CONFIG_VMSPLIT_3G_OPT is not available for the selected architecture x86.
Result is shown for architecture arm

3G/1G user/kernel split (for full 1G low memory)

configname: CONFIG_VMSPLIT_3G_OPT

Memory split
└─>3G/1G user/kernel split (for full 1G low memory)
In linux kernel since version 2.6.16 (release Date: 2006-03-19)
depends
NOT CONFIG_ARM_LPAE