Correct overhead number

README.rst

@@ -66,7 +66,7 @@ the `The LRU fairness issue`_:
 
 * The gross amount of memory is fixed, the storage engine will never
   take any more system memory than the configured amount plus a fixed
-  amount for metadata (typically 0.2% of the configured size).
+  amount for metadata (typically 0.4% of the configured size).
 
 * Storage allocation always implies fragmentation: Any freed storage
   allocation leaves a hole of that size only, unless neighboring