[JAX] Support for checkpointing quantizations (#2356)

* Support for checkpointing quantizations
Signed-off-by: Jeremy Berchtold <jberchtold@nvidia.com>

* Add jaxpr test for quant checkpoint name
Signed-off-by: Jeremy Berchtold <jberchtold@nvidia.com>

* Revert "Support for checkpointing quantizations"

This reverts commit f7b784940369d0da2a77c57fa6ea744e883c5832.
Signed-off-by: JAX Toolbox <jax@nvidia.com>

* Checkpoint quantizations
Signed-off-by: Jeremy Berchtold <jberchtold@nvidia.com>

* lint
Signed-off-by: Jeremy Berchtold <jberchtold@nvidia.com>

* revert other files
Signed-off-by: Jeremy Berchtold <jberchtold@nvidia.com>

* move checkpointing to VJPs
Signed-off-by: Jeremy Berchtold <jberchtold@nvidia.com>

* fix ci failure
Signed-off-by: Jeremy Berchtold <jberchtold@nvidia.com>

---------
Signed-off-by: Jeremy Berchtold <jberchtold@nvidia.com>
Signed-off-by: JAX Toolbox <jax@nvidia.com>
Co-authored-by: JAX Toolbox <jax@nvidia.com>

tests/jax/test_recipe_characteristics.py

@@ -263,23 +263,16 @@ class TestFP8Functions(unittest.TestCase):
 class TestJaxprAndHlo:
     """Tests to verify Jaxpr and/or HLO of compiled modules apply expected recipe functionality and optimizations."""
 
-    @pytest_parametrize_wrapper(
-        "quantization_recipe",
-        [
-            quantization_recipe
-            for quantization_recipe in SUPPORTED_RECIPES
-            if isinstance(quantization_recipe, NVFP4BlockScaling)
-        ],
-    )
-    def test_layernorm_mlp_reuses_amax_nvfp4(self, quantization_recipe):
-        """Tests that layernorm_mlp reuses the amax computed in layernorm and the activation and does not recompute it during quantizaton."""
-
+    def _generate_jaxpr_for_layernorm_mlp_fwd_bwd(self, quantization_recipe, ln_mlp_kwargs=None):
+        """Generates the jaxpr for a forward and backward pass of LayerNormMLP under the given quantization recipe."""
+        ln_mlp_kwargs = ln_mlp_kwargs or {}
         with te.autocast(enabled=True, recipe=quantization_recipe, mesh_resource=te.MeshResource()):
             model = te_flax.LayerNormMLP(
                 layernorm_type="rmsnorm",
                 return_layernorm_output=False,
                 intermediate_dropout_rate=0.0,
                 dtype=jnp.bfloat16,
+                **ln_mlp_kwargs,
             )
 
             var_collect = model.init(
@@ -292,7 +285,20 @@ class TestJaxprAndHlo:
 
             x = jax.random.normal(jax.random.PRNGKey(0), (128, 128), dtype=jnp.bfloat16)
             rngs = {"sr_rng": jax.random.PRNGKey(1), "dropout": jax.random.PRNGKey(2)}
-            jaxpr = jax.make_jaxpr(jax.value_and_grad(loss_fn))(x, rngs=rngs)
+            return jax.make_jaxpr(jax.value_and_grad(loss_fn))(x, rngs=rngs)
+
+    @pytest_parametrize_wrapper(
+        "quantization_recipe",
+        [
+            quantization_recipe
+            for quantization_recipe in SUPPORTED_RECIPES
+            if isinstance(quantization_recipe, NVFP4BlockScaling)
+        ],
+    )
+    def test_layernorm_mlp_reuses_amax_nvfp4(self, quantization_recipe):
+        """Tests that layernorm_mlp reuses the amax computed in layernorm and the activation and does not recompute it during quantizaton."""
+
+        jaxpr = self._generate_jaxpr_for_layernorm_mlp_fwd_bwd(quantization_recipe)
 
