How do I determine available device memory in OpenCL?

I would like to know how much free memory there is on my device before allocating buffers. Is this possible? I know there's CL_DEVICE_GLOBAL_MEM_SIZE for total memory, and CL_DE开发者_StackOverflow社区VICE_MAX_MEM_ALLOC_SIZE for max size of a single object, but I would like to know the current memory state.

As it stands I'm probably going to have to use OpenGL vendor-specific extensions.

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No, there is no way, and there is no need to know it, GPU memory can be virtualized and the driver will swap in/out memory from the GPU when it is/not needed.

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You can use GL_NVX_gpu_memory_info on nVidia.