pub fn get(&self, addr: u32) -> Option<&V> {
        let (upper, lower) = Self::indices(addr);
        let index = self.index[upper];
        if index == NO_PAGE {
            None
        } else {
            self.page_table[index as usize].0[lower].as_ref()
        }
    }
Get a reference to the memory value at the given address, if it exists.
crates/core/executor/src/memory.rs