Method dealloc

os/src/mm/frame_allocator.rs:72–80

(&mut self, ppn: PhysPageNum)

        }
    }
    fn dealloc(&mut self, ppn: PhysPageNum) {
        let ppn = ppn.0;
        // validity check
        if ppn >= self.current || self.recycled.iter().any(|&v| v == ppn) {
            panic!("Frame ppn={:#x} has not been allocated!", ppn);
        }
        // recycle
        self.recycled.push(ppn);
    }
}

type FrameAllocatorImpl = StackFrameAllocator;