def pretrain_on_domain(args):
    assert args.pregenerated_data.is_dir(), \
        "--pregenerated_data should point to the folder of files made by pregenerate_training_data.py!"

    samples_per_epoch = []
    for i in range(args.epochs):
        epoch_file = args.pregenerated_data / f"{BERT_PRETRAINED_MODEL}_epoch_{i}.json"
        metrics_file = args.pregenerated_data / f"{BERT_PRETRAINED_MODEL}_epoch_{i}_metrics.json"
        if epoch_file.is_file() and metrics_file.is_file():
            metrics = json.loads(metrics_file.read_text())
            samples_per_epoch.append(metrics['num_training_examples'])
        else:
            if i == 0:
                exit("No training data was found!")
            print(f"Warning! There are fewer epochs of pregenerated data ({i}) than training epochs ({args.epochs}).")
            print("This script will loop over the available data, but training diversity may be negatively impacted.")
            num_data_epochs = i
            break
    else:
        num_data_epochs = args.epochs

    if args.local_rank == -1 or args.no_cuda:
        device = torch.device("cuda" if torch.cuda.is_available() and not args.no_cuda else "cpu")
        n_gpu = torch.cuda.device_count()
    else:
        torch.cuda.set_device(args.local_rank)
        device = torch.device("cuda", args.local_rank)
        n_gpu = 1
        # Initializes the distributed backend which will take care of sychronizing nodes/GPUs
        torch.distributed.init_process_group(backend='nccl')
    logging.info("device: {} n_gpu: {}, distributed training: {}, 16-bits training: {}".format(
        device, n_gpu, bool(args.local_rank != -1), args.fp16))

    if args.gradient_accumulation_steps < 1:
        raise ValueError("Invalid gradient_accumulation_steps parameter: {}, should be >= 1".format(
                            args.gradient_accumulation_steps))

    args.train_batch_size = args.train_batch_size // args.gradient_accumulation_steps

    random.seed(args.seed)
    np.random.seed(args.seed)
    torch.manual_seed(args.seed)
    if n_gpu > 0:
        torch.cuda.manual_seed_all(args.seed)

    if args.output_dir.is_dir() and list(args.output_dir.iterdir()):
        logging.warning(f"Output directory ({args.output_dir}) already exists and is not empty!")
    args.output_dir.mkdir(parents=True, exist_ok=True)

    tokenizer = BertTokenizer.from_pretrained(args.bert_model, do_lower_case=args.do_lower_case)

    total_train_examples = 0
    for i in range(args.epochs):
        # The modulo takes into account the fact that we may loop over limited epochs of data
        total_train_examples += samples_per_epoch[i % len(samples_per_epoch)]

    num_train_optimization_steps = int(
        total_train_examples / args.train_batch_size / args.gradient_accumulation_steps)
    if args.local_rank != -1:
        num_train_optimization_steps = num_train_optimization_steps // torch.distributed.get_world_size()

    # Prepare model
    model = BertForMLMPreTraining.from_pretrained(args.bert_model)
    if args.fp16:
        model.half()
    model.to(device)
    if args.local_rank != -1:
        try:
            from apex.parallel import DistributedDataParallel as DDP
        except ImportError:
            raise ImportError(
                "Please install apex from https://www.github.com/nvidia/apex to use distributed and fp16 training.")
        model = DDP(model)
    elif n_gpu > 1:
        model = torch.nn.DataParallel(model)

    # Prepare optimizer
    param_optimizer = list(model.named_parameters())
    no_decay = ['bias', 'LayerNorm.bias', 'LayerNorm.weight']
    optimizer_grouped_parameters = [
        {'params': [p for n, p in param_optimizer if not any(nd in n for nd in no_decay)],
         'weight_decay': 0.01},
        {'params': [p for n, p in param_optimizer if any(nd in n for nd in no_decay)], 'weight_decay': 0.0}
    ]

    if args.fp16:
        try:
            from apex.optimizers import FP16_Optimizer
            from apex.optimizers import FusedAdam
        except ImportError:
            raise ImportError(
                "Please install apex from https://www.github.com/nvidia/apex to use distributed and fp16 training.")

