[9] RFR (L): 8037968: Add tests on alignment of objects copied to survivor space

Filipp Zhinkin filipp.zhinkin at oracle.com
Wed Oct 29 16:02:51 UTC 2014


Hi Jon,

thank you for looking at it!

On 10/29/2014 08:07 PM, Jon Masamitsu wrote:
> Filipp,
>
> Sorry for the delay.  These tests look good.
>
> Can you point me at the source for
>
>   59         CommandLineOptionTest.verifyJVMStartup(
>
>
> I just want to see what the messages are where there is
> a failure.
Sure:
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/file/f7cb546710c8/test/testlibrary/com/oracle/java/testlibrary/cli/CommandLineOptionTest.java#l71

Thanks,
Filipp.
>
> Thanks.
>
> Jon
>
> On 10/27/2014 6:58 AM, Filipp Zhinkin wrote:
>> friendly reminder
>>
>> On 10/07/2014 01:33 PM, Filipp Zhinkin wrote:
>>> Hi all,
>>>
>>> please review tests on survivor alignment feature (JDK-8031323 [1]).
>>>
>>> Webrev: http://cr.openjdk.java.net/~fzhinkin/8037968/webrev.00/
>>> Bug id: https://bugs.openjdk.java.net/browse/JDK-8037968
>>> Testing: manual, automated
>>> Description:
>>>
>>> There are 6 new tests:
>>> one verifies SurvivorAlignmentInBytes option processing
>>> and other 5 tests verify that that option only affect alignment
>>> of objects copied to survivor space and that their alignment is
>>> equal to SurvivorAlignmentInBytes value.
>>>
>>> Since there are no guarantee that _all_ objects copied to
>>> survivor space will be alignedthese tests are verifying that
>>> objects occupy some expected amount of memory depending on alignment.
>>>
>>> All tests use following algorithm:
>>> - decide how many objects should be allocated
>>> - allocate objects
>>> - force minor or full GCs if needed
>>> - verify usage of particular heap space (eden, survivor or tenured).
>>>
>>> There are several differences between Hotspot garbage collectors that affect
>>> memory usage measurements:
>>> 1) precision of such measurements;
>>> 2) min amount of heap space that will be occupied by a single object.
>>>
>>> The first one is about the G1 GC, where usage of eden and survivor regions
>>> is reported as (number_of_used_regions * G1HeapRegionSize) [2].
>>>
>>> Tests verify that actual memory usage is close to expected usage,
>>> i.e. difference between actual and expected usage hasto be lower
>>> or equal to 5% of expected usage.
>>> However, for G1 GC max allowed difference has to be aligned up to 
>>> G1HeapRegionSize.
>>>
>>> The second one is about the CMS GC, where an objecthas to occupy at least
>>> MinChunkSize bytes [3][4].
>>>
>>> And, of course, amount of memory occupied by an object depends on the alignment
>>> used in particular heap space: SurvivorAlignmentInBytes for survivor space and
>>> ObjectsAlignmentInBytes for other spaces.
>>>
>>> To take all such aspects into account tests use AlignmentHelper class,
>>> whose instances are created for each heap space.
>>>
>>> That class is aimed to answer following questions:
>>> - how much space will be occupied by an object whose size is M;
>>> - how many objects of size M should be allocated to occupy N bytes
>>> of memory in particular heap space;
>>> - how much space will be occupied by K objects whose size is M;
>>> - how close the actual memory usage has to be to the expected memory usage
>>> given the precision with which we can measure the memory usage.
>>>
>>> In order to avoid false failures caused by memory allocated by different 
>>> threads
>>> (for example, some agent was attached to tested JVM and allocated objects 
>>> during
>>> the test run) tests check that only the main test thread was allocating 
>>> objects.
>>>
>>> Thanks,
>>> Filipp.
>>>
>>> [1] https://bugs.openjdk.java.net/browse/JDK-8031323
>>> [2] 
>>> http://hg.openjdk.java.net/jdk9/jdk9/hotspot/file/5c722dffbc0f/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp#l124
>>> [3] 
>>> http://hg.openjdk.java.net/jdk9/jdk9/hotspot/file/5c722dffbc0f/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp#l1427
>>> [4] 
>>> http://hg.openjdk.java.net/jdk9/jdk9/hotspot/file/5c722dffbc0f/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp#l477 
>>>
>>
>



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