RFR: 8015107: NPG: Use consistent naming for metaspace concepts

harold seigel harold.seigel at oracle.com
Wed Sep 4 11:26:21 PDT 2013

Hi Erik,

I looked into this a bit.  You are correct in saying "has no effect".

Sorry,  Harold

On 9/4/2013 2:13 PM, harold seigel wrote:
> Hi Erik,
> These changes look good.  Just a small nit.  In arguments.cpp, I think 
> the new warning should say "has no affect" instead of "has no effect".
> Thanks, Harold
> On 9/4/2013 1:36 PM, Erik Helin wrote:
>> Hi all,
>> this patch changes the name of two flags:
>> - -XX:+UseCompressedKlassPointers becomes
>>    -XX:+UseCompressedClassPointers (note the 'K' instead of the 'C')
>> - -XX:ClassMetaspaceSize becomes -XX:CompressedClassSpaceSize
>> Background:
>> These two flags were introduced when metaspace was merged into hs25.
>> To use a smaller size for the Java object headers, the pointer in the
>> object header that points to the Klass instance for the object can be 32
>> bits on a 64-bit system. Such pointers has been called compressed klass
>> pointers. This is the same concept as compressed oops.
>> For the current implementation of compressed class pointers to work, the
>> Klass instances need to be placed in a continuous virtual memory space.
>> This virtual memory space was called ClassMetaspace but this patch
>> introduces the name CompressedClassSpace to emphasize that the concept
>> is closely related to compressed klass pointers.
>> The 'K' in the CompressedKlassPointers and CompressedClassSpace was
>> changed to a 'C' since the C++ class Klass is an implementation detail
>> that we do not want to expose to the users.
>> I've also added a check in Arguments::parse that checks if the user has
>> set CompressedClassSpaceSize when compressed class pointers
>> are _not_ used. If this is the case, then the VM will print a 
>> warning. I've
>> also added a test that verifies this actually happens.
>> The change touches a lot of files, but the change in each file is very
>> small.
>> Webrev:
>> http://cr.openjdk.java.net/~ehelin/8015107/webrev.00/
>> Bug:
>> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8015107
>> Testing:
>> - JPRT
>> - The jtreg tests in hotspot/test
>> - Newly added jtreg test
>> Thanks,
>> Erik

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