Oracle instant client memory footprint
You link to a FAQ that says


  The Instant Client libraries occupy a virtual address space that is
  equal to the size of the files. However, only frequently used error
  messages from the libraries occupy physical memory. Under most cases,
  the physical memory load is a few kilobytes despite the larger
  reserved virtual address space


This isn't saying that there is a memory leak in the Instant Client.  It is saying that using the Instant Client involves adding a few kb of physical memory and a bit more virtual memory to your application's memory footprint.  That's normally not something that would impact performance.  If you are running in an environment where a few kb of space is an issue (for example, you're building an application that is supposed to run 10's of thousands of copies of itself on a single server), then you might be better off with a full client install.  Of course, the full client will undoubtedly load more than a few kb of shared libraries into memory, they just won't count as part of your application's footprint.