fix: fix checkpointing when val_period does not divide save_period

nemo_rl/algorithms/dpo.py

@@ -633,9 +633,8 @@ def dpo_train(
                         ):
                             warnings.warn(
                                 f"You asked to save checkpoints based on {master_config['checkpointing']['metric_name']} but the metric is not found in the save state. "
-                                "Saving most recent k checkpoints instead."
+                                "This checkpoint will not be saved as top-k."
                             )
-                            master_config["checkpointing"]["metric_name"] = None
 
                     with timer.time("checkpointing"):
                         print(f"Saving checkpoint for step {total_steps + 1}...")

nemo_rl/algorithms/grpo.py

@@ -874,9 +874,8 @@ def grpo_train(
                         ):
                             warnings.warn(
                                 f"You asked to save checkpoints based on {master_config['checkpointing']['metric_name']} but the metric is not found in the save state. "
-                                "Saving most recent k checkpoints instead."
+                                "This checkpoint will not be saved as top-k."
                             )
-                            master_config["checkpointing"]["metric_name"] = None
 
                     with timer.time("checkpointing"):
                         print(

nemo_rl/algorithms/sft.py

@@ -506,9 +506,8 @@ def sft_train(
                         ):
                             warnings.warn(
                                 f"You asked to save checkpoints based on {master_config['checkpointing']['metric_name']} but the metric is not found in the save state. "
-                                "Saving most recent k checkpoints instead."
+                                "This checkpoint will not be saved as top-k."
                             )
-                            master_config["checkpointing"]["metric_name"] = None
 
                     with timer.time("checkpointing"):
                         print(f"Saving checkpoint for step {total_steps + 1}...")

nemo_rl/utils/checkpoint.py

@@ -202,25 +202,18 @@ def remove_old_checkpoints(self, exclude_latest: bool = True) -> None:
         if self.metric_name is None:
             checkpoint_history.sort(key=lambda x: x[0], reverse=True)
         else:
-            try:
-                # sort by metric value first, then by step number (for equal metrics, prefer more recent)
-                if self.higher_is_better:
-                    # For higher_is_better=True: higher metric values first, then higher step numbers
-                    checkpoint_history.sort(
-                        key=lambda x: (x[2][self.metric_name], x[0]), reverse=True
-                    )
-                else:
-                    # For higher_is_better=False: lower metric values first, then higher step numbers for equal values
-                    checkpoint_history.sort(
-                        key=lambda x: (x[2][self.metric_name], -x[0])
-                    )
-            except KeyError:
-                warnings.warn(
-                    f"Metric {self.metric_name} not found in checkpoint history. Keeping most recent k checkpoints."
+            # sort by metric value first, then by step number (for equal metrics, prefer more recent)
+            if self.higher_is_better:
+                # For higher_is_better=True: higher metric values first, then higher step numbers
+                checkpoint_history.sort(
+                    key=lambda x: (x[2].get(self.metric_name, -float("inf")), x[0]),
+                    reverse=True,
+                )
+            else:
+                # For higher_is_better=False: lower metric values first, then higher step numbers for equal values
+                checkpoint_history.sort(
+                    key=lambda x: (x[2].get(self.metric_name, float("inf")), -x[0])
                 )
-                checkpoint_history.sort(key=lambda x: x[0], reverse=True)
-
-                self.metric_name = None
 
         # remove checkpoints that are not in the top-k
         for checkpoint in checkpoint_history[self.keep_top_k :]:

tests/unit/utils/test_checkpoint.py

@@ -141,6 +141,85 @@ def test_remove_old_checkpoints_topk_bias_recent_if_equal(
     assert sorted(remaining_steps) == sorted(expected_steps)
 
 
+def test_remove_old_checkpoints_topk_some_missing_val_metric(
+    checkpoint_manager, checkpoint_dir
+):
+    # Create checkpoints where some have validation metrics and others don't
+    steps = [1, 2, 3, 4, 10, 11, 12]
+    # Some checkpoints have loss metrics, others don't have any validation metrics
+    training_infos = [
+        {"loss": 0.5},  # step 1 - has loss
+        {"loss": 0.3},  # step 2 - has loss
+        {"other_metric": 0.8},  # step 3 - missing loss metric
+        {"loss": 0.2},  # step 4 - has loss
+        {},  # step 10 - missing loss metric
+        {"loss": 1.0},  # has loss but not in top-k
+        {},  # step 12 - missing loss (latest)
+    ]
+
+    for step, training_info in zip(steps, training_infos):
+        tmp_dir = checkpoint_manager.init_tmp_checkpoint(step, training_info)
+        checkpoint_manager.finalize_checkpoint(tmp_dir)
+
+    # Check if only top-k checkpoints are kept
+    remaining_dirs = list(checkpoint_dir.glob("step_*"))
+    assert (
+        len(remaining_dirs) == checkpoint_manager.keep_top_k + 1
+    )  # +1 because we exclude the latest
+
+    # Checkpoints with missing validation metrics should be treated as having the worst possible value
+    # Since higher_is_better=False, missing metrics get float("inf") which is worst
+    # So checkpoints with actual loss values should be preferred over those without
+    remaining_steps = []
+    for dir_path in remaining_dirs:
+        step_num = int(dir_path.name.split("_")[1])
+        remaining_steps.append(step_num)
+
+    # Should keep checkpoints with actual loss values (steps 1, 2, 4, 12)
+    # and exclude those without loss metrics (steps 3, 10)
+    # The latest checkpoint (step 12) is always kept
+    expected_steps = [1, 2, 4, 12]  # Steps with loss metrics, plus latest
+    assert sorted(remaining_steps) == sorted(expected_steps)
+
+
+def test_remove_old_checkpoints_topk_most_missing_val_metric(
+    checkpoint_manager, checkpoint_dir
+):
+    # Create checkpoints where some have validation metrics and others don't
+    steps = [1, 2, 3, 4, 10, 12]
+    # Some checkpoints have loss metrics, others don't have any validation metrics
+    training_infos = [
+        {"loss": 0.2},  # step 1 - has loss
+        {},  # step 2 - has loss
+        {"other_metric": 0.8},  # step 3 - missing loss metric
+        {},  # step 4 - has loss
+        {},  # step 10 - missing loss metric
+        {},  # step 12 - missing loss (latest)
+    ]
+
+    for step, training_info in zip(steps, training_infos):
+        tmp_dir = checkpoint_manager.init_tmp_checkpoint(step, training_info)
+        checkpoint_manager.finalize_checkpoint(tmp_dir)
+
+    # Check if only top-k checkpoints are kept
+    remaining_dirs = list(checkpoint_dir.glob("step_*"))
+    assert len(remaining_dirs) == checkpoint_manager.keep_top_k
+
+    # Checkpoints with missing validation metrics should be treated as having the worst possible value
+    # Since higher_is_better=False, missing metrics get float("inf") which is worst
+    # So checkpoints with actual loss values should be preferred over those without
+    remaining_steps = []
+    for dir_path in remaining_dirs:
+        step_num = int(dir_path.name.split("_")[1])
+        remaining_steps.append(step_num)
+
+    # Should keep checkpoints with actual loss values (step 1)
+    # followed by the most recent steps
+    # The latest checkpoint (step 12) is always kept
+    expected_steps = [1, 10, 12]  # Steps with loss metrics, plus latest
+    assert sorted(remaining_steps) == sorted(expected_steps)
+
+
 def test_get_best_checkpoint_path(checkpoint_manager, checkpoint_dir):
     # Create multiple checkpoints with different loss values
     steps = [1, 2, 3]