RFR (XS): 8213927: G1 ignores AlwaysPreTouch when UseTransparentHugePages is enabled

[Thomas Schatzl]

Hi all,

  can I have reviews for this small fix that changes the page size to
use when pretouching if UseTransparentHugePages is enabled on the
command line?

The problem is that previously, with UseTransparentHugePages, G1 used
large page increments for pretouching, but since these huge pages are
"transparent" except for commit purposes (in the VM), we need to
pretouch on a small page size in this case.

This change just implements that.

CR:
https://bugs.openjdk.java.net/browse/JDK-8213927
Webrev:
http://cr.openjdk.java.net/~tschatzl/8213927/webrev/
Testing:
hs-tier1-3; manual checking RSS sizes on Linux with different options

Thanks,
  Thomas