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# Copyright 2019 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Functions and classes related to optimization (weight updates)."""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
import re
from absl import logging
import gin
import tensorflow as tf
import tensorflow_addons.optimizers as tfa_optimizers
class WarmUp(tf.keras.optimizers.schedules.LearningRateSchedule):
"""Applies a warmup schedule on a given learning rate decay schedule."""
def __init__(self,
initial_learning_rate,
decay_schedule_fn,
warmup_steps,
power=1.0,
name=None):
super(WarmUp, self).__init__()
self.initial_learning_rate = initial_learning_rate
self.warmup_steps = warmup_steps
self.power = power
self.decay_schedule_fn = decay_schedule_fn
self.name = name
def __call__(self, step):
with tf.name_scope(self.name or 'WarmUp') as name:
# Implements polynomial warmup. i.e., if global_step < warmup_steps, the
# learning rate will be `global_step/num_warmup_steps * init_lr`.
global_step_float = tf.cast(step, tf.float32)
warmup_steps_float = tf.cast(self.warmup_steps, tf.float32)
warmup_percent_done = global_step_float / warmup_steps_float
warmup_learning_rate = (
self.initial_learning_rate *
tf.math.pow(warmup_percent_done, self.power))
return tf.cond(
global_step_float < warmup_steps_float,
lambda: warmup_learning_rate,
lambda: self.decay_schedule_fn(step),
name=name)
def get_config(self):
return {
'initial_learning_rate': self.initial_learning_rate,
'decay_schedule_fn': self.decay_schedule_fn,
'warmup_steps': self.warmup_steps,
'power': self.power,
'name': self.name
}
@gin.configurable
def create_optimizer(init_lr,
num_train_steps,
num_warmup_steps,
end_lr=0.0,
optimizer_type='adamw'):
"""Creates an optimizer with learning rate schedule."""
# Implements linear decay of the learning rate.
lr_schedule = tf.keras.optimizers.schedules.PolynomialDecay(
initial_learning_rate=init_lr,
decay_steps=num_train_steps,
end_learning_rate=end_lr)
if num_warmup_steps:
lr_schedule = WarmUp(
initial_learning_rate=init_lr,
decay_schedule_fn=lr_schedule,
warmup_steps=num_warmup_steps)
if optimizer_type == 'adamw':
logging.info('using Adamw optimizer')
optimizer = AdamWeightDecay(
learning_rate=lr_schedule,
weight_decay_rate=0.01,
beta_1=0.9,
beta_2=0.999,
epsilon=1e-6,
exclude_from_weight_decay=['LayerNorm', 'layer_norm', 'bias'])
elif optimizer_type == 'lamb':
logging.info('using Lamb optimizer')
optimizer = tfa_optimizers.LAMB(
learning_rate=lr_schedule,
weight_decay_rate=0.01,
beta_1=0.9,
beta_2=0.999,
epsilon=1e-6,
exclude_from_weight_decay=['LayerNorm', 'layer_norm', 'bias'])
else:
raise ValueError('Unsupported optimizer type: ', optimizer_type)
return optimizer
class AdamWeightDecay(tf.keras.optimizers.Adam):
"""Adam enables L2 weight decay and clip_by_global_norm on gradients.
Just adding the square of the weights to the loss function is *not* the
correct way of using L2 regularization/weight decay with Adam, since that will
interact with the m and v parameters in strange ways.
Instead we want ot decay the weights in a manner that doesn't interact with
the m/v parameters. This is equivalent to adding the square of the weights to
the loss with plain (non-momentum) SGD.
"""
def __init__(self,
learning_rate=0.001,
beta_1=0.9,
beta_2=0.999,
epsilon=1e-7,
amsgrad=False,
weight_decay_rate=0.0,
include_in_weight_decay=None,
exclude_from_weight_decay=None,
name='AdamWeightDecay',
**kwargs):
super(AdamWeightDecay, self).__init__(learning_rate, beta_1, beta_2,
epsilon, amsgrad, name, **kwargs)
self.weight_decay_rate = weight_decay_rate
self._include_in_weight_decay = include_in_weight_decay
self._exclude_from_weight_decay = exclude_from_weight_decay
@classmethod
def from_config(cls, config):
"""Creates an optimizer from its config with WarmUp custom object."""
custom_objects = {'WarmUp': WarmUp}
return super(AdamWeightDecay, cls).from_config(
config, custom_objects=custom_objects)
def _prepare_local(self, var_device, var_dtype, apply_state):
super(AdamWeightDecay, self)._prepare_local(var_device, var_dtype,
apply_state)
apply_state[(var_device, var_dtype)]['weight_decay_rate'] = tf.constant(
self.weight_decay_rate, name='adam_weight_decay_rate')
def _decay_weights_op(self, var, learning_rate, apply_state):
do_decay = self._do_use_weight_decay(var.name)
if do_decay:
return var.assign_sub(
learning_rate * var *
apply_state[(var.device, var.dtype.base_dtype)]['weight_decay_rate'],
use_locking=self._use_locking)
return tf.no_op()
def apply_gradients(self,
grads_and_vars,
name=None,
experimental_aggregate_gradients=True):
grads, tvars = list(zip(*grads_and_vars))
if experimental_aggregate_gradients:
# when experimental_aggregate_gradients = False, apply_gradients() no
# longer implicitly allreduce gradients, users manually allreduce gradient
# and passed the allreduced grads_and_vars. For now, the
# clip_by_global_norm will be moved to before the explicit allreduce to
# keep the math the same as TF 1 and pre TF 2.2 implementation.
(grads, _) = tf.clip_by_global_norm(grads, clip_norm=1.0)
return super(AdamWeightDecay, self).apply_gradients(
zip(grads, tvars),
name=name,
experimental_aggregate_gradients=experimental_aggregate_gradients)
def _get_lr(self, var_device, var_dtype, apply_state):
"""Retrieves the learning rate with the given state."""
if apply_state is None:
return self._decayed_lr_t[var_dtype], {}
apply_state = apply_state or {}
coefficients = apply_state.get((var_device, var_dtype))
if coefficients is None:
coefficients = self._fallback_apply_state(var_device, var_dtype)
apply_state[(var_device, var_dtype)] = coefficients
return coefficients['lr_t'], dict(apply_state=apply_state)
def _resource_apply_dense(self, grad, var, apply_state=None):
lr_t, kwargs = self._get_lr(var.device, var.dtype.base_dtype, apply_state)
decay = self._decay_weights_op(var, lr_t, apply_state)
with tf.control_dependencies([decay]):
return super(AdamWeightDecay,
self)._resource_apply_dense(grad, var, **kwargs)
def _resource_apply_sparse(self, grad, var, indices, apply_state=None):
lr_t, kwargs = self._get_lr(var.device, var.dtype.base_dtype, apply_state)
decay = self._decay_weights_op(var, lr_t, apply_state)
with tf.control_dependencies([decay]):
return super(AdamWeightDecay,
self)._resource_apply_sparse(grad, var, indices, **kwargs)
def get_config(self):
config = super(AdamWeightDecay, self).get_config()
config.update({
'weight_decay_rate': self.weight_decay_rate,
})
return config
def _do_use_weight_decay(self, param_name):
"""Whether to use L2 weight decay for `param_name`."""
if self.weight_decay_rate == 0:
return False
if self._include_in_weight_decay:
for r in self._include_in_weight_decay:
if re.search(r, param_name) is not None:
return True
if self._exclude_from_weight_decay:
for r in self._exclude_from_weight_decay:
if re.search(r, param_name) is not None:
return False
return True
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