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

[Jonathan Dowland]

On Fri, 26 Aug 2022 13:32:35 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> 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.
>
> test/hotspot/jtreg/containers/docker/TestMemoryAwareness.java line 93:
> 
>> 91:             testOperatingSystemMXBeanIgnoresMemLimitExceedingPhysicalMemory();
>> 92:             testMetricsIgnoresMemLimitExceedingPhysicalMemory();
>> 93:             testContainerMemExceedsPhysical();
> 
> Could we pass `hostMaxMem` to the relevant test functions as a parameter, instead of relying on a static variable magically being set, please? It would be a good symmetry to other tests.

Good idea! Implemented in 0f37be83ff0.

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