RFR: 8255254: Split os::reserve_memory and os::map_memory_to_file interfaces

[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.

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Commit messages:
 - Split reserve and map interfaces

Changes: https://git.openjdk.java.net/jdk/pull/812/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=812&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255254
  Stats: 171 lines in 9 files changed: 88 ins; 56 del; 27 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