For a tensorflow SavedModel in pbtxt format, where is the device placement of an operation/node defined?

Question

I have a SavedModel with saved_model.pbtxt and variables\ which was pre-trained on a single GPU from this repo: https://github.com/sthalles/deeplab_v3. I'm trying to serve this SavedModel with tensorflow-serving, and it can only utilise GPU:0 in a multi-GPU machine. I learned from https://github.com/tensorflow/serving/issues/311 that tensorflow-serving loads the graph with tensorflow, and this model was trained on a single GPU. I tried to save the model with clear_devices=True flag but no help, still ran on GPU:0.

Then I try to read the GraphDef in saved_model.pbtxt, from https://www.tensorflow.org/guide/extend/model_files#device I know that the device assigned to one node/operation is defined in NodeDef.

My problem is, in this saved_model.pbtxt, only CPU was assigned for some operations/nodes in NodeDef as device: "/device:CPU:0", while no GPU was specifically assigned. All those operations executed on GPU don't have a device tag in their NodeDef.

I wonder where are the device placement infomation for GPU operations was saved in SavedModel and can I change the device info in a graph? Thanks for your help.

For example, in this saved_model.pbtxt a CPU op was defined as:

node {
     name: "save/RestoreV2/tensor_names"
     op: "Const"
     device: "/device:CPU:0"
     ...
     }

A computation op was:

node {
  name: "resnet_v2_50/block1/unit_1/bottleneck_v2/conv2/kernel/Regularizer/l2_regularizer"
  op: "Mul"
  input: "resnet_v2_50/block1/unit_1/bottleneck_v2/conv2/kernel/Regularizer/l2_regularizer/scale"
  input: "resnet_v2_50/block1/unit_1/bottleneck_v2/conv2/kernel/Regularizer/l2_regularizer/L2Loss"
  attr {
    key: "T"
    value {
      type: DT_FLOAT
    }
  }
  attr {
    key: "_class"
    value {
      list {
        s: "loc:@resnet_v2_50/block1/unit_1/bottleneck_v2/conv2/weights"
      }
    }
  }
  attr {
    key: "_output_shapes"
    value {
      list {
        shape {
        }
      }
    }
  }
}