JEP 291: Deprecate the Concurrent Mark Sweep (CMS) Garbage Collector

Jeremy Manson jeremymanson at google.com
Fri Nov 11 06:05:06 UTC 2016


Thanks, Erik.  Jungwoo will take a look (he already responded to one).

Jeremy

On Wed, Nov 9, 2016 at 7:26 AM, Erik Helin <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 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-N
> ovember/019215.html
> - "RFC: Parallel full collection for G1"
>
> http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-N
> ovember/019216.html
> - "RFC: Rebuilding remembered sets during concurrent mark"
>
> http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-N
> ovember/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>
>>
>> (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>> 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>> 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>
>>>
>>>         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>>
>>> 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>> 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>> 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>
>>>>                     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>
>>>>                     <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>> 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>
>>>>>                         <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>>
>>>>>>                             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>
>>>>>>                                 aph at redhat.com <mailto:aph at redhat.com
>>>>>> >
>>>>>>                                 volker.simonis at gmail.com
>>>>>>                                 <mailto:volker.simonis at gmail.com>
>>>>>>                                 jon.masamitsu at oracle.com
>>>>>>                                 <mailto:jon.masamitsu at oracle.com>
>>>>>>                                 jeremymanson at google.com
>>>>>>                                 <mailto:jeremymanson at google.com>
>>>>>>                                 martijnverburg at gmail.com
>>>>>>                                 <mailto:martijnverburg at gmail.com>
>>>>>>                                 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
>>>>>>                               @RichardWarburto
>>>>>>                             <http://twitter.com/richardwarburto>
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>>
>>>
>>
>>
>>
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