RFR: 8217432: MetaspaceGC::_capacity_until_GC exceeds MaxMetaspaceSize

[Yasumasa Suenaga]

Hi all,

I filed this issue to JBS:
   https://bugs.openjdk.java.net/browse/JDK-8217432

I investigated it, and I found that `minimum_desired_capacity` and
`maximum_desired_capacity` in `MetaspaceGC::compute_new_size()`
might exceed MaxMetaspaceSize.
They shouldn't exceed MaxMetaspaceSize.

I uploaded webrev for this bug. Could you review it?
   http://cr.openjdk.java.net/~ysuenaga/JDK-8217432/webrev.00/

This change has passed all tests on submit repo, :vmTestbase_vm_metaspace,
and :vmTestbase_nsk_sysdict jtreg tests.


Thanks,

Yasumasa


On 2019/01/15 18:30, Yasumasa Suenaga wrote:
> PING: Did you read my email?
> 
> I wrote the problem and suggested fix in it.
> Please tell me if you have question(s).
> 
> I can file it to JBS if it is a bug.
> 
> 
> Thanks,
> 
> Yasumasa
> 
> 
> On 2019/01/10 18:02, Yasumasa Suenaga wrote:
>> Hi all,
>>
>> I'm Yasumasa Suenaga (OpenJDK reviewer: ysuenaga)
>>
>> My customer uses OpenJDK 8u131 with following commandline arguments:
>>
>>    -XX:+CMSClassUnloadingEnabled -XX:CMSInitiatingOccupancyFraction=80
>>    -XX:CompressedClassSpaceSize=128m -Xms4500m -Xmx4500m
>>    -XX:MaxMetaspaceSize=256m -Xmn=768m -XX:MaxTenuringThreshold=15
>>    -XX:OnOutOfMemoryError="/bin/kill -ABRT %p"
>>    -XX:+UseCMSInitiatingOccupancyOnly -XX:+UseConcMarkSweepGC
>>
>> Their system has encountered OutOfMemoryError which is caused by Metaspace.
>>
>> I checked core image which was collected by OnOutOfMemoryError, and I saw
>> strange values in it as below:
>>
>> -------------------
>> (gdb) p Metaspace::_space_list->_reserved_words
>> $67 = 31195136
>> (gdb) p Metaspace::_class_space_list->_reserved_words
>> $68 = 16777216
>> (gdb) p MetaspaceGC::_capacity_until_GC
>> $75 = 448045056
>> -------------------
>>
>> MaxMetaspaceSize and CompressedClassSpaceSize seem to affect Metaspace.
>> However, MetaspaceGC::_capacity_until_GC exceeds MaxMetaspaceSize.
>> Is it correct?
>>
>> I checked used and committed memory from the core, they seem to be enough
>> to allocate new objects as below:
>>
>> -------------------
>> (gdb) p MetaspaceAux::_used_words
>> $62 = {1742673, 17905981}
>> (gdb) p Metaspace::_space_list->_committed_words
>> $64 = 30932992
>> (gdb) p Metaspace::_class_space_list->_committed_words
>> $65 = 2621440
>> -------------------
>>
>> I guess the cause of OOME is invalid value in _capacity_until_GC.
>> _capacity_until_GC is used for expanding / shrinking Metaspace.
>> However it is not checked when it changes.
>>
>> So I think we need to add the code to check it as below:
>> (The change is for jdk/jdk)
>> -------------------
>> diff -r 32c6cc430526 src/hotspot/share/memory/metaspace.cpp
>> --- a/src/hotspot/share/memory/metaspace.cpp    Wed Jan 09 22:59:49 2019 +0100
>> +++ b/src/hotspot/share/memory/metaspace.cpp    Thu Jan 10 17:56:55 2019 +0900
>> @@ -143,6 +143,10 @@
>>       new_value = align_down(max_uintx, Metaspace::commit_alignment());
>>     }
>>
>> +  if (new_value > MaxMetaspaceSize) {
>> +    return false;
>> +  }
>> +
>>     size_t prev_value = Atomic::cmpxchg(new_value, &_capacity_until_GC, old_capacity_until_GC);
>>
>>     if (old_capacity_until_GC != prev_value) {
>> -------------------
>>
>> _capacity_until_GC is set to MaxMetaspaceSize at MetaspaceGC::initialize(),
>> and it set to committed size or MetaspaceSize at MetaspaceGC::post_initialize().
>> So I guess max value of it is MaxMetaspaceSize.
>>
>>
>> What do you think?
>> If it is a bug, I will file JBS and send review request.
>>
>>
>> Thanks,
>>
>> Yasumasa
>>
>>
>>
>>