title: Questions about threadgroup memory in Metal
body: <ol>
  <li><em>Threadgroup memory</em> is shared between threads of a threadgroup, but is it preserved after the threadgroup finishes, allowing chaining (if I have a barrier let's say)?</li>
  <li>It seems it is limited to 16KB on current devices, any workaround if I need more?</li>
  <li>Does tiling interfer or influence the use of threadgroup memory in shaders?</li>
  </ol>