Specifying Memory Type for a Resource
The user-mode display driver receives information about the memory type that should be used when it receives a request to create a resource. The memory type is specified as either system or video memory through the D3DDDIPOOL_SYSTEMMEM or D3DDDIPOOL_VIDEOMEMORY enumerators, respectively, of the Pool member of the D3DDDIARG_CREATERESOURCE structure. In addition, the Microsoft Direct3D runtime provides hints to the driver about the type of video memory to use by specifying one of following enumerators in the Pool member:
The runtime recommends that the driver use local video memory.
The runtime recommends that the driver use nonlocal video memory (for example, AGP memory).
The runtime provides hints to the user-mode display driver to improve performance. For example, the runtime might specify D3DDDIPOOL_NONLOCALVIDMEM if the CPU writes to the surface, which is performed faster using nonlocal video memory.
The user-mode display driver passes the hints to the display miniport driver through the pPrivateDriverData members of the D3DDDI_ALLOCATIONINFO and DXGK_ALLOCATIONINFO structures in a vendor-specific way. The display miniport driver indicates to the video memory manager the appropriate memory segment to use by returning the identifier of the segment in the HintedSegmentId member of the DXGK_ALLOCATIONINFO structure from a call to the driver's DxgkDdiCreateAllocation function.
Regardless of the type of video memory that is used to create the resource, the user-mode display driver must not expose any semantic differences to the runtime. That is, for each video memory type, the driver must render information identically and must return the same return values.