$ perl -MDevel::Peek -e'
   sub x {
      my %h;
      Dump(%h, 0);
      keys(%h) = 100;
      Dump(%h, 0);
   }

   x() for 1..3;
' 2>&1 | grep MAX
  MAX = 7
  MAX = 127
  MAX = 127  <-- Preallocated even before C<< keys(%h) = 100; >>!
  MAX = 127
  MAX = 127  <-- Preallocated even before C<< keys(%h) = 100; >>!
  MAX = 127