partman-priorities.js

var min = [ 1024, 7000, 512];
var max = [ 1024, 1000000, 2048];
var pri = [ 1024, 7000, 512];
var fac = new Array(3);

var free_space = 35000;

for (var i = 0; i < min.length; ++i) {
  fac[i] = pri[i] - min[i]; 
}

var ready = false;

while (!ready) {
  var minsum = min[0] + min[1] + min[2];
  var facsum = fac[0] + fac[1] + fac[2];
  ready = true;
  for (var j = 0; i < min.length; ++i) {
    var x = min[i] + (free_space - minsum) * fac[i] / facsum;
    if (x > max[i]) {
       x = max[i];
    }
    if (x != min[i]) {
      ready = false;
      min[i] = x;
    }
  }

}

console.log(min[0], min[1], min[2]);