         rht_amax_eqns = [
             eqn for eqn in jaxpr.jaxpr.eqns if eqn.primitive.name == "te_rht_amax_ffi_wrapper"
@@ -318,3 +324,44 @@ class TestJaxprAndHlo:
         # No previous op before incoming dgrad in the backward so amax is not reused
         assert_param(2, "bwd dgrad", True)
         assert_param(3, "bwd dact+q", False)
+
+    @pytest_parametrize_wrapper("quantization_recipe", SUPPORTED_RECIPES)
+    @pytest_parametrize_wrapper(
+        "quantization_checkpoint_name",
+        [None, "quantization", "some_arbitrary_user_checkpoint_name"],
+    )
+    def test_recipe_supports_quantization_checkpointing(
+        self, quantization_recipe, quantization_checkpoint_name
+    ):
+        """Tests that all supported quantization recipes correctly use checkpoint_name."""
+
+        kwargs = {
+            "quantization_checkpoint_name": quantization_checkpoint_name,
+        }
+        jaxpr = self._generate_jaxpr_for_layernorm_mlp_fwd_bwd(quantization_recipe, kwargs)
+
+        checkpoint_name_eqns = [
+            eqn
+            for eqn in jaxpr.jaxpr.eqns
+            if eqn.primitive.name == "name" and eqn.params["name"] == quantization_checkpoint_name
+        ]
+
+        if quantization_checkpoint_name is None:
+            assert len(checkpoint_name_eqns) == 0, (
+                "Expected 0 checkpoint_name eqns when quantization_checkpoint_name is None, got"
+                f" {len(checkpoint_name_eqns)}"
+            )
+            return
+
+        # 12 checkpointed values:
+        # - Fwd pass:
+        #   - Input RMSNorm+Q -> 3 possible output tensors that will be used in the backward
+        #   - Kernel Q -> 3 possible output tensors that will be used in the backward
+        #   - Input Activation+Q -> 3 possible output tensors that will be used in the backward
+        #   - Kernel Q -> 3 possible output tensors that will be used in the backward
+        expected_checkpoint_eqn_count = 12
+
+        assert len(checkpoint_name_eqns) == expected_checkpoint_eqn_count, (
+            f"Expected {expected_checkpoint_eqn_count} checkpoint_name eqns when"
+            f" quantization_checkpoint_name is set, got {len(checkpoint_name_eqns)}"
+        )

transformer_engine/jax/dense.py

@@ -19,6 +19,7 @@ from . import cpp_extensions as tex
 from .cpp_extensions.amax import AmaxScope
 from .quantize import (
     ScaledTensorFactory,
+    ScaledTensor,
     ScalingMode,
     QuantizeLayout,
     QuantizerSet,
@@ -227,8 +228,8 @@ def _dense_fwd_rule(
         output += jnp.reshape(bias, bias_new_shape)
 
     ctx = (
-        casted_x.get_tensor(usage=TensorUsage.LHS_TRANS),
-        casted_kernel.get_tensor(usage=TensorUsage.RHS_TRANS),
+        casted_x.get_tensor(usage=TensorUsage.LHS_TRANS).checkpoint(quantizer_set.x),
+        casted_kernel.get_tensor(usage=TensorUsage.RHS_TRANS).checkpoint(quantizer_set.kernel),
         x.shape,
         kernel.shape,
         use_bias,
@@ -529,8 +530,12 @@ def _grouped_dense_fwd_rule(
 
     ctx = (
         group_sizes,
-        ctx_x,
-        ctx_kernel,
+        ctx_x.checkpoint(quantizer_set.x) if isinstance(ctx_x, ScaledTensor) else ctx_x,
+        (
+            ctx_kernel.checkpoint(quantizer_set.kernel)
+            if isinstance(ctx_kernel, ScaledTensor)
+            else ctx_kernel
+        ),
         x.shape,
         kernel.shape,
         use_bias,

transformer_engine/jax/flax/module.py

@@ -6,7 +6,7 @@ Wrapper module for Transformer related layers with FP8 support.
 """
 from functools import reduce
 import operator
-from typing import Any, Callable, Iterable, List, Sequence, Tuple, Union, NewType
+from typing import Any, Callable, Iterable, List, Sequence, Tuple, Union, NewType, Optional
 
 import numpy as np
 import jax.numpy as jnp
@@ -345,7 +345,11 @@ class TransformerEngineBase(nn.Module):  # pylint: disable=too-few-public-method
     """
 
