On Fri, May 08, 2020 at 12:20:03PM -0700, Ralph Campbell wrote: > hmm_range_fault() returns an array of page frame numbers and flags for > how the pages are mapped in the requested process' page tables. The PFN > can be used to get the struct page with hmm_pfn_to_page() and the page size > order can be determined with compound_order(page) but if the page is larger > than order 0 (PAGE_SIZE), there is no indication that the page is mapped > using a larger page size. To be fully general, hmm_range_fault() would need > to return the mapping size to handle cases like a 1GB compound page being > mapped with 2MB PMD entries. However, the most common case is the mapping > size the same as the underlying compound page size. > This series adds a new output flag to indicate this so that callers know it > is safe to use a large device page table mapping if one is available. > Nouveau and the HMM tests are updated to use the new flag. This explanation doesn't make any sense. It doesn't matter how somebody else has it mapped; if it's a PMD-sized page, you can map it with a 2MB mapping.
