RFR: 8330670: Obsolete ScavengeBeforeFullGC

[Stefan Karlsson]

On Fri, 19 Apr 2024 12:16:29 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> src/hotspot/share/gc/z/zDriver.cpp line 313:
>> 
>>> 311:   assert(!should_clear_soft_references(cause), "Clearing soft references without pre-cleaning young gen");
>>> 312: 
>>> 313:   return false;
>> 
>> I'm not sure if this is correct. We previously returned true here if the user didn't set ScavengeBeforeFullGC, right? Maybe we need a ZGC-specific flag to allow this "precleaning" to be turned off?
>
> `ScavengeBeforeFullGC` is true by default only for Parallel.
> 
> 
>   if (!UseParallelGC && FLAG_IS_DEFAULT(ScavengeBeforeFullGC)) {
>     FLAG_SET_DEFAULT(ScavengeBeforeFullGC, false);
>   }

Ahh, I missed that. Nowadays we typically put that kind of code in the GC-specific places and not in the shared code.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18861#discussion_r1572290559