Review request: 8004710: NPG: jmap could throw sun.jvm.hotspot.types.WrongTypeException after PermGen removal

[Stefan Karlsson]

On 2013-01-30 17:22, Stefan Karlsson wrote:
> On 30 jan 2013, at 17:17, Jon Masamitsu <jon.masamitsu at oracle.com> wrote:
>
>> Comment below.
>>
>> On 1/29/2013 2:01 PM, Stefan Karlsson wrote:
>>> On 29 jan 2013, at 22:53, Jon Masamitsu<jon.masamitsu at oracle.com>  wrote:
>>>
>>>> Stefan,
>>>>
>>>> Changes look correct.
>>> Thanks.
>>>
>>>> Did you consider calculating the value for endReserve() all
>>>> in the VM (similar to the way ReserveForAllocationPrefetch
>>>> is calculated during initialization) and passing the value
>>>> to the SA the way ReserveForAllocationPrefetch is passed?
>>>> If ReserveForAllocationPrefetch is not used anywhere else,
>>>> you could substitute it (TLabEndReserve as a possible name)
>>>> for ReserveForAllocationPrefetch.
>>> No i didn't think about that. I just tried to mimic the VM code in the SA code. Would you prefer if I changed it to use your alternative solution?
>> Scrap the alternate fix suggestion but I'd suggest changing the name
>>
>> intArrayHeaderSize
>>
>> to
>>
>> minFillerArraySize
>>
>> What caught my eye about this change is that it was hard
>> to understand the use of intArrayHeaderSize unless you knew
>> that tlab's had filler arrays inserted in them to make them
>> parsable and hotspot saved room at the end of each tlab so
>> that a filler object could always be inserted.  If you
>> make the name change that give the reader a clue to that.
> Sure, I'll update the name. Thanks again for the review.
Updated version:
http://cr.openjdk.java.net/~stefank/8004710/webrev.01/

I need a second review.

thanks,
StefanK
>
> StefanK
>
>> Ship it.
>>
>> Jon
>>
>>
>>> thanks,
>>> StefanK
>>>
>>>
>>>> Jon
>>>>
>>>> On 01/29/13 02:58, Stefan Karlsson wrote:
>>>>> http://cr.openjdk.java.net/~stefank/8004710/webrev/
>>>>>
>>>>> This bug is in the GC specific code in the SA agent.
>>>>>
>>>>>  From the bug report:
>>>>> There's a bug in ObjectHeap.collectLiveRegions(), which tries to collect the regions of the heap that contain live objects. It removes the [top, end) regions of a TLAB, since we don't have live objects in those regions. Unfortunately, this doesn't consider the small alignment_reserve() part at the end of the TLAB, and we try to decode an object in that unused memory region.
>>>>>
>>>>> It's not related to the PermGen removal, but the failure mode was probably changed.
>>>>>
>>>>> thanks,
>>>>> StefanK
>>>>>