[$] The kernel's genpool subsystem

The kernel is a huge program; among other things, that means that manyproblems encountered by a kernel developer have already been solvedsomewhere else in the tree. But those solutions are not always well knownor documented. Recently, a seasoned developer confessed to having never encountered the"genpool" memory allocator. This little subsystem does not appear in thekernel documentation, and is likely to be unknown to others as well. Inthe interest of fixing both of those problems, here is an overview ofgenpool (or "genalloc") and what it does.