        optimizer = FusedAdam(optimizer_grouped_parameters,
                              lr=args.learning_rate,
                              bias_correction=False,
                              max_grad_norm=1.0)
        if args.loss_scale == 0:
            optimizer = FP16_Optimizer(optimizer, dynamic_loss_scale=True)
        else:
            optimizer = FP16_Optimizer(optimizer, static_loss_scale=args.loss_scale)
    else:
        optimizer = AdamW(optimizer_grouped_parameters, lr=args.learning_rate, eps=args.adam_epsilon)
    scheduler = get_linear_schedule_with_warmup(optimizer,
                                                num_warmup_steps=args.warmup_steps,
                                                num_training_steps=num_train_optimization_steps)
    loss_dict = defaultdict(list)
    global_step = 0
    logging.info("***** Running training *****")
    logging.info(f"  Num examples = {total_train_examples}")
    logging.info("  Batch size = %d", args.train_batch_size)
    logging.info("  Num steps = %d", num_train_optimization_steps)
    model.train()
    for epoch in range(args.epochs):
        epoch_dataset = PregeneratedDataset(epoch=epoch, training_path=args.pregenerated_data, tokenizer=tokenizer,
                                            num_data_epochs=num_data_epochs, reduce_memory=args.reduce_memory)
        if args.local_rank == -1:
            train_sampler = RandomSampler(epoch_dataset)
        else:
            train_sampler = DistributedSampler(epoch_dataset)
        train_dataloader = DataLoader(epoch_dataset, sampler=train_sampler, batch_size=args.train_batch_size, num_workers=NUM_CPU)
        tr_loss = 0
        nb_tr_examples, nb_tr_steps = 0, 0
        with tqdm(total=len(train_dataloader), desc=f"Epoch {epoch}") as pbar:
            for step, batch in enumerate(train_dataloader):
                batch = tuple(t.to(device) for t in batch)
                input_ids, input_mask, lm_label_ids = batch
                outputs = model(input_ids=input_ids, attention_mask=input_mask, masked_lm_labels=lm_label_ids)
                loss = outputs[0]
                if n_gpu > 1:
                    loss = loss.mean() # mean() to average on multi-gpu.
                if args.gradient_accumulation_steps > 1:
                    loss = loss / args.gradient_accumulation_steps
                if args.fp16:
                    optimizer.backward(loss)
                else:
                    loss.backward()
                tr_loss += loss.item()
                nb_tr_examples += input_ids.size(0)
                nb_tr_steps += 1
                pbar.update(1)
                mean_loss = tr_loss * args.gradient_accumulation_steps / nb_tr_steps
                pbar.set_postfix_str(f"Loss: {mean_loss:.5f}")
                if (step + 1) % args.gradient_accumulation_steps == 0:
                    optimizer.step()
                    scheduler.step()  # Update learning rate schedule
                    optimizer.zero_grad()
                    global_step += 1
                loss_dict["epoch"].append(epoch)
                loss_dict["batch_id"].append(step)
                loss_dict["mlm_loss"].append(loss.item())
        # Save a trained model
        if epoch < num_data_epochs and (n_gpu > 1 and torch.distributed.get_rank() == 0 or n_gpu <= 1):
            logging.info("** ** * Saving fine-tuned model ** ** * ")
            epoch_output_dir = args.output_dir / f"epoch_{epoch}"
            epoch_output_dir.mkdir(parents=True, exist_ok=True)
            model.save_pretrained(epoch_output_dir)
            tokenizer.save_pretrained(epoch_output_dir)

    # Save a trained model
    if n_gpu > 1 and torch.distributed.get_rank() == 0 or n_gpu <=1:
        logging.info("** ** * Saving fine-tuned model ** ** * ")
        model.save_pretrained(args.output_dir)
        tokenizer.save_pretrained(args.output_dir)
        df = pd.DataFrame.from_dict(loss_dict)
        df.to_csv(args.output_dir/"losses.csv")
Example #2
0
def main():
    parser = ArgumentParser()
    parser.add_argument('--pregenerated_data', type=Path, required=True)
    parser.add_argument('--output_dir', type=Path, required=True)
    parser.add_argument(
        "--bert_model",
        type=str,
        required=True,
        help="Bert pre-trained model selected in the list: bert-base-uncased, "
        "bert-large-uncased, bert-base-cased, bert-base-multilingual, bert-base-chinese."
    )
    parser.add_argument("--do_lower_case", action="store_true")
    parser.add_argument(
        "--reduce_memory",
        action="store_true",
        help=
        "Store training data as on-disc memmaps to massively reduce memory usage"
    )

