RFR: 8292329: Enable CDS shared heap for zero builds [v2]

[Erik Joelsson]

On Tue, 23 Aug 2022 16:51:36 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> make/Images.gmk line 133:
>> 
>>> 131:   # Only G1 supports dumping the shared heap, so explicitly use G1
>>> 132:   # it if the JVM supports it. (Note: the default GC with zero is SerialGC)
>>> 133:   $1_$2_CDS_DUMP_FLAGS := $(CDS_DUMP_FLAGS) $(if $(filter g1gc, $(JVM_FEATURES_$1)),-XX:+UseG1GC)
>> 
>> I think it should be e.g. (untested):
>> 
>> Suggestion:
>> 
>>   $1_$2_CDS_DUMP_FLAGS := $(CDS_DUMP_FLAGS)
>>   ifeq ($(call check-jvm-feature, g1gc), true)
>>      $1_$2_CDS_DUMP_FLAGS += -XX:+UseG1GC
>>   endif
>
> That doesn't work because `check-jvm-feature` requires `JVM_VARIANT` to be set, but `CreateCDSArchive` is not called in a context where  `JVM_VARIANT` is set. ( `JVM_VARIANT` is set only in a few specific places in Main.gmk, etc).
> 
> One option is to change the foreach loop a few lines below to:
> 
> 
>   $(foreach JVM_VARIANT, $(JVM_VARIANTS), \
>     $(eval $(call CreateCDSArchive,)) \
>   )
> 
> 
> But I've not seen `JVM_VARIANT` being used this way, so I am a little hesitant about doing it.

Is the CDS archive dumped in a JVM variant specific way? If so, then it would make sense to dump it for each configured variant.

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PR: https://git.openjdk.org/jdk/pull/9984