RFR: 8292541: [Metrics] Reported memory limit may exceed physical machine memory [v6]

[Jonathan Dowland]

> When the container memory exceeds the physical host's memory, the Java metrics reporting is wrong.
> 
> https://bugs.openjdk.org/browse/JDK-8292541
> 
> This is the equivalent core-libs fix for Hotspot's [JDK-8292083](https://bugs.openjdk.org/browse/JDK-8292083)
> (https://github.com/openjdk/jdk/pull/9880)

Jonathan Dowland has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits:

 - Rework testContainerMemExceedsPhysical to use common hostMaxMem
   
   For 8292541, I wrote two further tests that used the same technique
   as testContainerMemExceedsPhysical to establish baseline physical
   RAM. Rework testContainerMemExceedsPhysical to use the shared
   variable hostMaxMem rather than recalculate the value itself.
 - Merge remote-tracking branch 'origin/master' into 8292541-cgroup-metrics
 - Add a log-line for total physical memory
   
   This is relied upon for tests in
   test/hotspot/jtreg/containers/docker/TestMemoryAwareness.java
 - use pre-defined constant over magic number
 - Address style nits
 - Address nit
   
   Thanks Thomas Stuefe
 - avoid calling subsystem.getMemoryLimit twice
 - catch CgroupMetrics.getMemoryLimit exceeding physical RAM
   
   Detect when the subsystem limit exceeds physical RAM and treat
   that situation as "unlimited".
   
   Add a private native method to establish physical RAM size.
   
   This presently is only likely to work on POSIX systems, but
   CgroupMetrics are Linux-specific. None the less the precise guards etc.
   may need adjusting.
 - Add two tests to catch deriving invalid max memory limit from cgroups
   
   One test for OperatingSystemMXBean and another for
   -XshowSettings:system, which exercises the Metrics sub-system.
   
   extend TestMemoryAwareness to cover OperatingSystemMXBean with bad cgroup memory limit
   
   add testMetricsIgnoresMemLimitExceedingPhysicalMemory and refactor
   
   Pull the code that establishes host physical max RAM out into a helper
   function.

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

Changes: https://git.openjdk.org/jdk/pull/10017/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10017&range=05
  Stats: 60 lines in 3 files changed: 46 ins; 9 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/10017.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10017/head:pull/10017

PR: https://git.openjdk.org/jdk/pull/10017