Question regarding X79 boards and DSDT patching

[r-o-n-i]

System

• Motherboard: Not sure right now, some X79
• BIOS Version: 2.15.1236
• GPU: None so far
• [ ] CSM is turned off. Make sure to confirm this in the BIOS and not with GPU-Z or similar since it can be inaccurate
• [*] 4G decoding is enabled. Make sure to confirm this in the BIOS and not with GPU-Z or similar since it can be inaccurate
• [ ] UEFIPatch is applied (see Using UEFIPatch for more information). On some motherboards DSDT Patching is also needed
• [*] I have read Common issues (and fixes)

Description

In the Northbridge settings I can set MMIOH Size to maximum 128G. Does that mean that this (and system RAM and other devices) limits the total amount of possible VRAM? Is it possible that there is a hidden option for 256G or even higher? If yes, how to unlock? if no, is it possible to increase MMIOH Size by any other way? Could the method described here

https://github.com/xCuri0/ReBarUEFI/wiki/DSDT-Patching#x79-dsdt-patch

help even if I did not apply any patch?