When a page fault occurs as a result of a userspace memory access or Object, or to delay allocation until the memory is needed (for instance Note that they can decide to allocate pages when initializing the GEM Uses system memory directly or as a backing store otherwise.ĭrivers are responsible for the actual physical pages allocation byĬalling shmem_read_mapping_page_gfp() for each page. Used as either main storage for the object when the graphics hardware Requested size and store it into the struct struct drm_gem_object filp field. GEM uses shmem to allocate anonymous pageable memory.ĭrm_gem_object_init() will create an shmfs file of the To the DRM device, a pointer to the GEM object and the buffer object Specific GEM object type and initializes the embedded struct To create a GEM object, a driver allocates memory for an instance of its Drivers usually need toĮxtend GEM objects with private information and thus create aĭriver-specific GEM object structure type that embeds an instance of GEM objects are represented by an instance of struct struct drm_gem_object. GEM splits creation of GEM objects and allocation of the memory that Read & write, mapping, and domain ownership transfers are left to Provided by Linux’s shmem layer, which provides memory to back eachĭevice-specific operations, such as command execution, pinning, buffer Aperture management at command execution timeīuffer object allocation is relatively straightforward and largely.On a fundamental level, GEM involves several operations: Primitives, are thus outside of the scope of GEM and must be implemented APIs that require knowledge of bufferĬontents or purpose, such as buffer allocation or synchronization It manages abstract buffer objects without knowing Buffer allocation and read and write operations, describedĪs part of the common GEM API, are currently implemented using Slightly outdated, the document provides a good overview of the GEM API The GEM userspace API is described in the GEM - the Graphics Execution Let drivers implement hardware-specific operations with their own Operations to userspace and a set of helper functions to drivers, and GEM exposes a set of standard memory-related Provide full coverage of all (or even all common) use cases in its The GEM design approach has resulted in a memory manager that doesn’t Object, ttm_global_item_ref() is used to create an initial referenceĬount for the TTM, which will call your initialization function. Again, driver-specific init and release functions mayīe provided, likely eventually calling ttm_bo_global_init() and TTM_GLOBAL_TTM_BO, and its size should be sizeof(struct Object TTM to provide a pool for buffer object allocation by clients and Once your global TTM accounting structure is set up and initialized byĬalling ttm_global_item_ref() on it, you need to create a buffer Point at your driver-specific init and release routines, which probablyĮventually call ttm_mem_global_init and ttm_mem_global_release, Sizeof(struct ttm_mem_global), and the init and release hooks should The size field for the global object should be There should be one global reference structure for your memory managerĪs a whole, and there will be others for each object created by the TTM, but has no video RAM management capabilities and is thus limited to GEM has simpler initialization and execution requirements than Identified common code between drivers and created a support library to Providing a solution to every graphics memory-related problems, GEM Its design philosophy is completely different: instead of GEM started as an Intel-sponsored project in reaction to TTM’sĬomplexity. This resulted in a large, complex piece of code that turned out to be It provides a single userspace API to accommodate the need ofĪll hardware, supporting both Unified Memory Architecture (UMA) devicesĪnd devices with dedicated video RAM (i.e. Manager to be developed and tried to be a one-size-fits-them all (TTM) and Graphics Execution Manager (GEM). The DRM core includes two memory managers, namely Translation Table Maps The very dynamic nature of many of that data, managing graphics memoryĮfficiently is thus crucial for the graphics stack and plays a central Modern Linux systems require large amount of graphics memory to storeįrame buffers, textures, vertices and other graphics-related data.
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