Fix the FSDP.optim_state_dict_to_load OOM (mosaicml#3184)

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composer/trainer/mosaic_fsdp.py

@@ -63,7 +63,13 @@ def patch_pytorch():
 
     elif version.parse(torch.__version__) < version.parse('2.2.9'):
         # Monkey patch for torch < 2.3.0 ie torch == 2.2.1/2.2.2 currently
-        pass
+
+        # Fix memory leak for FSDP.optim_state_dict_to_load
+        # https://github.com/pytorch/pytorch/issues/116553
+        from torch.distributed.fsdp import _optim_utils
+
+        from composer.trainer.mosaic_fsdp_utils import _shard_orig_param_state
+        _optim_utils._shard_orig_param_state = _shard_orig_param_state
 
     elif version.parse(torch.__version__) < version.parse('2.3.1'):
         # Monkey patch for torch < 2.3.1 ie torch == 2.3.0

composer/trainer/mosaic_fsdp_utils.py

@@ -1119,3 +1119,42 @@ def _same_storage(a, b):
         if isinstance(b, DTensor):
             b = b._local_tensor
         return a.untyped_storage().data_ptr() == b.untyped_storage().data_ptr()
+
+if version.parse(torch.__version__) >= version.parse('2.2.1') and version.parse(
+        torch.__version__,) < version.parse('2.2.9'):
+
+    from torch.distributed.fsdp._optim_utils import FSDPParamInfo
+    from torch.distributed.checkpoint._state_dict_utils import _gather_state_dict
+
+    @no_type_check
+    def _shard_orig_param_state(
+        fsdp_param_info: FSDPParamInfo,
+        fqn: str,
+        optim_state: Dict[str, Any],
+    ) -> Dict[str, Any]:
+        if not optim_state:
+            return {}
+        fsdp_state = fsdp_param_info.state
+        flat_param = fsdp_param_info.handle.flat_param
+        param_idx = fsdp_param_info.param_indices[fqn]
+        shard_param_info = flat_param._shard_param_infos[param_idx]  # type: ignore[attr-defined]
+        optim_state = _gather_state_dict(
+            optim_state, pg=fsdp_state.process_group, device=fsdp_state.compute_device,
+        )
+        if not shard_param_info.in_shard:
+            return {}
+        # Flatten and shard the state.
+        new_optim_state: Dict[str, Any] = {}
+        intra_param_start_idx = shard_param_info.intra_param_start_idx
+        intra_param_end_idx = shard_param_info.intra_param_end_idx
+        for state_name, value in optim_state.items():
+            if (
+                torch.is_tensor(value)
+                and value.dim() > 0
+                and fsdp_state.sharding_strategy != ShardingStrategy.NO_SHARD
+            ):
+                # This clone() is the patch to fix the OOM
+                # https://github.com/pytorch/pytorch/pull/117261
+                value = value.flatten()[intra_param_start_idx : intra_param_end_idx + 1].clone()  # type: ignore[operator]
+            new_optim_state[state_name] = value
+        return new_optim_state