title: DMA copy in splice()
body: <p>I am new to linux kernel. And recently, i've went through the sendfile syscall in kernel 2.6.33. The following is the sequence of my journey:</p>
  
  <pre><code>   do_sendfile()
  =&gt; do_splice_direct()
  =&gt; splice_direct_to_actor()
  =&gt; do_splice_to()
  =&gt; do_splice_from()
  =&gt; splice_read,splice_write
  </code></pre>
  
  <p>Throughout this sequence, I didn't find the place where splice use the DMA copy. So where is the DMA copying taking place?</p>