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# 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 math
import torch
import torch.nn.functional as F
from fairseq import metrics, utils
from fairseq.criterions import FairseqCriterion, register_criterion
from fairseq.criterions.label_smoothed_cross_entropy import label_smoothed_nll_loss
@register_criterion("label_smoothed_cross_entropy_r3f")
class LabelSmoothedCrossEntropyR3FCriterion(FairseqCriterion):
def __init__(
self, task, sentence_avg, label_smoothing, eps, r3f_lambda, noise_type
):
super().__init__(task)
self.sentence_avg = sentence_avg
self.label_smoothing = label_smoothing
self.eps = eps
self.r3f_lambda = r3f_lambda
self.noise_type = noise_type
if self.noise_type in {"normal"}:
self.noise_sampler = torch.distributions.normal.Normal(
loc=0.0, scale=self.eps
)
elif self.noise_type == "uniform":
self.noise_sampler = torch.distributions.uniform.Uniform(
low=-self.eps, high=self.eps
)
else:
raise Exception(f"unrecognized noise type {self.noise_type}")
@staticmethod
def add_args(parser):
"""Add criterion-specific arguments to the parser."""
# fmt: off
parser.add_argument('--label-smoothing', default=0., type=float, metavar='D',
help='epsilon for label smoothing, 0 means no label smoothing')
parser.add_argument('--eps', type=float, default=1e-5,
help='noise eps')
parser.add_argument('--r3f-lambda', type=float, default=1.0,
help='lambda for combining logistic loss and noisy KL loss')
parser.add_argument('--noise-type', type=str, default='normal',
choices=['normal', 'uniform'],
help='type of noises')
# fmt: on
def _get_symm_kl(self, noised_logits, input_logits):
return (
F.kl_div(
F.log_softmax(noised_logits, dim=-1, dtype=torch.float32),
F.softmax(input_logits, dim=-1, dtype=torch.float32),
None,
None,
"sum",
)
+ F.kl_div(
F.log_softmax(input_logits, dim=-1, dtype=torch.float32),
F.softmax(noised_logits, dim=-1, dtype=torch.float32),
None,
None,
"sum",
)
) / noised_logits.size(0)
def forward(self, model, sample, reduce=True):
"""Compute the loss for the given sample.
Returns a tuple with three elements:
1) the loss
2) the sample size, which is used as the denominator for the gradient
3) logging outputs to display while training
"""
token_embeddings = model.encoder.embed_tokens(sample["net_input"]["src_tokens"])
input_logits, extra = model(**sample["net_input"])
loss, nll_loss = self.compute_loss(
model, (input_logits, extra), sample, reduce=reduce
)
sample_size = (
sample["target"].size(0) if self.sentence_avg else sample["ntokens"]
)
if model.training:
noise = self.noise_sampler.sample(sample_shape=token_embeddings.shape).to(
token_embeddings
)
noised_embeddings = token_embeddings.clone() + noise
noised_logits, _ = model(
**sample["net_input"], token_embeddings=noised_embeddings
)
symm_kl = self._get_symm_kl(noised_logits, input_logits)
if model.training:
symm_kl = symm_kl * sample_size
loss = loss + self.r3f_lambda * symm_kl
logging_output = {
"loss": loss.data,
"nll_loss": nll_loss.data,
"ntokens": sample["ntokens"],
"nsentences": sample["target"].size(0),
"sample_size": sample_size,
}
if model.training:
logging_output.update(
symm_kl=utils.item(symm_kl.data) if reduce else symm_kl.data
)
return loss, sample_size, logging_output
def compute_loss(self, model, net_output, sample, reduce=True):
lprobs = model.get_normalized_probs(net_output, log_probs=True)
lprobs = lprobs.view(-1, lprobs.size(-1))
target = model.get_targets(sample, net_output).view(-1, 1)
loss, nll_loss = label_smoothed_nll_loss(
lprobs,
target,
self.label_smoothing,
ignore_index=self.padding_idx,
reduce=reduce,
)
return loss, nll_loss
@staticmethod
def reduce_metrics(logging_outputs) -> None:
"""Aggregate logging outputs from data parallel training."""
loss_sum = sum(log.get("loss", 0) for log in logging_outputs)
nll_loss_sum = sum(log.get("nll_loss", 0) for log in logging_outputs)
ntokens = sum(log.get("ntokens", 0) for log in logging_outputs)
sample_size = sum(log.get("sample_size", 0) for log in logging_outputs)
symm_kl_sum = sum(log.get("symm_kl", 0) for log in logging_outputs)
metrics.log_scalar("symm_kl", symm_kl_sum / sample_size, sample_size, round=3)
metrics.log_scalar(
"loss", loss_sum / sample_size / math.log(2), sample_size, round=3
)
metrics.log_scalar(
"nll_loss", nll_loss_sum / ntokens / math.log(2), ntokens, round=3
)
metrics.log_derived(
"ppl", lambda meters: utils.get_perplexity(meters["nll_loss"].avg)
)
@staticmethod
def logging_outputs_can_be_summed() -> bool:
"""
Whether the logging outputs returned by `forward` can be summed
across workers prior to calling `reduce_metrics`. Setting this
to True will improves distributed training speed.
"""
return True
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