api: add <transparent_hugepages/> element to <host/>
api: add <transparent_hugepages/> element to <host/>

Transparent Huge Pages is a kernel feature that can mean a performance
boost for KVM guests. See this article for more details:

  http://lwn.net/Articles/359158/

However, there is some level of conflict between KSM and THP (either
that KSM doesn't scan huge pages or that KSM tends to agresively
split up huge pages, I'm not sure which) so users choose between
optimizing for memory density (enable KSM) or optimizing for
performance (enable THP). Enabling THP automatically disables KSM
and disabling THP causes KSM to be re-enabled.

The <transparent_hugepages/> element reports whether THP is enabled
and can be used to enable/disable THP.

e.g.

  PUT /rhevm-api/hosts/2ab5e1da-b726-4274-bbf7-0a42b16a0fc3 HTTP/1.1
  Accept: application/xml
  Content-Type: application/xml

  <host>
    <transparent_hugepages>true</transparent_hugepages>
  </host>

Acked-by: Eoghan Glynn <05a930c6784d3745d96495f57f88bd6091b2dd36@redhat.com>

markmc/rhevm-api,markmc/rhevm-api,markmc/rhevm-api