RFR: 8277736: G1: Allow forced evacuation failure of first N regions in collection set [v2]

[Thomas Schatzl]

On Wed, 1 Dec 2021 01:40:56 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> Currently, debug options of evacuation failure, like G1EvacuationFailureALotInterval and G1EvacuationFailureALotCount only config the ratio of objects failing evacuation, basically the distribution of objects failing evacuation is even among regions.
>> 
>> JDK-8256265 is trying to improve parallelism in regions that failed evacuation, it'll be helpful if there is option to config the distribution of objects failing evacuation among regions, so implementation of JDK-8256265 could be profiled more precisely.
>> 
>> This is to add the support and necessary vm options, and the implementation will be to select regions from start, i.e. not randomly, the motivation is to configure a more stable selection of evacuation failure regions, which will help verify the effect of JDK-8256265 implementation.
>
> Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Albert review

Looks good. Please improve the flag text before pushing though :)

src/hotspot/share/gc/g1/g1_globals.hpp line 79:

> 77:                                                                             \
> 78:   product(uintx, G1EvacuationFailureALotCSetPercent, 100,                   \
> 79:           "Percent of the regions in cset that will fail evacuation")       \

Please spell out "cset" in the description text though as it is done everywhere else in `g1_globals.hpp`. Considering Albert's suggestion, maybe something like:


The percentage of regions in the collection set starting from the beginning where the forced evacuation failure injection will be applied.

-------------

Marked as reviewed by tschatzl (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6561