RFR(s): 8038461: Test gc/g1/TestStringDeduplicationMemoryUsage.java fails with unexpected memory usage

[Per Liden]

Hi Jon,

On 04/01/2014 11:49 PM, Jon Masamitsu wrote:
> Per,
>
> Is there a way you could get generateString() to return the
> sum of the sizes of the strings (minus 1 string)?  Instead of the doing
> the calculation of bytesSaved?

Could you elaborate a bit, I'm not quite sure I understand what you 
mean. Is there something about the bytesSaved calculation you don't like?

Each MemoryUsageTest instance could of course return the sizes of all 
character arrays it has created (instead of just the array header size), 
is that what you're suggesting? There would still be a bytesSaved 
calculation inside testMemoryUsage() though, so I have a feeling that's 
not what you meant.

Note that generateString()/createStrings() has no real understanding of 
whether deduplication is enabled or not and they are also used by other 
tests, which don't care about sizes.

cheers,
/Per

>
> Jon
>
> On 4/1/14 12:54 AM, Per Liden wrote:
>> Thanks Stefan! Need one more Review.
>>
>> /Per
>>
>> On 31 Mar 2014, at 10:49, Stefan Johansson
>> <stefan.johansson at oracle.com> wrote:
>>
>>> Looks good!
>>>
>>> Stefan
>>>
>>> On 2014-03-28 14:41, Per Liden wrote:
>>>> Hi,
>>>>
>>>> Could I please have this test fix reviewed.
>>>>
>>>> Summary: The test in question tries to calculate the amount of
>>>> memory saved when using string deduplication. The problem is that
>>>> the JVM doing this calculation could be running without compressed
>>>> class pointers when the JVM doing the actual string deduplication is
>>>> running with compressed class pointers. When this happens the JVMs
>>>> will have different views on the size of an array header, which in
>>>> the end makes the calculation incorrect and the test thinks the
>>>> deduplication failed. Exactly this situation happened in a nightly
>>>> test run. This fix makes sure that the array header size of the JVM
>>>> doing the deduplication is communicated to the JVM doing the memory
>>>> savings calculation.
>>>>
>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8038461
>>>> Webrev: http://cr.openjdk.java.net/~pliden/8038461/webrev.0/
>>>>
>>>> /Per
>>>>
>