RFR: 8079275: Remove CollectedHeap::use_parallel_gc_threads

Jon Masamitsu jon.masamitsu at oracle.com
Thu May 7 00:03:13 UTC 2015


Stefan,

Looks good.

Reviewed.

Jon

On 5/5/2015 1:16 AM, Stefan Karlsson wrote:
>
>
> On 2015-05-05 10:12, Stefan Johansson wrote:
>> Hi Stefan,
>>
>> On 2015-05-04 17:52, Stefan Karlsson wrote:
>>> Hi,
>>>
>>> On 2015-05-04 17:28, Stefan Johansson wrote:
>>>> Hi Stefan,
>>>>
>>>> On 2015-05-04 15:34, Stefan Karlsson wrote:
>>>>> Hi,
>>>>>
>>>>> Please review this patch to remove 
>>>>> CollectedHeap::use_parallel_gc_threads.
>>>>>
>>>>> http://cr.openjdk.java.net/~stefank/8079275/webrev.01/
>>>> Change looks good, nice cleanup.
>>>>
>>>> If I'm not missing anything you could remove the typedef in 
>>>> concurrentMarkSweepGeneration.cpp:
>>>>      typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
>>>> -    _par_gc_thread_states =
>>>> -      NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, 
>>>> mtGC);
>>>> +  _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, 
>>>> ParallelGCThreads, mtGC);
>>>>
>>>> The typedef is only used for in the NEW_C_HEAP_ARRAY-call and I 
>>>> can't see any good reason for keeping it.
>>>
>>> OK. I removed it. I also removed the unused _modUnionClosure.
>>>
>>> http://cr.openjdk.java.net/~stefank/8079275/webrev.02.delta/
>>> http://cr.openjdk.java.net/~stefank/8079275/webrev.02/
>>>
>> Looks good,
>
> Thanks, Stefan.
>
> StefanK
>
>>
>> StefanJ
>>> Thanks,
>>> StefanK
>>>
>>>>
>>>> Thanks,
>>>> Stefan
>>>>
>>>>> https://bugs.openjdk.java.net/browse/JDK-8079275
>>>>>
>>>>> This function is used from:
>>>>>
>>>>> 1) CMS - CMS can't be started with -XX:ParallelGCThreads=0 
>>>>> anymore, so all checks against use_parallel_gc_threads will always 
>>>>> be true.
>>>>>
>>>>> 2) GenCollectedHeap::process_roots - This usage could be replaced 
>>>>> with n_par_threads(), the same check the other parallel task 
>>>>> (Threads::possibly_parallel_oops_do) uses.
>>>>>
>>>>> This will change the executed code for CMS but not Serial.
>>>>>
>>>>> Serial will always return false for 
>>>>> CollectedHeap::use_parallel_gc_threads and 
>>>>> GenCollectedHeap:n_par_threads(). See:
>>>>> void GenCollectedHeap::set_par_threads(uint t) {
>>>>>   assert(t == 0 || !UseSerialGC, "Cannot have parallel threads");
>>>>>   CollectedHeap::set_par_threads(t);
>>>>>
>>>>> CMS will always return true for 
>>>>> CollectedHeap::use_parallel_gc_threads, but can now return either 
>>>>> true or false for n_par_threads() depending on how n_par_threads 
>>>>> was setup for the currently executing task. This means that some 
>>>>> CMS paths will now call StringTable::oops_do instead of 
>>>>> StringTable::possibly_parallel_oops_do, when running single threaded.
>>>>>
>>>>> Thanks,
>>>>> StefanK
>>>>
>>>
>>
>



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