# Copyright (c) 2017-present, Facebook, Inc.
# All rights reserved.
#
# This source code is licensed under the license found in the LICENSE file in
# the root directory of this source tree. An additional grant of patent rights
# can be found in the PATENTS file in the same directory.
import math
import torch.nn.functional as F
from fairseq import utils
from . import FairseqCriterion, register_criterion
[docs]@register_criterion('adaptive_loss')
class AdaptiveLoss(FairseqCriterion):
"""This is an implementation of the loss function accompanying the adaptive softmax approximation for
graphical processing units (GPU), described in the paper "Efficient softmax approximation for GPUs"
(http://arxiv.org/abs/1609.04309)."""
def __init__(self, args, task):
super().__init__(args, task)
if args.ddp_backend == 'c10d':
raise Exception(
'AdaptiveLoss is not compatible with the c10d '
'version of DistributedDataParallel. Please use '
'`--ddp-backend=no_c10d` instead.'
)
[docs] 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
"""
assert hasattr(model.decoder, 'adaptive_softmax') and model.decoder.adaptive_softmax is not None
adaptive_softmax = model.decoder.adaptive_softmax
net_output = model(**sample['net_input'])
orig_target = model.get_targets(sample, net_output)
nsentences = orig_target.size(0)
orig_target = orig_target.view(-1)
bsz = orig_target.size(0)
logits, target = adaptive_softmax(net_output[0], orig_target)
assert len(target) == len(logits)
loss = net_output[0].new(1 if reduce else bsz).zero_()
for i in range(len(target)):
if target[i] is not None:
assert (target[i].min() >= 0 and target[i].max() <= logits[i].size(1))
loss += F.cross_entropy(
logits[i],
target[i],
ignore_index=self.padding_idx,
reduction='sum' if reduce else 'none',
)
orig = utils.strip_pad(orig_target, self.padding_idx)
ntokens = orig.numel()
sample_size = sample['target'].size(0) if self.args.sentence_avg else ntokens
logging_output = {
'loss': utils.item(loss.data) if reduce else loss.data,
'ntokens': ntokens,
'nsentences': nsentences,
'sample_size': sample_size,
}
return loss, sample_size, logging_output
[docs] @staticmethod
def aggregate_logging_outputs(logging_outputs):
"""Aggregate logging outputs from data parallel training."""
loss_sum = sum(log.get('loss', 0) for log in logging_outputs)
ntokens = sum(log.get('ntokens', 0) for log in logging_outputs)
nsentences = sum(log.get('nsentences', 0) for log in logging_outputs)
sample_size = sum(log.get('sample_size', 0) for log in logging_outputs)
agg_output = {
'loss': loss_sum / sample_size / math.log(2),
'nll_loss': loss_sum / sample_size / math.log(2),
'ntokens': ntokens,
'nsentences': nsentences,
'sample_size': sample_size,
}
if sample_size != ntokens:
agg_output['nll_loss'] = loss_sum / ntokens / math.log(2)
return agg_output