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

[Bengt Rutisson]

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
>>
>