system_get_physmem - get amount of physical memory on the system
#include <zircon/syscalls.h>
size_t zx_system_get_physmem(void);
system_get_physmem() returns the total size of physical memory on the machine, in bytes.
system_get_physmem() returns a number in bytes.
system_get_physmem() cannot fail.
Currently the total size of physical memory cannot change during a run of the system, only at boot time. This might change in the future.