RFR: 8300658: memory_and_swap_limit() reporting wrong values on systems with swapaccount=0 [v5]

[Severin Gehwolf]

> Please review this change which brings the hotspot code up to date with how the Java metrics behave. On a system where swap accounting is disabled `VM.info` jcmd - for example - no longer reports an unsupported metric, but the memory limit instead as that is actually what is being in place.
> 
> I had to update the `TestMemoryWithCgroupV1.java` test as it skipped the swappiness testing based on the now gone output.
> 
> Testing:
> - [x] Linux container tests on cg1 and cg2 with and without swap accounting.
> - [x] New regression test fails on unpatched systems with `swapaccount=0` kernel option. Passes after.
> - [x] GHA (linux tier1 failure is unrelated).
> 
> Thoughts?

Severin Gehwolf has updated the pull request incrementally with one additional commit since the last revision:

  Use utility function for reading swap.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12262/files
  - new: https://git.openjdk.org/jdk/pull/12262/files/8d6c6601..408b0704

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12262&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12262&range=03-04

  Stats: 66 lines in 2 files changed: 29 ins; 29 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/12262.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12262/head:pull/12262

PR: https://git.openjdk.org/jdk/pull/12262