     def generate_quantizer_set(
-        self, postfix: str = "", variable_collection: str = None, fp8_recipe=None
+        self,
+        postfix: str = "",
+        variable_collection: str = None,
+        quantization_checkpoint_name: Optional[str] = None,
+        fp8_recipe=None,
     ):
         """
         Generate a set of FP8 meta for a GEMM.
@@ -375,7 +379,9 @@ class TransformerEngineBase(nn.Module):  # pylint: disable=too-few-public-method
         quantize_meta_set = QuantizeMetaSet(x=x_meta, kernel=kernel_meta, grad=grad_meta)
 
         quantizer_set = QuantizerFactory.create_set(
-            fp8_recipe=fp8_recipe, quantize_meta_set=quantize_meta_set
+            fp8_recipe=fp8_recipe,
+            quantize_meta_set=quantize_meta_set,
+            checkpoint_name=quantization_checkpoint_name,
         )
         return quantizer_set
 
@@ -424,6 +430,8 @@ class DenseGeneral(TransformerEngineBase):
         The data type used to allocate the initial parameters.
     transpose_batch_sequence: bool, default = False
         Indicate whether to transpose the batch and sequence dimensions of the input tensor.
+    quantization_checkpoint_name: Optional[str], default = None
+        The name for checkpointing quantizations.
     """
 
     features: Union[Iterable[int], int]
@@ -439,6 +447,7 @@ class DenseGeneral(TransformerEngineBase):
     dtype: DType = jnp.float32
     input_axes: Tuple[str, ...] = ()
     transpose_batch_sequence: bool = False
+    quantization_checkpoint_name: Optional[str] = None
 
     def __post_init__(self):
         if self.kernel_init is None:
@@ -496,7 +505,9 @@ class DenseGeneral(TransformerEngineBase):
         else:
             bias = None
 
-        quantizer_set = self.generate_quantizer_set()
+        quantizer_set = self.generate_quantizer_set(
+            quantization_checkpoint_name=self.quantization_checkpoint_name
+        )
         contract_ind = tuple(range(0, len(axis)))
         y = dense(
             inputs,
@@ -628,6 +639,8 @@ class LayerNormDenseGeneral(TransformerEngineBase):
         value or None. When None is set, then no scaling is applied.
     transpose_batch_sequence: bool, default = False
         Indicate whether to transpose the batch and sequence dimensions of the input tensor.
+    quantization_checkpoint_name: Optional[str], default = None
+        The name for checkpointing quantizations.
     """
 
     features: Union[Iterable[int], int]
@@ -654,6 +667,7 @@ class LayerNormDenseGeneral(TransformerEngineBase):
     dot_input_axes: Tuple[str, ...] = None
     depth_scaling: float = None
     transpose_batch_sequence: bool = False
+    quantization_checkpoint_name: Optional[str] = None
 
     def __post_init__(self):
         if self.kernel_init is None:
@@ -693,7 +707,9 @@ class LayerNormDenseGeneral(TransformerEngineBase):
         input_dtype = inputs.dtype
         ln_output = None
 
-        quantizer_set = self.generate_quantizer_set()
+        quantizer_set = self.generate_quantizer_set(
+            quantization_checkpoint_name=self.quantization_checkpoint_name
+        )
 
         fuse_layernorm = (
             get_quantize_config().is_fp8_enabled()
@@ -941,6 +957,8 @@ class LayerNormMLP(TransformerEngineBase):
         The data type used to allocate the initial parameters.
     transpose_batch_sequence: bool, default = False
         Indicate whether to transpose the batch and sequence dimensions of the input tensor.
+    quantization_checkpoint_name: Optional[str], default = None
+        The name for checkpointing quantizations.
     """
 
     intermediate_dim: int = 2048
@@ -976,6 +994,7 @@ class LayerNormMLP(TransformerEngineBase):
     ffn1_ckpt_name: str = "ffn1"
     ffn2_ckpt_name: str = "ffn2"
     transpose_batch_sequence: bool = False
+    quantization_checkpoint_name: Optional[str] = None
 
     def __post_init__(self):
         if self.kernel_init is None:
@@ -1010,8 +1029,12 @@ class LayerNormMLP(TransformerEngineBase):
         """
         assert self.axis == -1, "Only support axis == -1 at this moment"
 
