title: mmap with direct IO
body: <p>my doubt is,</p>
  
  <ol>
  <li><p>If I enables the IO buffer then mmaps shows better IOPS and less latency, why this is happening and what is the relation.</p></li>
  <li><p>Secondly, when the IO buffer is disabled, there is no value  upto block size 4kb i.e. no values when block size is 512b, 1k &amp; 2k, what is happening, Is it anything related to page size ( usually page size is 4kb and mmap operates in count of pages)</p></li>
  </ol>
  
  <p>I am using Flexible IO (fio) for benchmark the system. I have a confusion regarding using Direct IO with mmap (IO Engine). As per my understanding mmap uses the process space to create a virtual address mapping to the file and IO buffer enable to use the memory instead of direct IO.</p>
  
  <p>I searched a lot but it's not clear, can somebody explain to me please ...</p>