# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
import logging
import math
from collections.abc import Collection
from dataclasses import dataclass, field
from typing import List
import torch
import torch.distributed as dist
import torch.optim
from fairseq.dataclass import FairseqDataclass
from fairseq.optim import FairseqOptimizer, register_optimizer
from fairseq.optim.fused_adam import get_fused_adam_class
from omegaconf import II, DictConfig
logger = logging.getLogger(__name__)
@dataclass
class FairseqAdamConfig(FairseqDataclass):
adam_betas: str = field(
default="(0.9, 0.999)", metadata={"help": "betas for Adam optimizer"}
)
adam_eps: float = field(
default=1e-8, metadata={"help": "epsilon for Adam optimizer"}
)
weight_decay: float = field(default=0.0, metadata={"help": "weight decay"})
use_old_adam: bool = field(
default=False, metadata={"help": "Use fairseq.optim.adam.Adam"}
)
# TODO common vars below in parent
tpu: bool = II("common.tpu")
lr: List[float] = II("optimization.lr")
@register_optimizer("adam", dataclass=FairseqAdamConfig)
class FairseqAdam(FairseqOptimizer):
"""Adam optimizer for fairseq.
Important note: this optimizer corresponds to the "AdamW" variant of
Adam in its weight decay behavior. As such, it is most closely
analogous to torch.optim.AdamW from PyTorch.
"""
def __init__(self, cfg: DictConfig, params):
super().__init__(cfg)
fused_adam_cls = get_fused_adam_class()
use_fused_adam = (
not getattr(cfg, "use_old_adam", False)
and fused_adam_cls is not None
and torch.cuda.is_available()
)
if getattr(cfg, "tpu", False):
# on TPUs we use the Adam defined here, since it
# automatically casts gradients to FP32
self._optimizer = Adam(params, **self.optimizer_config)
elif use_fused_adam:
logger.info("using FusedAdam")
self._optimizer = fused_adam_cls(params, **self.optimizer_config)
else:
self._optimizer = Adam(params, **self.optimizer_config)
@property
def optimizer_config(self):
"""
Return a kwarg dictionary that will be used to override optimizer
args stored in checkpoints. This allows us to load a checkpoint and
resume training using a different set of optimizer args, e.g., with a
different learning rate.
"""
return {
"lr": self.cfg.lr[0]
if isinstance(self.cfg.lr, Collection)
else self.cfg.lr,
"betas": eval(self.cfg.adam_betas),
"eps": self.cfg.adam_eps,
"weight_decay": self.cfg.weight_decay,
}
def average_params(self):
"""Reduce Params is only used during BMUF distributed training."""
state_dict = self.optimizer.state_dict()
total_gpus = float(dist.get_world_size())
for _, value in state_dict["state"].items():
value["exp_avg"] /= total_gpus
value["exp_avg_sq"] /= total_gpus
dist.all_reduce(value["exp_avg"], op=dist.ReduceOp.SUM)
dist.all_reduce(value["exp_avg_sq"], op=dist.ReduceOp.SUM)
class Adam(torch.optim.Optimizer):
r"""Implements Adam algorithm.
This implementation is modified from torch.optim.Adam based on:
`Fixed Weight Decay Regularization in Adam`
(see https://arxiv.org/abs/1711.05101)
It has been proposed in `Adam: A Method for Stochastic Optimization`_.
Args:
params (iterable): iterable of parameters to optimize or dicts defining
parameter groups
lr (float, optional): learning rate (default: 1e-3)
betas (Tuple[float, float], optional): coefficients used for computing
running averages of gradient and its square (default: (0.9, 0.999))
eps (float, optional): term added to the denominator to improve
numerical stability (default: 1e-8)
weight_decay (float, optional): weight decay (L2 penalty) (default: 0)
amsgrad (boolean, optional): whether to use the AMSGrad variant of this
algorithm from the paper `On the Convergence of Adam and Beyond`_
.. _Adam\: A Method for Stochastic Optimization:
https://arxiv.org/abs/1412.6980
.. _On the Convergence of Adam and Beyond:
https://openreview.net/forum?id=ryQu7f-RZ
"""
def __init__(
self,
params,
lr=1e-3,
betas=(0.9, 0.999),
eps=1e-8,
weight_decay=0,
amsgrad=False,
):
defaults = dict(
lr=lr, betas=betas, eps=eps, weight_decay=weight_decay, amsgrad=amsgrad
)
super(Adam, self).__init__(params, defaults)
@property
def supports_memory_efficient_fp16(self):
return True
@property
def supports_flat_params(self):
return True
def step(self, closure=None):
"""Performs a single optimization step.
Args:
closure (callable, optional): A closure that reevaluates the model
and returns the loss.
"""
loss = None
if closure is not None:
loss = closure()
for group in self.param_groups:
for p in group["params"]:
if p.grad is None:
continue
grad = p.grad.data
if grad.dtype in {torch.float16, torch.bfloat16}:
grad = grad.float()
if grad.is_sparse:
raise RuntimeError(
"Adam does not support sparse gradients, please consider SparseAdam instead"
)
amsgrad = group.get("amsgrad", False)
p_data_fp32 = p.data
if p.data.dtype in {torch.float16, torch.bfloat16}:
p_data_fp32 = p_data_fp32.float()
state = self.state[p]
# State initialization
if len(state) == 0:
state["step"] = 0
# Exponential moving average of gradient values
state["exp_avg"] = torch.zeros_like(p_data_fp32)
# Exponential moving average of squared gradient values
state["exp_avg_sq"] = torch.zeros_like(p_data_fp32)
if amsgrad:
# Maintains max of all exp. moving avg. of sq. grad. values
state["max_exp_avg_sq"] = torch.zeros_like(p_data_fp32)
else:
state["exp_avg"] = state["exp_avg"].to(p_data_fp32)
state["exp_avg_sq"] = state["exp_avg_sq"].to(p_data_fp32)
if amsgrad:
state["max_exp_avg_sq"] = state["max_exp_avg_sq"].to(
p_data_fp32
)
exp_avg, exp_avg_sq = state["exp_avg"], state["exp_avg_sq"]
if amsgrad:
max_exp_avg_sq = state["max_exp_avg_sq"]
beta1, beta2 = group["betas"]
state["step"] += 1
# Decay the first and second moment running average coefficient
exp_avg.mul_(beta1).add_(grad, alpha=1 - beta1)
exp_avg_sq.mul_(beta2).addcmul_(grad, grad, value=1 - beta2)
if amsgrad:
# Maintains the maximum of all 2nd moment running avg. till now
torch.max(max_exp_avg_sq, exp_avg_sq, out=max_exp_avg_sq)
# Use the max. for normalizing running avg. of gradient
denom = max_exp_avg_sq.sqrt().add_(group["eps"])
else:
denom = exp_avg_sq.sqrt().add_(group["eps"])
bias_correction1 = 1 - beta1 ** state["step"]
bias_correction2 = 1 - beta2 ** state["step"]
step_size = group["lr"] * math.sqrt(bias_correction2) / bias_correction1
if group["weight_decay"] != 0:
p_data_fp32.add_(
p_data_fp32, alpha=-group["weight_decay"] * group["lr"]
)
p_data_fp32.addcdiv_(exp_avg, denom, value=-step_size)
if p.data.dtype in {torch.float16, torch.bfloat16}:
p.data.copy_(p_data_fp32)
return loss