title: do tmpfs and mmap play nice on xen?
body: <p>Will <code>mmap</code>ing in a tmpfs volume in linux cause active pages to be stored in RAM twice? My understanding is that the kernel uses a special <code>shmem_mmap</code> operation for mapping ramdisks so each page only consumes resources once. But I'm on a xen virtual machine and I assume xen messes with virtual memory operations as well.</p>
  
  <p>Context: I'm experimenting with mongodb on a tmpfs volume in AWS (i.e. on a xen virtual machine).</p>