RFR: 8335902: Parallel: Refactor VM_ParallelGCFailedAllocation and VM_ParallelGCSystemGC [v3]

[Albert Mingkun Yang]

On Fri, 12 Jul 2024 01:22:28 GMT, Guoxiong Li <gli at openjdk.org> wrote:

>> src/hotspot/share/gc/parallel/parallelScavengeHeap.cpp line 446:
>> 
>>> 444:   }
>>> 445:   return result;   // Could be null if we are out of space.
>>> 446: }
>> 
>> I notice the method `PSOldGen::allocate` can expand the size of the old gen, but the method `PSYoungGen::allocate` can't expand the size of the young gen. It is similar to a bug [1] in Serial. Fortunately, the size of the young generation can be resized during Parallel GC if the option `UseAdaptiveSizePolicy` is `true`. When the `UseAdaptiveSizePolicy` is set to `false` manually by the user, I suspect it is a bug in Parallel because of the unexpanded young generation size.
>> 
>> [1] https://bugs.openjdk.org/browse/JDK-8333386
>
> @albertnetymk Do you think whether we need to expand young generation during allocation (both Serial and Parallel)? In Serial, `UseAdaptiveSizePolicy` is not used, so it is indeed a bug in Serial (the young generation can't be resized and is always the initial size).

Due to the internal structure (eden/survivor) of young-gen, it's not super easy to expand young-gen during allocation like old-gen. Need a dedicated ticket to properly evaluate its cost/benefit.

> Serial (the young generation can't be resized and is always the initial size).

That sounds like a definite bug; at least young-gen should be resizable during young-gc/full-gc.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20077#discussion_r1675613933