Unfortunately, not all applications actually set priorities via VK_EXT_pageable_device_local_memory. As for native Vulkan applications, I haven’t observed any idTech game using the extension directly, at least :/

The D3D side looks a lot better, because vkd3d-proton already uses VK_EXT_pageable_device_local_memory when available, and translates both the ID3D12Device::MakeResident/ID3D12Device::Evict API calls as well as priorities set via ID3D12Device1::SetResidencyPriority to priority values set using the Vulkan vkSetDeviceMemoryPriority command. Lots of D3D12 games utilize at least one of these APIs, so the hints these games provide will now be utilized.

My experience with Linux gaming is that Proton tends to work better than native applications, even when both are available, and it seems this might extend the trend.

Nvidia vram leaks probably won't respect this either

So, is this virtual VRAM stored on the other memory chip we don't have supply for?

Only AMD GPUs? Cries in ancient 1070 Ti ;-;