pub fn saturating_sub(&self, older: &Self) -> Self {
        Self {
            cache_size: self.cache_size.saturating_sub(older.cache_size),
            storage_invocations_missed: self
                .storage_invocations_missed
                .saturating_sub(older.storage_invocations_missed),
            get_value_storage_invocations: self
                .get_value_storage_invocations
                .saturating_sub(older.get_value_storage_invocations),
            set_value_storage_invocations: self
                .set_value_storage_invocations
                .saturating_sub(older.set_value_storage_invocations),
            time_spent_on_storage_missed: self
                .time_spent_on_storage_missed
                .saturating_sub(older.time_spent_on_storage_missed),
            time_spent_on_get_value: self
                .time_spent_on_get_value
                .saturating_sub(older.time_spent_on_get_value),
            time_spent_on_set_value: self
                .time_spent_on_set_value
                .saturating_sub(older.time_spent_on_set_value),
        }
    }
Subtracts two sets of statistics. This can be used to measure increment between these stats and older stats for the same VM.
core/lib/vm_interface/src/storage/view.rs