[Examples] Add lazy init to OPT and GPT examples (#5924)

Co-authored-by: Edenzzzz <wtan45@wisc.edu>

examples/language/opt/opt_benchmark.py

@@ -1,4 +1,5 @@
 import time
+from contextlib import nullcontext
 
 import torch
 import tqdm
@@ -8,9 +9,11 @@ from transformers import AutoConfig, OPTForCausalLM
 from transformers.utils.versions import require_version
 
 import colossalai
+from colossalai.accelerator import get_accelerator
 from colossalai.booster import Booster
 from colossalai.booster.plugin import GeminiPlugin, LowLevelZeroPlugin, TorchDDPPlugin
 from colossalai.cluster import DistCoordinator
+from colossalai.lazy import LazyInitContext
 from colossalai.logging import disable_existing_loggers, get_dist_logger
 from colossalai.nn.optimizer import HybridAdam
 
@@ -62,14 +65,6 @@ def main():
     if args.mem_cap > 0:
         colo_memory_cap(args.mem_cap)
 
-    # Build OPT model
-    config = AutoConfig.from_pretrained(args.model_name_or_path)
-    model = OPTForCausalLM(config=config)
-    logger.info(f"Finish loading model from {args.model_name_or_path}", ranks=[0])
-
-    # Enable gradient checkpointing
-    model.gradient_checkpointing_enable()
-
     # Set plugin
     booster_kwargs = {}
     if args.plugin == "torch_ddp_fp16":
@@ -82,6 +77,19 @@ def main():
         plugin = LowLevelZeroPlugin(initial_scale=2**5)
     logger.info(f"Set plugin as {args.plugin}", ranks=[0])
 
+    # Build OPT model
+    init_ctx = (
+        LazyInitContext(default_device=get_accelerator().get_current_device())
+        if isinstance(plugin, (GeminiPlugin))
+        else nullcontext()
+    )
+    config = AutoConfig.from_pretrained(args.model_name_or_path)
+    with init_ctx:
+        model = OPTForCausalLM(config=config)
+    logger.info(f"Finish loading model from {args.model_name_or_path}", ranks=[0])
+
+    # Enable gradient checkpointing
+    model.gradient_checkpointing_enable()
     # Set optimizer
     optimizer = HybridAdam(model.parameters(), lr=args.learning_rate)