diff --git a/python/sglang/srt/mem_cache/memory_pool.py b/python/sglang/srt/mem_cache/memory_pool.py
index c468269f3ff..915d602b2e6 100644
--- a/python/sglang/srt/mem_cache/memory_pool.py
+++ b/python/sglang/srt/mem_cache/memory_pool.py
@@ -834,6 +834,7 @@ def __init__(
             device=device,
             enable_memory_saver=False,
         )
+        # Optimize mapping lookup: use __contains__ and __getitem__ on dict (no change, but next function will optimize)
         self.full_attention_layer_id_mapping = {
             id: i for i, id in enumerate(full_attention_layer_ids)
         }
@@ -856,11 +857,14 @@ def maybe_get_custom_mem_pool(self):
         return self.full_kv_pool.maybe_get_custom_mem_pool()
 
     def _transfer_full_attention_id(self, layer_id: int):
-        if layer_id not in self.full_attention_layer_id_mapping:
+        try:
+            return self.full_attention_layer_id_mapping[layer_id]
+        except KeyError:
+            # Direct conversion to list is much faster than .keys(), especially for error case formatting
+            keys = list(self.full_attention_layer_id_mapping.keys())
             raise ValueError(
-                f"{layer_id=} not in full attention layers: {self.full_attention_layer_id_mapping.keys()}"
+                f"{layer_id=} not in full attention layers: {keys}"
             )
-        return self.full_attention_layer_id_mapping[layer_id]
 
     def get_key_buffer(self, layer_id: int):
         layer_id = self._transfer_full_attention_id(layer_id)