RFR (XS): JDK-8017483: G1 tests fail with native OOME on Solaris x86 after HeapBaseMinAddress has been increased

[Vladimir Kozlov]

Good.

Vladimir

On 6/26/13 2:03 PM, Bengt Rutisson wrote:
>
> Thanks Stefan and Jon for looking at this!
>
> On 6/26/13 4:20 PM, Jon Masamitsu wrote:
>> Bengt,
>>
>> Change looks fine.  Is it worth a comment to say why you don't use
>> FLAG_SET_ERGO() ?
>
> Done.
>
> Updated webrev:
> http://cr.openjdk.java.net/~brutisso/8017483/webrev.01/
>
> Complete diff:
>
> diff --git a/src/share/vm/runtime/arguments.cpp
> b/src/share/vm/runtime/arguments.cpp
> --- a/src/share/vm/runtime/arguments.cpp
> +++ b/src/share/vm/runtime/arguments.cpp
> @@ -1571,7 +1571,9 @@
>       // By default HeapBaseMinAddress is 2G on all platforms except
> Solaris x86.
>       // G1 currently needs a lot of C-heap, so on Solaris we have to
> give G1
>       // some extra space for the C-heap compared to other collectors.
> -    FLAG_SET_ERGO(uintx, HeapBaseMinAddress, 1*G);
> +    // Use FLAG_SET_DEFAULT here rather than FLAG_SET_ERGO to make sure
> that
> +    // code that checks for default values work correctly.
> +    FLAG_SET_DEFAULT(HeapBaseMinAddress, 1*G);
>     }
>   }
>
> Also, I filed JDK-8019212 to track the strange behavior for
> HeapBaseMinAddress.
>
> Bengt
>
>>
>> Jon
>>
>> On 6/26/2013 4:57 AM, Bengt Rutisson wrote:
>>>
>>> Hi all,
>>>
>>> Could I have a couple of reviews for this really small change?
>>>
>>> http://cr.openjdk.java.net/~brutisso/8017483/webrev.00/
>>>
>>> Background:
>>>
>>> For JDK-8012265 I increased the default value for HeapBaseMinAddress
>>> on Solaris x86 from 256m to 1g when using G1. In that change I used
>>> FLAG_SET_ERGO() to set the new value of HeapBaseMinAddress. Now it
>>> turns out that there is code that checks
>>> !FLAG_IS_DEFAULT(HeapBaseMinAddress), which means that by setting the
>>> flag as "ergo" I changed the behavior of the VM.
>>>
>>> What happens is that Universe::preferred_heap_base() will use exactly
>>> the address HeapBaseMinAddress if it is not default. Otherwise it
>>> will calculate a base adress "backwards" from the maximum compressed
>>> oops heap size and the desired heap size. The effect is that if
>>> HeapBaseMinAddress=1g as default and we want a 16g heap we will get
>>> an actual heap base of at about address 16g. But if I set
>>> HeapBaseMinAddress=1g on the command line or using "ergo" we will
>>> pick the address 1g for the heap base.
>>>
>>> This means that in the first case we leave almost 16g free for the
>>> Solaris C-heap, but in the second case the C-heap will be limited to 1g.
>>>
>>> I think this is a strange behavior and I will file a separate bug to
>>> track that. There are also other issues with the compressed oops set
>>> up. But to make the currently failing tests pass I suggest to change
>>> from "ergo" to "default" when updating the HeapBaseMinAddress value.
>>> This is small, quick and safe change. Here is the complete diff:
>>>
>>> diff --git a/src/share/vm/runtime/arguments.cpp
>>> b/src/share/vm/runtime/arguments.cpp
>>> --- a/src/share/vm/runtime/arguments.cpp
>>> +++ b/src/share/vm/runtime/arguments.cpp
>>> @@ -1571,7 +1571,7 @@
>>>      // By default HeapBaseMinAddress is 2G on all platforms except
>>> Solaris x86.
>>>      // G1 currently needs a lot of C-heap, so on Solaris we have to
>>> give G1
>>>      // some extra space for the C-heap compared to other collectors.
>>> -    FLAG_SET_ERGO(uintx, HeapBaseMinAddress, 1*G);
>>> +    FLAG_SET_DEFAULT(HeapBaseMinAddress, 1*G);
>>>    }
>>>  }
>>>
>>> Thanks,
>>> Bengt
>>>
>>
>