[ONNX] Enable 'ExportOutput.save' for models larger than 2GB

test/onnx/dynamo/test_exporter_api.py

@@ -9,6 +9,7 @@
 from torch.onnx._internal import exporter, io_adapter
 from torch.onnx._internal.exporter import (
     ExportOutputSerializer,
+    LargeProtobufExportOutputSerializer,
     ProtobufExportOutputSerializer,
     ResolvedExportOptions,
 )
@@ -24,6 +25,16 @@ def forward(self, x):
         return (y, z)
 
 
+class _LargeModel(torch.nn.Module):
+    def __init__(self):
+        super().__init__()
+        self.param = torch.nn.Parameter(torch.randn(2**28))  # 1GB
+        self.param2 = torch.nn.Parameter(torch.randn(2**28))  # 1GB
+
+    def forward(self, x):
+        return self.param + self.param2 + x
+
+
 class TestExportOptionsAPI(common_utils.TestCase):
     def test_raise_on_invalid_argument_type(self):
         expected_exception_type = roar.BeartypeException
@@ -110,6 +121,17 @@ def serialize(
             with open(path) as fp:
                 self.assertEqual(fp.read(), expected_buffer)
 
+    def test_save_succeeds_when_model_greater_than_2gb_and_destination_is_str(self):
+        with common_utils.TemporaryFileName() as path:
+            dynamo_export(_LargeModel(), torch.randn(1)).save(path)
+
+    def test_save_raises_when_model_greater_than_2gb_and_destination_is_not_str(self):
+        with self.assertRaisesRegex(
+            ValueError,
+            "'destination' must be a string when saving model larger than 2GB.",
+        ):
+            dynamo_export(_LargeModel(), torch.randn(1)).save(io.BytesIO())
+
     def test_save_sarif_log_to_file_with_successful_export(self):
         with common_utils.TemporaryFileName(suffix=".sarif") as path:
             dynamo_export(SampleModel(), torch.randn(1, 1, 2)).save_diagnostics(path)
@@ -182,6 +204,21 @@ def test_raise_on_invalid_argument_type(self):
             serializer = ProtobufExportOutputSerializer()
             serializer.serialize(None, None)  # type: ignore[arg-type]
 
+    def test_serialize_raises_when_model_greater_than_2gb(self):
+        export_output = torch.onnx.dynamo_export(_LargeModel(), torch.randn(1))
+        serializer = ProtobufExportOutputSerializer()
+        with self.assertRaisesRegex(ValueError, "exceeds maximum protobuf size of 2GB"):
+            serializer.serialize(export_output, io.BytesIO())
+
+
+class TestLargeProtobufExportOutputSerializerAPI(common_utils.TestCase):
+    def test_serialize_succeeds_when_model_greater_than_2gb(self):
+        export_output = torch.onnx.dynamo_export(_LargeModel(), torch.randn(1))
+        with common_utils.TemporaryFileName() as path:
+            serializer = LargeProtobufExportOutputSerializer(path)
+            # `io.BytesIO()` is unused, but required by the Protocol interface.
+            serializer.serialize(export_output, io.BytesIO())
+
 
 if __name__ == "__main__":
     common_utils.run_tests()

torch/onnx/_internal/exporter.py

@@ -544,6 +544,36 @@
         destination.write(export_output.model_proto.SerializeToString())
 
 
+class LargeProtobufExportOutputSerializer:
+    """Serializes ONNX graph as Protobuf.
+
+    Fallback to serializing as Protobuf with external data for models larger than 2GB.
+    """
+
+    _destination_path: Final[str]
+
+    def __init__(self, destination_path: str):
+        self._destination_path = destination_path
+
+    @_beartype.beartype
+    def serialize(
+        self, export_output: ExportOutput, destination: io.BufferedIOBase
+    ) -> None:
+        """`destination` is ignored. The model is saved to `self._destination_path` instead."""
+        import onnx
+
+        try:
+            onnx.save_model(export_output.model_proto, self._destination_path)
+        except ValueError:
+            # ValueError: Message onnx.ModelProto exceeds maximum protobuf size of 2GB
+            # Fallback to serializing the model with external data.
+            onnx.save_model(
+                export_output.model_proto,
+                self._destination_path,
+                save_as_external_data=True,
+            )
+
+
 class ExportOutput:
     """An in-memory representation of a PyTorch model that has been exported to ONNX."""
 
@@ -724,7 +754,10 @@
         """
 
         if serializer is None:
-            serializer = ProtobufExportOutputSerializer()
+            if isinstance(destination, str):
+                serializer = LargeProtobufExportOutputSerializer(destination)
+            else:
+                serializer = ProtobufExportOutputSerializer()
 
         # Add initializers when symbolic tracing is enabled
         _model_state_dict_files: List[Union[str, io.BytesIO]] = []
@@ -779,7 +812,12 @@
                 with open(destination, "wb") as f:
                     serializer.serialize(self, f)
             else:
-                serializer.serialize(self, destination)
+                try:
+                    serializer.serialize(self, destination)
+                except ValueError:
+                    raise ValueError(
+                        "'destination' must be a string when saving model larger than 2GB."
+                    )
 
     @_beartype.beartype
     def save_diagnostics(self, destination: str) -> None: