Log files have lines that are long enough, I was thinking more of one/two-character long lines (such that the overhead of malloc bookkeeping would be more than

Log files have lines that are long enough, I was thinking more of one/two-character long lines (such that the overhead of malloc bookkeeping would be more than the line size in memory). Regardless, Emacs also stores the data in a single array with a gap in middle (and memcpy is relatively cheap), so what slows it down is probably not the choice of data structure but everything else built around it.