We're close to removing page->mapping from the kernel, and I've run into amdgpu's use of page->mapping (setting it to ->dev_mapping and comparing it against ->dev_mapping). What I need to understand to know how to fix this properly is who allocates these pages for what purpose? I've got this far: amdgpu_ttm_tt_set_user_pages() populates ttm->pages. That's called from amdgpu_cs_parser_bos() which got e->userpages from amdgpu_ttm_tt_get_user_pages(). amdgpu_ttm_tt_get_user_pages() got them from amdgpu_hmm_range_get_pages() amdgpu_hmm_range_get_pages() gets them from calling hmm_pfn_to_page() which ... could get pages from anywhere? But cleaarly they can't be _any_ pages because if they were anon or file pages, overwriting page->mapping would blow up horribly today. So they must be driver pages, but I can't see where they're allocated. Is it ttm_pool_alloc_page()?
