RFR: 8365880: Shenandoah: Unify memory usage accounting in ShenandoahFreeSet [v23]

[Y. Srinivas Ramakrishna]

On Tue, 7 Oct 2025 21:58:02 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> src/hotspot/share/gc/shared/gc_globals.hpp line 472:
>> 
>>> 470:   product(size_t, SoftMaxHeapSize, 0, MANAGEABLE,                           \
>>> 471:           "Soft limit for maximum heap size (in bytes)")                    \
>>> 472:           constraint(SoftMaxHeapSizeConstraintFunc,AfterMemoryInit)         \
>> 
>> Changing a common file might raise eyebrows. Why do we need this?
>
> ShenandoahHeap::initialize() makes use of SoftMaxHeapSize.  If the SoftMaxHeapSizeConstraintFunc is handled "after memory init", the value of SoftMaxHeapSize is not yet available when we try to use it.
> 
> I welcome an alternative approach if you have any ideas.

Did all tests pass, in particular `TestSoftMaxHeapSize`? The test now happens earlier. I am not sure why the value itself isn't available before, like you say. I am guessing you want to check the value after whatever adjustments have been made in `initialize()`? The value of the flag should be available already, irrespective of when the constraints check is done.


enum class JVMFlagConstraintPhase : char {
  // Will be validated during argument processing (Arguments::parse_argument).
  AtParse         = 0,
  // Will be validated inside Threads::create_vm(), right after Arguments::apply_ergo().
  AfterErgo       = 1,
  // Will be validated inside universe_init(), right after Metaspace::global_initialize().
  AfterMemoryInit = 2
};

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PR Review Comment: https://git.openjdk.org/jdk/pull/26867#discussion_r2414911580