feat: add arg to enable dft in liger (#3125)

* feat: add arg to enable dft in liger

* feat: add tests use_token_scaling

* fix: test

* fix: move check to args

src/axolotl/integrations/liger/README.md

@@ -18,6 +18,9 @@ liger_rms_norm: true
 liger_glu_activation: true
 liger_layer_norm: true
 liger_fused_linear_cross_entropy: true
+
+# FLCE-specific
+liger_use_token_scaling: true
 ```
 
 ## Supported Models

src/axolotl/integrations/liger/args.py

@@ -16,7 +16,7 @@
 Module for handling LIGER input arguments.
 """
 
-from pydantic import BaseModel, model_validator
+from pydantic import BaseModel, Field, model_validator
 
 from axolotl.utils.logging import get_logger
 
@@ -35,6 +35,15 @@ class LigerArgs(BaseModel):
     liger_glu_activation: bool | None = None
     liger_cross_entropy: bool | None = None
     liger_fused_linear_cross_entropy: bool | None = None
+    liger_use_token_scaling: bool | None = Field(
+        default=None,
+        json_schema_extra={
+            "description": (
+                "Enables use_token_scaling in fused_linear_cross_entropy. "
+                "When True, each token's loss is multiplied by its predicted probability (detached from gradients)."
+            )
+        },
+    )
 
     @model_validator(mode="before")
     @classmethod
@@ -75,6 +84,18 @@ class LigerArgs(BaseModel):
             )
         return data
 
+    @model_validator(mode="before")
+    @classmethod
+    def check_liger_use_token_scaling_flce(cls, data):
+        if data.get("liger_use_token_scaling") and not data.get(
+            "liger_fused_linear_cross_entropy"
+        ):
+            raise ValueError(
+                "`liger_use_token_scaling: true` requires `liger_fused_linear_cross_entropy` enabled."
+            )
+
+        return data
+
     @model_validator(mode="after")
     def check_tensor_parallel_size_liger_fused_linear_cross_entropy(self):
         # TODO @SalmanMohammadi this is a larger fix - investigate

src/axolotl/integrations/liger/plugin.py

@@ -48,6 +48,33 @@ class LigerPlugin(BasePlugin):
                 "Cannot have both `liger_cross_entropy` and `liger_fused_linear_cross_entropy` set."
             )
 
+        if cfg.liger_use_token_scaling:
+            # Patch FLCE to set token_scaling=True for function and class API
+            from liger_kernel.transformers import functional
+            from liger_kernel.transformers.fused_linear_cross_entropy import (
+                LigerFusedLinearCrossEntropyLoss,
+            )
+
+            old_liger_fused_linear_cross_entropy = (
+                functional.liger_fused_linear_cross_entropy
+            )
+
+            def patched_liger_fused_linear_cross_entropy(*args, **kwargs):
+                kwargs["use_token_scaling"] = True
+                return old_liger_fused_linear_cross_entropy(*args, **kwargs)
+
+            functional.liger_fused_linear_cross_entropy = (
+                patched_liger_fused_linear_cross_entropy
+            )
+
+            old_init = LigerFusedLinearCrossEntropyLoss.__init__
+
+            def patched_init(self, *args, **kwargs):
+                kwargs["use_token_scaling"] = True
+                return old_init(self, *args, **kwargs)
+
+            LigerFusedLinearCrossEntropyLoss.__init__ = patched_init
+
         if cfg.model_config_type in MODEL_TYPE_TO_APPLY_LIGER_FN:
             apply_liger_fn = MODEL_TYPE_TO_APPLY_LIGER_FN[cfg.model_config_type]
             liger_fn_sig = inspect.signature(apply_liger_fn)