What you should know about memory hotplug

Hotplug memory management overhead

Linux requires real memory to manage hotplug memory, generally around 2%. For example, to manage 5 GB, Linux needs 100 MB in the base allocation. This is the theoretical minimum needed to boot the Linux instance.

For large amounts of hotplug memory, sufficient initial memory must be available to manage memory blocks. Otherwise, booting Linux can fail due to insufficient memory or hang. When memmap-on-memory is enabled, this requirement is reduced because metadata (struct pages) can reside in the hotplugged memory.

Also, see Module parameters.