[DSA] Skip indexer KV cache for skip-topk layers (#30531)

Co-authored-by: Brayden Zhong <brayden@radixark.ai>
Co-authored-by: mmangkad <mohammad.angkad@radixark.ai>

python/sglang/srt/mem_cache/memory_pool.py

@@ -4365,6 +4365,7 @@ class DSATokenToKVPool(MLATokenToKVPool):
         start_layer: Optional[int] = None,
         end_layer: Optional[int] = None,
         index_buf_size: Optional[int] = None,
+        skip_topk_layers: Optional[List[bool]] = None,
     ):
         override_dim = (
             kv_cache_dim if kv_cache_dim != kv_lora_rank + qk_rope_head_dim else None
@@ -4393,6 +4394,13 @@ class DSATokenToKVPool(MLATokenToKVPool):
         # num head == 1 and head dim == 128 for index_k in DSA
         assert index_head_dim == 128
 
+        self.skip_topk_layers = (
+            list(skip_topk_layers)
+            if skip_topk_layers is not None
+            else [False] * layer_num
+        )
+        assert len(self.skip_topk_layers) == layer_num
+
         if _is_hip:
             if aiter_can_use_preshuffle_paged_mqa():
                 assert (