RFR: JDK-8301749: Tracking malloc pooled memory size [v2]

[David Holmes]

On Wed, 8 Feb 2023 13:49:27 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> This PR implements `os::malloc_info` by calling into glibc's `malloc_info` and provides a JCmd for asking the JVM to call `malloc_info` and print out the results. The user can make an informed decision regarding heap trimming by parsing the output of the JCmd. I wanted to avoid parsing the XML inside of the JVM , as this functionality may turn out to be "good enough". A future enhancement would be for the JVM to make this informed decision by parsing the output. Another may be to present this with other data, for example in NMT.
>> 
>> @tstuefe, I think you'd be interested in this PR as it builds upon your `trim_native_heap` functionality.
>> 
>> I'm using weak symbols (as per ELF) in order to compile this for both GLibc and Musl.
>> 
>> The original bug description is this:
>> 
>>>Memory not allocated via NMT and uncommitted memory contributes to a discrepancy between NMT and RSS.
>> It can be hard to distinguish between these cases.
>> If the VM can determine the amount of pooled memory by malloc it would help with both determining if a trim_native_memory is needed, or there are some allocations happening outside of NMT.
>>>
>>>It would be good if the VM can summarize the malloc pooled memory by using e.g. malloc_info(3).
>>>
>>>We can thus more precise account for RSS value.
>
> Johan Sjölen has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - Fix the test
>  - Note man section
>  - Add test
>  - Reimplement malloc_info as requested

test/hotspot/jtreg/serviceability/dcmd/vm/MallocInfoTest.java line 43:

> 41:     public void run(CommandExecutor executor) {
> 42:         OutputAnalyzer output = executor.execute("System.native_heap_info");
> 43:         output.reportDiagnosticSummary();

Do this after the other checks, else on error you will get the report twice.

test/hotspot/jtreg/serviceability/dcmd/vm/MallocInfoTest.java line 44:

> 42:         OutputAnalyzer output = executor.execute("System.native_heap_info");
> 43:         output.reportDiagnosticSummary();
> 44:         output.shouldNotMatch(".*Error.*");

Can you test exitValue instead of parsing for an error?

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PR: https://git.openjdk.org/jdk/pull/12455