Fix tot update in trainer (#37923)

* fix total updates in epoch

* add test; fix max_steps

* replace with multi-gpu decorator

src/transformers/trainer.py

@@ -2495,13 +2495,13 @@ class Trainer:
             step = -1
             epoch_iterator = iter(epoch_dataloader)
             # We chunkify the epoch iterator into gradient accumulation steps `n` batches
-            remainder = num_examples % args.gradient_accumulation_steps
+            remainder = steps_in_epoch % args.gradient_accumulation_steps
             if remainder == 0:
                 remainder = args.gradient_accumulation_steps
             update_step = -1
-            total_updates = steps_in_epoch // args.gradient_accumulation_steps + 1
-            if args.gradient_accumulation_steps == 1:
-                total_updates -= 1
+            total_updates = steps_in_epoch // args.gradient_accumulation_steps + int(
+                remainder < args.gradient_accumulation_steps
+            )
             for _ in range(total_updates):
                 update_step += 1
                 num_batches = args.gradient_accumulation_steps if update_step != (total_updates - 1) else remainder
@@ -5319,7 +5319,11 @@ class Trainer:
 
         # Case 2: We have a dataloader length and can extrapolate
         if len_dataloader is not None:
-            num_update_steps_per_epoch = max(len_dataloader // args.gradient_accumulation_steps, 1)
+            num_update_steps_per_epoch = max(
+                len_dataloader // args.gradient_accumulation_steps
+                + int(len_dataloader % args.gradient_accumulation_steps > 0),
+                1,
+            )
             # Case 3: We have a length but are using epochs, we can extrapolate the number of steps
             if epoch_based:
                 max_steps = math.ceil(args.num_train_epochs * num_update_steps_per_epoch)

tests/trainer/test_trainer.py

@@ -97,6 +97,7 @@ from transformers.testing_utils import (
     require_torch_fp16,
     require_torch_gpu,
     require_torch_multi_accelerator,
+    require_torch_multi_gpu,
     require_torch_non_multi_accelerator,
     require_torch_non_multi_gpu,
     require_torch_tensorrt_fx,
@@ -3763,6 +3764,37 @@ class TrainerIntegrationTest(TestCasePlus, TrainerIntegrationCommon):
             train_output = trainer.train()
             self.assertEqual(train_output.global_step, int(self.n_epochs))
 
+    @require_torch_multi_gpu
+    def test_num_batches_in_training_with_gradient_accumulation(self):
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            for num_train_epochs in [1, 2]:
+                for train_len in [123, 120]:
+                    trainer = get_regression_trainer(
+                        train_len=train_len,
+                        per_device_train_batch_size=4,
+                        gradient_accumulation_steps=5,
+                        num_train_epochs=num_train_epochs,
+                        output_dir=tmp_dir,
+                    )
+
+                    total_batch_samples = []
+
+                    def wrap_get_batch_samples(fn):
+                        def wrapped_fn(epoch_iterator, num_batches, device):
+                            self.assertGreater(num_batches, 0)
+                            batch_samples, num_items_in_batch = fn(epoch_iterator, num_batches, device)
+                            self.assertEqual(len(batch_samples), num_batches)
+                            total_batch_samples.append(num_batches)
+                            return batch_samples, num_items_in_batch
+
+                        return wrapped_fn
+
+                    trainer.get_batch_samples = wrap_get_batch_samples(trainer.get_batch_samples)
+
+                    trainer.train()
+
+                    self.assertEqual(len(trainer.get_train_dataloader()) * num_train_epochs, sum(total_batch_samples))
+
     def test_early_stopping_callback(self):
         # early stopping stops training before num_training_epochs
         with tempfile.TemporaryDirectory() as tmp_dir: