RFR (XXS) 8008964 - Thread::_metadata_handles uses 1 KB per thread

[Ioi Lam]

On 06/19/2013 12:19 PM, Coleen Phillimore wrote:
>
> Ioi,
> Code looks good.   We can also reduce the HandleArea per thread now 
> that metadata aren't oops.
> I'll file a bug for that or have you already?
>
I already filed JDK-8016903 Thread::_handle_area initial size too big, 
and have linked the two bugs together,

Thanks
- Ioi

> Thanks,
> Coleen
>
> On 6/19/2013 12:40 PM, Ioi Lam wrote:
>> Please review a very small fix:
>>
>> http://cr.openjdk.java.net/~iklam/8008964/metadata_handles_001/
>>
>> Bug: NPG: Memory regression: Thread::_metadata_handles uses 1 KB per 
>> thread.
>>
>> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8008964
>>     https://jbs.oracle.com/bugs/browse/JDK-8008964
>>
>> Background:
>>
>>     Thread::_metadata_handles is a GrowableArray that keeps class 
>> metadata
>>     alive during class redefinitions. See metadataOnStackMark.cpp.
>>
>>     The initial allocation size is 300 elements per Thread. This 
>> seems too big.
>>
>> Summary of fix:
>>
>>     I changed the initial allocation of 300 elements to 30 elements.
>>
>>     I added traces in a private build and found that the max array 
>> length
>>     is usually around 100, and most of the threads never use more than
>>     30 elements.
>>
>>     For Eclipse:
>>
>>         metadata_handles expanded from [  0] = 34 time(s) // a total 
>> 34 threads have been created
>>         metadata_handles expanded from [ 30] =  9 time(s)
>>         metadata_handles expanded from [ 60] =  2 time(s)
>>         _metadata_handles_max_len = 114
>>
>>     For MedRec:
>>
>>         metadata_handles expanded from [  0] = 156 time(s)
>>         metadata_handles expanded from [ 30] =  19 time(s)
>>         metadata_handles expanded from [ 60] =   4 time(s)
>>         _metadata_handles_max_len = 104
>>
>>     So it looks like we can safely reduce the initialize of 
>> Thread::_metadata_handles from 300 to 30,
>>     a saving of 2160 bytes per live Thread (64-bit VM) or 1080 bytes 
>> for 32-bit VM.
>>
>> Tests:
>>
>>     UTE (vm.runtime.testlist, vm.quick.testlist, 
>> vm.parallel_class_loading.testlist)
>>
>> Thanks
>> - Ioi
>>
>

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