This GL 4.4 extension was added to the open-source Radeon drivers and then in March for supporting the Intel Mesa driver. Ilia Mirkin has now wired-up the ARB_buffer_storage support for the Nouveau Gallium3D drivers: NV30, NV50, and NVC0.
The ARB_buffer_storage extension was one of the big additions to the OpenGL 4.4 core specification. This OpenGL buffer storage extension allows more fine-grained control for developers to request where memory buffer objects are stored when it comes to dealing with APUs/SoCs and other systems with separated discrete video memory, system memory, etc. Having more control over the memory buffer placement and its cache handling can lead to greater performance by games and applications. More details on the ARB_buffer_storage OpenGL extension from the Khronos Group can be found via the official OpenGL.org registry.
The Nouveau support landed this morning into Git and will be part of the upcoming Mesa 10.2 release that should happen within the next month.