On Wed, Jun 22, 2022 at 11:50:37AM -0700, Nadav Amit wrote: > From: Nadav Amit <namit@xxxxxxxxxx> > > When userfaultfd provides a zeropage in response to ioctl, it provides a > readonly alias to the zero page. If the page is later written (which is > the likely scenario), page-fault occurs and the page-fault allocator > allocates a page and rewires the page-tables. > > This is an expensive flow for cases in which a page is likely be written > to. Users can use the copy ioctl to initialize zero page (by copying > zeros), but this is also wasteful. > > Allow userfaultfd users to efficiently map initialized zero-pages that > are writable. IF UFFDIO_ZEROPAGE_MODE_WRITE_LIKELY is provided would map > a clear page instead of an alias to the zero page. > > For consistency, introduce also UFFDIO_ZEROPAGE_MODE_ACCESS_LIKELY. > > Suggested-by: David Hildenbrand <david@xxxxxxxxxx> > Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> > Cc: Peter Xu <peterx@xxxxxxxxxx> > Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx> > Signed-off-by: Nadav Amit <namit@xxxxxxxxxx> Acked-by: Peter Xu <peterx@xxxxxxxxxx> -- Peter Xu
