On Mon, Aug 03, 2020 at 05:50:32PM -0700, Peter Collingbourne wrote: > On Mon, Aug 3, 2020 at 5:01 AM Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > I think this would work even for the arm64 MTE (though I haven't tried): > > use memfd_create() to get such file descriptor, mmap() it as MAP_SHARED > > to populate the initial pattern, mmap() it as MAP_PRIVATE for any > > subsequent mapping that needs to be copied-on-write. > > That would require a separate mmap() (i.e. separate VMA) for each > page, no? That sounds like it could be expensive both in terms of VMAs > and the number of mmap syscalls required (i.e. N/PAGE_SIZE). You could > decrease these costs by increasing the size of the memfd files to more > than a page, but that would also increase the amount of memory > required for the reference pages. I think I get it now. You'd like a multiple page mmap() to be covered by a single reference page. The memfd trick wouldn't give you this without multiple mmap() calls, one for each page. -- Catalin
