fixed deserializing issue with old checkpoint

megatron/utils.py

@@ -338,7 +338,19 @@ def load_checkpoint(model, optimizer, lr_scheduler, args):
             torch.distributed.get_rank(), checkpoint_name))
 
     # Load the checkpoint.
-    sd = torch.load(checkpoint_name, map_location='cpu')
+    try:
+        sd = torch.load(checkpoint_name, map_location='cpu')
+    except ModuleNotFoundError:
+        # For backward compatibility.
+        print_rank_0(' > deserializing using the old code structure ...')
+        import sys
+        sys.modules['fp16.loss_scaler'] = sys.modules[
+            'megatron.fp16.loss_scaler']
+        sd = torch.load(checkpoint_name, map_location='cpu')
+        sys.modules.pop('fp16.loss_scaler', None)
+    except:
+        print_rank_0('could not load the checkpoint')
+        exit()
 
     # Iterations.
     if args.finetune or release: