This page is suposed to be big, thus I pasted a few excerpts copied from the internet.
This JEP is paired with a companion "Unify the Basic Primitives with Objects (Preview)" which provides the retrofitting of Java's primitive types into the structure of primitive objects, and making all Java values objects (although primitive objects lack object identity).
These two JEPs do not cover everything that is needed to fully implement Valhalla - for example a additional, separate JEP will be needed to update Java's generics to allow primitive classes to be used as type parameters - but this has not been published yet.
The specialization of bytecode and generic classes is also not covered by the current JEPs, and would also appear as part of another JEP.