>>> import torch
>>> import gc
>>> _ = torch.randn(1, device='cuda')
>>> del _
>>> torch.cuda.synchronize()
>>> gc.collect()
0
>>> print(torch.cuda.memory_allocated())
865280
>>> x = torch.randn(1, device='cuda', requires_grad=True)
>>> y = x.tanh()
>>> y.backward(torch.ones_like(y), create_graph=True)
>>> del x, y
>>> torch.cuda.synchronize()
>>> gc.collect()
0
>>> print(torch.cuda.memory_allocated())
867328