see the links I posted above, if every package (or a subset of packages based on the underlying source package) in a traditional linux distribution is treated as an independent layer that can be composed together on demand (i.e. what happens when you install a package, except much slower) using a traditional union file system you get deduplication (as every image using that package will be sharing the same exact portion of the file systme) and you get memory sharing for free (for exact same reason, as its fundamentally no different than multiple processes on a single host dynamically linking the same binaries).
