add DTensor to optimizer state dict (pytorch#2585)

Summary:

To support 2D parallelism checkpointing, we introduce DTensor to the optimizer state dict. It is enabled through fused_params["output_dtensor"] = True, meaning when table shards are outputted in DTensor so are optimizer shards.

This diff allows us to leverage N-dimensional device meshes with support for abritrary replication/sharding groups - making checkpointing easy as DCP/Modelstore support replicated/sharded placements on a device mesh (something that is unsupported in ShardedTensor)

Differential Revision: D65555455

torchrec/distributed/batched_embedding_kernel.py

@@ -46,15 +46,18 @@
     PartiallyMaterializedTensor,
 )
 from torch import nn
+from torch.distributed._tensor import DTensor, Replicate, Shard as DTensorShard
 from torchrec.distributed.comm import get_local_rank, get_node_group_size
 from torchrec.distributed.composable.table_batched_embedding_slice import (
     TableBatchedEmbeddingSlice,
 )
 from torchrec.distributed.embedding_kernel import BaseEmbedding, get_state_dict
 from torchrec.distributed.embedding_types import (
     compute_kernel_to_embedding_location,
+    DTensorMetadata,
     GroupedEmbeddingConfig,
 )
+from torchrec.distributed.shards_wrapper import LocalShardsWrapper
 from torchrec.distributed.types import (
     Shard,
     ShardedTensor,
@@ -213,6 +216,7 @@ class ShardParams:
             optimizer_states: List[Optional[Tuple[torch.Tensor]]]
             local_metadata: List[ShardMetadata]
             embedding_weights: List[torch.Tensor]
+            dtensor_metadata: List[DTensorMetadata]
 
         def get_optimizer_single_value_shard_metadata_and_global_metadata(
             table_global_metadata: ShardedTensorMetadata,
@@ -389,7 +393,10 @@ def get_optimizer_pointwise_shard_metadata_and_global_metadata(
                 continue
             if table_config.name not in table_to_shard_params:
                 table_to_shard_params[table_config.name] = ShardParams(
-                    optimizer_states=[], local_metadata=[], embedding_weights=[]
+                    optimizer_states=[],
+                    local_metadata=[],
+                    embedding_weights=[],
+                    dtensor_metadata=[],
                 )
             optimizer_state_values = None
             if optimizer_states:
@@ -410,6 +417,9 @@ def get_optimizer_pointwise_shard_metadata_and_global_metadata(
             table_to_shard_params[table_config.name].local_metadata.append(
                 local_metadata
             )
+            table_to_shard_params[table_config.name].dtensor_metadata.append(
+                table_config.dtensor_metadata
+            )
             table_to_shard_params[table_config.name].embedding_weights.append(weight)
 
         seen_tables = set()
@@ -474,7 +484,7 @@ def get_optimizer_pointwise_shard_metadata_and_global_metadata(
                 # pyre-ignore
                 def get_sharded_optim_state(
                     momentum_idx: int, state_key: str
-                ) -> ShardedTensor:
+                ) -> Union[ShardedTensor, DTensor]:
                     assert momentum_idx > 0
                     momentum_local_shards: List[Shard] = []
                     optimizer_sharded_tensor_metadata: ShardedTensorMetadata
@@ -528,12 +538,41 @@ def get_sharded_optim_state(
                             )
                         )
 
-                    # TODO we should be creating this in SPMD fashion (e.g. init_from_local_shards), and let it derive global metadata.
-                    return ShardedTensor._init_from_local_shards_and_global_metadata(
-                        local_shards=momentum_local_shards,
-                        sharded_tensor_metadata=optimizer_sharded_tensor_metadata,
-                        process_group=self._pg,
-                    )
+                    # Convert optimizer state to DTensor if enabled
+                    if table_config.dtensor_metadata:
+                        # if rowwise state we do Shard(0), regardless of how the table is sharded
+                        if optim_state.dim() == 1:
+                            stride = (1,)
+                            placements = (
+                                (Replicate(), DTensorShard(0))
+                                if table_config.dtensor_metadata.mesh.ndim == 2
+                                else (DTensorShard(0),)
+                            )
+                        else:
+                            stride = table_config.dtensor_metadata.stride
+                            placements = table_config.dtensor_metadata.placements
+
+                        return DTensor.from_local(
+                            local_tensor=LocalShardsWrapper(
+                                local_shards=[x.tensor for x in momentum_local_shards],
+                                local_offsets=[  # pyre-ignore[6]
+                                    x.metadata.shard_offsets
+                                    for x in momentum_local_shards
+                                ],
+                            ),
+                            device_mesh=table_config.dtensor_metadata.mesh,
+                            placements=placements,
+                            shape=optimizer_sharded_tensor_metadata.size,
+                            stride=stride,
+                            run_check=False,
+                        )
+                    else:
+                        # TODO we should be creating this in SPMD fashion (e.g. init_from_local_shards), and let it derive global metadata.
+                        return ShardedTensor._init_from_local_shards_and_global_metadata(
+                            local_shards=momentum_local_shards,
+                            sharded_tensor_metadata=optimizer_sharded_tensor_metadata,
+                            process_group=self._pg,
+                        )
 
                 num_states: int = min(
                     # pyre-ignore

torchrec/distributed/shards_wrapper.py

@@ -68,10 +68,15 @@ def __new__(
 
         # we calculate the total tensor size by "concat" on second tensor dimension
         cat_tensor_shape = list(local_shards[0].size())
-        if len(local_shards) > 1:  # column-wise sharding
+        if len(local_shards) > 1 and local_shards[0].ndim == 2:  # column-wise sharding
             for shard in local_shards[1:]:
                 cat_tensor_shape[1] += shard.size()[1]
 
