hotplug seems missing:
─ % zgrep CONFIG_SPARSEMEM /proc/config.gz
CONFIG_SPARSEMEM_MANUAL=y
CONFIG_SPARSEMEM=y
CONFIG_SPARSEMEM_EXTREME=y
CONFIG_SPARSEMEM_VMEMMAP_ENABLE=y
CONFIG_SPARSEMEM_VMEMMAP=y
╭─[~/git/nixpkgs]
╰─ % zgrep CONFIG_MEMORY_HOTPLUG /proc/config.gz
# CONFIG_MEMORY_HOTPLUG is not set