    parser.add_argument("--epochs",
                        type=int,
                        default=3,
                        help="Number of epochs to train for")
    parser.add_argument("--local_rank",
                        type=int,
                        default=-1,
                        help="local_rank for distributed training on gpus")
    parser.add_argument("--no_cuda",
                        action='store_true',
                        help="Whether not to use CUDA when available")
    parser.add_argument(
        '--gradient_accumulation_steps',
        type=int,
        default=1,
        help=
        "Number of updates steps to accumulate before performing a backward/update pass."
    )
    parser.add_argument("--train_batch_size",
                        default=32,
                        type=int,
                        help="Total batch size for training.")
    parser.add_argument(
        '--fp16',
        action='store_true',
        help="Whether to use 16-bit float precision instead of 32-bit")
    parser.add_argument(
        '--loss_scale',
        type=float,
        default=0,
        help=
        "Loss scaling to improve fp16 numeric stability. Only used when fp16 set to True.\n"
        "0 (default value): dynamic loss scaling.\n"
        "Positive power of 2: static loss scaling value.\n")
    parser.add_argument("--warmup_steps",
                        default=0,
                        type=int,
                        help="Linear warmup over warmup_steps.")
    parser.add_argument("--adam_epsilon",
                        default=1e-8,
                        type=float,
                        help="Epsilon for Adam optimizer.")
    parser.add_argument("--learning_rate",
                        default=3e-5,
                        type=float,
                        help="The initial learning rate for Adam.")
    parser.add_argument('--seed',
                        type=int,
                        default=42,
                        help="random seed for initialization")
    args = parser.parse_args()

    assert args.pregenerated_data.is_dir(), \
        "--pregenerated_data should point to the folder of files made by pregenerate_training_data.py!"

    samples_per_epoch = []
    for i in range(args.epochs):
        epoch_file = args.pregenerated_data / f"epoch_{i}.json"
        metrics_file = args.pregenerated_data / f"epoch_{i}_metrics.json"
        if epoch_file.is_file() and metrics_file.is_file():
            metrics = json.loads(metrics_file.read_text())
            samples_per_epoch.append(metrics['num_training_examples'])
        else:
            if i == 0:
                exit("No training data was found!")
            print(
                f"Warning! There are fewer epochs of pregenerated data ({i}) than training epochs ({args.epochs})."
            )
            print(
                "This script will loop over the available data, but training diversity may be negatively impacted."
            )
            num_data_epochs = i
            break
    else:
        num_data_epochs = args.epochs

    if args.local_rank == -1 or args.no_cuda:
        device = torch.device("cuda" if torch.cuda.is_available()
                              and not args.no_cuda else "cpu")
        n_gpu = torch.cuda.device_count()
    else:
        torch.cuda.set_device(args.local_rank)
        device = torch.device("cuda", args.local_rank)
        n_gpu = 1
        # Initializes the distributed backend which will take care of sychronizing nodes/GPUs
        torch.distributed.init_process_group(backend='nccl')
    logging.info(
        "device: {} n_gpu: {}, distributed training: {}, 16-bits training: {}".
        format(device, n_gpu, bool(args.local_rank != -1), args.fp16))

    if args.gradient_accumulation_steps < 1:
        raise ValueError(
            "Invalid gradient_accumulation_steps parameter: {}, should be >= 1"
            .format(args.gradient_accumulation_steps))

    args.train_batch_size = args.train_batch_size // args.gradient_accumulation_steps

    random.seed(args.seed)
    np.random.seed(args.seed)
    torch.manual_seed(args.seed)
    if n_gpu > 0:
        torch.cuda.manual_seed_all(args.seed)

    if args.output_dir.is_dir() and list(args.output_dir.iterdir()):
        logging.warning(
            f"Output directory ({args.output_dir}) already exists and is not empty!"
        )
    args.output_dir.mkdir(parents=True, exist_ok=True)

    tokenizer = BertTokenizer.from_pretrained(args.bert_model,
                                              do_lower_case=args.do_lower_case)

    total_train_examples = 0
    for i in range(args.epochs):
        # The modulo takes into account the fact that we may loop over limited epochs of data
        total_train_examples += samples_per_epoch[i % len(samples_per_epoch)]

    num_train_optimization_steps = int(total_train_examples /
                                       args.train_batch_size /
                                       args.gradient_accumulation_steps)
    if args.local_rank != -1:
        num_train_optimization_steps = num_train_optimization_steps // torch.distributed.get_world_size(
        )

    # Prepare model
    model = BertForPreTraining.from_pretrained(args.bert_model)
    if args.fp16:
        model.half()
    model.to(device)
    if args.local_rank != -1:
        try:
            from apex.parallel import DistributedDataParallel as DDP
        except ImportError:
            raise ImportError(
                "Please install apex from https://www.github.com/nvidia/apex to use distributed and fp16 training."
            )
        model = DDP(model)
    elif n_gpu > 1:
        model = torch.nn.DataParallel(model)

    # Prepare optimizer
    param_optimizer = list(model.named_parameters())
    no_decay = ['bias', 'LayerNorm.bias', 'LayerNorm.weight']
    optimizer_grouped_parameters = [{
        'params':
        [p for n, p in param_optimizer if not any(nd in n for nd in no_decay)],
        'weight_decay':
        0.01
    }, {
        'params':
        [p for n, p in param_optimizer if any(nd in n for nd in no_decay)],
        'weight_decay':
        0.0
    }]

    if args.fp16:
        try:
            from apex.optimizers import FP16_Optimizer
            from apex.optimizers import FusedAdam
        except ImportError:
            raise ImportError(
                "Please install apex from https://www.github.com/nvidia/apex to use distributed and fp16 training."
            )

        optimizer = FusedAdam(optimizer_grouped_parameters,
                              lr=args.learning_rate,
                              bias_correction=False,
                              max_grad_norm=1.0)
        if args.loss_scale == 0:
            optimizer = FP16_Optimizer(optimizer, dynamic_loss_scale=True)
        else:
            optimizer = FP16_Optimizer(optimizer,
                                       static_loss_scale=args.loss_scale)
    else:
        optimizer = AdamW(optimizer_grouped_parameters,
                          lr=args.learning_rate,
                          eps=args.adam_epsilon)
    scheduler = WarmupLinearSchedule(optimizer,
                                     warmup_steps=args.warmup_steps,
                                     t_total=num_train_optimization_steps)

    global_step = 0
    logging.info("***** Running training *****")
    logging.info(f"  Num examples = {total_train_examples}")
    logging.info("  Batch size = %d", args.train_batch_size)
    logging.info("  Num steps = %d", num_train_optimization_steps)
    model.train()
    for epoch in range(args.epochs):
        epoch_dataset = PregeneratedDataset(
            epoch=epoch,
            training_path=args.pregenerated_data,
            tokenizer=tokenizer,
            num_data_epochs=num_data_epochs,
            reduce_memory=args.reduce_memory)
        if args.local_rank == -1:
            train_sampler = RandomSampler(epoch_dataset)
        else:
            train_sampler = DistributedSampler(epoch_dataset)
        train_dataloader = DataLoader(epoch_dataset,
                                      sampler=train_sampler,
                                      batch_size=args.train_batch_size)
        tr_loss = 0
        nb_tr_examples, nb_tr_steps = 0, 0
        with tqdm(total=len(train_dataloader), desc=f"Epoch {epoch}") as pbar:
            for step, batch in enumerate(train_dataloader):
                batch = tuple(t.to(device) for t in batch)
                input_ids, input_mask, segment_ids, lm_label_ids, is_next = batch
                outputs = model(input_ids, segment_ids, input_mask,
                                lm_label_ids, is_next)
                loss = outputs[0]
                if n_gpu > 1:
                    loss = loss.mean()  # mean() to average on multi-gpu.
                if args.gradient_accumulation_steps > 1:
                    loss = loss / args.gradient_accumulation_steps
                if args.fp16:
                    optimizer.backward(loss)
                else:
                    loss.backward()
                tr_loss += loss.item()
                nb_tr_examples += input_ids.size(0)
                nb_tr_steps += 1
                pbar.update(1)
                mean_loss = tr_loss * args.gradient_accumulation_steps / nb_tr_steps
                pbar.set_postfix_str(f"Loss: {mean_loss:.5f}")
                if (step + 1) % args.gradient_accumulation_steps == 0:
                    scheduler.step()  # Update learning rate schedule
                    optimizer.step()
                    optimizer.zero_grad()
                    global_step += 1

    # Save a trained model
    if n_gpu > 1 and torch.distributed.get_rank() == 0 or n_gpu <= 1:
        logging.info("** ** * Saving fine-tuned model ** ** * ")
        model.save_pretrained(args.output_dir)
        tokenizer.save_pretrained(args.output_dir)
def main():
    parser = argparse.ArgumentParser()

    ## Required parameters
    parser.add_argument("--train_corpus",
                        default=None,
                        type=str,
                        required=True,
                        help="The input train corpus.")
    parser.add_argument(
        "--bert_model",
        default=None,
        type=str,
        required=True,
        help="Bert pre-trained model selected in the list: bert-base-uncased, "
        "bert-large-uncased, bert-base-cased, bert-base-multilingual, bert-base-chinese."
    )
    parser.add_argument(
        "--output_dir",
        default=None,
        type=str,
        required=True,
        help="The output directory where the model checkpoints will be written."
    )

    ## Other parameters
    parser.add_argument(
        "--max_seq_length",
        default=128,
        type=int,
        help=
        "The maximum total input sequence length after WordPiece tokenization. \n"
        "Sequences longer than this will be truncated, and sequences shorter \n"
        "than this will be padded.")
    parser.add_argument("--do_train",
                        action='store_true',
                        help="Whether to data training.")
    parser.add_argument("--train_batch_size",
                        default=32,
                        type=int,
                        help="Total batch size for training.")
    parser.add_argument("--learning_rate",
                        default=3e-5,
                        type=float,
                        help="The initial learning rate for Adam.")
    parser.add_argument("--adam_epsilon",
                        default=1e-8,
                        type=float,
                        help="Epsilon for Adam optimizer.")
    parser.add_argument("--num_train_epochs",
                        default=3.0,
                        type=float,
                        help="Total number of training epochs to perform.")
    parser.add_argument("--warmup_steps",
                        default=0,
                        type=int,
                        help="Linear warmup over warmup_steps.")
    parser.add_argument("--no_cuda",
                        action='store_true',
                        help="Whether not to use CUDA when available")
    parser.add_argument(
        "--on_memory",
        action='store_true',
        help="Whether to load train samples into memory or use disk")
    parser.add_argument(
        "--do_lower_case",
        action='store_true',
        help=
        "Whether to lower case the input text. True for uncased models, False for cased models."
    )
    parser.add_argument("--local_rank",
                        type=int,
                        default=-1,
                        help="local_rank for distributed training on gpus")
    parser.add_argument('--seed',
                        type=int,
                        default=42,
                        help="random seed for initialization")
    parser.add_argument(
        '--gradient_accumulation_steps',
        type=int,
        default=1,
        help=
        "Number of updates steps to accumualte before performing a backward/update pass."
    )
    parser.add_argument(
        '--fp16',
        action='store_true',
        help="Whether to use 16-bit float precision instead of 32-bit")
    parser.add_argument(
        '--loss_scale',
        type=float,
        default=0,
        help=
        "Loss scaling to improve fp16 numeric stability. Only used when fp16 set to True.\n"
        "0 (default value): dynamic loss scaling.\n"
        "Positive power of 2: static loss scaling value.\n")

    args = parser.parse_args()

    if args.local_rank == -1 or args.no_cuda:
        device = torch.device("cuda" if torch.cuda.is_available()
                              and not args.no_cuda else "cpu")
        n_gpu = torch.cuda.device_count()
    else:
        torch.cuda.set_device(args.local_rank)
        device = torch.device("cuda", args.local_rank)
        n_gpu = 1
        # Initializes the distributed backend which will take care of sychronizing nodes/GPUs
        torch.distributed.init_process_group(backend='nccl')
    logger.info(
        "device: {} n_gpu: {}, distributed training: {}, 16-bits training: {}".
        format(device, n_gpu, bool(args.local_rank != -1), args.fp16))

    if args.gradient_accumulation_steps < 1:
        raise ValueError(
            "Invalid gradient_accumulation_steps parameter: {}, should be >= 1"
            .format(args.gradient_accumulation_steps))

    args.train_batch_size = args.train_batch_size // args.gradient_accumulation_steps

    random.seed(args.seed)
    np.random.seed(args.seed)
    torch.manual_seed(args.seed)
    if n_gpu > 0:
        torch.cuda.manual_seed_all(args.seed)

    if not args.do_train:
        raise ValueError(
            "Training is currently the only implemented execution option. Please set `do_train`."
        )

    if os.path.exists(args.output_dir) and os.listdir(args.output_dir):
        raise ValueError(
            "Output directory ({}) already exists and is not empty.".format(
                args.output_dir))
    if not os.path.exists(args.output_dir) and (
            n_gpu > 1 and torch.distributed.get_rank() == 0 or n_gpu <= 1):
        os.makedirs(args.output_dir)

    tokenizer = BertTokenizer.from_pretrained(args.bert_model,
                                              do_lower_case=args.do_lower_case)

    #train_examples = None
    num_train_optimization_steps = None
    if args.do_train:
        print("Loading Train Dataset", args.train_corpus)
        train_dataset = BERTDataset(args.train_corpus,
                                    tokenizer,
                                    seq_len=args.max_seq_length,
                                    corpus_lines=None,
                                    on_memory=args.on_memory)
        num_train_optimization_steps = int(
            len(train_dataset) / args.train_batch_size /
            args.gradient_accumulation_steps) * args.num_train_epochs
        if args.local_rank != -1:
            num_train_optimization_steps = num_train_optimization_steps // torch.distributed.get_world_size(
            )

    # Prepare model
    model = BertForPreTraining.from_pretrained(args.bert_model)
    if args.fp16:
        model.half()
    model.to(device)
    if args.local_rank != -1:
        try:
            from apex.parallel import DistributedDataParallel as DDP
        except ImportError:
            raise ImportError(
                "Please install apex from https://www.github.com/nvidia/apex to use distributed and fp16 training."
            )
        model = DDP(model)
    elif n_gpu > 1:
        model = torch.nn.DataParallel(model)

    # Prepare optimizer
    if args.do_train:
        param_optimizer = list(model.named_parameters())
        no_decay = ['bias', 'LayerNorm.bias', 'LayerNorm.weight']
        optimizer_grouped_parameters = [{
            'params': [
                p for n, p in param_optimizer
                if not any(nd in n for nd in no_decay)
            ],
            'weight_decay':
            0.01
        }, {
            'params':
            [p for n, p in param_optimizer if any(nd in n for nd in no_decay)],
            'weight_decay':
            0.0
        }]

        if args.fp16:
            try:
                from apex.optimizers import FP16_Optimizer
                from apex.optimizers import FusedAdam
            except ImportError:
                raise ImportError(
                    "Please install apex from https://www.github.com/nvidia/apex to use distributed and fp16 training."
                )

            optimizer = FusedAdam(optimizer_grouped_parameters,
                                  lr=args.learning_rate,
                                  bias_correction=False,
                                  max_grad_norm=1.0)
            if args.loss_scale == 0:
                optimizer = FP16_Optimizer(optimizer, dynamic_loss_scale=True)
            else:
                optimizer = FP16_Optimizer(optimizer,
                                           static_loss_scale=args.loss_scale)

        else:
            optimizer = AdamW(optimizer_grouped_parameters,
                              lr=args.learning_rate,
                              eps=args.adam_epsilon)
        scheduler = WarmupLinearSchedule(optimizer,
                                         warmup_steps=args.warmup_steps,
                                         t_total=num_train_optimization_steps)

    global_step = 0
    if args.do_train:
        logger.info("***** Running training *****")
        logger.info("  Num examples = %d", len(train_dataset))
        logger.info("  Batch size = %d", args.train_batch_size)
        logger.info("  Num steps = %d", num_train_optimization_steps)

        if args.local_rank == -1:
            train_sampler = RandomSampler(train_dataset)
        else:
            #TODO: check if this works with current data generator from disk that relies on next(file)
            # (it doesn't return item back by index)
            train_sampler = DistributedSampler(train_dataset)
        train_dataloader = DataLoader(train_dataset,
                                      sampler=train_sampler,
                                      batch_size=args.train_batch_size)

        model.train()
        for _ in trange(int(args.num_train_epochs), desc="Epoch"):
            tr_loss = 0
            nb_tr_examples, nb_tr_steps = 0, 0
            for step, batch in enumerate(
                    tqdm(train_dataloader, desc="Iteration")):
                batch = tuple(t.to(device) for t in batch)
                input_ids, input_mask, segment_ids, lm_label_ids, is_next = batch
                outputs = model(input_ids, segment_ids, input_mask,
                                lm_label_ids, is_next)
                loss = outputs[0]
                if n_gpu > 1:
                    loss = loss.mean()  # mean() to average on multi-gpu.
                if args.gradient_accumulation_steps > 1:
                    loss = loss / args.gradient_accumulation_steps
                if args.fp16:
                    optimizer.backward(loss)
                else:
                    loss.backward()
                tr_loss += loss.item()
                nb_tr_examples += input_ids.size(0)
                nb_tr_steps += 1
                if (step + 1) % args.gradient_accumulation_steps == 0:
                    scheduler.step()  # Update learning rate schedule
                    optimizer.step()
                    optimizer.zero_grad()
                    global_step += 1

        # Save a trained model
        if args.do_train and (n_gpu > 1 and torch.distributed.get_rank() == 0
                              or n_gpu <= 1):
            logger.info("** ** * Saving fine - tuned model ** ** * ")
            model.save_pretrained(args.output_dir)
            tokenizer.save_pretrained(args.output_dir)