[8u] RFR: 8017629: G1: UseSHM in combination with a G1HeapRegionSize > os::large_page_size() falls back to use small pages

[Andreas Eriksson]

Hi,

Please review this JDK 8 backport of 8017629: G1: UseSHM in combination 
with a G1HeapRegionSize > os::large_page_size() falls back to use small 
pages.

https://bugs.openjdk.java.net/browse/JDK-8017629
http://cr.openjdk.java.net/~aeriksso/8017629/webrev.00/

The changeset is functionally identical to the JDK 9 version, but 
several differences in whitespace, and a few context differences (mainly 
a comment that were in 8 but not in 9) made it not apply cleanly.

JDK 9 webrev can be found here for comparison:
http://cr.openjdk.java.net/~stefank/8017629/webrev.03/

Note: I'll also be backporting 8077276 
(https://bugs.openjdk.java.net/browse/JDK-8077276) since this changeset 
depends on that fix.

Regards,
Andreas