[hotfix] the bug of numel() in ColoTensor (#845)

colossalai/tensor/colo_tensor.py

+from numpy import product
 import torch
-from .op_wrapper import _COLOSSAL_OPS
 from typing import Tuple
+import numpy
+from .op_wrapper import _COLOSSAL_OPS
 
 
 class ColoTensor(object):
@@ -31,7 +33,7 @@ class ColoTensor(object):
         self._torch_tensor = torch_tensor
 
     def numel(self):
-        return sum(self._size)
+        return product(self._size)
 
     @staticmethod
     def init_from_torch_tensor(tensor: torch.Tensor, save_payload=True) -> 'ColoTensor':
@@ -44,9 +46,17 @@ class ColoTensor(object):
         return colo_t
 
     def del_torch_tensor(self, save_shape=False) -> None:
-        if save_shape:
+        """
+        delete the payload of the torch tensor.
+
+        Args:
+            save_shape (bool, optional): if saving the shape of the torch_tensor. 
+            If saving the shape, the size of self._torch_tensor is inconsist with the self._size.
+            Defaults to False.
+        """
+        if not save_shape:
             self._size = (0,)
-        self._torch_tensor = torch.empty((0,))
+        self._torch_tensor = torch.empty((0,), device=self._device, dtype=self._dtype)
 
     def torch_tensor(self) -> torch.Tensor:
         if self._torch_tensor.numel() == 0:

tests/test_tensor/test_op.py

@@ -3,6 +3,7 @@ import torch
 from colossalai.tensor import ColoTensor
 from copy import deepcopy
 
+
 def test_linear():
     in_dim = 4
     out_dim = 5
@@ -44,6 +45,7 @@ def test_linear():
 #     torch.nn.init.uniform_(t)
 #     print(t)
 
+
 def test_element_wise():
     t_ref = torch.randn(3, 5)
     t = ColoTensor.init_from_torch_tensor(t_ref.clone())
@@ -59,10 +61,12 @@ def test_no_wrap_op():
     assert torch.sum(t) == torch.sum(t_ref)
     assert torch.sum(input=t) == torch.sum(input=t_ref)
 
+
 def test_lazy_init_tensor():
     lazy_t = ColoTensor(2, 3, dtype=torch.float32, requires_grad=True)
     assert lazy_t._torch_tensor.numel() == 0
-    assert lazy_t.torch_tensor().numel() == 6
+    assert lazy_t.numel() == 6 == lazy_t.torch_tensor().numel()
+
 
 def check_all():
     test_linear()
@@ -70,5 +74,6 @@ def check_all():
     test_no_wrap_op()
     test_lazy_init_tensor()
 
+
 if __name__ == '__main__':
-    check_all()
+    test_lazy_init_tensor()