feat: expose bnb kwargs (#1018)

* feat: expose bnb kwargs

* chore: added examples and link per suggestion

* Uncomment defaults per suggestion for readability

Co-authored-by: Hamel Husain <hamel.husain@gmail.com>

---------

Co-authored-by: Hamel Husain <hamel.husain@gmail.com>

README.md

@@ -520,6 +520,14 @@ model_config:
     type: # linear | dynamic
     factor: # float
 
+# optional overrides to the bnb 4bit quantization configuration
+# https://huggingface.co/docs/transformers/main/main_classes/quantization#transformers.BitsAndBytesConfig
+bnb_config_kwargs:
+  # These are default values
+  llm_int8_has_fp16_weight: false
+  bnb_4bit_quant_type: nf4
+  bnb_4bit_use_double_quant: true
+
 
 # Whether you are training a 4-bit GPTQ quantized model
 gptq: true

src/axolotl/utils/models.py

@@ -301,13 +301,20 @@ def load_model(
                 **model_config.quantization_config
             )
     if cfg.adapter == "qlora" and cfg.load_in_4bit:
+        bnb_config = {
+            "load_in_4bit": True,
+            "llm_int8_threshold": 6.0,
+            "llm_int8_has_fp16_weight": False,
+            "bnb_4bit_compute_dtype": cfg.torch_dtype,
+            "bnb_4bit_use_double_quant": True,
+            "bnb_4bit_quant_type": "nf4",
+        }
+
+        if cfg.bnb_config_kwargs:
+            bnb_config.update(cfg.bnb_config_kwargs)
+
         model_kwargs["quantization_config"] = BitsAndBytesConfig(
-            load_in_4bit=True,
-            llm_int8_threshold=6.0,
-            llm_int8_has_fp16_weight=False,
-            bnb_4bit_compute_dtype=cfg.torch_dtype,
-            bnb_4bit_use_double_quant=True,
-            bnb_4bit_quant_type="nf4",
+            **bnb_config,
         )
     # sample packing uses custom FA2 patch
     if cfg.flash_attention: