committed > max in MemoryMXBean#getHeapMemoryUsage()

[Erik Helin]

On 07/12/2018 10:34 PM, mandy chung wrote:
> It's indeed strange that no one reports this issue.  I created:
>     https://bugs.openjdk.java.net/browse/JDK-8207200

Mandy: I moved the bug over to hotspot/gc, this is much more likely to 
be a problem with how the GC calculates the sizes. I don't think there 
is a bug in the serviceability layer, the JNI getMemoryUsage function 
only summarizes the data it gets from the GC.

Thanks for creating the bug, we will follow up with Daniel.
Erik

> Mandy
> 
> On 7/12/18 6:35 AM, Daniel Mitterdorfer wrote:
>> Hi,
>>
>> while working on a change in Elasticsearch, I discovered an interesting
>> situation related to the implementation of jmm_getMemoryUsage (see
>> [jdk-mem-usage]). In one of the test runs, a test failed with the 
>> following
>> exception:
>>
>> java.lang.IllegalArgumentException: committed = 542113792 should be <
>> max = 536870912
>> at java.lang.management.MemoryUsage.<init>(MemoryUsage.java:166)
>> at sun.management.MemoryImpl.getMemoryUsage0(Native Method)
>> at sun.management.MemoryImpl.getHeapMemoryUsage(MemoryImpl.java:71)
>> at 
>> org.elasticsearch.indices.breaker.HierarchyCircuitBreakerService.currentMemoryUsage(HierarchyCircuitBreakerService.java:246) 
>>
>> [...]
>>
>> This happened on MacOS 10.12.6 with JDK 10 (build 10.0.1+10). The only 
>> JVM flags
>> specified where -Xms512M -Xmx512M. So far this failure occurred only 
>> once and I
>> could not reproduce it yet.
>>
>> The values reported in the exception message are:
>>
>> * "max": 536870912 = 512MB (exactly)
>> * "committed": 542113792 = 517MB (exactly), i.e. 5MB more than "max".
>>
>> As the value of "max" is exactly what we have specified with -Xmx this 
>> indicates
>> to me that the problem seems to be the calculation of "committed".
>>
>> As the value of "max" is exactly what we have specified with -Xmx it 
>> seems to
>> indicate that the problem is the calculation of "committed". I do not
>> understand under which conditions this can happen thus I post this to the
>> mailing list in case anybody has ideas what might cause this.
>>
>> I plan to run further tests with JVM trace logging enabled
>> (-Xlog:gc*=trace,heap*=trace,tlab*=off:stdout:time,pid,tid,level,tags 
>> to be
>> precise) in the hope that this problem will occur again and I can 
>> provide logs
>> that help to debug / fix the problem.
>>
>> Searching for that error message, there is [JDK-8020530] but that one 
>> is about
>> *non-heap* memory usage and has already been resolved a while ago. 
>> Several
>> sources (e.g. [apache-ignite-workaround] or [netbeans-bug]) seem to 
>> indicate
>> that this problem happened indeed in the wild but what I find odd is 
>> that I
>> could not find a single ticket in the OpenJDK bug tracker or a 
>> discussion on a
>> JDK mailing list about this problem.
>>
>> I'd be glad to get any pointers on what might cause this or requests for
>> additional info that I need to provide to help analyze this problem.
>>
>> Thanks,
>> Daniel
>>
>> [jdk-mem-usage]
>> http://hg.openjdk.java.net/jdk-updates/jdk10u/file/142f0ed9ff5b/src/hotspot/share/services/management.cpp#l728 
>>
>> [JDK-8020530] https://bugs.openjdk.java.net/browse/JDK-8020530
>> [apache-ignite-workaround]
>> https://github.com/apache/ignite/blob/df4fd65a32/modules/core/src/main/java/org/apache/ignite/internal/managers/discovery/GridDiscoveryManager.java#L336-L346 
>>
>> [netbeans-bug] https://netbeans.org/bugzilla/show_bug.cgi?id=194733
>>