Hi Christian,
We are looking into using shmem as a ttm_tt backend in i915 for cached system memory objects. We would also like to make such objects visible to the i915-gem shrinker, so that they may be swapped out or discarded when under memory pressure.
One idea for handling this is roughly something like: - Add a new TTM_PAGE_FLAG_SHMEM flag, or similar. - Skip the ttm_pages_allocated accounting on such objects, similar to how FLAG_SG is already handled. - Skip all the page->mapping and page->index related bits, like in tt_add_mapping, since it looks like these are set and used by shmem. Not sure what functionally this might break, but looks like it's maybe only driver specific? - Skip calling into ttm_bo_swap_out/in and just have ttm_populate/unpopulate handle this directly for such objects. - Make such objects visible to the i915-gem shrinker.
Does this approach look acceptable?