RFR: Bitmap size might not be page aligned when large page is used

[Zhengyu Gu]

I discovered this when running tests for idling regions.

#  Out of Memory Error 
(/home/zgu/workspace/shenandoah-jdk10/src/hotspot/os/linux/os_linux.cpp:2598), 
pid=23493, tid=23494
#
# JRE version:  (10.0) (fastdebug build )
# Java VM: OpenJDK 64-Bit Server VM (fastdebug 
10-internal+0-adhoc.zgu.shenandoah-jdk10, mixed mode, aot, tiered, 
compressed oops, Shenandoah gc, linux-amd64)
# Core dump will be written. Default location: 
/home/zgu/workspace/shenandoah-jdk10/test/hotspot/jtreg/gc/arguments/core.%p
#

This bug is only reproducible when large pages are actually used (when 
system has enough large pages)

http://cr.openjdk.java.net/~zgu/shenandoah/bitmap_size_large_page/webrev.00/


Test:

   hotspot_gc_shenandoah (fastdebug + release)


Thanks,

-Zhengyu