Database Software

I'd like to understand exactly how smart flash cache algorithm works.
I’ve read the Oracle white paper on smart flash cache. It says following:
Exadata Smart Flash Cache provides an automated caching mechanism for frequently-accessed data in the Exadata Database Machine.
What is the algorithm to figure out "frequently accessed data”?

It also say following -
The Oracle Database and Exadata Storage Server Software work closely together to cache frequently accessed data.
When the database sends a read or write request to Exadata Storage Server, it includes additional information in the request about whether the data is likely to be read again and therefore whether it should be cached.
Again what's the algorithm to figure out that data is likely to be read again?
Does it simply cache all random reads against tables and indexes and ignores all sequential reads, scans, writing backups and mirrored blocks?

I’ve also read that, Exadata tags each DB I/O is with metadata indicating I/O type which influence caching . Can somebody shed light on what are various I/O types and which ones are cached?