On Tue, Jan 07, 2020 at 02:45:40PM -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 > decrementing the refcount for ZONE_DEVICE pages. > > * Change callers (just release_pages() and put_page()) to check > page_is_devmap_managed() before calling the new > put_devmap_managed_page() routine. This is a performance > point: put_page() is a hot path, so we need to avoid non- > inline function calls where possible. > > * 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'm really not sold on this scheme. Note that I think it is particularly bad, but it also doesn't seem any better than what we had before, and it introduced quite a bit more code.
