Support for hugepages in KVM VMs

[akrasnov-drv]

The required feature described as a wish

We use hugepages and some other tweaks to optimize performance of KVM VMs.
I managed to use our KVM VM config in CloudStack by updating VM xml via hook.
The problem is that CloudStack checks free memory of Linux and ignores free hugepages.
As I understand, in the earlier version of CloudStack it used shell to get free memory info, but now it uses Java calls that I can't change without patching and rebuilding agent code.

The following changes should do what I miss:
I'd like to have config option (in Cloudstack config, or in agent.properties) to enable hugepages (defaults to off). IMHO, it's quite easy to do. The option will

• add the following block to each KVM VM created

  <memoryBacking>
    <hugepages/>
  </memoryBacking>

• change check of free memory from MemFree to HugePages_Free × Hugepagesize

Something like the following

long hpFree  = map.getOrDefault(HUGEPAGE_FREE_KEY, 0L);
    long hpSize  = map.getOrDefault(HUGEPAGE_SIZE_KEY, 1024L);  // KiB
    return (hpFree * hpSize) + memFree;

Another option, though less preferable, is to allow using external script (e.g. host.stats.command.script) to override internally acquired values (e.g. MemFree)