Get high conventional memory usage when torch loads model to GPU

I have specified map_location to GPU:0 and expect that video memory would go high. But I found conventional memory usage is 1.5GB and video memory usage 550MB.

# record memory usage here as baseline.

# the size of model file is about 15MB
self.device = torch.device('cuda:0')
self.model = torch.load('weights/', map_location=self.device)['model'].float().eval()

# check the increment of memory usage here.

Why does torch.load consume so much conventional memory? Is there something wrong in my code?