Remove batch norm weight decay + a few other fixes (tensorflow#2755)

Author: nealwu

official/resnet/imagenet_main.py

@@ -184,10 +184,11 @@ def resnet_model_fn(features, labels, mode, params):
   tf.identity(cross_entropy, name='cross_entropy')
   tf.summary.scalar('cross_entropy', cross_entropy)
 
-  # Add weight decay to the loss. We perform weight decay on all trainable
-  # variables, which includes batch norm beta and gamma variables.
+  # Add weight decay to the loss. We exclude the batch norm variables because
+  # doing so leads to a small improvement in accuracy.
   loss = cross_entropy + _WEIGHT_DECAY * tf.add_n(
-      [tf.nn.l2_loss(v) for v in tf.trainable_variables()])
+      [tf.nn.l2_loss(v) for v in tf.trainable_variables()
+       if 'batch_normalization' not in v.name])
 
   if mode == tf.estimator.ModeKeys.TRAIN:
     # Scale the learning rate linearly with the batch size. When the batch size

official/resnet/resnet_model.py

@@ -242,8 +242,8 @@ def cifar10_resnet_v2_generator(resnet_size, num_classes, data_format=None):
   def model(inputs, is_training):
     """Constructs the ResNet model given the inputs."""
     if data_format == 'channels_first':
-      # Convert from channels_last (NHWC) to channels_first (NCHW). This
-      # provides a large performance boost on GPU. See
+      # Convert the inputs from channels_last (NHWC) to channels_first (NCHW).
+      # This provides a large performance boost on GPU. See
       # https://www.tensorflow.org/performance/performance_guide#data_formats
       inputs = tf.transpose(inputs, [0, 3, 1, 2])
 
@@ -302,8 +302,9 @@ def imagenet_resnet_v2_generator(block_fn, layers, num_classes,
   def model(inputs, is_training):
     """Constructs the ResNet model given the inputs."""
     if data_format == 'channels_first':
-      # Convert from channels_last (NHWC) to channels_first (NCHW). This
-      # provides a large performance boost on GPU.
+      # Convert the inputs from channels_last (NHWC) to channels_first (NCHW).
+      # This provides a large performance boost on GPU. See
+      # https://www.tensorflow.org/performance/performance_guide#data_formats
       inputs = tf.transpose(inputs, [0, 3, 1, 2])
 
     inputs = conv2d_fixed_padding(