On Sun, Nov 17, 2019 at 11:09 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > On Thu, Nov 14, 2019 at 04:11:34PM -0800, John Hubbard wrote: > > An upcoming patch changes and complicates the refcounting and > > especially the "put page" aspects of it. In order to keep > > everything clean, refactor the devmap page release routines: > > > > * Rename put_devmap_managed_page() to page_is_devmap_managed(), > > and limit the functionality to "read only": return a bool, > > with no side effects. > > > > * Add a new routine, put_devmap_managed_page(), to handle checking > > what kind of page it is, and what kind of refcount handling it > > requires. > > > > * Rename __put_devmap_managed_page() to free_devmap_managed_page(), > > and limit the functionality to unconditionally freeing a devmap > > page. > > > > This is originally based on a separate patch by Ira Weiny, which > > applied to an early version of the put_user_page() experiments. > > Since then, Jérôme Glisse suggested the refactoring described above. > > I can't say I'm a big fan of this as it adds a lot more inlined > code to put_page, which has a lot of callsites. Can't we instead > try to figure out a way to move away from the off by one refcounting? That might be possible. David and I are discussing a pfn_online() helper that might be a replacement for keeping ZONE_DEVICE pages out of the page allocator rather than keeping their reference count elevated.
