On Tue, Jul 30, 2019 at 12:25:57PM +0200, Christoph Hellwig wrote: > On Mon, Jul 29, 2019 at 04:57:21PM -0400, Jerome Glisse wrote: > > > All pages releases by bio_release_pages should come from > > > get_get_user_pages, so I don't really see the point here. > > > > No they do not all comes from GUP for see various callers > > of bio_check_pages_dirty() for instance iomap_dio_zero() > > > > I have carefully tracked down all this and i did not do > > anyconvertion just for the fun of it :) > > Well, the point is _should_ not necessarily do. iomap_dio_zero adds the > ZERO_PAGE, which we by definition don't need to refcount. So we can > mark this bio BIO_NO_PAGE_REF safely after removing the get_page there. > > Note that the equivalent in the old direct I/O code, dio_refill_pages, > will be a little more complicated as it can match user pages and the > ZERO_PAGE in a single bio, so a per-bio flag won't handle it easily. > Maybe we just need to use a separate bio there as well. > > In general with series like this we should not encode the status quo an > pile new hacks upon the old one, but thing where we should be and fix > up the old warts while having to wade through all that code. Other user can also add page that are not coming from GUP but need to have a reference see __blkdev_direct_IO() saddly bio get fill from many different places and not always with GUP. So we can not say that all pages here are coming from bio. I had a different version of the patchset i think that was adding a new release dirty function for GUP versus non GUP bio. I posted it a while ago, i will try to dig it up once i am back. Cheers, Jérôme
