On Thu, 11 May 2023 12:12:56 GMT, Stefan Karlsson <stef...@openjdk.org> wrote:
>> Hi all, >> >> Please review the implementation of Generational ZGC, which can be turned on >> by adding -XX:+ZGenerational in addition to using -XX:+UseZGC. Generational >> ZGC is a major rewrite of the non-generational ZGC version that exists in >> the openjdk/jdk repository. It splits the heap into two generations; the >> young generation where newly allocated objects are born, and the old >> generation where long-lived objects get promoted to. The motivation for >> introducing generations is to allow ZGC to reclaim memory faster by not >> having to walk the entire object graph every time a garbage collection is >> run. This should make Generational ZGC suitable for more workloads. In >> particular workloads that previously hit allocation stalls because of high >> allocation rates, large live sets, or limited spare machine resources, have >> the potential to work better with Generational ZGC. For an in-depth >> description of Generational ZGC, see https://openjdk.org/jeps/439. >> >> The development of Generational ZGC started around the same time as the >> development of JDK 17. At that point we forked off the Generational ZGC >> development into its own branch and let non-generational live unaffected in >> openjdk/jdk. This safe-guarded non-generational ZGC and allowed Generational >> ZGC to move unhindered, without the shackles of having to fit into another >> GC implementation's design and quirks. Since then, almost all of the ZGC >> files have been changed. Moving forward to today, when it's ready for us to >> upstream Generational ZGC, we now need to deliver Generational ZGC without >> disrupting our current user-base. We have therefore opted to initially >> include both versions of ZGC in the code base, but with the intention to >> deprecate non-generational ZGC in a future release. Existing users running >> with only -XX:+UseZGC will get the non-generational ZGC, and users that want >> the new Generational ZGC need to run with -XX:+ZGenerational in addition to >> -XX:+UseZGC. The intention is to give the users time to validate and deploy their workloads with the new GC implementation. >> >> Including both the new evolution of a GC and its legacy predecessor poses a >> few challenges for us GC developers. The first reaction could be to try to >> mash the two implementations together and sprinkle the GC code with >> conditional statements or dynamic dispatches. We have done similar >> experiments before. When ZGC was first born, we started an experiment where >> we converted G1 into getting the same features as the evolving ZGC. It was >> qu... > > Stefan Karlsson has updated the pull request with a new target base due to a > merge or a rebase. The pull request now contains 932 commits: > > - Merge remote-tracking branch 'upstream/master' into zgc_generational_review > - Make barrier_Relocation inherit from Relocation instead of DataRelocation > - ZGC: Generational > > Co-authored-by: Stefan Karlsson <stef...@openjdk.org> > Co-authored-by: Per Liden <pli...@openjdk.org> > Co-authored-by: Albert Mingkun Yang <ay...@openjdk.org> > Co-authored-by: Erik Österlund <eosterl...@openjdk.org> > Co-authored-by: Axel Boldt-Christmas <abold...@openjdk.org> > Co-authored-by: Stefan Johansson <kstef...@openjdk.org> > - UPSTREAM: RISCV tmp reg cleanup resolve_jobject > - CLEANUP: barrierSetNMethod_aarch64.cpp > - UPSTREAM: assembler_ppc CMPLI > > Co-authored-by: TheRealMDoerr <martin.do...@sap.com> > - UPSTREAM: assembler_ppc ANDI > > Co-authored-by: TheRealMDoerr <martin.do...@sap.com> > - Merge branch 'zgc_generational' into zgc_generational_rebase_target > - Workaround failed reservation in ZForwardingTest > - ZGC: Generational > > Co-authored-by: Stefan Karlsson <stef...@openjdk.org> > Co-authored-by: Per Liden <pli...@openjdk.org> > Co-authored-by: Albert Mingkun Yang <ay...@openjdk.org> > Co-authored-by: Erik Österlund <eosterl...@openjdk.org> > Co-authored-by: Axel Boldt-Christmas <abold...@openjdk.org> > Co-authored-by: Stefan Johansson <kstef...@openjdk.org> > - ... and 922 more: https://git.openjdk.org/jdk/compare/0cbfbc40...9dd9681b Thanks all who have helped building Generational ZGC! I think it is time to integrate. ------------- PR Comment: https://git.openjdk.org/jdk/pull/13771#issuecomment-1544037094
