Added custom prepare_model_for_kbit_training to save VRAM (#4335)

Co-authored-by: Kashif Rasul <[email protected]>

Author: sergiopaniego

trl/models/__init__.py

@@ -26,6 +26,7 @@
         "clone_chat_template",
         "prepare_deepspeed",
         "prepare_fsdp",
+        "prepare_model_for_kbit_training",
         "prepare_peft_model",
         "setup_chat_format",
         "unwrap_model_for_generation",
@@ -42,6 +43,7 @@
         clone_chat_template,
         prepare_deepspeed,
         prepare_fsdp,
+        prepare_model_for_kbit_training,
         prepare_peft_model,
         setup_chat_format,
         unwrap_model_for_generation,

trl/models/utils.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import inspect
 import itertools
 import warnings
 from collections.abc import Callable
@@ -32,7 +33,7 @@
 
 if is_peft_available():
     import peft
-    from peft import PeftConfig, PeftModel, get_peft_model, prepare_model_for_kbit_training
+    from peft import PeftConfig, PeftModel, get_peft_model
 
 
 if TYPE_CHECKING:
@@ -471,6 +472,51 @@ def on_after_outer_forward(self, wrapper_module: nn.Module, original_module: nn.
         pass
 
 
+def prepare_model_for_kbit_training(model, use_gradient_checkpointing=True, gradient_checkpointing_kwargs=None):
+    r"""
+    Prepare a k-bit quantized transformers model for training (PEFT/QLoRA).
+    """
+    loaded_in_kbit = getattr(model, "is_loaded_in_8bit", False) or getattr(model, "is_loaded_in_4bit", False)
+    quant_methods = ["gptq", "aqlm", "eetq", "torchao", "hqq"]
+    is_quantized = getattr(model, "quantization_method", None) in quant_methods or getattr(
+        model, "hqq_quantized", False
+    )
+
+    if gradient_checkpointing_kwargs is None:
+        gradient_checkpointing_kwargs = {}
+
+    n_upcasted = 0
+    for name, param in model.named_parameters():
+        # freeze all parameters
+        param.requires_grad = False
+
+        # upcast LayerNorm / Norm to float32 for numerical stability
+        if (param.dtype in [torch.float16, torch.bfloat16]) and (
+            "norm" in name.lower() or "layernorm" in name.lower()
+        ):
+            param.data = param.data.to(torch.float32)
+            n_upcasted += 1
+
+    # Enable gradient checkpointing if needed
+    if (loaded_in_kbit or is_quantized) and use_gradient_checkpointing:
+        if hasattr(model, "enable_input_require_grads"):
+            model.enable_input_require_grads()
+        else:
+            # backward-compatible hook
+            def make_inputs_require_grad(module, input, output):
+                output.requires_grad_(True)
+
+            model.get_input_embeddings().register_forward_hook(make_inputs_require_grad)
+
+        supports_gc_kwargs = "gradient_checkpointing_kwargs" in list(
+            inspect.signature(model.gradient_checkpointing_enable).parameters
+        )
+        gc_kwargs = {"gradient_checkpointing_kwargs": gradient_checkpointing_kwargs} if supports_gc_kwargs else {}
+        model.gradient_checkpointing_enable(**gc_kwargs)
+
+    return model
+
+
 def enable_gradient_checkpointing(
     model: PreTrainedModel, gradient_checkpointing_kwargs: Optional[dict]
 ) -> PreTrainedModel: