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: process.rs
    path of file: ./repos/linkerd2-proxy/linkerd/metrics/src
    
    the code of the file until where you have to start completion: use crate::prom::{self, encoding::EncodeMetric};
use std::time::{SystemTime, UNIX_EPOCH};
use tokio::time::Instant;

pub fn register(reg: &mut prom::Registry) {
    let start_time = Instant::now();
    let start_time_from_epoch = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .expect("process start time");

    reg.register_with_unit(
        "start_time",
        "Time that the process started (in seconds since the UNIX epoch)",
        prom::Unit::Seconds,
        prom::ConstGauge::new(start_time_from_epoch.as_secs_f64()),
    
        pub fn new() -> Self {
            let page_size = match sys::page_size() {
                Ok(ps) => Some(ps),
                Err(err) => {
                    tracing::debug!("Failed to load page size: {}", err);
                    None
                }
            };
            let ms_per_tick = match sys::ms_per_tick() {
                Ok(mpt) => Some(mpt),
                Err(err) => {
                    tracing::debug!("Failed to load cpu clock speed: {}", err);
                    None
                }
            };

            Self {
                page_size,
                ms_per_tick,
            }
        }