Anatomy of Linux Kernel Shared Memory
An anonymous reader sends in an IBM DeveloperWorks backgrounder on Kernel Shared Memory in the 2.6.32 Linux kernel. KSM allows the hypervisor to increase the number of concurrent virtual machines by consolidating identical memory pages. The article covers the ideas behind KSM (such as storage de-duplication), its implementation, and how you manage it.
If your OS isn't sharing duplicate memory blocks already, you're using a shitty OS. (Linux already shares dup read only blocks for many things, like most modern OSes).
Umm, no.
Most modern OSes share memory for executable images and shared libraries. In addition, some OSes, such as Linux, support copy-on-write semantics for memory pages in child processes created with fork (note, Solaris is an example of an OS that *doesn't* do this).
Aside from that, there is no automated sharing of memory between processes. Frankly, I have no idea where you got the idea there was.