On Wed, May 15, 2024 at 05:43:04PM -0300, Jason Gunthorpe wrote: > On Wed, May 15, 2024 at 03:06:36PM +0800, Yan Zhao wrote: > > > > So it has to be calculated on closer to a page by page basis (really a > > > span by span basis) if flushing of that span is needed based on where > > > the pages came from. Only pages that came from a hwpt that is > > > non-coherent can skip the flushing. > > Is area by area basis also good? > > Isn't an area either not mapped to any domain or mapped into all domains? > > Yes, this is what the span iterator turns into in the background, it > goes area by area to cover things. > > > But, yes, considering the limited number of non-coherent domains, it appears > > more robust and clean to always flush for non-coherent domain in > > iopt_area_fill_domain(). > > It eliminates the need to decide whether to retain the area flag during a split. > > And flush for pin user pages, so you basically always flush because > you can't tell where the pages came from. As a summary, do you think it's good to flush in below way? 1. in iopt_area_fill_domains(), flush before mapping a page into domains when iopt->noncoherent_domain_cnt > 0, no matter where the page is from. Record cache_flush_required in pages for unpin. 2. in iopt_area_fill_domain(), pass in hwpt to check domain non-coherency. flush before mapping a page into a non-coherent domain, no matter where the page is from. Record cache_flush_required in pages for unpin. 3. in batch_unpin(), flush if pages->cache_flush_required before unpin_user_pages.
