Expected JDK version of when CMS code is suppose to be dropped, is it JDK11?

Jeremy Manson jeremymanson at google.com
Wed Jan 31 01:15:27 UTC 2018

Thanks, Paul.  We're definitely going to re-evaluate G1 with a more modern
JDK, but to do it for real, we need to re-evaluate it alongside something
that can run CMS in a production setting.  Getting a JDK and our codebase
to the point where that is possible at Google is quite a bit of work, so it
would be a lot of work for us to rush to do it for 9 or 10 and then start
again for 10/11.

(The work for 9/10 would help us for 11, but there would be quite a bit of
extra work, as well.)

In short: "unlikely" is definitely good news for us.  :)  We'll watch this
space for updates, in case that changes.


On Tue, Jan 30, 2018 at 4:07 PM, Paul Su <paul.su at oracle.com> wrote:

> Hi Jeremy, Wessam,
>   At this time, removal of CMS is still under consideration for JDK 11 but
> unlikely to happen within that timeframe. However, there were significant
> performance improvements to G1 in JDK 9 and 10, so it may be worthwhile to
> evaluate those with your use cases. As always, any feedback is welcome and
> appreciated.
> Thanks,
> Paul
> Subject: Re: Expected JDK version of when CMS code is suppose to be
> dropped, is it JDK11?
> Date: Tue, 30 Jan 2018 10:25:27 -0800
> From: Jeremy Manson <jeremymanson at google.com> <jeremymanson at google.com>
> To: Wessam Hassanein <wessam at google.com> <wessam at google.com>
> CC: hotspot-gc-dev at openjdk.java.net openjdk.java.net
> <hotspot-gc-dev at openjdk.java.net> <hotspot-gc-dev at openjdk.java.net>
> Hi folks,
> Wessam's question is pretty important to our planning.
> As many of you know, we were unable to get the G1 collector as it shipped
> with JDK 8 to work well with our services.  We want to try a newer branch.
> However, it also takes us a lot of work to make a JDK workable for
> internal use.  We have to patch it to work with our systems, and we have to
> make a whole lot of tests and infrastructure functional.
> We'd rather not rush to get out a Java version that will stop being
> supported in a few months.  Java 9 has already seen its last release, and
> we aren't really all that close to making it work for the kinds of systems
> that actually care about the GC they are using.  We are debating whether to
> try to continue to make Java 9 work, move to Java 10, or to skip both and
> go with Java 11, which will see long term support.
> (If we went to 11, we'd continue to experiment with 9 and 10, but we
> wouldn't push it hard.)
> In order to switch to G1, we need a release where our services can compare
> a recent G1 with CMS.  If the last release with both of them is Java 10,
> then we need to work on Java 10, in spite of its September expiration
> date.  If the last release with both of them is Java 11, then we will have
> a lot more breathing room for the G1 migration, and we can target that
> instead.
> So, it would be really helpful if someone could chime in with more
> information about the timeline for CMS removal.  Is it likely to be before
> the door closes for the Java 11 release?
> Thanks!
> Jeremy
> On Fri, Jan 26, 2018 at 12:36 PM, Wessam Hassanein <wessam at google.com>
> wrote:
>> Hi All,
>> Per JEP 291( http://openjdk.java.net/jeps/291) the CMS collector was
>> deprecated but there was no clear date of when it is expected for the CMS
>> code to be dropped. I see code refactoring in JDK10 JEP 304 (
>> http://openjdk.java.net/jeps/304) and I am wondering whether CMS is
>> planned to be dropped in JDK11 or when it is expected to be dropped?
>> Thanks,
>> Wessam Hassanein
>> Google GC TL
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