In GNOME, pixel scaling is managed with the inevitable gsettings registry value; to turn on 2-to-1 scaling, a command like this can be used:
gsettings set org.gnome.desktop.interface scaling-factor 2
Setting the scaling factor back to one turns off scaling. Scaling should be enabled by default if GNOME detects a high-DPI display; otherwise a command like the above can be used. This value can also be adjusted in gnome-tweak-tool. Should you run into bugs or weirdness (like only a quarter of the screen being used), setting the scaling factor to one then back to two will often straighten them out; your editor has ended up creating a fixscaling script for just this eventuality.
This is kind of why I can't seriously consider abandoning OS X for Linux, even though part of me really