Source code for transformers.optimization_tf

# 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)."""


import re

import tensorflow as tf


[docs]class WarmUp(tf.keras.optimizers.schedules.LearningRateSchedule): """Applys 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().__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, }
[docs]def create_optimizer(init_lr, num_train_steps, num_warmup_steps): """Creates an optimizer with learning rate schedule.""" # Implements linear decay of the learning rate. learning_rate_fn = tf.keras.optimizers.schedules.PolynomialDecay( initial_learning_rate=init_lr, decay_steps=num_train_steps, end_learning_rate=0.0 ) if num_warmup_steps: learning_rate_fn = WarmUp( initial_learning_rate=init_lr, decay_schedule_fn=learning_rate_fn, warmup_steps=num_warmup_steps ) optimizer = AdamWeightDecay( learning_rate=learning_rate_fn, weight_decay_rate=0.01, beta_1=0.9, beta_2=0.999, epsilon=1e-6, exclude_from_weight_decay=["layer_norm", "bias"], ) return optimizer
[docs]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().__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
[docs] @classmethod def from_config(cls, config): """Creates an optimizer from its config with WarmUp custom object.""" custom_objects = {"WarmUp": WarmUp} return super().from_config(config, custom_objects=custom_objects)
def _prepare_local(self, var_device, var_dtype, apply_state): super()._prepare_local(var_device, var_dtype, apply_state) apply_state["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["weight_decay_rate"], use_locking=self._use_locking ) return tf.no_op()
[docs] def apply_gradients(self, grads_and_vars, clip_norm, name=None): grads, tvars = list(zip(*grads_and_vars)) (grads, _) = tf.clip_by_global_norm(grads, clip_norm=clip_norm) return super().apply_gradients(zip(grads, tvars))
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()._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()._resource_apply_sparse(grad, var, indices, **kwargs)
[docs] def get_config(self): config = super().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
# Inspired from https://github.com/OpenNMT/OpenNMT-tf/blob/master/opennmt/optimizers/utils.py
[docs]class GradientAccumulator(object): """Distribution strategies-aware gradient accumulation utility.""" def __init__(self): """Initializes the accumulator.""" self._gradients = [] self._accum_steps = tf.Variable( initial_value=0, dtype=tf.int64, trainable=False, aggregation=tf.VariableAggregation.ONLY_FIRST_REPLICA ) @property def step(self): """Number of accumulated steps.""" return self._accum_steps.value() @property def gradients(self): """The accumulated gradients.""" return list( gradient.value() if gradient is not None else gradient for gradient in self._get_replica_gradients() ) def __call__(self, gradients): """Accumulates :obj:`gradients`.""" if not self._gradients: self._gradients.extend( [ tf.Variable(tf.zeros_like(gradient), trainable=False) if gradient is not None else gradient for gradient in gradients ] ) if len(gradients) != len(self._gradients): raise ValueError("Expected %s gradients, but got %d" % (len(self._gradients), len(gradients))) for accum_gradient, gradient in zip(self._get_replica_gradients(), gradients): if accum_gradient is not None: accum_gradient.assign_add(gradient) self._accum_steps.assign_add(1) def reset(self): """Resets the accumulated gradients.""" if self._gradients: self._accum_steps.assign(0) for gradient in self._get_replica_gradients(): if gradient is not None: gradient.assign(tf.zeros_like(gradient)) def _get_replica_gradients(self): if tf.distribute.has_strategy(): # In a replica context, we want to accumulate gradients on each replica # without synchronization, so we directly assign the value of the # current replica. replica_context = tf.distribute.get_replica_context() if replica_context is None or tf.distribute.get_strategy().num_replicas_in_sync == 1: return self._gradients return ( gradient.device_map.select_for_current_replica(gradient.values, replica_context) for gradient in self._gradients ) else: return self._gradients