-        ffn1_quantizer_set = self.generate_quantizer_set("_0")
-        ffn2_quantizer_set = self.generate_quantizer_set("_1")
+        ffn1_quantizer_set = self.generate_quantizer_set(
+            "_0", quantization_checkpoint_name=self.quantization_checkpoint_name
+        )
+        ffn2_quantizer_set = self.generate_quantizer_set(
+            "_1", quantization_checkpoint_name=self.quantization_checkpoint_name
+        )
 
         input_dtype = inputs.dtype
         ln_output = None

transformer_engine/jax/layernorm_dense.py

@@ -236,8 +236,8 @@ def _layernorm_dense_fwd_rule(
         output += jnp.reshape(bias, bias_new_shape)
 
     ctx = (
-        casted_ln_out.get_tensor(TensorUsage.LHS_TRANS),
-        casted_kernel.get_tensor(TensorUsage.RHS_TRANS),
+        casted_ln_out.get_tensor(TensorUsage.LHS_TRANS).checkpoint(quantizer_set.x),
+        casted_kernel.get_tensor(TensorUsage.RHS_TRANS).checkpoint(quantizer_set.kernel),
         x.shape,
         kernel.shape,
         mu,

transformer_engine/jax/layernorm_mlp.py

@@ -390,11 +390,11 @@ def _layernorm_mlp_fwd_rule(
         rsigma,
         gamma,
         beta,
-        casted_ln_out.get_tensor(TensorUsage.LHS_TRANS),
-        casted_kernel_1.get_tensor(TensorUsage.RHS_TRANS),
+        casted_ln_out.get_tensor(TensorUsage.LHS_TRANS).checkpoint(ffn1_quantizer_set.x),
+        casted_kernel_1.get_tensor(TensorUsage.RHS_TRANS).checkpoint(ffn1_quantizer_set.kernel),
         dot_1_output,
-        casted_act_out.get_tensor(TensorUsage.LHS_TRANS),
-        casted_kernel_2.get_tensor(TensorUsage.RHS_TRANS),
+        casted_act_out.get_tensor(TensorUsage.LHS_TRANS).checkpoint(ffn2_quantizer_set.x),
+        casted_kernel_2.get_tensor(TensorUsage.RHS_TRANS).checkpoint(ffn2_quantizer_set.kernel),
         x_contracting_dims,
         k_contracting_dims,
         kernel_1.shape,

transformer_engine/jax/quantize/quantizer.py

@@ -83,12 +83,15 @@ class Quantizer(ABC):
         q_dtype: The data type for quantized values
         scaling_mode: The scaling mode to use for quantization
         q_layout: The quantization axis (row-wise, column-wise, or both)
+        data_layout: The data layout string (e.g., "NT")
+        checkpoint_name: Optional name for checkpointing quantization state
     """
 
     q_dtype: jnp.dtype
     scaling_mode: ScalingMode
     q_layout: QuantizeLayout
     data_layout: str
+    checkpoint_name: Optional[str] = None
 
     def tree_flatten(self):
         """Flatten the quantizer for JAX tree operations.
@@ -97,7 +100,13 @@ class Quantizer(ABC):
             Tuple of (children, aux_data) for tree operations
         """
         children = ()
-        aux_data = (self.q_dtype, self.scaling_mode, self.q_layout, self.data_layout)
+        aux_data = (
+            self.q_dtype,
+            self.scaling_mode,
+            self.q_layout,
+            self.data_layout,
+            self.checkpoint_name,
+        )
         return (children, aux_data)
 
     @classmethod
@@ -337,7 +346,13 @@ class DelayedScaleQuantizer(CurrentScaleQuantizer):
             Tuple of (children, aux_data) for tree operations
         """
         children = (self.scale, self.amax_history)
-        aux_data = (self.q_dtype, self.scaling_mode, self.q_layout, self.data_layout)
+        aux_data = (
+            self.q_dtype,
+            self.scaling_mode,
+            self.q_layout,
+            self.data_layout,
+            self.checkpoint_name,
+        )
         return (children, aux_data)
 
     def _quantize_func(
@@ -588,7 +603,14 @@ class NVFP4Quantizer(Quantizer):
             Tuple of (children, aux_data) for tree operations
         """
         children = (self.stochastic_rounding_rng_state,)
-        aux_data = (self.q_dtype, self.scaling_mode, self.q_layout, self.data_layout, self.use_rht)
+        aux_data = (
+            self.q_dtype,
+            self.scaling_mode,
+            self.q_layout,
+            self.data_layout,
+            self.checkpoint_name,
+            self.use_rht,
+        )
         return (children, aux_data)
 
