-XX:MetaspaceSize is correct?

Jon Masamitsu jon.masamitsu at oracle.com
Wed Apr 9 21:51:44 UTC 2014


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
>



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