On Thu, May 25, 2023 at 09:45:34PM +0100, Matthew Wilcox wrote: > > > Isn't "long term pinning" the wrong description of the problem? Long term > > > pins suggest to me FOLL_LONGTERM. I think this is simple short term > > > pins that we care about here. > > > > vfio pins are held for a long time - Steve > > So this is a third sense of "pinned pages" that is neither what > filesystems nor the mm means by pinned pages, but whatever it is that > vfio means by pinned pages? If only "pin" weren't such a desirable > word. Can somebody explain to me in small words what a vfio pin looks > like because I've tried reading vfio_iommu_type1_pin_pages() and I > don't recognise anything there that looks like pinning in either of > the other two senses. 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().
