[s2s] distill t5-large -> t5-small (#8376)

Co-authored-by: Sam Shleifer <sshleifer@gmail.com>

examples/seq2seq/README.md

@@ -380,7 +380,7 @@ cp xsum/test* all_pl
 then use `all_pl` as DATA in the command above.
 
 #### Direct Knowledge Distillation (KD)
-+ In this method, we use try to enforce that the student and teacher produce similar encoder_outputs, logits, and hidden_states using `BartSummarizationDistiller`.
++ In this method, we use try to enforce that the student and teacher produce similar encoder_outputs, logits, and hidden_states using `SummarizationDistiller`.
 + This method was used for `sshleifer/distilbart-xsum-12-6`, `6-6`, and `9-6` checkpoints were produced.
 + You must use [`distillation.py`](./distillation.py). Note that this command initializes the student for you.
 

examples/seq2seq/distillation.py

@@ -25,8 +25,8 @@ sys.path.insert(2, str(Path(__file__).resolve().parents[1]))
 from lightning_base import generic_train  # noqa
 
 
-class BartSummarizationDistiller(SummarizationModule):
+class SummarizationDistiller(SummarizationModule):
-    """Supports Bart, Pegasus and other models that inherit from Bart."""
+    """Supports T5, Bart, Pegasus and other models that inherit from Bart."""
 
     loss_names = ["loss", "ce_loss", "mlm_loss", "hid_loss_enc", "hid_loss_dec"]
 
@@ -40,26 +40,38 @@ class BartSummarizationDistiller(SummarizationModule):
         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)
-        model_type = student.config.model_type
+        assert (
-        self.e_layer_ids, self.d_layer_ids = e_layer_ids, d_layer_ids  # type: List[int], List[int]
+            student.config.model_type == teacher.config.model_type
+        ), f"teacher, student model types should be the same, got {student.config.model_type} != {teacher.config.model_type}"
 
-        if model_type == "t5":
+        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_encoder = hparams.student_encoder_layers != teacher_encoder_layers
+        self.different_base_models = not (hparams.student is None or hparams.teacher == hparams.student)
-        self.different_decoder = hparams.student_decoder_layers != teacher_decoder_layers
+        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)
 
@@ -68,13 +80,28 @@ class BartSummarizationDistiller(SummarizationModule):
                 del self.teacher.model.encoder
             except AttributeError:  # T5
                 del self.teacher.encoder
-        # Intermediate supervision: Decide which layers to supervise
+
+        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.e_matches = get_layers_to_supervise(
-            self.d_matches = get_layers_to_supervise(n_student=len(self.d_layer_ids), n_teacher=teacher_decoder_layers)
+                    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
@@ -84,22 +111,8 @@ class BartSummarizationDistiller(SummarizationModule):
         gc.collect()
         torch.cuda.empty_cache()
 
-    def calc_mse_loss(self, teacher_outputs: torch.Tensor, student_outputs: torch.Tensor, mask) -> torch.FloatTensor:
-        """Supervise MSE(teacher.encoder_outputs, student.encoder_outputs)."""
-        # raise NotImplementedError()
-        if mask is not None:
-            # mask has False at padding_idx
-            sel_mask = mask[:, :, None].expand_as(student_outputs).bool()
-            s_logits_slct = torch.masked_select(student_outputs, sel_mask)
-            t_logits_slct = torch.masked_select(teacher_outputs, sel_mask)
-        else:
-            t_logits_slct = teacher_outputs
-            s_logits_slct = student_outputs
-        return F.mse_loss(s_logits_slct, t_logits_slct)
-
     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)
@@ -123,8 +136,8 @@ class BartSummarizationDistiller(SummarizationModule):
         add_distill_args(parser)
         return parser
 
-    def _step(self, batch):
+    def _step(self, batch: dict) -> tuple:
-        # assert is_frozen(self.teacher) copied_decoder_layers
+        """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):
@@ -133,14 +146,16 @@ class BartSummarizationDistiller(SummarizationModule):
             decoder_input_ids = shift_tokens_right(labels, pad_token_id)
 
         # noinspection PyCallingNonCallable
-        lm_logits, dec_hidden, enc_outputs, enc_hidden_state = self(
+        student_outputs = self(
             input_ids,
             attention_mask=src_mask,
             decoder_input_ids=decoder_input_ids,
-            output_hidden_states=True,
+            output_hidden_states=self.do_calc_hidden_loss,
             output_attentions=False,
             use_cache=False,
+            return_dict=True,
         )
+        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
@@ -149,7 +164,7 @@ class BartSummarizationDistiller(SummarizationModule):
             loss_fct = torch.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 = torch.nn.functional.log_softmax(lm_logits, dim=-1)
+            lprobs = F.log_softmax(lm_logits, dim=-1)
             student_lm_loss, _ = label_smoothed_nll_loss(
                 lprobs, labels, self.hparams.label_smoothing, ignore_index=pad_token_id
             )
@@ -157,37 +172,44 @@ class BartSummarizationDistiller(SummarizationModule):
         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
-            with torch.no_grad():
+            all_teacher_encoder_outputs = self.teacher.get_encoder()(
-                teacher_enc_hid = self.teacher.get_encoder()(
+                input_ids,
-                    input_ids, attention_mask=src_mask, output_hidden_states=True, return_dict=True
+                attention_mask=src_mask,
-                ).hidden_states
+                output_hidden_states=self.do_calc_hidden_loss,
-
+                return_dict=True,
+            )
+            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,
-                enc_hidden_state,
+                    student_outputs.encoder_hidden_states,
-                teacher_enc_hid,
+                    all_teacher_encoder_outputs.hidden_states,
                     self.e_matches,
                     normalize_hidden=self.hparams.normalize_hidden,
                 )
 
