RFR: 8079275: Remove CollectedHeap::use_parallel_gc_threads
Stefan Karlsson
stefan.karlsson at oracle.com
Tue May 5 08:16:25 UTC 2015
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
>>>
>>
>
More information about the hotspot-gc-dev
mailing list