RFR (S): 8233301: Implementation of JEP 366: Deprecate the ParallelScavenge + SerialOld GC Combination

Per Liden per.liden at oracle.com
Tue Nov 5 08:26:07 UTC 2019

Hi Thomas,

On 11/4/19 11:46 AM, Thomas Schatzl wrote:
> Hi,
> On 01.11.19 00:05, Bernd Eckenfels wrote:
>> The help message:
>> Use the Parallel Old garbage collector. Deprecated.
>    product(bool, UseParallelOldGC, false,     \
>            "Use the Serial Old garbage collection algorithm for old "     \
>            "generation. Deprecated."     \

I know it's not easy to get this right, but I think the above might 
perhaps be even more confusing. How about something like:

UseParallelGC -> "Use the Parallel garbage collector"

UseParallelOldGC -> "Use the Parallel or the Serial garbage collector 
when collecting the old generation (Deprecated)."


>> Looks a bit missleading to me. I know it means the option is 
>> deprecated (especially the non default negative value
>  > but it could easily be understood as ParallelOld beeing deprecated.
> I hope the new text is better understandable and does not lead to the 
> confusion you suggested.
> Note that the default value of "false" is correct although maybe 
> surprising, as this change does not modify it. It's only that 
> -XX:+UseParallelGC is actually a shorthand for "-XX:+UseParallelGC 
> -XX:+UseParallelOldGC" for like forever.
> I do not want to change this here.
> Note that these strings are not the official documentation, but the 
> manpage. They read:
> `-XX:+UseParallelGC`
> :   Enables the use of the parallel scavenge garbage collector (also 
> known as
>      the throughput collector) to improve the performance of your 
> application by
>      leveraging multiple processors.
>      By default, this option is disabled and the default collector is used.
>      If it's enabled, then the `-XX:+UseParallelOldGC` option is
>      automatically enabled, unless you explicitly disable it.
> and (with this change, as part of the "Deprecated" section):
> `-XX:+UseParallelOldGC`
> :   Enables the use of the parallel garbage collector for full GCs. By 
> default,
>      this option is disabled. Enabling it automatically enables the
>      `-XX:+UseParallelGC` option.
> Which seems in line with what is now told in the sources too.
>> There is no jtreg for +UseParallelOld. It would need to document that 
>> deprecation warning is expected for that as well?
> There is a separate test case in 
> test/hotspot/jtreg/runtime/CommandLine/VMDeprecatedOptions.java which 
> does not seem updated for any and all deprecated options. I added this 
> flag to it anyway.
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8233301/webrev/
> Testing:
> local compilation + local jtreg test
> Thanks,
>    Thomas

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