JEP 291: Deprecate the Concurrent Mark Sweep (CMS) Garbage Collector
Erik Helin
erik.helin at oracle.com
Wed Nov 16 16:03:38 UTC 2016
On 11/11/2016 08:04 AM, kirk at kodewerk.com wrote:
>> 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.
Thanks for your feedback, and I again want to emphasize that we are
actively looking for contributions in these areas.
Thanks,
Erik
> 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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