title: memory usage of mmap on shm_open or memfd_create
body: <p>I need named growing shared memory for my application. Earlier I used memory mapped files, however they became too slow with many IOps. My boss decided to move those files into a ramdisk. I suspect mmap from always making its own memory buffer for both regular files and ramdisk. Is there any difference between ramdisk and shm_openo r memfd_create except lifetime ? Does mmap created pagetable just link to memfd's buffer or mmap creates a copy and memory is consumed twice ?</p>
  
  <p>Regards, Martin</p>