I have a mid-2014 MacBook Pro [2.8 Ghz i7 (4980HQ Haswell/Crystalwell), NVIDIA GEForce GT 750M (2040 MB VRAM)], running 10.13.6, connected to a Dell P2715Q 27" 4K external monitor. Since the last High Sierra security/Safari update, Expose on my Mac has become quite laggy (~1 - 2 sec delay between when my mouse cursor reaches a hot corner and when it activates). It's much less laggy when I unplug the Dell and use the MBP's internal monitor—at which time, because it no longer needs to drive the 4K monitor, it has switched from the discrete GPU to the integrated Intel Iris Pro graphics (1536 MB VRAM).
I've checked CPU, GPU, and RAM usage in Activity Monitor while activating Expose, and all stay fairly low (<50%). That makes me wonder if the lag is caused by high GPU memory pressure, but I don't know how to check VRAM usage (other than by installing iStat Menus).
vm_stat provide this info. Is there a Terminal command for this?