104     pub user_stack: Option<UserStack>,
305         addr: Option<VirtAddr>,  in mmap()
479     pub fn user_stack_mut(&mut self) -> Option<&mut UserStack> {  in user_stack_mut()
607     pub fn contains(&self, vaddr: VirtAddr) -> Option<Arc<LockedVMA>> {  in contains()
633     pub fn find_free(&self, min_vaddr: VirtAddr, size: usize) -> Option<VirtRegion> {  in find_free()
703         let prev_hole: Option<(&VirtAddr, &mut usize)> =  in reserve_hole()
726         let next_hole_size: Option<usize> = self.vm_holes.remove(&region.end());  in unreserve_hole()
759     pub fn remove_vma(&mut self, region: &VirtRegion) -> Option<Arc<LockedVMA>> {  in remove_vma()
880     ) -> Option<(  in extract()
881         Option<Arc<LockedVMA>>,  in extract()
883         Option<Arc<LockedVMA>>,  in extract()
896             let intersect: Option<VirtRegion> = guard.region.intersect(&region);  in extract()
908         let before: Option<Arc<LockedVMA>> = guard.region.before(&region).map(|virt_region| {  in extract()
916         let after: Option<Arc<LockedVMA>> = guard.region.after(&region).map(|virt_region| {  in extract()
942     user_address_space: Option<Weak<AddressSpace>>,
1152     fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {  in partial_cmp()
1184         stack_bottom: Option<VirtAddr>,  in new()