In Win32 Api
Take a look at QueryWorkingSet function to query the state of the memory of your process.
As an efficient way to load pages on physical memory see PrefetchVirtualMemory
The lowest level, cross-platform API compatible with Windows and Linux that I know is POSIX specification.
Also I recomend you to take a look on numa Win32 memory functions and intel cache line and L2 memory opcodes, It is a very tricky stuff but it could increment heavily the performance of memory reads/writes (if this is the main objective).