It is visible in profiles for lots of applications that reading the SC cache file at startup costs significantly. On JavacBenchApp example, loading ~25M code requires about 30ms. This is ~1 GB/sec, so it is I/O limited.

We should really mmap the SC cache file to alleviate these costs. Let the actual SC readers (separate threads) to eat the cost of reading from the backing file.

https://github.com/openjdk/leyden/pull/34