improve docs

docs/source/distributed/tensors.rst

@@ -4,3 +4,7 @@
 .. automodule:: olmo_core.distributed.tensors
    :members:
    :member-order: bysource
+
+.. automodule:: olmo_core.distributed.tensors.dtensor_utils
+   :members:
+   :member-order: bysource

src/olmo_core/distributed/checkpoint.py

@@ -8,7 +8,8 @@
 --------
 
 - Sharded distributed models, such OLMo-core's :class:`~olmo_core.distributed.fsdp.FSDP` or PyTorch's
-  :class:`~torch.distributed.fsdp.FullyShardedDataParallel` are supported out-of-the-box.
+  :class:`~torch.distributed.fsdp.FullyShardedDataParallel` (with ``use_orig_params=True``)
+  are supported out-of-the-box.
 - Utilizes `safetensors <https://huggingface.co/docs/safetensors/>`_ under the hood for fast, efficient, and
   safe serialization/deserialization.
 - Save with one distributed topology, seamlessly load with a different one. For example,

src/olmo_core/distributed/tensors/dtensor_utils.py

@@ -16,6 +16,16 @@
 def get_local_shape_and_global_offset(
     dtensor: DTensor, rank: Optional[int] = None
 ) -> Tuple[Tuple[int, ...], Tuple[int, ...]]:
+    """
+    Like :func:`compute_local_shape_and_global_offset`, but acts directly on a :class:`DTensor`
+    instance.
+
+    :param dtensor: A DTensor instance.
+    :param rank: The global rank to compute the local shape and global offsets for. If ``None``,
+        defaults to the current rank.
+
+    :returns: The local shape and global offset.
+    """
     global_shape = dtensor.shape
     mesh = dtensor.device_mesh
     placements = dtensor.placements
@@ -41,9 +51,11 @@ def compute_local_shape_and_global_offset(
     :param rank: The global rank to compute the local shape and global offsets for. If ``None``,
         defaults to the current rank.
 
-    Example (2 host with 4GPUs each):
+    :returns: The local shape and global offset.
+
+    Example (2 host with 4GPUs each)::
 
-        # Below is a DeviceMesh with mesh_shape of ``(2, 4)``
+        # Below is a DeviceMesh with mesh_shape of (2, 4)
         mesh = DeviceMesh(device_type="cuda", mesh=[
             [0, 1, 2, 3],
             [4, 5, 6, 7]
@@ -53,27 +65,29 @@ def compute_local_shape_and_global_offset(
     with a placements of ``[Shard(0), Shard(0)]``.
 
     The local shape and global offset will be as follows:
-    rank0 -- local_shape:[1, 4], global_offset:[0, 0]
-    rank1 -- local_shape:[1, 4], global_offset:[1, 0]
-    rank2 -- local_shape:[1, 4], global_offset:[2, 0]
-    rank5 -- local_shape:[1, 4], global_offset:[5, 0]
-    rank3 -- local_shape:[1, 4], global_offset:[3, 0]
-    rank4 -- local_shape:[1, 4], global_offset:[4, 0]
-    rank6 -- local_shape:[1, 4], global_offset:[6, 0]
-    rank7 -- local_shape:[1, 4], global_offset:[7, 0]
+
+    - ``rank0 -- local_shape:[1, 4], global_offset:[0, 0]``
+    - ``rank1 -- local_shape:[1, 4], global_offset:[1, 0]``
+    - ``rank2 -- local_shape:[1, 4], global_offset:[2, 0]``
+    - ``rank5 -- local_shape:[1, 4], global_offset:[5, 0]``
+    - ``rank3 -- local_shape:[1, 4], global_offset:[3, 0]``
+    - ``rank4 -- local_shape:[1, 4], global_offset:[4, 0]``
+    - ``rank6 -- local_shape:[1, 4], global_offset:[6, 0]``
+    - ``rank7 -- local_shape:[1, 4], global_offset:[7, 0]``
 
     Let's say we distribute a global_tensor of shape ``(2,)`` over the above DeviceMesh with
     a placements of ``[Shard(0)]``. We will not have non-empty local tensor for all the ranks.
 
     The local shape and global offset will be as follows:
-    rank0 -- local_shape:[1,], global_offset:[0,]
-    rank1 -- local_shape:[1,], global_offset:[1,]
-    rank2 -- local_shape:[0,], global_offset:[2,]
-    rank5 -- local_shape:[0,], global_offset:[2,]
-    rank3 -- local_shape:[0,], global_offset:[2,]
-    rank4 -- local_shape:[0,], global_offset:[2,]
-    rank6 -- local_shape:[0,], global_offset:[2,]
-    rank7 -- local_shape:[0,], global_offset:[2,]
+
+    - ``rank0 -- local_shape:[1,], global_offset:[0,]``
+    - ``rank1 -- local_shape:[1,], global_offset:[1,]``
+    - ``rank2 -- local_shape:[0,], global_offset:[2,]``
+    - ``rank5 -- local_shape:[0,], global_offset:[2,]``
+    - ``rank3 -- local_shape:[0,], global_offset:[2,]``
+    - ``rank4 -- local_shape:[0,], global_offset:[2,]``
+    - ``rank6 -- local_shape:[0,], global_offset:[2,]``
+    - ``rank7 -- local_shape:[0,], global_offset:[2,]``
     """
     my_coordinate = mesh.get_coordinate() if rank is None else get_mesh_coordinates(mesh, rank)