RFR: Expand old on demand [v44]

[Kelvin Nilsen]

On Sat, 13 May 2023 01:33:27 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Report number of old- and young cset regions when preparing to rebuild free set
>
> src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp line 206:
> 
>> 204:           "milliseconds. Setting this to 0 disables the feature.")          \
>> 205:                                                                             \
>> 206:   product(uintx, ShenandoahGuaranteedYoungGCInterval, 30*1000,  EXPERIMENTAL,  \
> 
> Why was this made so small? Are there cases where, say, for a quiescent/idle service instance with little or no load, we must still, for some reason, trigger young gc's twice each minute?

Let me experiment with reverting to original value.  There were times when our heuristics were getting flat-footed and we triggered late after long idle spans, but this "fix" may have just masked a different problem that may now be resolved.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/248#discussion_r1204323814