Codecache is for compiled code, so it doesn't necessarily correlate to the original program's source code size. You can have the same methods inlined in many places, load the same classes in multiple class loaders (which means they are separate classes to the JVM), generate code at runtime, etc.

For example, Presto is a SQL query engine that generates code for each query (a SQL query is effectively a program), so it can need a lot of codecache depending on the query rate and concurrency.