RFR (L): 8037968: Add tests on alignment of objects copied to survivor space
filipp.zhinkin at oracle.com
Wed Oct 29 16:02:51 UTC 2014
thank you for looking at it!
On 10/29/2014 08:07 PM, Jon Masamitsu wrote:
> 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.
> 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 ).
>>> Webrev: http://cr.openjdk.java.net/~fzhinkin/8037968/webrev.00/
>>> Bug id: https://bugs.openjdk.java.net/browse/JDK-8037968
>>> Testing: manual, automated
>>> 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) .
>>> 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
>>> The second one is about the CMS GC, where an objecthas to occupy at least
>>> MinChunkSize bytes .
>>> 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
>>> (for example, some agent was attached to tested JVM and allocated objects
>>> the test run) tests check that only the main test thread was allocating
>>>  https://bugs.openjdk.java.net/browse/JDK-8031323
More information about the hotspot-gc-dev