RFR (XXS): 8048088: Conservative maximum heap alignment should take vm_allocation_granularity into account

[Thomas Schatzl]

Hi all,

  can I have reviews for the following small change? It fixes a at this
time benign issue when calculating the conservative maximum heap
alignment.

In particular, it does not take the os::vm_allocation_granularity() into
account.

It is benign for two reasons:
  - at this time, the conservative maximum heap alignment is always
larger than the vm allocation granularity (64k on Windows, vm_page_size
on others), which is 2M for some reason.
  - even if that were not the case, code further ahead would cause
assertion failures. I.e. the ReservedHeap checks.

As it is a bug, although it is hidden by other code, and caught already
later too, I thought it would still be worth fixing this.

This code touches runtime code, so I cc'ed hotspot-runtime-dev.

Webbug:
http://cr.openjdk.java.net/~tschatzl/8048088/webrev/

CR:
https://bugs.openjdk.java.net/browse/JDK-8048088

Testing:
JPRT

Thanks,
  Thomas