Garbage collection

[James Gray]

I am writing a web application using vibe.d (not sure whether 
that is relevant or not), and have run into a memory leak. I 
wrote the following code to try and replicate the problem.

import std.algorithm;
import std.range;
import std.format;
import std.stdio;
import core.thread;
import core.memory;

auto f(R)(R r) {
  return format("%s", r);
}

void main()
{
  while(true)
  {
   writeln("Starting");
   {
    auto str = f(iota(100000000).map!(x=>x+1));
   }
   writeln("Done");
   GC.collect();
   Thread.sleep( dur!("msecs")( 30000 ) );
  }
}

  It doesn't replicate the problem but it still doesn't behave as 
I would expect. I would expect the memory usage of this code to 
grow and shrink. However, I find that the memory usage grows to 
about 1.5GB and never decreases. Is there something I am not 
understanding?