[shardformer] support sharded checkpoint IO for models of HybridParallelPlugin (#4506)

* add APIs

* implement save_sharded_model

* add test for hybrid checkpointio

* implement naive loading for sharded model

* implement efficient sharded model loading

* open a new file for hybrid checkpoint_io

* small fix

* fix circular importing

* fix docstring

* arrange arguments and apis

* small fix

colossalai/checkpoint_io/utils.py

@@ -13,7 +13,12 @@ from torch.optim import Optimizer
 
 from colossalai.interface import OptimizerWrapper
 from colossalai.nn.optimizer import ColossalaiOptimizer
-from colossalai.tensor.d_tensor import is_distributed_tensor
+from colossalai.tensor.d_tensor import (
+    is_customized_distributed_tensor,
+    is_distributed_tensor,
+    to_global,
+    to_global_for_customized_distributed_tensor,
+)
 
 SAFE_WEIGHTS_NAME = "model.safetensors"
 WEIGHTS_NAME = "pytorch_model.bin"
@@ -88,8 +93,28 @@ def is_safetensor_checkpoint(checkpoint_file_path: str) -> bool:
         return False
 
 
+def gather_distributed_param(param: torch.Tensor, keep_vars: bool = False):
+    """
+    Gather the complete parameter for saving if passed in param is distributed.
+
+    Args:
+        param (torch.Tensor): A model parameter, might be d_tensor.
+        keep_vars (bool, optional): Whether to return the parameter in calculation graph. Defaults to False.
+
+    Returns:
+        torch.Tensor: the complete parameter
+    """
+    param_ = param if keep_vars else param.detach()
+    if is_distributed_tensor(param_):
+        return to_global(param_)
+    elif is_customized_distributed_tensor(param_):
+        return to_global_for_customized_distributed_tensor(param_)
+    else:
+        return param_
+
+
 # ======================================
-# Helper functions for saving shard file
+# Helper classes and functions for saving shard file
 # ======================================
 def unwrap_optimizer(optimizer: OptimizerWrapper):
     '''
@@ -104,6 +129,31 @@ def unwrap_optimizer(optimizer: OptimizerWrapper):
     return unwrapped_optim
 
 
+class StateDictSharder:
+
+    def __init__(self, size_per_shard: int) -> None:
+        self.max_shard_size = size_per_shard
+        self.current_block = OrderedDict()
+        self.current_block_size = 0
+
+    def append(self, name: str, tensor: torch.Tensor) -> Tuple[Optional[OrderedDict], int]:
+        tensor_size = calculate_tensor_size(tensor)
+        ret_block = None
+        ret_block_size = 0
+
+        # before we return the current block and create a new block,
+        # we need to ensure that the current block is not empty
+        if self.current_block_size + tensor_size > self.max_shard_size and self.current_block_size > 0:
+            ret_block = self.current_block
+            ret_block_size = self.current_block_size
+            self.current_block = OrderedDict()
+            self.current_block_size = 0
+
+        self.current_block[name] = tensor
+        self.current_block_size += tensor_size
+        return ret_block, ret_block_size
+
+
 def save_state_dict_shards(sharded_state_dict: Iterator[Tuple[OrderedDict, int]],
                            checkpoint: str,
                            index_file: "CheckpointIndexFile",
@@ -126,9 +176,10 @@ def save_state_dict_shards(sharded_state_dict: Iterator[Tuple[OrderedDict, int]]
 
     total_size = 0
     for idx, shard_pair in enumerate(sharded_state_dict):
-        if not is_master:
-            continue
         shard, current_size = shard_pair
+        if not is_master:
+            del shard
+            continue
         shard_file = get_shard_filename(base_filename, idx)
         total_size = total_size + current_size
         for key in shard.keys():
@@ -137,6 +188,7 @@ def save_state_dict_shards(sharded_state_dict: Iterator[Tuple[OrderedDict, int]]
 
         # Only save on master rank.
         save_state_dict(shard, checkpoint_file_path, use_safetensors=use_safetensors)
+        del shard
 
     return total_size