title: Deadline I/O Scheduler front_merges scenario
body: <p>I'm working on a research on Linux IO Schedulers. Linux Deadline IO Scheduler uses 'front_merges' property to decide the request is front or back merge. But I couldn't understand how can it work because of it sets 'front_merges' property just in one place and it is only set to 1 as follows.</p>
  
  <pre><code>dd-&gt;front_merges = 1;
  </code></pre>
  
  <p>I want to know how can Deadline IO Scheduler sets the 'front_merges' somewhere else. If it doesn't, what is the scenario of deadline front merge algorithm?</p>
  
  <p>Thanks..</p>