title: What is specific to an unevictable page?
body: <p>I was browsing the ramfs code and was puzzled by the notion of unevictable pages.</p>
  
  <p>I've been reading the kernel's documentation at Documentation/vm/unevictable-lru.txt and this answer:</p>
  
  <p><a href="https://stackoverflow.com/questions/4343249/unevictable-page/4343338#4343338">unevictable page</a></p>
  
  <p>but it did not fully answer my question. It said that the kernel "cannot touch it" or "cannot evict it", but what does that mean ?</p>
  
  <p>I thought that anyways, once a page is being used it could not be removed until it is volontarily released ? Or does it mean that it cannot be moved to swap ? Or is there some kind of a cache involved, outside of the ram, containing all of the unevictable pages ?</p>
  
  <p>When building my own virtual filesystem, do I have to mark my inodes as unevictable ?</p>
  
  <p>Thanks in advance for your answers.</p>