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

Stefan Karlsson stefan.karlsson at oracle.com
Wed Jun 26 12:24:18 UTC 2013

On 06/26/2013 01:57 PM, 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/

Looks good.


> 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

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