Fix checkpoint deletion (#11748)

src/transformers/trainer.py

@@ -1523,10 +1523,6 @@ class Trainer:
         if self.is_world_process_zero():
             self.state.save_to_json(os.path.join(output_dir, "trainer_state.json"))
 
-        # Maybe delete some older checkpoints.
-        if self.is_world_process_zero():
-            self._rotate_checkpoints(use_mtime=True, output_dir=run_dir)
-
         # Save RNG state in non-distributed training
         rng_states = {
             "python": random.getstate(),
@@ -1552,6 +1548,10 @@ class Trainer:
         else:
             torch.save(rng_states, os.path.join(output_dir, f"rng_state_{local_rank}.pth"))
 
+        # Maybe delete some older checkpoints.
+        if self.is_world_process_zero():
+            self._rotate_checkpoints(use_mtime=True, output_dir=run_dir)
+
     def _load_optimizer_and_scheduler(self, checkpoint):
         """If optimizer and scheduler states exist, load them."""
         if checkpoint is None:
@@ -1924,7 +1924,7 @@ class Trainer:
                 ordering_and_checkpoint_path.append((os.path.getmtime(path), path))
             else:
                 regex_match = re.match(f".*{checkpoint_prefix}-([0-9]+)", path)
-                if regex_match and regex_match.groups():
+                if regex_match is not None and regex_match.groups() is not None:
                     ordering_and_checkpoint_path.append((int(regex_match.groups()[0]), path))
 
         checkpoints_sorted = sorted(ordering_and_checkpoint_path)
@@ -1932,10 +1932,8 @@ class Trainer:
         # Make sure we don't delete the best model.
         if self.state.best_model_checkpoint is not None:
             best_model_index = checkpoints_sorted.index(str(Path(self.state.best_model_checkpoint)))
-            checkpoints_sorted[best_model_index], checkpoints_sorted[-1] = (
-                checkpoints_sorted[-1],
-                checkpoints_sorted[best_model_index],
-            )
+            for i in range(best_model_index, len(checkpoints_sorted) - 2):
+                checkpoints_sorted[i], checkpoints_sorted[i + 1] = checkpoints_sorted[i + 1], checkpoints_sorted[i]
         return checkpoints_sorted
 
     def _rotate_checkpoints(self, use_mtime=False, output_dir=None) -> None:
@@ -1947,7 +1945,17 @@ class Trainer:
         if len(checkpoints_sorted) <= self.args.save_total_limit:
             return
 
-        number_of_checkpoints_to_delete = max(0, len(checkpoints_sorted) - self.args.save_total_limit)
+        # If save_total_limit=1 with load_best_mode_at_end=True, we could end up deleting the last checkpoint, which
+        # we don't do to allow resuming.
+        save_total_limit = self.args.save_total_limit
+        if (
+            self.state.best_model_checkpoint is not None
+            and self.args.save_total_limit == 1
+            and checkpoints_sorted[-1] != self.state.best_model_checkpoint
+        ):
+            save_total_limit = 2
+
+        number_of_checkpoints_to_delete = max(0, len(checkpoints_sorted) - save_total_limit)
         checkpoints_to_be_deleted = checkpoints_sorted[:number_of_checkpoints_to_delete]
         for checkpoint in checkpoints_to_be_deleted:
             logger.info(f"Deleting older checkpoint [{checkpoint}] due to args.save_total_limit")

tests/test_trainer.py

@@ -21,6 +21,7 @@ import random
 import re
 import tempfile
 import unittest
+from pathlib import Path
 
 import numpy as np
 
@@ -45,6 +46,7 @@ from transformers.testing_utils import (
     require_torch_multi_gpu,
     slow,
 )
+from transformers.trainer_utils import PREFIX_CHECKPOINT_DIR
 from transformers.utils.hp_naming import TrialShortNamer
 
 
@@ -1048,6 +1050,35 @@ class TrainerIntegrationTest(TestCasePlus, TrainerIntegrationCommon):
         trainer.train()
         self.assertTrue(isinstance(trainer.state.total_flos, float))
 
+    def check_checkpoint_deletion(self, trainer, output_dir, expected):
+        # Make fake checkpoints
+        for n in [5, 10, 15, 20, 25]:
+            os.makedirs(os.path.join(output_dir, f"{PREFIX_CHECKPOINT_DIR}-{n}"), exist_ok=True)
+        trainer._rotate_checkpoints(output_dir=output_dir)
+        glob_checkpoints = [str(x) for x in Path(output_dir).glob(f"{PREFIX_CHECKPOINT_DIR}-*")]
+        values = [int(re.match(f".*{PREFIX_CHECKPOINT_DIR}-([0-9]+)", d).groups()[0]) for d in glob_checkpoints]
+        self.assertSetEqual(set(values), set(expected))
+
+    def test_checkpoint_rotation(self):
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            # Without best model at end
+            trainer = get_regression_trainer(output_dir=tmp_dir, save_total_limit=2)
+            self.check_checkpoint_deletion(trainer, tmp_dir, [20, 25])
+
+            # With best model at end
+            trainer = get_regression_trainer(output_dir=tmp_dir, load_best_model_at_end=True, save_total_limit=2)
+            trainer.state.best_model_checkpoint = os.path.join(tmp_dir, "checkpoint-5")
+            self.check_checkpoint_deletion(trainer, tmp_dir, [5, 25])
+
+            # Edge case: we don't always honor save_total_limit=1 if load_best_model_at_end=True to be able to resume
+            # from checkpoint
+            trainer = get_regression_trainer(output_dir=tmp_dir, load_best_model_at_end=True, save_total_limit=1)
+            trainer.state.best_model_checkpoint = os.path.join(tmp_dir, "checkpoint-25")
+            self.check_checkpoint_deletion(trainer, tmp_dir, [25])
+
+            trainer.state.best_model_checkpoint = os.path.join(tmp_dir, "checkpoint-5")
+            self.check_checkpoint_deletion(trainer, tmp_dir, [5, 25])
+
     def check_mem_metrics(self, trainer, check_func):
         metrics = trainer.train().metrics
         check_func("init_mem_cpu_alloc_delta", metrics)