-XX:MetaspaceSize is correct?

[Yasumasa Suenaga]

Hi Jon,
Thank you for replying.

I filed this issue as JDK-8039867: Incorrect description: -XX:MetaspaceSize .

I attached a patch to this entry.
I will upload webrev later.


Thanks,

Yasumasa



2014-04-10 6:51 GMT+09:00, Jon Masamitsu <jon.masamitsu at oracle.com>:
>
> On 04/09/2014 06:22 AM, Yasumasa Suenaga wrote:
>> Hi all,
>>
>> I checked initial metaspace size through jcmd PerfCounter.print .
>> However, it seems to be incorrect:
>>
>>  - Java command:
>>   java -XX:-UseCompressedClassPointers -XX:+PrintFlagsFinal LongSleep
>>
>>  - Output from -XX:+PrintFlagsFinal:
>>     uintx MetaspaceSize                             =
>> 21807104                            {pd product}
>>
>>  - Result of "PerfCounter.print"
>> sun.gc.metaspace.capacity=4194304
>> sun.gc.metaspace.maxCapacity=8388608
>> sun.gc.metaspace.minCapacity=0
>>
>>
>> I checked metaspace.cpp, initial size of metaspace is detected by
>> InitialBootClassLoaderMetaspaceSize.
>> However, description of MetaspaceSize in globals.hpp is
>> "Initial size of Metaspaces (in bytes)" .
>>
>> Is description of MetaspaceSize is correct?
>
> Description is not correct.
>
>> And this behavior is correct?
>
> Behavior is correct.
>
>>
>> I have two plan for this mismatch:
>>
>>  A) Change description of MetaspaceSize
>>   MetaspaceSize is used to HWM in metaspace.cpp .
>>   So we should change description for this behavior.
>> ------------
>> diff -r 48ce2e6e1add src/share/vm/runtime/globals.hpp
>> --- a/src/share/vm/runtime/globals.hpp  Fri Apr 04 10:04:44 2014 -0700
>> +++ b/src/share/vm/runtime/globals.hpp  Wed Apr 09 22:05:18 2014 +0900
>> @@ -3160,7 +3156,7 @@
>>            "non-daemon thread (in
>> bytes)")                                   \
>> \
>>    product_pd(uintx,
>> MetaspaceSize,                                          \
>> -          "Initial size of Metaspaces (in
>> bytes)")                          \
>> +          "Initial HWM of Metaspaces (in
>> bytes)")                           \
>
> Explain what HWM is if you're going to use it.
>
>> \
>>    product(uintx, MaxMetaspaceSize,
>> max_uintx,                               \
>>            "Maximum size of Metaspaces (in
>> bytes)")                          \
>> ------------
>>
>>  B) Remove InitialBootClassLoaderMetaspaceSize and use MetaspaceSize
>>   In currently, InitialBootClassLoaderMetaspaceSize is used to initialize
>>   metaspace.
>>   InitialBootClassLoaderMetaspaceSize is only to use for it.
>>   Thus we should remove this option and use MetaspaceSize to initialize
>>   metaspace.
>
> InitialBootClassLoaderMetaspaceSize is an optimization.  It allows
> approximately
> enough space for the system classes without repeated  allocations of
> Metaspaces.
> Not everyone agrees with this optimization but I would like it kept.
>
>> ------------
>> diff -r 48ce2e6e1add src/share/vm/memory/metaspace.cpp
>> --- a/src/share/vm/memory/metaspace.cpp Fri Apr 04 10:04:44 2014 -0700
>> +++ b/src/share/vm/memory/metaspace.cpp Wed Apr 09 22:05:18 2014 +0900
>> @@ -3172,7 +3172,7 @@
>>  #endif
>>
>>      // Initialize these before initializing the VirtualSpaceList
>> -    _first_chunk_word_size = InitialBootClassLoaderMetaspaceSize /
>> BytesPerWord;
>> +    _first_chunk_word_size = MetaspaceSize / BytesPerWord;
>>      _first_chunk_word_size = align_word_size_up(_first_chunk_word_size);
>>      // Make the first class chunk bigger than a medium chunk so it's
>> not put
>>      // on the medium chunk list.   The next chunk will be small and
>> progress
>> diff -r 48ce2e6e1add src/share/vm/runtime/globals.hpp
>> --- a/src/share/vm/runtime/globals.hpp  Fri Apr 04 10:04:44 2014 -0700
>> +++ b/src/share/vm/runtime/globals.hpp  Wed Apr 09 22:05:18 2014 +0900
>> @@ -2333,10 +2333,6 @@
>>    develop(bool, TraceClassLoaderData,
>> false,                                \
>>            "Trace class loader loader_data
>> lifetime")                        \
>> \
>> -  product(uintx,
>> InitialBootClassLoaderMetaspaceSize,                       \
>> -          NOT_LP64(2200*K)
>> LP64_ONLY(4*M),                                  \
>> -          "Initial size of the boot class loader data
>> metaspace")           \
>> - \
>>    product(bool, TraceGen0Time,
>> false,                                       \
>>            "Trace accumulated time for Gen 0
>> collection")                    \
>> \
>> ------------
>>
>> I prefer "B" .
>> Because, I guess many users think MetaspaceSize decides initial
>> metaspace size.
>>
>> If my idea is correct, I will file this to JBS and upload patch to
>> webrev.
>
> Please only correct the description of MetaspaceSize.
>
> Jon
>
>>
>>
>> Thanks,
>>
>> Yasumasa
>>
>
>