On Thu, 29 Aug 2024 17:24:47 GMT, Markus Grönlund <[email protected]> wrote:
>> With UseCompressedClassPointers off, I think
>> Metaspace::is_in_shared_metaspace() would still return true but I don't
>> think he compression base is the bottom of the CDS archive. I asked Markus
>> to have a look.
>
> The code supports the JfrTraceID load barrier that enqueues tagged Klass*. It
> selects a more compact representation (a single word, instead of two words),
> if a Klass* can be compressed (i.e. there exists a compress class scheme in
> place (CompressedKlassPointers::encode(const_cast<Klass*>(klass)); AND the
> traceid (u8) value is low enough to be represented by only 4 bytes).
>
> struct JfrEpochQueueKlassElement {
> traceid id;
> const Klass* klass;
> };
>
> struct JfrEpochQueueNarrowKlassElement {
> u4 id;
> narrowKlass compressed_klass;
> };
// Return TRUE only if UseCompressedClassPointers is True.
static bool using_class_space() {
return NOT_LP64(false) LP64_ONLY(UseCompressedClassPointers);
}
I see now that was wrong for 32-bit.
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PR Review Comment: https://git.openjdk.org/jdk/pull/19157#discussion_r1736779802
