Repository: huggingface/transformers
File: src/transformers/integrations/deepspeed.py (Python)

Code before:
        inference_config = ds_config.get("inference", {})
        if isinstance(inference_config, dict):
            tp_size = max(tp_size, inference_config.get("tensor_parallel", {}).get("tp_size", 1))
        if tp_size > 1:
            raise NotImplementedError(
                "Weight conversions (e.g., MoE expert fusion) with DeepSpeed Tensor Parallelism "
                "are not yet implemented but support is coming soon. Please disable tensor_parallel "
                "in your DeepSpeed config or convert your checkpoint to the expected format first."
            )

    from ..core_model_loading import WeightConverter, WeightRenaming, dot_natural_key, rename_source_key

    # Preserve metadata from the original state dict
    metadata = getattr(state_dict, "_metadata", None)

    prefix = model.base_model_prefix
    meta_model_state_dict = model.state_dict()

    renamings = [entry for entry in weight_mapping if isinstance(entry, WeightRenaming)]
    converters = [entry for entry in weight_mapping if isinstance(entry, WeightConverter)]

    # Fast path: if we only have simple renamings and no converters, we can skip the expensive collection logic
    if len(converters) == 0:
        new_state_dict = {}
        for original_key, tensor in state_dict.items():
            renamed_key, _ = rename_source_key(original_key, renamings, [], prefix, meta_model_state_dict)
            if renamed_key in meta_model_state_dict:
                new_state_dict[renamed_key] = tensor
        # Attach metadata to the new state dict
        if metadata is not None:
            new_state_dict._metadata = metadata
        return new_state_dict

    # Full path: we have WeightConverter operations that require tensor fusion/splitting
    pattern_to_converter = {k: converter for converter in converters for k in converter.source_patterns}

    # Build a mapping of what needs to be converted
    # Sort the state dict items to ensure consistent ordering (important for MoE conversions)
    conversion_mapping = {}
    key_rename_cache = {}  # Cache rename results to avoid redundant processing in cleanup loop
    sorted_state_dict = sorted(state_dict.items(), key=lambda kv: dot_natural_key(kv[0]))
    for original_key, tensor in sorted_state_dict:
        # Rename the key according to all renaming pattern and optional weight converter patterns
        renamed_key, source_pattern = rename_source_key(
            original_key, renamings, converters, prefix, meta_model_state_dict
        )

        # Cache the rename result for use in the cleanup loop
        key_rename_cache[original_key] = renamed_key

        # Only process if the renamed key is in the model's state dict

Review comment (suggestion):
```suggestion
            renamed_key, _ = rename_source_key(original_key, renamings, [], prefix, model_state_dict)
```

Code after:
        inference_config = ds_config.get("inference", {})
        if isinstance(inference_config, dict):
            tp_size = max(tp_size, inference_config.get("tensor_parallel", {}).get("tp_size", 1))
        if tp_size > 1:
            raise NotImplementedError(
                "Weight conversions (e.g., MoE expert fusion) with DeepSpeed Tensor Parallelism "
                "are not yet implemented but support is coming soon. Please disable tensor_parallel "
                "in your DeepSpeed config or convert your checkpoint to the expected format first."
            )

    from ..core_model_loading import WeightConverter, WeightRenaming, dot_natural_key, rename_source_key

    # Preserve metadata from the original state dict
    metadata = getattr(state_dict, "_metadata", None)

    prefix = model.base_model_prefix

    # Build a meta state dict for matching - only keys/shapes, no actual tensor data
    # This minimizes memory since we don't duplicate the model's parameters
    model_state_dict = {}
    for key, param in model.state_dict().items():
        model_state_dict[key] = torch.empty(param.shape, dtype=param.dtype, device="meta")

    renamings = [entry for entry in weight_mapping if isinstance(entry, WeightRenaming)]
    converters = [entry for entry in weight_mapping if isinstance(entry, WeightConverter)]

    # Fast path: if we only have simple renamings and no converters, we can skip the expensive collection logic
    if len(converters) == 0:
        new_state_dict = {}
        for original_key, tensor in state_dict.items():
            renamed_key, _ = rename_source_key(original_key, renamings, [], prefix, model_state_dict)
            if renamed_key in model_state_dict:
                new_state_dict[renamed_key] = tensor
        # Attach metadata to the new state dict
        if metadata is not None:
            new_state_dict._metadata = metadata
        return new_state_dict

    # Full path: we have WeightConverter operations that require tensor fusion/splitting
    pattern_to_converter = {k: converter for converter in converters for k in converter.source_patterns}

    # Build a mapping of what needs to be converted
    # Sort keys to ensure consistent ordering (important for MoE conversions)
    # Iterate over sorted keys and pop from state_dict to free memory immediately
    conversion_mapping = {}
    key_rename_cache = {}  # Cache rename results to avoid redundant processing
    sorted_keys = sorted(state_dict.keys(), key=lambda k: dot_natural_key(k))
    for original_key in sorted_keys:
        tensor = state_dict.pop(original_key)  # Pop to free memory immediately
        # Rename the key according to all renaming pattern and optional weight converter patterns
        renamed_key, source_pattern = rename_source_key(original_key, renamings, converters, prefix, model_state_dict)