Fix memory regression in Seq2Seq example (#9713)

* Fix memory regression in Seq2Seq example

* Fix test and properly deal with -100

* Easier condition with device safety

* Patch for MBartTokenzierFast

examples/seq2seq/finetune_trainer.py

@@ -26,6 +26,7 @@ from transformers import (
     AutoTokenizer,
     HfArgumentParser,
     MBartTokenizer,
+    MBartTokenizerFast,
     Seq2SeqTrainer,
     Seq2SeqTrainingArguments,
     set_seed,
@@ -220,11 +221,14 @@ def main():
         data_args.eval_beams = model.config.num_beams
 
     # set decoder_start_token_id for MBart
-    if model.config.decoder_start_token_id is None and isinstance(tokenizer, MBartTokenizer):
+    if model.config.decoder_start_token_id is None and isinstance(tokenizer, (MBartTokenizer, MBartTokenizerFast)):
         assert (
             data_args.tgt_lang is not None and data_args.src_lang is not None
         ), "mBart requires --tgt_lang and --src_lang"
-        model.config.decoder_start_token_id = tokenizer.lang_code_to_id[data_args.tgt_lang]
+        if isinstance(tokenizer, MBartTokenizer):
+            model.config.decoder_start_token_id = tokenizer.lang_code_to_id[data_args.tgt_lang]
+        else:
+            model.config.decoder_start_token_id = tokenizer.convert_tokens_to_ids(data_args.tgt_lang)
 
     if model_args.freeze_embeds:
         freeze_embeds(model)
@@ -284,7 +288,9 @@ def main():
         args=training_args,
         train_dataset=train_dataset,
         eval_dataset=eval_dataset,
-        data_collator=Seq2SeqDataCollator(tokenizer, data_args, training_args.tpu_num_cores),
+        data_collator=Seq2SeqDataCollator(
+            tokenizer, data_args, model.config.decoder_start_token_id, training_args.tpu_num_cores
+        ),
         compute_metrics=compute_metrics_fn,
         tokenizer=tokenizer,
     )

examples/seq2seq/utils.py

@@ -33,8 +33,9 @@ from torch import nn
 from torch.utils.data import Dataset, Sampler
 
 from sentence_splitter import add_newline_to_end_of_each_sentence
-from transformers import BartTokenizer, EvalPrediction, PreTrainedTokenizer
+from transformers import BartTokenizer, EvalPrediction, PreTrainedTokenizer, T5Tokenizer
 from transformers.file_utils import cached_property
+from transformers.models.bart.modeling_bart import shift_tokens_right
 
 
 try:
@@ -274,9 +275,10 @@ class Seq2SeqDataset(AbstractSeq2SeqDataset):
 
 
 class Seq2SeqDataCollator:
-    def __init__(self, tokenizer, data_args, tpu_num_cores=None):
+    def __init__(self, tokenizer, data_args, decoder_start_token_id, tpu_num_cores=None):
         self.tokenizer = tokenizer
         self.pad_token_id = tokenizer.pad_token_id
+        self.decoder_start_token_id = decoder_start_token_id
         assert (
             self.pad_token_id is not None
         ), f"pad_token_id is not defined for ({self.tokenizer.__class__.__name__}), it must be defined."
@@ -304,9 +306,15 @@ class Seq2SeqDataCollator:
             labels = trim_batch(labels, self.pad_token_id)
             input_ids, attention_mask = trim_batch(input_ids, self.pad_token_id, attention_mask=attention_mask)
 
+        if isinstance(self.tokenizer, T5Tokenizer):
+            decoder_input_ids = self._shift_right_t5(labels)
+        else:
+            decoder_input_ids = shift_tokens_right(labels, self.pad_token_id, self.decoder_start_token_id)
+
         batch = {
             "input_ids": input_ids,
             "attention_mask": attention_mask,
+            "decoder_input_ids": decoder_input_ids,
             "labels": labels,
         }
         return batch

src/transformers/trainer.py

@@ -1297,14 +1297,18 @@ class Trainer:
 
         Subclass and override for custom behavior.
         """
+        if self.label_smoother is not None and "labels" in inputs:
+            labels = inputs.pop("labels")
+        else:
+            labels = None
         outputs = model(**inputs)
         # Save past state if it exists
         # TODO: this needs to be fixed and made cleaner later.
         if self.args.past_index >= 0:
             self._past = outputs[self.args.past_index]
 
-        if self.label_smoother is not None and "labels" in inputs:
-            return self.label_smoother(outputs, inputs["labels"])
+        if labels is not None:
+            return self.label_smoother(outputs, labels)
         else:
             # We don't use .loss here since the model may return tuples instead of ModelOutput.
             return outputs["loss"] if isinstance(outputs, dict) else outputs[0]

src/transformers/trainer_pt_utils.py

@@ -380,17 +380,26 @@ class LabelSmoother:
     ignore_index: int = -100
 
     def __call__(self, model_output, labels):
-        model_loss = model_output["loss"] if isinstance(model_output, dict) else model_output[0]
-        logits = model_output["logits"] if isinstance(model_output, dict) else model_output[1]
+        logits = model_output["logits"] if isinstance(model_output, dict) else model_output[0]
         log_probs = -torch.nn.functional.log_softmax(logits, dim=-1)
+        if labels.dim() == log_probs.dim() - 1:
+            labels = labels.unsqueeze(-1)
 
-        # Look at the ignored index and mask the corresponding log_probs.
-        padding_mask = labels.unsqueeze(-1).eq(self.ignore_index)
-        log_probs.masked_fill_(padding_mask, 0.0)
+        padding_mask = labels.eq(self.ignore_index)
+        # In case the ignore_index is -100, the gather will fail, so we replace labels by 0. The padding_mask
+        # will ignore them in any case.
+        labels.clamp_min_(0)
+        nll_loss = log_probs.gather(dim=-1, index=labels)
+        smoothed_loss = log_probs.sum(dim=-1, keepdim=True)
+
+        nll_loss.masked_fill_(padding_mask, 0.0)
+        smoothed_loss.masked_fill_(padding_mask, 0.0)
 
         # Take the mean over the label dimensions, then divide by the number of active elements (i.e. not-padded):
-        smoothed_loss = log_probs.mean(dim=-1).sum() / (padding_mask.numel() - padding_mask.long().sum())
-        return (1 - self.epsilon) * model_loss + self.epsilon * smoothed_loss
+        num_active_elements = padding_mask.numel() - padding_mask.long().sum()
+        nll_loss = nll_loss.sum() / num_active_elements
+        smoothed_loss = smoothed_loss.sum() / (num_active_elements * log_probs.shape[-1])
+        return (1 - self.epsilon) * nll_loss + self.epsilon * smoothed_loss
 
 
 def get_length_grouped_indices(lengths, batch_size, mega_batch_mult=None, generator=None):

tests/test_trainer_utils.py

@@ -71,7 +71,7 @@ class TrainerUtilsTest(unittest.TestCase):
         random_logits = torch.randn(4, 5, num_labels)
         random_labels = torch.randint(0, num_labels, (4, 5))
         loss = torch.nn.functional.cross_entropy(random_logits.view(-1, num_labels), random_labels.view(-1))
-        model_output = SequenceClassifierOutput(loss=loss, logits=random_logits)
+        model_output = SequenceClassifierOutput(logits=random_logits)
         label_smoothed_loss = LabelSmoother(0.1)(model_output, random_labels)
         log_probs = -torch.nn.functional.log_softmax(random_logits, dim=-1)
         expected_loss = (1 - epsilon) * loss + epsilon * log_probs.mean()
@@ -83,7 +83,7 @@ class TrainerUtilsTest(unittest.TestCase):
         random_labels[2, 3] = -100
 
         loss = torch.nn.functional.cross_entropy(random_logits.view(-1, num_labels), random_labels.view(-1))
-        model_output = SequenceClassifierOutput(loss=loss, logits=random_logits)
+        model_output = SequenceClassifierOutput(logits=random_logits)
         label_smoothed_loss = LabelSmoother(0.1)(model_output, random_labels)
         log_probs = -torch.nn.functional.log_softmax(random_logits, dim=-1)
         # Mask the log probs with the -100 labels