     @classmethod
@@ -867,7 +889,14 @@ class GroupedQuantizer(Quantizer):
             Tuple of (children, aux_data) for tree operations
         """
         children = (self.quantizers,)
-        aux_data = (self.q_dtype, self.scaling_mode, self.q_layout, self.data_layout, self.n_groups)
+        aux_data = (
+            self.q_dtype,
+            self.scaling_mode,
+            self.q_layout,
+            self.data_layout,
+            self.checkpoint_name,
+            self.n_groups,
+        )
         return (children, aux_data)
 
     def __post_init__(self):
@@ -1041,6 +1070,7 @@ class QuantizerFactory:
         q_dtype: jnp.dtype = None,
         q_layout: QuantizeLayout = None,
         n_groups: int = None,
+        checkpoint_name: Optional[str] = None,
         **kwargs,
     ) -> Quantizer:
         """Create one or more quantizers with specified parameters.
@@ -1052,6 +1082,7 @@ class QuantizerFactory:
             q_layout: Quantization axis
             flatten_axis: The quantization axis for the tensor
             n_groups: Number of quantizers if GroupedQuantizer
+            checkpoint_name: Optional name for checkpointing quantizations
             **kwargs: Additional arguments for quantizer initialization
 
         Returns:
@@ -1075,7 +1106,11 @@ class QuantizerFactory:
             for _ in range(n_quantizers):
                 quantizers.append(
                     quantizer_type(
-                        q_dtype=q_dtype, scaling_mode=scaling_mode, q_layout=q_layout, **kwargs
+                        q_dtype=q_dtype,
+                        scaling_mode=scaling_mode,
+                        q_layout=q_layout,
+                        checkpoint_name=checkpoint_name,
+                        **kwargs,
                     )
                 )
         return quantizers[0] if len(quantizers) == 1 else tuple(quantizers)
@@ -1089,6 +1124,7 @@ class QuantizerFactory:
         bwd_dtype,
         is_2x2x,
         n_groups,
+        checkpoint_name: Optional[str] = None,
         **kwargs,
     ) -> QuantizerSet:
         """Create a set of quantizers for forward and backward passes.
@@ -1101,6 +1137,7 @@ class QuantizerFactory:
             bwd_dtype: Data type for backward pass
             is_2x2x: Whether to use 2x2x quantization
             n_groups
+            checkpoint_name: Optional name for checkpointing quantizations
             **kwargs: Additional arguments for quantizer initialization
 
         Returns:
@@ -1123,12 +1160,32 @@ class QuantizerFactory:
         else:
             args_x = args_kernel = args_grad = {}
 
-        q_x = QuantizerFactory.create(1, x_scaling_mode, fwd_dtype, q_layout_x, n_groups, **args_x)
+        q_x = QuantizerFactory.create(
+            1,
+            x_scaling_mode,
+            fwd_dtype,
+            q_layout_x,
+            n_groups,
+            checkpoint_name=checkpoint_name,
+            **args_x,
+        )
         q_kernel = QuantizerFactory.create(
-            1, kernel_scaling_mode, fwd_dtype, q_layout_kernel, n_groups, **args_kernel
+            1,
+            kernel_scaling_mode,
+            fwd_dtype,
+            q_layout_kernel,
+            n_groups,
+            checkpoint_name=checkpoint_name,
+            **args_kernel,
         )
         q_dgrad = QuantizerFactory.create(
-            1, grad_scaling_mode, bwd_dtype, q_layout_dgrad, n_groups, **args_grad
+            1,
+            grad_scaling_mode,
+            bwd_dtype,
+            q_layout_dgrad,
+            n_groups,
+            checkpoint_name=checkpoint_name,
+            **args_grad,
         )
         return QuantizerSet(x=q_x, kernel=q_kernel, dgrad=q_dgrad)
 
