RFR: 8254972: Fix pretouch chunk calculations [v2]

[Thomas Schatzl]

> Hi all,
> 
>   can I have reviews for this follow-up to JDK-8252221 where Kim noticed that the code in the pretouch task has some minor issues?
> 
> In particular, some code could be simplified and due to some inconsistencies, and used less than ideal number of workers. There is also a fix to avoid an overflow if you want to pretouch >= 16TB of heap with 4k pages (order of casts in calculation of ``num_workers``).
> 
> Testing: tier1
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  sjohanss review

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/884/files
  - new: https://git.openjdk.java.net/jdk/pull/884/files/eeb40132..e72dc261

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=884&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=884&range=00-01

  Stats: 11 lines in 1 file changed: 9 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/884.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/884/head:pull/884

PR: https://git.openjdk.java.net/jdk/pull/884