Comment by aucisson_masque
14 hours ago
> i'm playing a bit fast and loose with what lives on the GPU and what lives on the CPU here. On many systems, they share a memory pool anyway. But on systems with discrete GPUs, most of this is gonna be video memory
Yeah this is irrelevant here, windows doesn't share both in 99 of the case.
What do you mean by "windows doesn't share both"? Windows doesn't get a say, Intel iGPU systems literally don't have video memory
IGPU systems on Windows usually set aside a fixed pool of memory for the graphics usually set by the platform. As in, if you need more video memory you need to go to the BIOS and reconfigure it. When you look at total system memory available in Windows it's the total installed minus however much you defined for the video memory. If you need to have the GPU mess with something you still have to a copy it from the system side to the GPU side. Applications can run out of video memory while still having available system memory.
It's only been somewhat recent that I've personally seen much hardware that allows for that reservation to be dynamically defined, and not with any Intel integrated graphics so far.
Iris Xe in 12th-gen do this, no idea since when it's added. There's still a minimum configurable shared allocation option in the BIOS, probably for legacy OS, but after booting Windows it can take up to 8 GB of the system RAM.
DWM quite literally does that all the time. For the general case it allocates GPU memory, but also swaps to system RAM or uses it as a synchronization mechanic when you have one screen on an igpu and the other on a dgpu.