Online the newly added memory blocks by default

configname: CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE

Linux Kernel Configuration
└─>Memory Management options
└─>Memory hotplug
└─>Online the newly added memory blocks by default
In linux kernel since version 3.10 (release Date: 2013-06-30)  
This option sets the default policy setting for memory hotplug
onlining policy (/sys/devices/system/memory/auto_online_blocks) which
determines what happens to newly added memory regions. Policy setting
can always be changed at runtime.
See Documentation/admin-guide/mm/memory-hotplug.rst for more information.

Say Y here if you want all hot-plugged memory blocks to appear in
'online' state by default.
Say N here if you want the default policy to keep all hot-plugged
memory blocks in 'offline' state.