main.rs

use std::ptr;

const SIZE: usize = 50 * 1024 * 1024;

fn main() {
    unsafe {
        let ptr = libc::mmap(
            ptr::null_mut(),
            SIZE,
            libc::PROT_READ | libc::PROT_WRITE,
            libc::MAP_PRIVATE | libc::MAP_ANONYMOUS,
            -1,
            0,
        );
        assert!(
            ptr != libc::MAP_FAILED,
            "failed to mmap: {}",
            std::io::Error::last_os_error()
        );
        let start = std::time::Instant::now();
        let rc = libc::mprotect(ptr, SIZE, libc::PROT_READ | libc::PROT_EXEC);
        assert!(
            rc == 0,
            "failed to mprotect: {}",
            std::io::Error::last_os_error()
        );
        println!("mprotect with no touched pages {:?}", start.elapsed());

        let ptr = libc::mmap(
            ptr::null_mut(),
            SIZE,
            libc::PROT_READ | libc::PROT_WRITE,
            libc::MAP_PRIVATE | libc::MAP_ANONYMOUS,
            -1,
            0,
        );
        assert!(
            ptr != libc::MAP_FAILED,
            "failed to mmap: {}",
            std::io::Error::last_os_error()
        );
        for i in 0..SIZE / 4096 {
            *(ptr as *mut u8).add(i * 4096) = 1;
        }
        let start = std::time::Instant::now();
        let rc = libc::mprotect(ptr, SIZE, libc::PROT_READ | libc::PROT_EXEC);
        assert!(
            rc == 0,
            "failed to mprotect: {}",
            std::io::Error::last_os_error()
        );
        println!("mprotect with touched pages {:?}", start.elapsed());
    }
}