#!/usr/bin/env python
import argparse
import gc
import os
import sys
from pathlib import Path
from typing import List # noqa: F401
import pytorch_lightning as pl
import torch
from finetune import SummarizationModule, TranslationModule
from finetune import main as ft_main
from make_student import create_student_by_copying_alternating_layers, get_layers_to_supervise
from torch import nn
from transformers import AutoModelForSeq2SeqLM, MBartTokenizer, T5ForConditionalGeneration
from transformers.models.bart.modeling_bart import shift_tokens_right
from utils import calculate_bleu, check_output_dir, freeze_params, label_smoothed_nll_loss, use_task_specific_params
# need the parent dir module
sys.path.insert(2, str(Path(__file__).resolve().parents[1]))
from lightning_base import generic_train # noqa
class SummarizationDistiller(SummarizationModule):
"""Supports T5, Bart, Pegasus and other models that inherit from Bart."""
loss_names = ["loss", "ce_loss", "mlm_loss", "hid_loss_enc", "hid_loss_dec"]
def __init__(self, hparams):
assert Path(hparams.data_dir).exists()
self.output_dir = Path(hparams.output_dir)
self.output_dir.mkdir(exist_ok=True)
save_dir = self.output_dir.joinpath("student")
hparams.model_name_or_path = str(save_dir) # Tell lightning we are training the student
teacher = AutoModelForSeq2SeqLM.from_pretrained(hparams.teacher).eval()
use_task_specific_params(teacher, hparams.task) # We copy good generation parameters to student by default
if hparams.student is not None:
student = AutoModelForSeq2SeqLM.from_pretrained(hparams.student)
use_task_specific_params(student, hparams.task)
e_layer_ids, d_layer_ids = None, None
else:
student, e_layer_ids, d_layer_ids = create_student_by_copying_alternating_layers(
teacher, e=hparams.student_encoder_layers, d=hparams.student_decoder_layers, save_path=save_dir
)
if hparams.length_penalty != -1:
student.config.length_penalty = hparams.length_penalty
hparams.tokenizer_name = hparams.teacher # Use teacher's tokenizer
super().__init__(hparams, model=student, config=student.config)
assert student.config.model_type == teacher.config.model_type, (
f"teacher, student model types should be the same, got {student.config.model_type} !="
f" {teacher.config.model_type}"
)
if student.config.model_type == "t5":
student_encoder_layers = len(student.get_encoder().block)
student_decoder_layers = len(student.get_decoder().block)
teacher_encoder_layers = len(teacher.get_encoder().block)
teacher_decoder_layers = len(teacher.get_decoder().block)
else:
student_encoder_layers = student.config.encoder_layers
student_decoder_layers = student.config.decoder_layers
teacher_encoder_layers = teacher.config.encoder_layers
teacher_decoder_layers = teacher.config.decoder_layers
self.different_base_models = not (hparams.student is None or hparams.teacher == hparams.student)
self.do_calc_hidden_loss = (not self.different_base_models) and hparams.alpha_hid > 0
self.different_encoder = self.different_base_models or (student_encoder_layers != teacher_encoder_layers)
# self.different_encoder determines whether we need to run the teacher encoder
self.teacher = teacher
freeze_params(self.teacher)
if not self.different_encoder: # To save RAM, delete teacher encoder and freeze student encoder.
