RFR: Disable ShHeapUncommit on too-large large-pages

[Roman Kennke]

OMG, the webrev was totally garbled. Look at this one:
cr.openjdk.java.net/~rkennke/disable-uncommit/webrev.01/


> On my aarch64-test-box I get large pages of 512MB. When running the
> HeapUncommit test with just -Xmx1g and -XX:+UseLargePages we attempt to
> have at least large-page-size-sized regions, which would result in just
> 2 regions, which is not possible (and rightly trips an assert).
> 
> The reason why we need to do this is for heap-region-uncommit: if we had
> regions smaller than page size, we would accidently uncommit adjacent
> regions too.
> 
> After some discussions with Aleksey off-list, I propose to disable heap
> region uncommit if large-page-size is too large:
> 
> http://cr.openjdk.java.net/~rkennke/disable-uncommit/webrev.00/
> 
> Testing: tier3_gc_shenandoah/aarch64 (except 1 remaining test that fails
> for other reasons)
> 
> Good?
> 
> Roman
>