[lworld] RFR: 8372261: [lworld] Augment vmTestbase array tests with large flat arrays [v2]

[Leonid Mesnik]

On Fri, 13 Feb 2026 16:00:49 GMT, Leonid Mesnik <lmesnik at openjdk.org> wrote:

>> test/hotspot/jtreg/vmTestbase/nsk/share/gc/Memory.java line 139:
>> 
>>> 137:                 return getReferenceSize();
>>> 138:             }
>>> 139:             return 8;
>> 
>> This comment applies to all `getXXXArrayElementSize` methods. The element size depends on many things, such as the properties of the array (controls flattening decisions and/or layout) and the VM (flattening can be disabled). 
>> 
>> For JEP 401, we only consider the nullable atomic layout. Even for this simple case, we should, in my opinion, do the following:
>> - Check if flattening is enabled. For this, we can use the `WhiteBox` API to get the VM flag values. Some relevant flags may be: `UseArrayFlattening`, `UseFieldFlattening`, `UseNullableValueFlattening`, `UseAtomicValueFlattening`. 
>> - File an RFE to track hardcoding the size, such that we can change it once there are more layouts available.
>> 
>> A more robust solution would be to use `test/hotspot/jtreg/runtime/valhalla/inlinetypes/field_layout/FieldLayoutAnalyzer.java` in order to get more comprehensive layout information.
>
> Thanks for pointer.  It is very good example.
> But as I said, we need to find single solution for Memory sizes. And more important is it worth for these tests or such "rough" estimation is enough.

I filed https://bugs.openjdk.org/browse/JDK-8377906
to implement the generic solution and mainline and then we can improve it in valhalla.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/2099#discussion_r2804998011