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# Copyright (c) 2022, NVIDIA CORPORATION. All rights reserved.
"""BERT model."""
import torch
from megatron import get_args
from megatron.core import tensor_parallel
from megatron.model.enums import AttnMaskType
from megatron.model.language_model import parallel_lm_logits
from megatron.model.language_model import get_language_model
from megatron.model import LayerNorm
from megatron.model.utils import openai_gelu, erf_gelu
from megatron.model.utils import get_linear_layer
from megatron.model.utils import init_method_normal
from megatron.model.utils import scaled_init_method_normal
from .module import MegatronModule
def bert_extended_attention_mask(attention_mask):
# We create a 3D attention mask from a 2D tensor mask.
# [b, 1, s]
attention_mask_b1s = attention_mask.unsqueeze(1)
# [b, s, 1]
attention_mask_bs1 = attention_mask.unsqueeze(2)
# [b, s, s]
attention_mask_bss = attention_mask_b1s * attention_mask_bs1
# [b, 1, s, s]
extended_attention_mask = attention_mask_bss.unsqueeze(1)
# Convert attention mask to binary:
extended_attention_mask = (extended_attention_mask < 0.5)
return extended_attention_mask
def bert_position_ids(token_ids):
# Create position ids
seq_length = token_ids.size(1)
position_ids = torch.arange(seq_length, dtype=torch.long,
device=token_ids.device)
position_ids = position_ids.unsqueeze(0).expand_as(token_ids)
return position_ids
class BertLMHead(MegatronModule):
"""Masked LM head for Bert
Arguments:
config: TransformerConfig object
mpu_vocab_size: model parallel size of vocabulary.
hidden_size: hidden size
parallel_output: whether output logits being distributed or not.
"""
def __init__(self, mpu_vocab_size, hidden_size, config, parallel_output):
super().__init__(config=config)
args = get_args()
self.bias = torch.nn.Parameter(torch.zeros(mpu_vocab_size))
tensor_parallel.set_tensor_model_parallel_attributes(self.bias, True, 0, 1)
self.parallel_output = parallel_output
self.dense = get_linear_layer(hidden_size, hidden_size, config.init_method, gather_params_on_init=args.zero_stage == 3)
setattr(self.dense.weight, 'sequence_parallel', config.sequence_parallel)
setattr(self.dense.bias, 'sequence_parallel', config.sequence_parallel)
self.layernorm = LayerNorm(hidden_size,
eps=config.layernorm_epsilon,
sequence_parallel=config.sequence_parallel)
self.gelu = torch.nn.functional.gelu
if args.openai_gelu:
self.gelu = openai_gelu
elif args.onnx_safe:
self.gelu = erf_gelu
def forward(self, hidden_states, word_embeddings_weight):
hidden_states = self.dense(hidden_states)
hidden_states = self.gelu(hidden_states)
hidden_states = self.layernorm(hidden_states)
output = parallel_lm_logits(hidden_states,
word_embeddings_weight,
self.parallel_output,
bias=self.bias)
return output
def post_language_model_processing(lm_output, pooled_output,
lm_head, binary_head,
lm_labels,
logit_weights,
fp16_lm_cross_entropy):
# Output.
lm_logits = lm_head(
lm_output, logit_weights)
binary_logits = None
if binary_head is not None:
binary_logits = binary_head(pooled_output)
if lm_labels is None:
# [s b h] => [b s h]
return lm_logits.transpose(0,1).contiguous(), binary_logits
else:
# [b s] => [s b]
lm_labels = lm_labels.transpose(0,1).contiguous()
# lm_logits : [s, b, h] and lm_labels: [s, b]
if fp16_lm_cross_entropy:
assert lm_logits.dtype == torch.half
lm_loss = tensor_parallel.vocab_parallel_cross_entropy(lm_logits, lm_labels)
else:
lm_loss = tensor_parallel.vocab_parallel_cross_entropy(lm_logits.float(),
lm_labels)
# [s, b] => [b s]
lm_loss = lm_loss.transpose(0,1).contiguous()
return lm_loss, binary_logits
class BertModel(MegatronModule):
"""Bert Language model."""
