RFR (L): 8065972: Remove support for ParNew+SerialOld and DefNew+CMS

Stefan Karlsson stefan.karlsson at oracle.com
Wed Nov 26 13:42:55 UTC 2014


Hi Bengt,

The changes looks good. There are a couple of follow-up cleanups that 
can be done as separate changes, but I don't think they are blocking 
this patch.

http://cr.openjdk.java.net/~brutisso/8065972/hotspot-webrev.00/test/gc/startup_warnings/TestParNewSerialOld.java.frames.html

I think the summary should be changed to:

   28 * @summary Test that the unsupported ParNew+SerialOld combination does not start


StefanK

On 2014-11-26 13:09, Bengt Rutisson wrote:
>
> Hi everyone,
>
> Can I have a couple of reviews for this change to remove the support 
> for ParNew+SerialOld and DefNew+CMS?
>
> This work is part of  JEP 214 (http://openjdk.java.net/jeps/214).
>
> The main change is in the hotspot repo:
> http://cr.openjdk.java.net/~brutisso/8065972/hotspot-webrev.00/
>
> I also removed the ParNew runs from the jprt configuration:
> http://cr.openjdk.java.net/~brutisso/8065972/root-webrev.00/
>
> JBS bug:
> https://bugs.openjdk.java.net/browse/JDK-8065972
>
> Some notes about the change:
>
> - UseParNewGC is now a redundant flag. It can only be used with CMS, 
> so it will always have the same value as UseConcMarkSweepGC. Since 
> UseParNewGC was not one of the flags that were deprecated in JDK 8, we 
> decided to leave the flag in for JDK 9 but print a warning message 
> that it is deprecated. We plan on removing UseParNewGC in JDK 10.
>
> Here's how the VM will behave with different values of UseParNewGC 
> after my change:
>
> $ java -XX:+UseParNewGC -version
> It is not possible to combine the ParNew young collector with the 
> Serial old collector.
> Error: Could not create the Java Virtual Machine.
> Error: A fatal exception has occurred. Program will exit.
>
> $ java -XX:-UseParNewGC -version
> Java HotSpot(TM) 64-Bit Server VM warning: The UseParNewGC flag is 
> deprecated and will likely be removed in a future release
> java version "1.9.0-internal-debug"
> Java(TM) SE Runtime Environment (build 
> 1.9.0-internal-debug-brutisso_2014_11_05_09_40-b00)
> Java HotSpot(TM) 64-Bit Server VM (build 
> 1.9.0-internal-debug-brutisso_2014_11_05_09_40-b00, mixed mode)
>
> $ java -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -version
> Java HotSpot(TM) 64-Bit Server VM warning: The UseParNewGC flag is 
> deprecated and will likely be removed in a future release
> java version "1.9.0-internal-debug"
> Java(TM) SE Runtime Environment (build 
> 1.9.0-internal-debug-brutisso_2014_11_05_09_40-b00)
> Java HotSpot(TM) 64-Bit Server VM (build 
> 1.9.0-internal-debug-brutisso_2014_11_05_09_40-b00, mixed mode)
>
> $ java -XX:-UseParNewGC -XX:+UseConcMarkSweepGC -version
> It is not possible to combine the DefNew young collector with the CMS 
> collector.
> Error: Could not create the Java Virtual Machine.
> Error: A fatal exception has occurred. Program will exit.
>
> - The NEW_C_HEAP_ARRAY and "new" calls in initialize_generations() 
> methods will exit if they fail. No need to check for null after those 
> calls. This simplified the two implementations significantly.
>
> - At a few places I've changed from "DefNewGeneration* dng = 
> (DefNewGeneration*)_young_gen;" to "DefNewGeneration* dng = 
> _young_gen->as_DefNewGeneration();". The as_DefNewGeneration() method 
> does the asserts that were often placed before the original casting code.
>
> - In concurrentMarkSweepGeneration.cpp I left the casting to 
> DefNewGeneration even though we could now use the more specific 
> ParNewGeneration. I prefer to do such an update later (if at all) 
> since that might come with its own complications regarding virtual 
> calls etc.
>
> - The two methods must_be_youngest() and must_be_oldest() were unused. 
> Removing them was not strictly needed for this change, but seemed like 
> a nice thing to do anyway and I don't think it clutters the webrev much.
>
> - UseParNewGC is now always true when UseConcMarkSweepGC is true. And 
> it is always false when UseConcMarkSweepGC is false. If statements 
> that used to test against both flags have been simplified to only test 
> against UseConcMarkSweepGC. This means that UseParNewGC is now only 
> used in arguments.cpp
>
> - Similarly JTreg tests that used UseParNewGC have been changed to use 
> UseConcMarkSweepGC instead. This should make it easy to remove in JDK 10.
>
> - The change to make/jprt.properties only affects the internal testing 
> system we have. It will no longer test the ParNew+SerialOld 
> combination (which is no longer supported). Note that DefNew+CMS was 
> not tested at all by JPRT.
>
> Thanks,
> Bengt



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