On Fri, May 26, 2023 at 09:44:34AM -0600, Khalid Aziz wrote: > > Oh, I think I found it! pin_user_pages_remote() is called by > > vaddr_get_pfns(). If these are the pages you're concerned about, > > then the efficient way to do what you want is simply to call > > folio_maybe_dma_pinned(). Far more efficient than the current mess > > of total_mapcount(). > > vfio pinned pages triggered this change. Wouldn't checking refcounts against > mapcount provide a more generalized way of detecting non-migratable pages? Well, you changed the comment to say that we were concerned about long-term pins. If we are, than folio_maybe_dma_pinned() is how to test for long-term pins. If we want to skip pages which are short-term pinned, then we need to not change the comment, and keep using mapcount/refcount differences.
