RFR (S/M): 8169703: G1 crashes with guarantee(pretouch_gang != NULL) failed: No pretouch gang specified

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that fixes use of AlwaysPreTouch
with CDS?

Basically, AlwaysPreTouch is apparently not used very often, so some
use cases were missed, causing a guarantee to fail.

The patch adds support for:
 - parallel pretouch during (potentially concurrent) humongous object
allocation.
 - allocating CDS/archive regions during archive creation. In this case
the code uses only one thread because archive regions are always
allocated region by region anyway.
 - mapping in a memory range covered by a CDS archive

All these cases are covered by new regression tests.

CR:
https://bugs.openjdk.java.net/browse/JDK-8169703
Webrev:
http://cr.openjdk.java.net/~tschatzl/8169703/webrev/
Testing:
runtime tier0-5 tests with -XX:+AlwaysPreTouch, new tests

Thanks,
  Thomas