Cycles texture mipmapping/tilecache

Currently, Cycles (in SVM mode) uses a very simple texture loader where all maps are loaded from disk at render startup, or shared from Blender. This is very memory-inefficient and can significantly impact render startup times in scenes with many high-resolution textures. In addition, due to a lack of mipmapping, textures that are much higher-resolution than needed can cause aliasing problems. Optimizing texture sizes manually is not always viable as the full resolution map may be needed for a later frame or another camera angle.In OSL mode, Cycles makes some use out of OpenImageIO's texture caching functionality for tiled EXRs or the OIIO .tx format. This allows textures to be streamed on-demand in individual chunks. This automatically optimizes textures that are excessively large, unnecessary, or contain unused texture space, and VASTLY improves startup time for preview renders. However, OSL is very slow compared to SVM, even on CPU. Additionally, even in OSL mode there is no control over the behavior of the cache, such as limiting size or forcing a flush or reload. Finally, Blender has no functionality to easily mipmap and tile textures that were not saved this way which can make conversion a hassle.See this documentation for Arnold renderer's texture cache (which is also based on OpenImageIO) for behaviors/benefits: support.solidangle.com/display/AFMUG/Textures