You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: region.rs
    path of file: ./repos/nebulet/src/memory
    
    the code of the file until where you have to start completion: 
use x86_64::{VirtAddr, PhysAddr};
use x86_64::structures::paging::{Page, PhysFrame, PageSize, Size4KiB,
    PageTableFlags, PageRangeInclusive, MapToError, UnmapError};

use arch::paging::PageMapper;
use arc
    
    fn unmap(&mut self) -> Result<()> {
        let mut mapper = unsafe { PageMapper::new() };

        for page in self.pages() {
            match mapper.unmap(page) {
                Ok(mf) => mf.flush(),
                Err(UnmapError::PageNotMapped) => {},
                Err(_) => return Err(internal_error!()),
            }
        }
        Ok(())
    }