Add IR serializer for KTRegroupAsDict Module (pytorch#1900)

Summary:
Pull Request resolved: pytorch#1900

# context
* previously `KTRegroupAsDict` can't really supported by torch.export (IR) because this module has an intialization step as running the first batch.
* during the export the `KTRegroupAsDict` module will be initialized by a fake_tensor which is wrong
* if we initialize the module before torch.export, the device would be an issue.
* another issue is that current torch.export [can't support conditional logic in training](https://pytorch.org/docs/stable/cond.html), where initialization step only runs once.
> torch.cond is a prototype feature in PyTorch. It has limited support for input and output types and doesn’t support training currently. Please look forward to a more stable implementation in a future version of PyTorch.

NOTE: this is more like a workaround solution, real solution needs support from pytorch compile for conditional logic

# details
* we treat the `KTRegroupAsDict` as another sparse_arch and do the model swap before and after torch.export.
* more context: D59019375

Differential Revision: D56282744

torchrec/ir/schema.py

@@ -48,3 +48,9 @@ class PositionWeightedModuleMetadata:
 @dataclass
 class PositionWeightedModuleCollectionMetadata:
     max_feature_lengths: List[Tuple[str, int]]
+
+
+@dataclass
+class KTRegroupAsDictMetadata:
+    groups: List[List[str]]
+    keys: List[str]

torchrec/ir/serializer.py

@@ -8,15 +8,15 @@
 # pyre-strict
 
 import json
-from typing import Any, Dict, List, Optional, Tuple, Type
+from typing import Any, Dict, List, Optional, Type
 
 import torch
-
 from torch import nn
 from torchrec.ir.schema import (
     EBCMetadata,
     EmbeddingBagConfigMetadata,
     FPEBCMetadata,
+    KTRegroupAsDictMetadata,
     PositionWeightedModuleCollectionMetadata,
     PositionWeightedModuleMetadata,
 )
@@ -32,6 +32,7 @@
     PositionWeightedModuleCollection,
 )
 from torchrec.modules.fp_embedding_modules import FeatureProcessedEmbeddingBagCollection
+from torchrec.modules.regroup import KTRegroupAsDict
 from torchrec.sparse.jagged_tensor import KeyedJaggedTensor, KeyedTensor
 
 
@@ -125,6 +126,22 @@ def fpebc_meta_forward(
     )
 
 
+def kt_regroup_meta_forward(
+    op_module: KTRegroupAsDict, keyed_tensors: List[KeyedTensor]
+) -> Dict[str, torch.Tensor]:
+    lengths_dict: Dict[str, int] = {}
+    batch_size = keyed_tensors[0].values().size(0)
+    for kt in keyed_tensors:
+        for key, length in zip(kt.keys(), kt.length_per_key()):
+            lengths_dict[key] = length
+    out_lengths: List[int] = [0] * len(op_module._groups)
+    for i, group in enumerate(op_module._groups):
+        out_lengths[i] = sum(lengths_dict[key] for key in group)
+    arg_list = [kt.values() for kt in keyed_tensors]
+    outputs = torch.ops.torchrec.ir_custom_op(arg_list, batch_size, out_lengths)
+    return dict(zip(op_module._keys, outputs))
+
+
 class JsonSerializer(SerializerInterface):
     """
     Serializer for torch.export IR using json.
@@ -364,3 +381,42 @@ def deserialize_from_dict(
 JsonSerializer.module_to_serializer_cls["FeatureProcessedEmbeddingBagCollection"] = (
     FPEBCJsonSerializer
 )
+
+
+class KTRegroupAsDictJsonSerializer(JsonSerializer):
+    _module_cls = KTRegroupAsDict
+
+    @classmethod
+    def swap_meta_forward(cls, module: nn.Module) -> None:
+        assert isinstance(module, cls._module_cls)
+        # pyre-ignore
+        module.forward = kt_regroup_meta_forward.__get__(module, cls._module_cls)
+
+    @classmethod
+    def serialize_to_dict(
+        cls,
+        module: nn.Module,
+    ) -> Dict[str, Any]:
+        metadata = KTRegroupAsDictMetadata(
+            keys=module._keys,
+            groups=module._groups,
+        )
+        return metadata.__dict__
+
+    @classmethod
+    def deserialize_from_dict(
+        cls,
+        metadata_dict: Dict[str, Any],
+        device: Optional[torch.device] = None,
+        unflatten_ep: Optional[nn.Module] = None,
+    ) -> nn.Module:
+        metadata = KTRegroupAsDictMetadata(**metadata_dict)
+        return KTRegroupAsDict(
+            keys=metadata.keys,
+            groups=metadata.groups,
+        )
+
+
+JsonSerializer.module_to_serializer_cls["KTRegroupAsDict"] = (
+    KTRegroupAsDictJsonSerializer
+)

