Function track_peaks_and_exits 

fn track_peaks_and_exits(
    st: &mut State,
    procs: &[ProcInfo],
    now: Instant,
) -> (Vec<Option<u64>>, Vec<Exited>)

Update each process’s peak memory, and note the tasks’ members that were in the previous measurement and are gone from this one. Returns the peaks by index and the exited processes still within EXITED_LINGER.