[moe] add checkpoint for moe models (#3354)

* [moe] add checkpoint for moe models

* [hotfix] fix bugs in unit test

tests/test_moe/test_moe_checkpoint.py

@@ -0,0 +1,54 @@
+import os
+from functools import partial
+
+import pytest
+import torch
+import torch.distributed as dist
+import torch.multiprocessing as mp
+
+import colossalai
+from colossalai.context import MOE_CONTEXT
+from colossalai.nn.layer.moe import load_moe_model, save_moe_model
+from colossalai.testing import parameterize, rerun_if_address_is_in_use
+from colossalai.utils import free_port, get_current_device
+from colossalai.utils.model.colo_init_context import ColoInitContext
+from tests.test_moe.test_moe_zero_init import MoeModel
+from tests.test_tensor.common_utils import debug_print
+from tests.test_zero.common import CONFIG
+
+
+def exam_moe_checkpoint():
+    with ColoInitContext(device=get_current_device()):
+        model = MoeModel(checkpoint=True)
+    save_moe_model(model, 'temp_path.pth')
+
+    with ColoInitContext(device=get_current_device()):
+        other_model = MoeModel(checkpoint=True)
+    load_moe_model(other_model, 'temp_path.pth')
+
+    state_0 = model.state_dict()
+    state_1 = other_model.state_dict()
+    for k, v in state_0.items():
+        u = state_1.get(k)
+        assert torch.equal(u.data, v.data)
+
+    if dist.get_rank() == 0:
+        os.remove('temp_path.pth')
+
+
+def _run_dist(rank, world_size, port):
+    colossalai.launch(config=CONFIG, rank=rank, world_size=world_size, host='localhost', port=port, backend='nccl')
+    MOE_CONTEXT.setup(seed=42)
+    exam_moe_checkpoint()
+
+
+@pytest.mark.dist
+@pytest.mark.parametrize("world_size", [2, 4])
+@rerun_if_address_is_in_use()
+def test_moe_checkpoint(world_size):
+    run_func = partial(_run_dist, world_size=world_size, port=free_port())
+    mp.spawn(run_func, nprocs=world_size)
+
+
+if __name__ == '__main__':
+    test_moe_checkpoint(world_size=4)