try:
del self.teacher.model.encoder
except AttributeError: # T5
del self.teacher.encoder
if e_layer_ids is None:
e_layer_ids = list(range(student_encoder_layers))
if d_layer_ids is None:
d_layer_ids = list(range(student_decoder_layers))
self.e_layer_ids, self.d_layer_ids = e_layer_ids, d_layer_ids # type: List[int], List[int]
if self.do_calc_hidden_loss: # Intermediate supervision: Decide which layers to supervise
if hparams.supervise_forward:
self.e_matches = get_layers_to_supervise(
n_student=len(self.e_layer_ids), n_teacher=teacher_encoder_layers
)
self.d_matches = get_layers_to_supervise(
n_student=len(self.d_layer_ids), n_teacher=teacher_decoder_layers
)
else: # student layer should emulate hidden states of the teacher layer it was copied from
self.e_matches = self.e_layer_ids
self.d_matches = self.d_layer_ids
else:
self.e_matches = None
self.d_matches = None
self.ce_loss_fct = nn.KLDivLoss(reduction="batchmean")
self.temperature = 2.0
self.alpha_mlm = hparams.alpha_mlm
self.alpha_ce = hparams.alpha_ce
self.alpha_hid = hparams.alpha_hid
gc.collect()
torch.cuda.empty_cache()
def calc_ce_loss(self, mask, s_logits, t_logits):
"""Copy pasted from distillbert (transformers/examples/distillation/)"""
# mask has False at padding_idx
sel_mask = mask[:, :, None].expand_as(s_logits)
vocab_size = s_logits.size(-1)
s_logits_slct = torch.masked_select(s_logits, sel_mask) # (bs * seq_length * voc_size) modulo the 1s in mask
t_logits_slct = torch.masked_select(t_logits, sel_mask) # (bs * seq_length * voc_size) modulo the 1s in mask
s_logits_slct = s_logits_slct.view(-1, vocab_size) # (bs * seq_length, voc_size) modulo the 1s in mask
t_logits_slct = t_logits_slct.view(-1, vocab_size) # (bs * seq_length, voc_size) modulo the 1s in mask
assert t_logits_slct.size() == s_logits_slct.size()
loss_ce = (
self.ce_loss_fct(
nn.functional.log_softmax(s_logits_slct / self.temperature, dim=-1),
nn.functional.softmax(t_logits_slct / self.temperature, dim=-1),
)
* (self.temperature) ** 2
)
return loss_ce
@staticmethod
def add_model_specific_args(parser, root_dir):
SummarizationModule.add_model_specific_args(parser, root_dir)
add_distill_args(parser)
return parser
def _step(self, batch: dict) -> tuple:
"""Compute the loss for a batch"""
pad_token_id = self.tokenizer.pad_token_id
input_ids, src_mask, labels = batch["input_ids"], batch["attention_mask"], batch["labels"]
if isinstance(self.model, T5ForConditionalGeneration):
decoder_input_ids = self.model._shift_right(labels)
else:
decoder_input_ids = shift_tokens_right(labels, pad_token_id)
# noinspection PyCallingNonCallable
student_outputs = self(
input_ids,
attention_mask=src_mask,
decoder_input_ids=decoder_input_ids,
output_hidden_states=self.do_calc_hidden_loss,
output_attentions=False,
use_cache=False,
)
lm_logits = student_outputs["logits"]
# Same cross entropy vs. label smoothing logic as finetune.py
assert lm_logits.shape[-1] == self.model.config.vocab_size
if self.hparams.label_smoothing == 0:
# Same behavior as modeling_bart.py, besides ignoring pad_token_id
loss_fct = nn.CrossEntropyLoss(ignore_index=pad_token_id)
student_lm_loss = loss_fct(lm_logits.view(-1, lm_logits.shape[-1]), labels.view(-1))
else:
lprobs = nn.functional.log_softmax(lm_logits, dim=-1)
student_lm_loss, _ = label_smoothed_nll_loss(
lprobs, labels, self.hparams.label_smoothing, ignore_index=pad_token_id
)
def zero_tensor():
return torch.tensor(0.0).type_as(student_lm_loss)
teacher_enc_outputs = student_outputs[
"encoder_last_hidden_state"
] # use this unless self.different_base_models
hid_loss_enc, hid_loss_dec = zero_tensor(), zero_tensor()
if self.different_encoder: # compute encoder hidden state loss
all_teacher_encoder_outputs = self.teacher.get_encoder()(
input_ids,
attention_mask=src_mask,
output_hidden_states=self.do_calc_hidden_loss,
)
if self.different_base_models:
teacher_enc_outputs = all_teacher_encoder_outputs["last_hidden_state"]
elif self.do_calc_hidden_loss:
hid_loss_enc = self.calc_hidden_loss(
src_mask,
student_outputs["encoder_hidden_states"],
all_teacher_encoder_outputs["hidden_states"],
self.e_matches,
normalize_hidden=self.hparams.normalize_hidden,
)
teacher_outputs = self.teacher(
input_ids,
attention_mask=src_mask,
encoder_outputs=(teacher_enc_outputs,),
decoder_input_ids=decoder_input_ids,
output_hidden_states=self.do_calc_hidden_loss,
use_cache=False, # since we are not passing labels, never let this default to True
)
dec_mask = decoder_input_ids.ne(pad_token_id)
loss_ce = self.calc_ce_loss(dec_mask, lm_logits, teacher_outputs["logits"])
if self.do_calc_hidden_loss: # Intermediate supervision of decoder hidden states
hid_loss_dec = self.calc_hidden_loss(
dec_mask,
student_outputs["decoder_hidden_states"],
teacher_outputs["decoder_hidden_states"],
self.d_matches,
normalize_hidden=self.hparams.normalize_hidden,
)
blended_loss = (
self.alpha_ce * loss_ce
+ self.alpha_mlm * student_lm_loss
+ self.hparams.alpha_hid * (hid_loss_enc + hid_loss_dec)
)
return blended_loss, loss_ce, student_lm_loss, hid_loss_enc, hid_loss_dec
@staticmethod
def calc_hidden_loss(attention_mask, hidden_states, hidden_states_T, matches, normalize_hidden):
"""MSE(student_hid, teacher_hid[matches]). Called "Intermediate supervision" in paper. Inspired by TinyBERT."""
msg = "expected list or tuple for hidden_states, got tensor of shape: "
assert not isinstance(hidden_states, torch.Tensor), f"{msg}{hidden_states.shape}"
assert not isinstance(hidden_states_T, torch.Tensor), f"{msg}{hidden_states_T.shape}"
mask = attention_mask.to(hidden_states[0])
valid_count = mask.sum() * hidden_states[0].size(-1)
student_states = torch.stack([hidden_states[i] for i in range(len(matches))])
teacher_states = torch.stack([hidden_states_T[j] for j in matches])
assert student_states.shape == teacher_states.shape, f"{student_states.shape} != {teacher_states.shape}"
if normalize_hidden:
student_states = nn.functional.layer_norm(student_states, student_states.shape[1:])
teacher_states = nn.functional.layer_norm(teacher_states, teacher_states.shape[1:])
mse = nn.functional.mse_loss(student_states, teacher_states, reduction="none")
masked_mse = (mse * mask.unsqueeze(0).unsqueeze(-1)).sum() / valid_count
return masked_mse
def add_distill_args(parser):
# NOTE: if --student argument was specified and the teacher and student base models
# are different, the models still have to have the same tokenizer, specified by
# --tokenizer_name. So, for example, you can distill from t5_large to t5_small but not
# from bart to t5. This s because if the tokenizers are different, the output space
# for the two models is also different and their logits are not comparable.
parser.add_argument("--teacher", type=str)
parser.add_argument("--alpha_ce", default=0.8, type=float)
parser.add_argument("--alpha_mlm", default=0.2, type=float)
parser.add_argument("--alpha_hid", default=0.0, type=float, required=False)
parser.add_argument("--student", type=str, required=False)
parser.add_argument("--student_decoder_layers", default=12, type=int, required=False)
parser.add_argument("--student_encoder_layers", default=12, type=int, required=False)
parser.add_argument("--no_teacher", action="store_true", default=False)
parser.add_argument("--length_penalty", type=float, default=-1)
parser.add_argument("--supervise_forward", action="store_true", default=False)
parser.add_argument("--normalize_hidden", action="store_true", default=False)
class TranslationDistiller(SummarizationDistiller):
"""Supports T5, mBART, Marian, other models that inherit from Bart."""
mode = "translation"
metric_names = ["bleu"]
default_val_metric = "bleu"
def __init__(self, hparams, **kwargs):
super().__init__(hparams, **kwargs)
assert hparams.src_lang is not None
assert hparams.tgt_lang is not None
self.dataset_kwargs["src_lang"] = hparams.src_lang
self.dataset_kwargs["tgt_lang"] = hparams.tgt_lang
if self.model.config.decoder_start_token_id is None and isinstance(self.tokenizer, MBartTokenizer):
self.decoder_start_token_id = self.tokenizer.lang_code_to_id[hparams.tgt_lang]
def calc_generative_metrics(self, preds, target) -> dict:
return calculate_bleu(preds, target)
@staticmethod
def add_model_specific_args(parser, root_dir):
TranslationModule.add_model_specific_args(parser, root_dir)
add_distill_args(parser)
return parser
def create_module(args):
if args.no_teacher:
module_cls = TranslationModule if "translation" in args.task else SummarizationModule
else: # DISTILL WITH TEACHER
module_cls = TranslationDistiller if "translation" in args.task else SummarizationDistiller
args.setup_cls: str = module_cls.__name__
print(f"using module {args.setup_cls}")
model = module_cls(args)
return model
def distill_main(args):
Path(args.output_dir).mkdir(exist_ok=True)
check_output_dir(args, expected_items=3)
model = create_module(args)
return ft_main(args, model=model)
if __name__ == "__main__":
parser = argparse.ArgumentParser()
parser = pl.Trainer.add_argparse_args(parser)
parser = SummarizationDistiller.add_model_specific_args(parser, os.getcwd())
args = parser.parse_args()
distill_main(args)