malloc() and free() is what I meant by "standard memory allocation functions". I'd say program that is in the position to use madvise() effectively has implemented it's own heap allocator.

Also, MADV_DONTNEED is only usable in some specific situations, like caches. I don't see how it could be used to implement things like "on low memory, trigger garbage collection and trim the heap to the smallest possible with munmap()".