[BugFix] Fix interleaved sliding window not set for Gemma3n (#21863)

Signed-off-by: Yong Hoon Shin <yhshin@meta.com>

vllm/config.py

@@ -723,11 +723,16 @@ class ModelConfig:
         )
 
         # Workaround for Gemma 2 which uses interleaved sliding window
-        # attention, but it's not specified in its config. TODO: remove this
-        # when Gemma 2 is fixed in Transformers.
+        # attention, but it's not specified in its config.
+        # TODO: remove this when Gemma 2 config updated in HuggingFace.
         if self.hf_text_config.model_type == "gemma2":
             self.hf_text_config.sliding_window_pattern = 2
 
+        # TODO: remove this when Gemma 3n config updated in HuggingFace.
+        if self.hf_text_config.model_type == "gemma3n_text":
+            # 4 sliding window attention followed by 1 full attention
+            self.hf_text_config.sliding_window_pattern = "LLLLG"
+
         sliding_window = getattr(self.hf_text_config, "sliding_window", None)
         sliding_window_pattern = getattr(self.hf_text_config,
                                          "sliding_window_pattern", None)

vllm/model_executor/models/gemma3n.py

@@ -297,8 +297,13 @@ class Gemma3nAttention(nn.Module):
                               has_weight=False)
 
         layer_idx = extract_layer_index(prefix)
-        if config.layer_types[layer_idx] == "sliding_attention":
-            self.sliding_window = config.sliding_window
+
+        is_sliding_window = (
+            getattr(config, "interleaved_sliding_window", None) is not None
+            and config.layer_types[layer_idx] == "sliding_attention")
+
+        if is_sliding_window:
+            self.sliding_window = config.interleaved_sliding_window
             rope_theta = config.rope_local_base_freq
             rope_scaling = {"rope_type": "default"}
         else: