From John's comments in JDK-8340171:

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I'm racking my brain to figure out if there is some kind of regression test we could write to detect a future situation like this: (a) Someone changes the AOT cache so that there is a burst of new oops or metadata pointers injected, and then (b) the pointer bitmap loses its clever compression. How will we notice such a thing?

I have an idea; this is the best I've got ATM: Print a log message that gives the density of one-bits in the pointer map (out of total map size). Maybe also the density of non-zero WORDS in the pointer map. It's a "figure of merit"; 50-100% would be awesomely good, 1% would be very bad . Write a regression test that detects if that metric goes out of some reasonable range, for some representative workload. It has to be a tentative failure, kind of like a test timeout or excessive pause time.

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