code: def _defragment_memory(self):
      empty_addresses = sorted(self.contiguous_sizes.keys())
      tensor_addresses = sorted(self.tensor_addresses.values())
  
      tensor_index = 0
  
      while tensor_index < len(tensor_addresses):
          empty_addr = empty_addresses[0]
          empty_size = self.contiguous_sizes[empty_addr]
  
          tensor_addr = tensor_addresses[tensor_index]
          tensor_size = self.tensor_sizes[tensor_addr]
          tensor_id = self.tensor_ids[tensor_addr]
          tensor = self.tensor_map[self.tensor_ids[tensor_addr]]
  
          assert (
              tensor_size == tensor.numel()
          ), "Size mismatch. {tensor_size} is allocated at addr {tensor_addr} but tensor size is {tensor.numel()} "
  
          assert (
              empty_addr != tensor_addr
          ), f"Cannot have same empty address {empty_addr} and tensor address {tensor_addr}"
  
          if empty_addr < tensor_addr:
              if empty_size >= tensor_size:
                  dest_buffer = self.buffer.narrow(
                      0, empty_addr, tensor_size
                  )
                  src_buffer = self.buffer.narrow(
                      0, tensor_addr, tensor_size
                  )
                  dest_buffer.data.copy_(src_buffer.data)
              else:
                  # print_rank_0(f'empty addr : {empty_addr}, empty size {empty_size} tensor addr {tensor_addr} tensor size {tensor_size}')
                  src_addr = tensor_addr
                  dest_addr = empty_addr
                  while src_addr < (tensor_addr + tensor_size):
                      copy_size = min(
                          empty_size,
                          tensor_addr + tensor_size - src_addr,
                      )
  
                      dest_buffer = self.buffer.narrow(
                          0, dest_addr, copy_size
                      )
                      src_buffer = self.buffer.narrow(
                          0, src_addr, copy_size
                      )
  
                      dest_buffer.data.copy_(src_buffer.data)
  
                      src_addr += copy_size
                      dest_addr += copy_size
  
              self._replace_old_address_with_new(tensor_id, empty_addr)
  
              tensor_index += 1
  
          else:
              tensor_index += 1
  
          empty_addresses = sorted(self.contiguous_sizes.keys())
  
imports: import torch
  from deepspeed import comm
label_desc: Use image node_id 12 for calling the ContiguousMemoryAllocator obj's underlying member method code with example usage: obj._defragment_memory() without return types