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<div dir="ltr">Hi Thomas,</div>
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<div dir="ltr">The use of UseCompressedClassPointers used to be intertwined weirdly with UseCompressedOops due to historic reasons. I broke that connection because we wanted compressed class pointers in ZGC, even though we don’t use compressed oops.</div>
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<div dir="ltr">After that was cleaned up I tend to think of -XX:-UseCompressedClassPointers in my head as some kind of alias for -XX:+WasteMemory which you would configure purely because you want to waste memory just for the sake of it.</div>
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<div dir="ltr">/Erik</div>
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<blockquote type="cite">On 22 Feb 2024, at 15:35, Thomas Stüfe <thomas.stuefe@gmail.com> wrote:<br>
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<div>Greetings,</div>
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<div>Are there any realistic scenarios that would require UseCompressedClassPointers=false? Or could we make it constant at some point or remove the switch altogether?</div>
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<div>The only reason I can see for UseCompressedClassPointers=off would be if the maximum class space size of 3GB is not enough. But how realistic is this really? Some numbers:</div>
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<div>On average, a Klass is ~600-700 bytes. Therefore, 3GB of class space would be enough for ~5 million classes. Note that the typical size ratio of Klass-to-non-class-metadata is 1:6 .. 1:10, which means that 3 GB class space come with ~18..30 GB of non-class
metaspace (see [1]). I think these are outlandish numbers. Do we need to support these scenarios? Some weird class generator scenarios maybe?<br>
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<div>Other than class space max size not being enough, are there any reasons for -UseCompressedClassPointers?<br>
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<div>Thank you,</div>
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<div>Thomas<br>
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<div>[1] <a href="https://github.com/tstuefe/metaspace-statistics/blob/master/Histogram.svg">
https://github.com/tstuefe/metaspace-statistics/blob/master/Histogram.svg</a></div>
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