1. A method implemented by a non-volatile memory (NVM) controller comprising: obtaining a NVM express (NVMe) command comprising a namespace identifier (NSID) from a host memory via a peripheral component interconnect express (PCIe) function; determining a mapping between the PCIe function and a namespace identified by the NSID based on a data structure stored in a PCIe memory address space; and accessing the namespace based on the mapping between the PCIe function and the namespace.