JEP 291: Deprecate the Concurrent Mark Sweep (CMS) Garbage Collector
kirk at kodewerk.com
kirk at kodewerk.com
Fri Nov 11 07:04:19 UTC 2016
> Thanks Eric,
These RFCs looks very good. The RFC on throughput barriers would be the highest priority item. My discussions with low latency people suggest that this will be a huge barrier to them migrating to 9. I would suggest that a parallel full is the least important on the list as I would hope we can find strategies to tune them out of systems so that one would only see them in (pseudo-) failure conditions that are often a result of “work queues” backing up and thus are outside the realm of GC tuning.
I look forward to testing them.
Kind regards,
Kirk
>
> On Wed, Nov 9, 2016 at 7:26 AM, Erik Helin <erik.helin at oracle.com <mailto:erik.helin at oracle.com>> wrote:
> Hi Jeremy,
>
> Thanks for taking notes. I have created separate email threads on hotspot-gc-dev at openjdk.java.net <mailto:hotspot-gc-dev at openjdk.java.net> for three enhancements to G1 that we think will make G1 be more like CMS for the use cases discussed during the meeting. The ideas are described in:
> - "RFC: Throughput barriers for G1"
>
> http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-November/019215.html <http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-November/019215.html>
> - "RFC: Parallel full collection for G1"
>
> http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-November/019216.html <http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-November/019216.html>
> - "RFC: Rebuilding remembered sets during concurrent mark"
>
> http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-November/019217.html <http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-November/019217.html>
>
> Please respond to these ideas in the respective email thread. We would be happy to help out with the design and integration if you and/or any external contributor would like too look into any (or all) of these ideas.
>
> Thanks,
> Erik
>
> On 10/21/2016 08:37 PM, Jeremy Manson wrote:
> Hi folks,
>
> We had the face to face at JavaOne on 9/20. I took notes, which are
> linked from the bug:
>
> https://bugs.openjdk.java.net/browse/JDK-8142518 <https://bugs.openjdk.java.net/browse/JDK-8142518>
> <https://bugs.openjdk.java.net/browse/JDK-8142518 <https://bugs.openjdk.java.net/browse/JDK-8142518>>
>
> (Sorry about the delay - anything that happens at a quarterly boundary
> takes me twice as long because of the Google planning cycle).
>
> The current plan for followup includes Erik Helin figuring out what
> extracting CMS code from Hotspot will actually look like, and Paul Su
> providing a list of ideas for helping G1 close the performance gap. See
> meeting notes for more followup actions.
>
> We didn't specify a timeline for the next meeting. Paul (cc'd) said he
> had to go do some due diligence about getting the list of ideas. It
> would be great if he and / or Erik could talk about when a good time for
> the next sync would be.
>
> Jeremy
>
> On Sat, Aug 27, 2016 at 5:42 PM, Jeremy Manson <jeremymanson at google.com <mailto:jeremymanson at google.com>
> <mailto:jeremymanson at google.com <mailto:jeremymanson at google.com>>> wrote:
>
> Thanks, Jon.
>
> If we are going to do it, I'd (selfishly) like to see it done
> earlier in the JDK 10 time frame, so that we can start contributing
> our patches for it for JDK 10 earlier, rather than later. But JDK
> 10 time frame is fine.
>
> Assuming you are asking me about management issues: I just
> (Thursday) got back from the vacation I mentioned, so I've only just
> spoken about it with our management. Naturally, no immediate
> answer, but there's a lot of interest, and we plan to have more
> conversations in the near term.
>
> For a variety of reasons (most of which I've already articulated), I
> strongly believe we will have to do *something*, and it will mostly
> be a question of whether this is the right path. Since we have
> ~three years before the issue becomes immediate, that gives us a bit
> of breathing room to do the right thing. Other possibilities
> include spending the time until JDK 10 making G1 do what we need, or
> figuring out another GC entirely (we'd want to evaluate, e.g.,
> Shenandoah).