@@ -1140,6 +1197,7 @@ class QuantizerFactory:
         bwd_dtype: jnp.dtype = None,
         is_2x2x: bool = None,
         n_groups: int = None,
+        checkpoint_name: Optional[str] = None,
         # TODO(jberchtold): rename fp8_recipe to quantization_recipe
         fp8_recipe: Optional[recipe.Recipe] = None,
         **kwargs,
@@ -1153,6 +1211,7 @@ class QuantizerFactory:
             bwd_dtype: Data type for backward pass, default is get_quantize_config().BWD_DTYPE
             is_2x2x: Whether to use 2x2x quantization, default is get_quantize_config().IF_QUANTIZE_2X
             n_groups:
+            checkpoint_name: Optional name for checkpointing quantizations
             fp8_recipe: Recipe to use for quantization. Scaling mode can be specified directly via the scaling_mode parameter or indirectly via recipe. Recipe is preferred as it will support additional recipes in future where scaling mode differs between x, kernel, and grad in the quantizer set.
             **kwargs: Additional arguments for quantizer initialization
 
@@ -1208,6 +1267,7 @@ class QuantizerFactory:
                     bwd_dtype=bwd_dtype,
                     is_2x2x=is_2x2x,
                     n_groups=n_groups,
+                    checkpoint_name=checkpoint_name,
                     **kwargs,
                 )
             )

transformer_engine/jax/quantize/tensor.py

@@ -14,6 +14,7 @@ from abc import ABC, abstractmethod
 
 import jax.numpy as jnp
 from jax.tree_util import register_pytree_node_class
+from jax.ad_checkpoint import checkpoint_name as jax_checkpoint_name
 
 
 from .scaling_modes import ScalingMode, TensorUsage
@@ -89,6 +90,17 @@ class AbstractBaseTensor(ABC):
             The tensor with applied sharding constraints
         """
 
+    @abstractmethod
+    def checkpoint(self, quantizer):
+        """Checkpoints the tensor with the given quantizer's checkpoint name if available.
+
+        Args:
+            quantizer: The quantizer to use for checkpointing. If None, no checkpointing is applied.
+
+        Returns:
+            The checkpointed tensor
+        """
+
 
 @dataclass
 class AbstractBaseTensor1x(AbstractBaseTensor):
@@ -150,6 +162,18 @@ class NoScaleTensor(AbstractBaseTensor1x):
             amax=self.amax,
         )
 
+    def checkpoint(self, quantizer):
+        """Checkpoints the tensor with the given quantizer's checkpoint name if available.
+
+        Args:
+            quantizer: The quantizer to use for checkpointing. If None, no checkpointing is applied.
+
+        Returns:
+            The checkpointed tensor
+        """
+        assert quantizer is None, "NoScaleTensor does not support quantization."
+        return self
+
 
 class ScaledTensor(ABC):
     """Abstract base class for scaled tensors."""
@@ -317,6 +341,20 @@ class ScaledTensor1x(AbstractBaseTensor1x, ScaledTensor):
             has_rht_applied=self.has_rht_applied,
         )
 
+    def checkpoint(self, quantizer):
+        """Checkpoints the tensor with the given quantizer's checkpoint name if available.
+
+        Args:
+            quantizer: The quantizer to use for checkpointing. If None, no checkpointing is applied.
+
+        Returns:
+            The checkpointed tensor
+        """
+        if quantizer is None or quantizer.checkpoint_name is None:
+            return self
+
+        return jax_checkpoint_name(self, name=quantizer.checkpoint_name)
+
 
 @register_pytree_node_class
 @dataclass
@@ -420,6 +458,20 @@ class GroupedScaledTensor1x(ScaledTensor1x):
     def apply_sharding_constraint_by_logical_axes(self, logical_axis_names: Tuple[str, ...]):
         raise NotImplementedError
 
+    def checkpoint(self, quantizer):
+        """Checkpoints the tensor with the given quantizer's checkpoint name if available.
+
+        Args:
+            quantizer: The quantizer to use for checkpointing. If None, no checkpointing is applied.
+
+        Returns:
+            The checkpointed tensor
+        """
+        if quantizer is None or quantizer.checkpoint_name is None:
+            return self
+
+        return jax_checkpoint_name(self, name=quantizer.checkpoint_name)
+
 
 @register_pytree_node_class
 @dataclass
@@ -496,6 +548,9 @@ class ScaledTensor2x(AbstractBaseTensor, ScaledTensor):
 
         return ScaledTensor2x(rowwise_tensor, colwise_tensor)
 
+    def checkpoint(self, quantizer):
+        raise NotImplementedError
+
 
 @dataclass
 class ScaledTensorFactory: