[$] Top-tier memory management

Modern computing systems can feature multiple types of memory that differ intheir performance characteristics. The most common example is NUMAarchitectures, where memory attached to the local node is faster to accessthan memory on other nodes. Recently, persistent memory hasstarted appearing in deployed systems as well; this type of memory isbyte-addressable like DRAM, but it is available in larger sizes and is slower toaccess, especially for writes. This new memory type makes memory allocation even more complicatedfor the kernel, driving the need for a method to better manage multiple types ofmemory in one system.