Where does video memory go?

Question

X Window System

Good afternoon!
When you turn on xinerama, the application bites off a solid piece of video memory, how to fix it?
I have 3 gtx970 video cards (I did not combine them in sli) and 8 monitors, each in its own
Debian 8 screen, openbox shell, latest drivers from nxidia.
When you start a heavy graphics application, if you disable all monitors except 1 in the settings, then the application consumes 1.5-2GB of video memory on its video card.
When additional monitors are turned on, the application consumes 4GB of video memory on other vidyuhi and 2 on its own
How to wean the application from eating someone else's video memory?
Is this normal or is there something wrong with the settings?