RFR: 8255254: Split os::reserve_memory and os::map_memory_to_file interfaces [v2]

[Anton Kozlov]

> Hi,
> 
> Please review a change to extract map_memory_to_file interface out of reserve_memory when the latter takes file descriptor.
> 
> The change should be a pure refactoring without changes in functionality. The only part is disturbing: a comment in original os_posix.cpp:316 seems to refer to else clause and it contradicts to the actual code.

Anton Kozlov has updated the pull request incrementally with one additional commit since the last revision:

  Fix review findings

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/812/files
  - new: https://git.openjdk.java.net/jdk/pull/812/files/f9423ddd..df6fb834

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=812&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=812&range=00-01

  Stats: 7 lines in 2 files changed: 3 ins; 3 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/812.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/812/head:pull/812

PR: https://git.openjdk.java.net/jdk/pull/812