RFR: 8285710: miscalculation of G1CardSetAllocator wasted memory size [v3]

[tqxia]

On Fri, 6 May 2022 09:38:01 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>>> is the idea here to include free slots and exclude pending slots when counting unused slots?
>> 
>> I think not treating slots on pending lists as unused (or equivalently, treating slots on pending lists as "in-use") is cleaner. Since the free/pending counters are not strictly synchronized (`Atomic::add(&_free_count, count);` in `try_transfer_pending`), adding the pending counter in that formula could cause "unused slots > total slots", which is extremely confusing.
>
> These statistics are calculated during safepoint/gc, so there can be no synchronization issues.

Got it. Thank you both for the explanation.

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PR: https://git.openjdk.java.net/jdk/pull/8424