That would be read-only though, so not an ideal solution for Sublime. Although one could mmap and then reference the original from a structure describing how th

That would be read-only though, so not an ideal solution for Sublime. Although one could mmap and then reference the original from a structure describing how the file was modified. However mmaping files which can be modified by another process concurrently is tricky. You can just get killed by SIGBUS.