Fix error when training is resumed

slime/backends/megatron_utils/actor.py

@@ -78,7 +78,11 @@ def init(
             Timer().start("train_wait")
             return
 
-        start_rollout_id = loaded_rollout_id + 1
+        expected_start_rollout_id = 0 if loaded_rollout_id == 0 else (loaded_rollout_id + 1)
+        assert (
+            args.start_rollout_id == expected_start_rollout_id
+        ), f"{args.start_rollout_id=} {expected_start_rollout_id=}"
+
         self.weights = {"actor": {}}
         self.update_cpu_params_dict(self.weights["actor"])
 
@@ -137,7 +141,6 @@ def init(
             self.prof.start()
 
         Timer().start("train_wait")
-        return start_rollout_id
 
     @torch.no_grad()
     def update_cpu_params_dict(self, params_dict: Dict[str, torch.Tensor]) -> None:

slime/ray/placement_group.py

@@ -140,13 +140,7 @@ def create_training_models(args, pgs, rollout_manager, wandb_run_id):
     else:
         critic_model = None
 
-    start_rollout_ids = ray.get(
-        actor_model.async_init(args, role="actor", with_ref=args.kl_coef != 0 or args.use_kl_loss)
-    )
-
-    assert len(set(start_rollout_ids)) == 1
-    if args.start_rollout_id is None:
-        args.start_rollout_id = start_rollout_ids[0]
+    ray.get(actor_model.async_init(args, role="actor", with_ref=args.kl_coef != 0 or args.use_kl_loss))
 
     if args.use_critic:
         ray.get(critic_init_handle)

slime/utils/arguments.py

@@ -8,6 +8,7 @@
 
 from slime.backends.sglang_utils.arguments import add_sglang_arguments
 from slime.backends.sglang_utils.arguments import validate_args as sglang_validate_args
+from slime.utils.checkpoint_utils import get_latest_checkpointed_iteration
 
 
 def reset_arg(parser, name, **kwargs):
@@ -1126,19 +1127,17 @@ def slime_validate_args(args):
                 "please make sure it is a valid megatron checkpoint directory."
             )
 
-    # TODO: During loading, we need to set the start_rollout_id here.
-    if (
-        args.load is None
-        or not os.path.exists(args.load)
-        or not os.path.exists(os.path.join(args.load, "latest_checkpointed_iteration.txt"))
-    ):
+    load_ckpt_iter = get_latest_checkpointed_iteration(args)
+    if load_ckpt_iter is None:
         args.no_load_optim = True
         args.no_load_rng = True
         args.finetune = True
         args.load = args.ref_load
         if args.ref_ckpt_step is not None:
             args.ckpt_step = args.ref_ckpt_step
         args.start_rollout_id = 0
+    else:
+        args.start_rollout_id = load_ckpt_iter + 1
 
     if args.eval_interval is not None:
         assert args.eval_prompt_data is not None, "eval_prompt_data must be set when eval_interval is set"

slime/utils/checkpoint_utils.py

@@ -0,0 +1,19 @@
+from pathlib import Path
+from typing import Optional
+
+
+def get_latest_checkpointed_iteration(args) -> Optional[int]:
+    """
+    :param args: The Megatron arguments
+    """
+    if (x := args.ckpt_step) is not None:
+        return x
+
+    if args.load is None:
+        return None
+
+    path_txt = Path(args.load) / "latest_checkpointed_iteration.txt"
+    if not path_txt.exists():
+        return None
+
+    return int(path_txt.read_text())