[Gemma2] add bitsandbytes support for Gemma2 (#8338)

vllm/model_executor/models/gemma2.py

@@ -312,6 +312,14 @@ class Gemma2ForCausalLM(nn.Module, SupportsLoRA):
     # Gemma does not apply LoRA to the embedding layer.
     embedding_modules = {}
     embedding_padding_modules = []
+    bitsandbytes_stacked_params_mapping = {
+        # shard_name, weight_name, index
+        "q_proj": ("qkv_proj", 0),
+        "k_proj": ("qkv_proj", 1),
+        "v_proj": ("qkv_proj", 2),
+        "gate_proj": ("gate_up_proj", 0),
+        "up_proj": ("gate_up_proj", 1),
+    }
 
     def __init__(
         self,