[core] gemma2 full context length support (#10584)

Signed-off-by: youkaichao <youkaichao@gmail.com>

vllm/model_executor/models/gemma2.py

@@ -143,12 +143,12 @@ class Gemma2Attention(nn.Module):
             is_neox_style=True,
         )
 
-        # FIXME(woosuk): While Gemma 2 uses sliding window attention for every
-        # odd layer, vLLM currently ignores it and uses global attention for
-        # all layers.
-        use_sliding_window = (layer_idx % 2 == 1
-                              and config.sliding_window is not None)
-        del use_sliding_window  # Unused.
+        # reference:
+        # https://github.com/huggingface/transformers/blob/54be2d7ae87e873482b984cc956e165ca4dc0ba3/src/transformers/models/gemma2/modeling_gemma2.py#L312 # noqa
+        use_sliding_window = (layer_idx % 2 == 0 and
+                              config.interleaved_sliding_window is not None)
+        sliding_window = config.interleaved_sliding_window if \
+            use_sliding_window else None
         self.attn = Attention(self.num_heads,
                               self.head_dim,
                               self.scaling,
@@ -156,6 +156,7 @@ class Gemma2Attention(nn.Module):
                               cache_config=cache_config,
                               quant_config=quant_config,
                               logits_soft_cap=attn_logits_soft_cap,
+                              per_layer_sliding_window=sliding_window,
                               prefix=f"{prefix}.attn")
 
     def forward(