sS gcRenderChangesInUsedMemory(GcInfo info) {
  Map<S, MemoryUsage> map1 = info.getMemoryUsageBeforeGc();
  Map<S, MemoryUsage> map2 = info.getMemoryUsageAfterGc();
  
  new L<S> changes;
  for (S pool, MemoryUsage after : map2) {
    MemoryUsage before = map1.get(pool);
    if (before == null) continue;
    long change = after.getUsed()-before.getUsed();
    if (change != 0)
      changes.add(pool + ": " + toK(change) + " K");
  }
  ret joinWithComma(changes);
}