torchrec/ir/tests/test_serializer.py

@@ -30,6 +30,7 @@
     PositionWeightedModuleCollection,
 )
 from torchrec.modules.fp_embedding_modules import FeatureProcessedEmbeddingBagCollection
+from torchrec.modules.regroup import KTRegroupAsDict
 from torchrec.sparse.jagged_tensor import KeyedJaggedTensor, KeyedTensor
 
 
@@ -433,3 +434,90 @@ def forward(self, features: KeyedJaggedTensor) -> List[torch.Tensor]:
         self.assertEqual(len(deserialized_out), len(eager_out))
         for x, y in zip(deserialized_out, eager_out):
             self.assertTrue(torch.allclose(x, y))
+
+    def test_regroup_as_dict_module(self) -> None:
+        class Model(nn.Module):
+            def __init__(self, ebc, fpebc, regroup):
+                super().__init__()
+                self.ebc = ebc
+                self.fpebc = fpebc
+                self.regroup = regroup
+
+            def forward(
+                self,
+                features: KeyedJaggedTensor,
+            ) -> Dict[str, torch.Tensor]:
+                kt1 = self.ebc(features)
+                kt2 = self.fpebc(features)
+                return self.regroup([kt1, kt2])
+
+        tb1_config = EmbeddingBagConfig(
+            name="t1",
+            embedding_dim=3,
+            num_embeddings=10,
+            feature_names=["f1", "f2"],
+        )
+        tb2_config = EmbeddingBagConfig(
+            name="t2",
+            embedding_dim=4,
+            num_embeddings=10,
+            feature_names=["f3", "f4"],
+        )
+        tb3_config = EmbeddingBagConfig(
+            name="t3",
+            embedding_dim=5,
+            num_embeddings=10,
+            feature_names=["f5"],
+        )
+
+        ebc = EmbeddingBagCollection(
+            tables=[tb1_config, tb3_config],
+            is_weighted=False,
+        )
+        max_feature_lengths = {"f3": 100, "f4": 100}
+        fpebc = FeatureProcessedEmbeddingBagCollection(
+            EmbeddingBagCollection(
+                tables=[tb2_config],
+                is_weighted=True,
+            ),
+            PositionWeightedModuleCollection(
+                max_feature_lengths=max_feature_lengths,
+            ),
+        )
+        regroup = KTRegroupAsDict([["f1", "f3", "f5"], ["f2", "f4"]], ["odd", "even"])
+        model = Model(ebc, fpebc, regroup)
+
+        id_list_features = KeyedJaggedTensor.from_offsets_sync(
+            keys=["f1", "f2", "f3", "f4", "f5"],
+            values=torch.tensor([0, 1, 2, 3, 2, 3, 4, 5, 6, 7, 8, 9, 1, 1, 2]),
+            offsets=torch.tensor([0, 2, 2, 3, 4, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15]),
+        )
+        self.assertFalse(model.regroup._is_inited)
+
+        # Serialize EBC
+        model, sparse_fqns = encapsulate_ir_modules(model, JsonSerializer)
+        ep = torch.export.export(
+            model,
+            (id_list_features,),
+            {},
+            strict=False,
+            # Allows KJT to not be unflattened and run a forward on unflattened EP
+            preserve_module_call_signature=(tuple(sparse_fqns)),
+        )
+
+        self.assertFalse(model.regroup._is_inited)
+        eager_out = model(id_list_features)
+        self.assertFalse(model.regroup._is_inited)
+
+        # Run forward on ExportedProgram
+        ep_output = ep.module()(id_list_features)
+        for key in eager_out.keys():
+            self.assertEqual(ep_output[key].shape, eager_out[key].shape)
+        # Deserialize EBC
+        unflatten_ep = torch.export.unflatten(ep)
+        deserialized_model = decapsulate_ir_modules(unflatten_ep, JsonSerializer)
+        self.assertFalse(deserialized_model.regroup._is_inited)
+        deserialized_out = deserialized_model(id_list_features)
+        self.assertTrue(deserialized_model.regroup._is_inited)
+        for key in eager_out.keys():
+            self.assertEqual(deserialized_out[key].shape, eager_out[key].shape)