>
> (Since the G1 possibility is clearly of interest to you folks: We
> would have to decide a) that it is technically feasible, and b) that
> you folks were likely to take the patches. In addition to finding a
> path forward to lowering the cost of the write barrier dramatically
> and dealing with the memory footprint issues (not sure this is
> possible), we would also have to reimplement, e.g., our parallel
> Full GC patch, as well as a number of other changes we've made to
> CMS locally.)
>
> I'd like what we end up doing to be something palatable to the
> community, since CMS is obviously filling a very important role in
> the ecosystem that won't get filled if it gets abandoned.
>
> Jeremy
>
> On Tue, Aug 23, 2016 at 9:23 PM, Jon Masamitsu
> <jon.masamitsu at oracle.com <mailto:jon.masamitsu at oracle.com> <mailto:jon.masamitsu at oracle.com <mailto:jon.masamitsu at oracle.com>>> wrote:
>
> All,
>
> I've been working on the examples and we're been discussing
> (arguing)
> about them here. They are failing into at least the following
> classes
>
> - Use inheritance to specialize for CMS (specialize card table is
> envisioned as an example).
> - Use a GC Interface to request something different for CMS
> (different write
> barriers for example).
> - Compile code under macros
> Similar to INCLUDE_ALL_GCS
> Leaves calls to specialized CMS code visible in the shared code
> Involves some code refactoring
> - Move more code to the cms directory (ParNew for example)
> - Custom solutions which might use one or more of the above
> techniques.
> - Argument processing I don't know about yet.
>
> We're still arguing about the example so they're not here.
>
> As I've said Oracle would not drop support of CMS until at least
> jdk 10 so working on separating out the code would be work
> for the jdk 10 time frame. Do people have reasons to get that
> done earlier rather than later?
>
> Also is your management's support for spending engineering time
> on this effort a slam-dunk? Or a qualified maybe? I'm trying to
> get a feel for how real this CMS project is.
>
> Jon
>
>
>
> On 8/1/2016 1:49 PM, Jeremy Manson wrote:
> For those following along at home, the meeting happened last
> week. We took notes, which are linked from the bug:
>
> https://bugs.openjdk.java.net/browse/JDK-8142518 <https://bugs.openjdk.java.net/browse/JDK-8142518>
> <https://bugs.openjdk.java.net/browse/JDK-8142518 <https://bugs.openjdk.java.net/browse/JDK-8142518>>
>
> The current plan for followup is to set up a meeting for the
> end of August, and then a f2f during JavaOne.
>
> Jeremy
>
> On Thu, Jul 21, 2016 at 9:46 AM, Jeremy Manson
> <jeremymanson at google.com <mailto:jeremymanson at google.com> <mailto:jeremymanson at google.com <mailto:jeremymanson at google.com>>> wrote:
>
> I was drafting an agenda. My expectation is that the
> meeting will go something like this:
>
> Introductions
>
> Discussion of motivations for JEP 291 (Jon M)
>
> Discussions of concerns about JEP 291 (roundtable)
>
> Discussion / Brainstorming about potential ways forward,
> as well as an understanding of what level of commitment
> organizations are willing to make.
>
> Discussion of action items and followup.
>
> Jeremy
>
>
> On Thu, Jul 21, 2016 at 7:39 AM, Martijn Verburg
> <martijnverburg at gmail.com <mailto:martijnverburg at gmail.com>
> <mailto:martijnverburg at gmail.com <mailto:martijnverburg at gmail.com>>> wrote:
>
> Hi Jon,
>
> For me it's to see if there are enough folks who are
> willing *and* capable (to be blunt, it will need the
> backing of large companies) of maintaining CMS as a
> collector going forwards (it's important to several of
> our customers). If that's a yes then I'd hope to have
> a technical discussion around the options of how we
> could achieve that without causing a major headache
> for the Oracle GC engineers.
>
>
> Cheers,
> Martijn
>
> On 20 July 2016 at 23:50, Jon Masamitsu
> <jon.masamitsu at oracle.com <mailto:jon.masamitsu at oracle.com>
> <mailto:jon.masamitsu at oracle.com <mailto:jon.masamitsu at oracle.com>>> wrote:
>
> What are peoples expectations for this meeting?
>
> Jon
>
> On 07/18/2016 10:16 AM, Jeremy Manson wrote:
> Presumably, everyone will be happy with meeting
> notes rather than an actual recording.
>
> Otherwise, I'll add:
>
> ysr1729 at gmail.com <mailto:ysr1729 at gmail.com> <mailto:ysr1729 at gmail.com <mailto:ysr1729 at gmail.com>>
> mark.reinhold at oracle.com <mailto:mark.reinhold at oracle.com>
> <mailto:mark.reinhold at oracle.com <mailto:mark.reinhold at oracle.com>>
>
>
>
> On Mon, Jul 18, 2016 at 8:13 AM,
> kirk.pepperdine at gmail.com <mailto:kirk.pepperdine at gmail.com>
> <mailto:kirk.pepperdine at gmail.com <mailto:kirk.pepperdine at gmail.com>>
> <kirk.pepperdine at gmail.com <mailto:kirk.pepperdine at gmail.com>
> <mailto:kirk.pepperdine at gmail.com <mailto:kirk.pepperdine at gmail.com>>> wrote:
>
> ok we can record if everyone is open to that.
>
> On Jul 18, 2016, at 7:48 AM, Jeremy Manson
> <jeremymanson at google.com <mailto:jeremymanson at google.com>
> <mailto:jeremymanson at google.com <mailto:jeremymanson at google.com>>> wrote:
>
> Richard - I'll bring someone who can take
> readable notes. :)
>
> Jeremy
>
> On Sat, Jul 16, 2016 at 5:07 AM,
> kirk.pepperdine at gmail.com <mailto:kirk.pepperdine at gmail.com>
> <mailto:kirk.pepperdine at gmail.com <mailto:kirk.pepperdine at gmail.com>>
> <kirk.pepperdine at gmail.com <mailto:kirk.pepperdine at gmail.com>
> <mailto:kirk.pepperdine at gmail.com <mailto:kirk.pepperdine at gmail.com>>> wrote:
>
> Hi Richard,
>
> I think it’s in everyone’s interest to
> keep this out in the open.
>
> Kind regards,
> Kirk
>
> On Jul 16, 2016, at 1:34 AM, Richard
> Warburton <richard.warburton at gmail.com <mailto:richard.warburton at gmail.com>
> <mailto:richard.warburton at gmail.com <mailto:richard.warburton at gmail.com>>>
> wrote:
>
> Hi,
>
> Sounds as if the consensus is a
> telephone / video conference in the
> near term, and then a F2F during /
> close to JavaOne.
>
> People who want to be invited include:
>
> kirk at kodewerk.com <mailto:kirk at kodewerk.com>
> <mailto:kirk at kodewerk.com <mailto:kirk at kodewerk.com>>
> aph at redhat.com <mailto:aph at redhat.com> <mailto:aph at redhat.com <mailto:aph at redhat.com>>
> volker.simonis at gmail.com <mailto:volker.simonis at gmail.com>
> <mailto:volker.simonis at gmail.com <mailto:volker.simonis at gmail.com>>
> jon.masamitsu at oracle.com <mailto:jon.masamitsu at oracle.com>
> <mailto:jon.masamitsu at oracle.com <mailto:jon.masamitsu at oracle.com>>
> jeremymanson at google.com <mailto:jeremymanson at google.com>
> <mailto:jeremymanson at google.com <mailto:jeremymanson at google.com>>
> martijnverburg at gmail.com <mailto:martijnverburg at gmail.com>
> <mailto:martijnverburg at gmail.com <mailto:martijnverburg at gmail.com>>
> jwha at google.com <mailto:jwha at google.com>
> <mailto:jwha at google.com <mailto:jwha at google.com>>
>
> Did I miss anyone? We can take
> date / time planning and logistics
> off-list.
>
>
> Given that this change affects a lot of
> organisations and people in the wider
> Java community I think it would be
> really appreciated that a brief summary
> of the discussion be published
> somewhere in public. Maybe this mailing
> list?
>
> regards,
>
> Richard Warburton
>
> http://insightfullogic.com <http://insightfullogic.com/>
> @RichardWarburto
> <http://twitter.com/richardwarburto <http://twitter.com/richardwarburto>>
>
>
>
>
>
>
>
>
>
>
>
>
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