RFR: 8292083: Detected container memory limit may exceed physical machine memory

[Jonathan Dowland]

We discovered some systems configured with cgroups v1 which report a bogus container memory limit value which is above the physical memory of the host. OpenJDK then calculates flags such as InitialHeapSize based on this invalid value; this can be larger than the available memory which can result in the OS terminating the process due to OOM.

hotspot's container awareness attempts to sanity check the limit value by ensuring it's below `_unlimited_memory = (LONG_MAX / os::vm_page_size()) * os::vm_page_size()`, but that still leaves a large range of potential invalid values between physical RAM and that ceiling value.

Cgroups V1 in particular returns an uninitialised value for the memory limit when one has not been explicitly set. Cgroups v2 does not suffer the same problem: however, it's possible for any value to be set for the max memory, including values exceeding the available physical memory, in either v1 or v2.

This fixes the problem in two places. Further work may be required in the area of Java metrics / MXBeans. I'd also look again at whether the existing ceiling value `_unlimited_memory` serves any useful purpose. I personally don't feel those improvements should hold up this fix.

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Commit messages:
 - Add a test for 8292083
 - Linux: clamp os::physical_memory by Linux::physical_memory
 - Bound container memory above by host memory

Changes: https://git.openjdk.org/jdk/pull/9880/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9880&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292083
  Stats: 45 lines in 3 files changed: 39 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/9880.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9880/head:pull/9880

PR: https://git.openjdk.org/jdk/pull/9880