[$] Hastening process cleanup with process_mrelease()

One of the fundamental invariants of computing is that, regardless of how
much memory is installed in a system, it is never enough. This is
especially true of systems with tight performance constraints, where every
page of memory is allocated and in use, making it difficult to find
more when it is badly needed. One way to make more memory
available is to kill one or more processes, freeing their resources for
other users. But that often does not work as quickly or reliably as users
would like. In an attempt to improve the situation, Suren Baghdasaryan has
proposed
the addition of a system call named process_mrelease().