[feat] support ktransformers for dpo (#9621)

Co-authored-by: poryfly <porykid@gmail.com>

src/llamafactory/train/dpo/ktrainer.py

@@ -0,0 +1,71 @@
+# Copyright 2025 HuggingFace Inc. and the LlamaFactory team.
+#
+# This code is inspired by the HuggingFace's TRL library.
+# https://github.com/huggingface/trl/blob/v0.8.0/trl/trainer/dpo_trainer.py
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from typing import TYPE_CHECKING, Optional
+import torch
+import torch.nn.functional as F
+from transformers import Trainer
+from trl import DPOTrainer
+from trl.trainer import disable_dropout_in_model
+from typing_extensions import override
+
+from ...extras.constants import IGNORE_INDEX
+from ...extras.packages import is_transformers_version_greater_than
+from ..callbacks import SaveProcessorCallback
+from ..trainer_utils import create_custom_optimizer, create_custom_scheduler, get_batch_logps, nested_detach
+from .trainer import CustomDPOTrainer as BaseDPOTrainer
+from ktransformers.sft.lora import KTrainer
+
+
+if TYPE_CHECKING:
+    from transformers import PreTrainedModel, ProcessorMixin
+
+    from ...hparams import FinetuningArguments
+
+
+class CustomDPOTrainer(KTrainer, BaseDPOTrainer):
+    @override
+    def concatenated_forward(
+            self, model: "PreTrainedModel", batch: dict[str, "torch.Tensor"], is_ref_model: bool = False
+    ) -> tuple["torch.Tensor", "torch.Tensor", "torch.Tensor", "torch.Tensor", "torch.Tensor"]:
+        r"""Compute the sum log probabilities of the labels under given logits if loss_type is not IPO, ORPO or SimPO.
+
+        Otherwise the average log probabilities.
+        """
+        if self.finetuning_args.use_ref_model:
+            batch = nested_detach(batch, clone=True)  # avoid error
+        labels = batch["labels"]
+        # dpo not need compute loss in forward, waste mem
+        del batch["labels"]
+        all_logits: torch.Tensor = model(**batch, return_dict=True, use_cache=False).logits.to(torch.float32)
+        all_logits = all_logits.to("cpu")
+        labels = labels.to(all_logits.device)
+        all_logps, valid_length = get_batch_logps(
+            logits=all_logits, labels=labels, ld_alpha=(self.ld_alpha if not is_ref_model else None)
+        )
+        if self.loss_type in ["ipo", "orpo", "simpo"]:
+            all_logps = all_logps / valid_length
+
+        batch_size = batch["input_ids"].size(0) // 2
+        chosen_logps, rejected_logps = all_logps.split(batch_size, dim=0)
+        chosen_logits, rejected_logits = all_logits.split(batch_size, dim=0)
+        chosen_length, _ = valid_length.split(batch_size, dim=0)
+
+        if self.loss_type in ["ipo", "orpo", "simpo"]:
+            return chosen_logps, rejected_logps, chosen_logits, rejected_logits, chosen_logps
+        else:
+            return chosen_logps, rejected_logps, chosen_logits, rejected_logits, chosen_logps / chosen_length