-        with torch.no_grad():
+        teacher_outputs = self.teacher(
-            outputs = self.teacher(
             input_ids,
             attention_mask=src_mask,
-                encoder_outputs=(enc_outputs,),
+            encoder_outputs=(teacher_enc_outputs,),
             decoder_input_ids=decoder_input_ids,
-                lm_labels=labels,
+            output_hidden_states=self.do_calc_hidden_loss,
-                output_hidden_states=True,
+            use_cache=False,  # since we are not passing labels, never let this default to True
             return_dict=True,
         )
-            tlogits, tdec_hidden = outputs.logits, outputs.decoder_hidden_states
         dec_mask = decoder_input_ids.ne(pad_token_id)
-        loss_ce = self.calc_ce_loss(dec_mask, lm_logits, tlogits)
+        loss_ce = self.calc_ce_loss(dec_mask, lm_logits, teacher_outputs.logits)
-        if self.alpha_hid > 0:  # Intermediate supervision of decoder hidden states
+        if self.do_calc_hidden_loss:  # Intermediate supervision of decoder hidden states
             hid_loss_dec = self.calc_hidden_loss(
-                dec_mask, dec_hidden, tdec_hidden, self.d_matches, normalize_hidden=self.hparams.normalize_hidden
+                dec_mask,
+                student_outputs.decoder_hidden_states,
+                teacher_outputs.decoder_hidden_states,
+                self.d_matches,
+                normalize_hidden=self.hparams.normalize_hidden,
             )
 
         blended_loss = (
@@ -207,6 +229,7 @@ class BartSummarizationDistiller(SummarizationModule):
         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 = F.layer_norm(student_states, student_states.shape[1:])
             teacher_states = F.layer_norm(teacher_states, teacher_states.shape[1:])
@@ -216,10 +239,16 @@ class BartSummarizationDistiller(SummarizationModule):
 
 
 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)
@@ -228,8 +257,8 @@ def add_distill_args(parser):
     parser.add_argument("--normalize_hidden", action="store_true", default=False)
 
 
-class BartTranslationDistiller(BartSummarizationDistiller):
+class TranslationDistiller(SummarizationDistiller):
-    """Supports Mbart, Marian, other models that inherit from Bart."""
+    """Supports T5, mBART, Marian, other models that inherit from Bart."""
 
     mode = "translation"
     metric_names = ["bleu"]
@@ -258,7 +287,7 @@ def create_module(args):
     if args.no_teacher:
         module_cls = TranslationModule if "translation" in args.task else SummarizationModule
     else:  # DISTILL WITH TEACHER
-        module_cls = BartTranslationDistiller if "translation" in args.task else BartSummarizationDistiller
+        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)
@@ -276,7 +305,7 @@ def distill_main(args):
 if __name__ == "__main__":
     parser = argparse.ArgumentParser()
     parser = pl.Trainer.add_argparse_args(parser)
-    parser = BartSummarizationDistiller.add_model_specific_args(parser, os.getcwd())
+    parser = SummarizationDistiller.add_model_specific_args(parser, os.getcwd())
     args = parser.parse_args()
 
     distill_main(args)

examples/seq2seq/test_bash_script.py

@@ -9,7 +9,7 @@ import pytorch_lightning as pl
 import timeout_decorator
 import torch
 
-from distillation import BartSummarizationDistiller, distill_main
+from distillation import SummarizationDistiller, distill_main
 from finetune import SummarizationModule, main
 from transformers import MarianMTModel
 from transformers.file_utils import cached_path
@@ -170,7 +170,7 @@ class TestDistilMarianNoTeacher(TestCasePlus):
         with patch.object(sys, "argv", testargs):
             parser = argparse.ArgumentParser()
             parser = pl.Trainer.add_argparse_args(parser)
-            parser = BartSummarizationDistiller.add_model_specific_args(parser, os.getcwd())
+            parser = SummarizationDistiller.add_model_specific_args(parser, os.getcwd())
             args = parser.parse_args()
             # assert args.gpus == gpus THIS BREAKS for multi_gpu
 

examples/seq2seq/test_seq2seq_examples.py

@@ -96,6 +96,7 @@ CHEAP_ARGS = {
     "freeze_encoder": False,
     "auto_scale_batch_size": False,
     "overwrite_output_dir": False,
+    "student": None,
 }
 
 
@@ -107,6 +108,7 @@ def _dump_articles(path: Path, articles: list):
 ARTICLES = [" Sam ate lunch today.", "Sams lunch ingredients."]
 SUMMARIES = ["A very interesting story about what I ate for lunch.", "Avocado, celery, turkey, coffee"]
 T5_TINY = "patrickvonplaten/t5-tiny-random"
+T5_TINIER = "sshleifer/t5-tinier-random"
 BART_TINY = "sshleifer/bart-tiny-random"
 MBART_TINY = "sshleifer/tiny-mbart"
 MARIAN_TINY = "sshleifer/tiny-marian-en-de"
@@ -239,6 +241,16 @@ class TestSummarizationDistiller(TestCasePlus):
         )
         self._test_distiller_cli(updates)
 
+    @require_torch_non_multi_gpu_but_fix_me
+    def test_distill_different_base_models(self):
+        updates = dict(
+            teacher=T5_TINY,
+            student=T5_TINIER,
+            model_name_or_path=T5_TINIER,
+            tokenizer_name=T5_TINIER,
+        )
+        self._test_distiller_cli(updates)
+
     def _test_distiller_cli(self, updates, check_contents=True):
         default_updates = dict(
             label_smoothing=0.0,