currently, we just check if the given `safetensors_file_path` exists and if not
@@ -245,18 +319,35 @@ def _offload_to_memory(self):
 
             for group_module in self.modules:
                 for param in group_module.parameters():
-                    param.data = self.cpu_param_dict[param]
+                    if _is_torchao_tensor(param):
+                        _restore_torchao_tensor(param, self.cpu_param_dict[param])
+                    else:
+                        param.data = self.cpu_param_dict[param]
             for param in self.parameters:
-                param.data = self.cpu_param_dict[param]
+                if _is_torchao_tensor(param):
+                    _restore_torchao_tensor(param, self.cpu_param_dict[param])
+                else:
+                    param.data = self.cpu_param_dict[param]
             for buffer in self.buffers:
-                buffer.data = self.cpu_param_dict[buffer]
+                if _is_torchao_tensor(buffer):
+                    _restore_torchao_tensor(buffer, self.cpu_param_dict[buffer])
+                else:
+                    buffer.data = self.cpu_param_dict[buffer]
         else:
             for group_module in self.modules:
                 group_module.to(self.offload_device, non_blocking=False)
             for param in self.parameters:
-                param.data = param.data.to(self.offload_device, non_blocking=False)
+                if _is_torchao_tensor(param):
+                    moved = param.to(self.offload_device, non_blocking=False)
+                    _swap_torchao_tensor(param, moved)
+                else:
+                    param.data = param.data.to(self.offload_device, non_blocking=False)
             for buffer in self.buffers:
-                buffer.data = buffer.data.to(self.offload_device, non_blocking=False)
+                if _is_torchao_tensor(buffer):
+                    moved = buffer.to(self.offload_device, non_blocking=False)
+                    _swap_torchao_tensor(buffer, moved)
+                else:
+                    buffer.data = buffer.data.to(self.offload_device, non_blocking=False)
 
     @torch.compiler.disable()
     def onload_(self):