RFR: 8011218 Kitchensink hanged, likely NMT is to blame

[Zhengyu Gu]

Thanks, Dan.

>   What motivated the new: #include "runtime/thread.inline.hpp"

This is for Thread::current()

-Zhengyu


On Apr 24, 2013, at 6:06 PM, "Daniel D. Daugherty" <daniel.daugherty at oracle.com> wrote:

> On 4/23/13 8:23 AM, Zhengyu Gu wrote:
>> Round 2:
>> 
>> Based on feedback from David, Dan and Karen, transition thread state to _thread_in_native is dangerous. This fix keeps query  thread state in _thread_in_vm, but make locks safepoint aware and explicitly check for safepoint during lengthy baseline operation.
>> 
>> Webrev: http://cr.openjdk.java.net/~zgu/8011218/webrev.01/
> 
> Thumbs up.
> 
> src/share/vm/services/memBaseline.cpp
>    What motivated the new: #include "runtime/thread.inline.hpp"
> 
> src/share/vm/services/memBaseline.hpp
>    No comments.
> 
> src/share/vm/services/memTracker.cpp
>    No comments.
> 
> Dan
> 
> 
>> 
>> 
>> Test:
>>   - Manual test, ran kitchensink stress tests with additional NMT queries to stress query threads, monitored gc.log.
>>    After 17 hours, found no long pause between gc messages.
>> 
>> Thanks,
>> 
>> -Zhengyu
>> 
>> 
>> 
>> On Apr 18, 2013, at 9:46 AM, Zhengyu Gu wrote:
>> 
>>> Hi David,
>>> 
>>> On 4/17/2013 10:59 PM, David Holmes wrote:
>>>> On 18/04/2013 7:33 AM, Zhengyu Gu wrote:
>>>>> The thread that runs NMT query can be blocked on NMT snapshot lock,
>>>>> which prevents JVM to reach safepoints.
>>>> How? I don't understand this part.
>>> Currently, NMT acquires locks without safepoint checks (I assumed that query is coming from _thread_in_native, obviously a mistake). Since NMT query can be lengthy, I still want it to run in _thread_in_native state.
>>> 
>>>>> NMT query does not change Java heap, it does not have to stop for
>>>>> safepoints. So the solution is to transition to _vm_in_native state,
>>>>> before executing NMT query.
>>>> To add to Dan's comments you don't need the assertion:
>>>> 
>>>>  81   assert(((JavaThread*)thr)->thread_state() == _thread_in_vm,
>>>>  82     "Just check");
>>>> 
>>>> because this will be checked by ThreadToNativeFromVM.
>>>> 
>>>> However I am far from convinced that it is valid to make this state change. You need to be sure that nothing you call from this method - including debug/tracing code that might only be enabled under certain flags - will assume/expect that you are _thread_in_vm.
>>> NMT query code acquires two locks, both with no_safepoint_check. Besides assertion and tty->print(), I don't recall it uses any vm specific methods, but is there a way to ensure that?
>>> 
>>> Thanks,
>>> 
>>> -Zhengyu
>>> 
>>> 
>>>> Thanks,
>>>> David
>>>> -----
>>>> 
>>>> 
>>>>> JBS: https://jbs.oracle.com/bugs/browse/JDK-8011218
>>>>> Public bug: not available
>>>>> Webrev: http://cr.openjdk.java.net/~zgu/8011218/webrev.00/
>>>>> <http://cr.openjdk.java.net/%7Ezgu/8011218/webrev.00/>
>>>>> 
>>>>> 
>>>>> Test:
>>>>>   - Run Kitchensink stress test on low power machine Linux x86 machine
>>>>> with GC trace on, stress out NMT query thread by submitting NMT query in
>>>>> a loop, NMT query executions become very slow, but GC trace continues
>>>>> generating message, and does not show long pause.
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> -Zhengyu
>