fix: caching allocator behaviour for quantization.

src/diffusers/models/model_loading_utils.py

@@ -726,23 +726,29 @@ def _caching_allocator_warmup(
     very large margin.
     """
     factor = 2 if hf_quantizer is None else hf_quantizer.get_cuda_warm_up_factor()
-    # Remove disk and cpu devices, and cast to proper torch.device
+
+    # Keep only accelerator devices
     accelerator_device_map = {
         param: torch.device(device)
         for param, device in expanded_device_map.items()
         if str(device) not in ["cpu", "disk"]
     }
-    total_byte_count = defaultdict(lambda: 0)
+    if not accelerator_device_map:
+        return
+
+    elements_per_device = defaultdict(int)
     for param_name, device in accelerator_device_map.items():
         try:
-            param = model.get_parameter(param_name)
+            p = model.get_parameter(param_name)
         except AttributeError:
-            param = model.get_buffer(param_name)
-        # The dtype of different parameters may be different with composite models or `keep_in_fp32_modules`
-        param_byte_count = param.numel() * param.element_size()
+            try:
+                p = model.get_buffer(param_name)
+            except AttributeError:
+                raise AttributeError(f"Parameter {param_name} not found in model")
         # TODO: account for TP when needed.
-        total_byte_count[device] += param_byte_count
+        elements_per_device[device] += p.numel()
 
     # This will kick off the caching allocator to avoid having to Malloc afterwards
-    for device, byte_count in total_byte_count.items():
-        _ = torch.empty(byte_count // factor, dtype=dtype, device=device, requires_grad=False)
+    for device, elem_count in elements_per_device.items():
+        warmup_elems = max(1, elem_count // factor)
+        _ = torch.empty(warmup_elems, dtype=dtype, device=device, requires_grad=False)