Our game creates and destroys 3D resources during running. This over time causes more and more video memory fragments. When a stage is changed, some resources are not released and continues to be used. I'm considering doing defragmenting when a stage is changed. How to do video memory defragmenting? Is there an API to do this?
there is not such an API.
depending on your OS, the driver or the OS are managing the video memory and will defragment when appropriate.