def __init__(self,
config,
num_tokentypes=2,
add_binary_head=True,
parallel_output=True,
pre_process=True,
post_process=True,
return_moe_loss=False):
super().__init__(config=config)
args = get_args()
# TODO this option is not yet implemented in BERT
assert args.untie_embeddings_and_output_weights is False
self.fp16_lm_cross_entropy = args.fp16_lm_cross_entropy
self.add_binary_head = add_binary_head
self.parallel_output = parallel_output
self.pre_process = pre_process
self.post_process = post_process
self.return_moe_loss = return_moe_loss
self.return_embeddings = args.output_bert_embeddings
if self.return_embeddings:
assert self.post_process and self.add_binary_head
self.language_model, self._language_model_key = get_language_model(
config=config,
num_tokentypes=num_tokentypes,
add_pooler=self.add_binary_head,
encoder_attn_mask_type=AttnMaskType.padding,
pre_process=self.pre_process,
post_process=self.post_process,
num_experts=args.num_experts,
)
self.initialize_word_embeddings()
if self.post_process:
self.lm_head = BertLMHead(self.shared_embedding_or_output_weight().size(0), config.hidden_size,
config, parallel_output)
self._lm_head_key = 'lm_head'
self.binary_head = None
if self.add_binary_head:
self.binary_head = get_linear_layer(config.hidden_size, 2,
config.init_method,
args.zero_stage == 3)
self._binary_head_key = 'binary_head'
def set_input_tensor(self, input_tensor):
"""See megatron.model.transformer.set_input_tensor()"""
self.language_model.set_input_tensor(input_tensor)
def forward(self, bert_model_input, attention_mask,
tokentype_ids=None, lm_labels=None):
extended_attention_mask = bert_extended_attention_mask(attention_mask)
input_ids = bert_model_input
position_ids = bert_position_ids(input_ids)
lm_output = self.language_model(
input_ids,
position_ids,
extended_attention_mask,
tokentype_ids=tokentype_ids
)
if self.post_process and self.add_binary_head:
lm_output, pooled_output, moe_losses = lm_output
# Return pooled output (e.g., when computing Bert embeddings).
if self.return_embeddings:
# Sum attention mask.
embeddings = torch.transpose(lm_output, 0, 1)
masks = torch.sum(attention_mask, dim=1)
# Collect masked embeddings.
output = torch.zeros(
size=(embeddings.shape[0], embeddings.shape[2]),
dtype=torch.float32,
device=torch.cuda.current_device())
for i, (embedding, mask) in enumerate(zip(embeddings, masks)):
output[i, :] = torch.mean(embedding[1: mask - 1], dim=0)
return output
else:
pooled_output = None
if self.post_process:
if not self.add_binary_head:
lm_output, moe_losses = lm_output
lm_output = post_language_model_processing(lm_output, pooled_output,
self.lm_head, self.binary_head,
lm_labels,
self.shared_embedding_or_output_weight(),
self.fp16_lm_cross_entropy)
return *lm_output, moe_losses if self.return_moe_loss else lm_output
else:
return lm_output
def state_dict_for_save_checkpoint(self, prefix='', keep_vars=False):
"""For easy load when model is combined with other heads,
add an extra key."""
state_dict_ = {}
state_dict_[self._language_model_key] \
= self.language_model.state_dict_for_save_checkpoint(prefix=prefix,
keep_vars=keep_vars)
if self.post_process:
state_dict_[self._lm_head_key] \
= self.lm_head.state_dict_for_save_checkpoint(prefix=prefix,
keep_vars=keep_vars)
if self.post_process and self.add_binary_head:
state_dict_[self._binary_head_key] \
= self.binary_head.state_dict(prefix=prefix, keep_vars=keep_vars)
# Save word_embeddings.
if self.post_process and not self.pre_process:
state_dict_[self._word_embeddings_for_head_key] \
= self.word_embeddings.state_dict(prefix=prefix, keep_vars=keep_vars)
return state_dict_
def load_state_dict(self, state_dict, strict=True):
"""Customized load."""
self.language_model.load_state_dict(
state_dict[self._language_model_key], strict=strict)
if self.post_process:
self.lm_head.load_state_dict(
state_dict[self._lm_head_key], strict=strict)
if self.post_process and self.add_binary_head:
self.binary_head.load_state_dict(
state_dict[self._binary_head_key], strict=strict)
# Load word_embeddings.
if self.post_process and not self.pre_process:
self.word_embeddings.load_state_dict(
state_dict[self._word_embeddings_for_head_key], strict=strict)
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