On Wed, 10 Feb 2021 22:47:28 GMT, Chris Plummer <[email protected]> wrote:
>> Hi Lin, >> Sure, let's discuss -histo in this thread first. >> >> Hi @sspitsyn @plummercj @linzang >> My following point is based on my humble opinion that parallel=N is not >> necessary for user and we should use the largest parallel capability of JVM >> to do heap histo when user intend to do it in parallel. But if you think >> this basic opinion is not that correct, please kindly ignore following >> opinion. :-) >> IMHO, maybe we could make the option simple and automatically speed up heap >> scan by disabling "parallel=" option and adding "noparallel" at the same >> time? From user's point of view, "noparallel" will speed up their histo/dump >> automatically, if they are migrating from jdk15 or prior to jdk15, and also >> give them a way to fall back to previous serial scan if they would like to >> do that. Although This way will introduce the compability issue, fortunately >> JDK16 is not LTS, and maybe we could backport to 16 updates if necessary? >> How do you think about it? Thanks for discussion. >> >> ( BTW, I might not be able to response timely, as it will be long public >> holiday the next few days, I'm sorry for the inconvenience. ) > > I'm in favor of just having a `noparallel` option (default to using parallel) > instead of using `parallel=<n>`. This would be for both the histo and heap > dump features, and for both the `jmap` and `jcmd` support of these features. > > As for the current `parallel=<n>` support for jmap histo already in JDK 16, > hopefully there would be no objections to removing that in JDK 17 in favor of > the `noparallel` approach, but I think the CSR for that change should get > some good scrutiny. I think it would good to get approval from @AlanBateman > and/or @dholmes-ora since they are both in the CSR group and have good > serviceability knowledge. > > For reference, the JDK 16 CSR for adding `parallel=<n>` support to `jmap > -histo` is [8239290](https://bugs.openjdk.java.net/browse/JDK-8239290), and > the bug to change this to a `noparallel` opiton in JDK 17 is > [JDK-8261482](https://bugs.openjdk.java.net/browse/JDK-8261482). I don't > think there is a CSR yet. Dear All, I took the liberity to create a PR (#2519) for the "noparallel" option. Maybe we could discuss there. And I also found @Hamlin-Li has created a CSR for that. Thanks a lot! BRs, Lin ------------- PR: https://git.openjdk.java.net/jdk/pull/2379
