UseCompressedOops switch with more than 32gb heaps...

Vladimir Kozlov vladimir.kozlov at
Thu May 27 20:30:52 UTC 2010

I don't have answer on this question. I don't know why 6954029 is not exposed.


atulksh wrote:
> Hi Vladimir,
> I did not find the two bugs you mentioned in the Hotspot bug database. Are
> they only accessible to you internally and not exposed to the public world?
> I looked here.
> Thanks,
> Atul
> Vladimir Kozlov-6 wrote:
>> Very soon. Watch for next changes coming into hotspot (jdk7).
>> I don't know when it will appear in the 6 update release.
>> "6916623: Align object to 16 bytes to use Compressed Oops with java heap
>> up to 64Gb"
>> "6954029: Improve implicit null check generation with COOP"
>> The first bug is closed so you may not see it but I will open it when I am
>> done with changes.
>> Vladimir
>> atulksh wrote:
>>> Hi Vladimir,
>>> So what you are saying is, in a future Hotspot release, we will have the
>>> ability to specify a heap greater than 32Gb for a VM and still use the
>>> useCompressedOops switch. The VM will use compressed oops references,
>>> while
>>> still allowing the VM overall to address more than 32Gb of heap.
>>> What is the timeframe of such a feature (even if it is vague and not
>>> precise
>>> it is fine) are we looking at - is it coming soon (less than a year)?
>>> Thanks for your quick response.
>>> Atul
>>> Vladimir Kozlov-6 wrote:
>>>> I am currently working on this. You have to increase java objects
>>>> alignment
>>>> (from current 8 bytes) to be able to use compressed pointers (which are
>>>> 32
>>>> bit)
>>>> which large heaps.
>>>> Thanks,
>>>> Vladimir
>>>> atulksh wrote:
>>>>> Hi,
>>>>> We are currently running our application servers with 26Gb of heap and
>>>>> have
>>>>> the UseCompressedOops enabled for memory savings. We are intending to
>>>>> boost
>>>>> the memory on our servers more, in which event, we would be bumping the
>>>>> heap
>>>>> above 32Gb. I know that the UseCompressedOops switch works only if you
>>>>> have
>>>>> a heap of 32Gb or less.
>>>>> Is there anything in the Hotspot VM roadmap where there may be support
>>>>> of
>>>>> heaps larger than 32Gb, and still using the UseCompressedOops switch
>>>>> for
>>>>> memory optimization (32 bit object pointers within the heap)? Or is
>>>>> this
>>>>> question irrelevent - meaning there is no possibility to have such a
>>>>> support
>>>>> on the 64 bit machines?
>>>>> Thank you for your response in advance.
>>>>> Atul

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