The pmap_init function initializes the pmap(9) sub-system. It is called during system initialization by vm_init, to initialize any structures that the pmap_init system needs in order to map between physical and virtual memory.
The pmap_init2 function initializes a zone for the PV entries. These are used to implement page sharing at the physical level. A high water mark is set so that the system can recover from excessive numbers of PV entries.