[zero] a shard strategy in granularity of tensor (#307)

colossalai/zero/shard_utils/__init__.py

+from colossalai.zero.shard_utils.base_shard_strategy import BaseShardStrategy
+from colossalai.zero.shard_utils.tensor_shard_strategy import TensorShardStrategy
+
+__all__ = ['BaseShardStrategy', 'TensorShardStrategy']

colossalai/zero/shard_utils/base_shard_strategy.py

+from abc import ABC, abstractmethod
+from colossalai.zero.sharded_param.sharded_tensor import ShardedTensor
+import torch.distributed as dist
+from typing import List, Optional
+
+
+class BaseShardStrategy(ABC):
+
+    def __init__(self, process_group: Optional[dist.ProcessGroup] = None) -> None:
+        self.process_group = process_group
+        self.world_size = dist.get_world_size(self.process_group)
+        self.local_rank = dist.get_rank(self.process_group)
+        super().__init__()
+
+    @abstractmethod
+    def shard(self, tensor_list: List[ShardedTensor]):
+        r"""
+        sharded the memory of tensor on multiple processes.
+        """
+        pass
+
+    @abstractmethod
+    def gather(self, tensor_list: List[ShardedTensor]):
+        r"""
+        duplicate tensor payload on each processes.
+        """
+        pass

colossalai/zero/shard_utils/tensor_shard_strategy.py

+from colossalai.zero.shard_utils import BaseShardStrategy
+import torch.distributed as dist
+from typing import List, Optional
+from colossalai.zero.sharded_param.sharded_tensor import ShardedTensor
+
+
+class TensorShardStrategy(BaseShardStrategy):
+
+    def __init__(self, process_group: Optional[dist.ProcessGroup] = None) -> None:
+        super().__init__(process_group)
+
+    def shard(self, tensor_list: List[ShardedTensor]):
+        for t in tensor_list:
+            t.shard()
+
+    def gather(self, tensor_list: List[ShardedTensor]):
+        for t in tensor_list:
+            t.gather()

tests/test_zero_data_parallel/test_shard_param.py

@@ -7,6 +7,8 @@ import colossalai
 import pytest
 import torch
 import torch.multiprocessing as mp
+
+from colossalai.zero.shard_utils import TensorShardStrategy
 from colossalai.zero.sharded_param import ShardedTensor, ShardedParam
 from colossalai.utils import free_port
 from colossalai.logging import get_dist_logger, disable_existing_loggers
@@ -18,19 +20,14 @@ def run_shard_tensor(rank, world_size, port):
     t = ShardedTensor(tensor=torch.randn(world_size * 2, 3))
 
     assert list(t.shape) == [world_size * 2, 3]
-    t.shard()
-    # The shape is flattened
-    assert list(t.shape) == [6]
-    # Do nothing
-    t.shard()
-    assert list(t.shape) == [6]
+    shard_strategy = TensorShardStrategy(process_group=None)
 
-    t.gather()
+    # test shard strategy
+    shard_strategy.shard([t])
+    assert list(t.shape) == [6]
+    shard_strategy.gather([t])
     assert list(t.shape) == [world_size * 2, 3]
 
-    t.payload = torch.zeros(world_size * 2, 3)
-    assert torch.sum(t.payload).cpu() == 0
-
 
 @pytest.mark.dist
 def test_shard_tensor():