Directx 11 Memory Management

Question

I've been studying Directx 11 for a while now, but I'm still confused on how Directx 11 manages memory. For example, if I create a vertex buffer using ID3D11Device::CreateBuffer, where is the new buffer stored? I know it returns a pointer to the buffer, so that means it must be stored on CPU RAM right? However, I thought that this would make ID3D11DeviceContext::IASetVertexBuffers a very slow process, because it would have to copy the buffer from CPU RAM to GPU RAM. But if all of the buffers created with ID3D11Device:CreateBuffer were stored on GPU RAM, then wouldn't the GPU RAM fill up really quickly? Basically I would like to know: when I create a buffer, where is that data stored? In CPU RAM or GPU RAM? Also, what is ID3D11DeviceContext::IASetVertexBuffers doing with the buffer (copying/setting?).

Answer 1

The general answer is that "it's wherever the driver wants it to be". For "DYNAMIC" resources, they are typically put into memory that is accessible to both the CPU and the GPU (on modern PCs this is shared across the PCIe bus). For "STATIC" resources, they can be on video RAM that is only accessible by the GPU which is copied via the 'shared' memory window, or if there's limited space they are put in the 'shared' memory window. Render Targets are usually put in video RAM as well.

For a deeper dive on Direct3D video memory management, check out the talk "Why Your Windows Game Won't Run In 2,147,352,576?" which is no longer on MSDN Downloads but can be found on my blog.

If you want the nitty-gritty hardware details, read the driver writer's documentation.

You may also find the Video Memory sample on MSDN Code Gallery educational.