On 6/10/19 3:40 PM, Yu-cheng Yu wrote: > Ok, we will go back to do_mmap() with MAP_PRIVATE, MAP_NORESERVE and > VM_DONTDUMP. The bitmap will cover only 48-bit address space. Could you make sure to discuss the downsides of only doing a 48-bit address space? What are the reasons behind and implications of VM_DONTDUMP? > We then create PR_MARK_CODE_AS_LEGACY. The kernel will set the bitmap, but it > is going to be slow. Slow compared to what? We're effectively adding one (quick) system call to a path that, today, has at *least* half a dozen syscalls and probably a bunch of page faults. Heck, we can probably avoid the actual page fault to populate the bitmap if we're careful. That alone would put a syscall on equal footing with any other approach. If the bit setting crossed a page boundary it would probably win. > Perhaps we still let the app fill the bitmap? I think I'd want to see some performance data on it first.
