On Sun, Aug 26, 2018 at 6:25 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > For an overlayfs file/inode, page io is operating on the real underlying > file, so sync_file_range() should operate on the real underlying file > mapping to take affect. The man page tells us that this syscall basically gives no guarantees at all and shouldn't be used in portable programs. So, I'd just let the non-functionality be for now. If someone complains of a regression (unlikely) we can look into it. Thanks, Miklos