+        # in cases of sharding optimizer rowwise, we calculate total tensor size by "concat" on first tensor dimension
+        if len(local_shards) > 1 and local_shards[0].ndim == 1:  # column-wise sharding
+            for shard in local_shards[1:]:
+                cat_tensor_shape[0] += shard.size()[0]
+
         wrapper_properties = TensorProperties.create_from_tensor(local_shards[0])
         wrapper_shape = torch.Size(cat_tensor_shape)
         chunks_meta = [
@@ -110,6 +115,7 @@ def __torch_dispatch__(cls, func, types, args=(), kwargs=None):
             aten.equal.default: cls.handle_equal,
             aten.detach.default: cls.handle_detach,
             aten.clone.default: cls.handle_clone,
+            aten.new_empty.default: cls.handle_new_empty,
         }
 
         if func in dispatcher:
@@ -153,18 +159,28 @@ def handle_to_copy(args, kwargs):
     def handle_view(args, kwargs):
         view_shape = args[1]
         res_shards_list = []
-        if (
-            len(args[0].local_shards()) > 1
-            and args[0].storage_metadata().size[0] == view_shape[0]
-            and args[0].storage_metadata().size[1] == view_shape[1]
-        ):
-            # This accounts for a DTensor quirk, when multiple shards are present on a rank, DTensor on
-            # init calls view_as() on the global tensor shape
-            # will fail because the view shape is not applicable to individual shards.
-            res_shards_list = [
-                aten.view.default(shard, shard.shape, **kwargs)
-                for shard in args[0].local_shards()
-            ]
+        if len(args[0].local_shards()) > 1:
+            if args[0].local_shards()[0].ndim == 2:
+                assert (
+                    args[0].storage_metadata().size[0] == view_shape[0]
+                    and args[0].storage_metadata().size[1] == view_shape[1]
+                )
+                # This accounts for a DTensor quirk, when multiple shards are present on a rank, DTensor on
+                # init calls view_as() on the global tensor shape
+                # will fail because the view shape is not applicable to individual shards.
+                res_shards_list = [
+                    aten.view.default(shard, shard.shape, **kwargs)
+                    for shard in args[0].local_shards()
+                ]
+            elif args[0].local_shards()[0].ndim == 1:
+                assert args[0].storage_metadata().size[0] == view_shape[0]
+                # This case is for optimizer sharding as regardles of sharding type, optimizer state is row wise sharded
+                res_shards_list = [
+                    aten.view.default(shard, shard.shape, **kwargs)
+                    for shard in args[0].local_shards()
+                ]
+            else:
+                raise NotImplementedError("No support for view on tensors ndim > 2")
         else:
             # view is called per shard
             res_shards_list = [
@@ -220,6 +236,16 @@ def handle_clone(args, kwargs):
         ]
         return LocalShardsWrapper(cloned_local_shards, self_ls.local_offsets())
 
+    @staticmethod
+    # pyre-fixme[3]: Return type must be annotated.
+    # pyre-fixme[2]: Parameter must be annotated.
+    def handle_new_empty(args, kwargs):
+        self_ls = args[0]
+        return LocalShardsWrapper(
+            [torch.empty_like(shard) for shard in self_ls._local_shards],
+            self_ls.local_offsets(),
+        )
+
     @property
     def device(self) -> torch._C.device:  # type: ignore[override]
         return (

torchrec/optim/keyed.py

@@ -27,6 +27,8 @@
 
 from torch import optim
 from torch.distributed._shard.sharded_tensor import ShardedTensor
+from torch.distributed.tensor import DTensor
+from torchrec.distributed.shards_wrapper import LocalShardsWrapper
 
 
 OptimizerFactory = Callable[[List[Union[torch.Tensor, ShardedTensor]]], optim.Optimizer]
@@ -134,6 +136,24 @@ def _update_param_state_dict_object(
                     )
                 for shard, new_shard in zip(v.local_shards(), new_v.local_shards()):
                     shard.tensor.detach().copy_(new_shard.tensor)
+            elif isinstance(v, DTensor):
+                assert isinstance(new_v, DTensor)
+                # pyre-ignore[16]
+                if isinstance(v.to_local(), LocalShardsWrapper):
+                    assert isinstance(new_v.to_local(), LocalShardsWrapper)
+                    num_shards = len(v.to_local().local_shards())
+                    num_new_shards = len(new_v.to_local().local_shards())
+                    if num_shards != num_new_shards:
+                        raise ValueError(
+                            f"Different number of shards {num_shards} vs {num_new_shards} for the path of {json.dumps(parent_keys)}"
+                        )
+                    for shard, new_shard in zip(
+                        v.to_local().local_shards(), new_v.to_local().local_shards()
+                    ):
+                        shard.detach().copy_(new_shard)
+                else:
+                    assert isinstance(new_v.to_local(), torch.Tensor)
+                    v.detach().copy_(new_v)
             elif isinstance(v, torch.Tensor):
                 v.detach().copy_(new_v)
             else: