Since we make memory update and memory limit working base on memory hotplug(see #624 #786), and memory hotplug need to be memblock align, which is defined by linux kernel and can be read from /sys/devices/system/memory/block_size_bytes. But users may not let memory to be memblock align, and actually, they shouldn't know what is "memblock". Now we make every update or limit to be forcing on memblock align to make hotplug success. It isn't good enough and waste memory. So we need a more elastic way, just like #624 (comment) mentions.