In a graphics processing system comprising a graphics processor, a main memory, and a memory management unit, when rendering a frame that represents a view of a scene comprising one or more objects using a ray tracing process and the ray tracing process requires a traversal of a ray tracing acceleration data structure indicative of the distribution of geometry for the scene being rendered to determine geometry for the scene that may be intersected by a ray, at least part of the traversal of the ray tracing acceleration data structure is performed by the memory management unit (MMU).