ArrayAllocatorMallocLimit was introduced in JDK-7197666 for Solaris support:

https://github.com/openjdk/jdk/commit/4a685f181b71f534118a40a3314cb09e285c84e8

// Uses the OS malloc for allocations smaller than ArrayAllocatorMallocLimit
// and uses mapped memory for larger allocations.
// Most OS mallocs do something similar but Solaris malloc does not revert
// to mapped memory for large allocations. By default ArrayAllocatorMallocLimit
// is set so that we always use malloc except for Solaris where we set the
// limit to get mapped memory.

Since the removal of Solaris support in JDK-8244224, ArrayAllocatorMallocLimit is not useful for any existing ports. It has remained an experimental VM option since its addition more than 10 years ago. I suspect no one is actually using it, since this flag must be set with -XX:+ArrayAllocatorMallocLimit.

ArrayAllocatorMallocLimit should be removed, along with MmapArrayAllocator. We should also remove the 'length' and 'old_length' parameters to ArrayAllocator::freeI() and ArrayAllocator::reallocate(), respectively.