CMS option for Java7 ignored (was Re: 1.7 G1GC significantly slower than 1.6 Mark and Sweep?)

Bengt Rutisson bengt.rutisson at oracle.com
Mon May 2 01:41:41 PDT 2011


John,

For some reason I didn't manage to reply to your email address - only to 
the hotspot-gc-use alias. Re-sending this to make sure you get it, even 
though I assume you are on the hotspot-gc-use alias.

Bengt

On 2011-05-02 09:00, Bengt Rutisson wrote:
> John,
>
>>> .... I don't know how to activate CMS for Java 7, it ignores the option that I'd use
>>> for Java 6.
>> ...
>>> Java6: -ea -Xms256M -Xmx256M -XX:UseConcMarkSweepGC -verbose:gc
>> ...
> What do you mean when you say "ignores"? Does the VM start and just
> ignores your option or does the VM complain that it is an unknown option?
>
> I am asking since the error message that you get if you use the command
> line that you posted is somewhat confusing. Maybe this is just a typo in
> the email, but your command line is missing the plus sign in front of
> UseConcMarkSweepGC. If you run the command line from your email you get
> this error message:
>
> Unrecognized VM option 'UseConcMarkSweepGC'
> Could not create the Java virtual machine.
>
> Which, I admit, is confusing. The VM does recognize the option, what is
> missing is just the value for the option. If you use this command line
> instead you get CMS and no error message:
>
> -Xms256M -Xmx256M -XX:+UseConcMarkSweepGC -verbose:gc
>
> But then again, maybe this was not what you were asking...
>
> Bengt
>
>
>
>
>>>>>>> For 1.6.0_22: -Xms256M -Xmx256M -XX:+UseConcMarkSweepGC
>> Are you saying that if you do:
>>
>>       -Xms256M -Xmx256M -XX:UseConcMarkSweepGC -verbose:gc
>>
>> you do not get CMS? If not, what does the GC log say?
>> Can you provide the following details:
>>
>> % java -version
>>
>> and also
>>
>> % jinfo<pid>
>>
>> as well as:
>>
>> % jnifo -flag UseConcMarkSweepGC<pid>
>>
>> where<pid>   is yr JVM process.
>>
>> The main issue will be dealt with in the original thread.
>> Sorry for the digression.
>>
>> -- ramki
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