RFR: 8255254: Split os::reserve_memory and os::map_memory_to_file interfaces [v4]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into 8255254-split-reserve-memory
 - Fix reviewing findings 2
 - Fix review findings
 - Split reserve and map interfaces

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/812/files
  - new: https://git.openjdk.java.net/jdk/pull/812/files/8908acb7..6335d8ce

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=812&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=812&range=02-03

  Stats: 27860 lines in 409 files changed: 23579 ins; 2888 del; 1393 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