Parallelizing the full compaction of CMS
Jon Masamitsu
jon.masamitsu at oracle.com
Wed Jun 3 18:57:50 UTC 2015
On 6/3/2015 2:32 AM, Volker Simonis wrote:
> Hi Jeremy,
>
> thanks for your answer. Maybe you misunderstood Ivan but it is
> definitely his and our (i.e. SAP's) intention to make this part of the
> OpenJDK.
>
> I can also fully understand the pains you have with integrating
> changes into the HotSpot. We've gone through this painful process with
> our ppc64 port a year ago but we think it will finally pay off. After
> all you (i.e. Google) used it as the base for your ppc64le port
> (Alexander Smundak contributed most of the LE-specific changes).
>
> We're facing the exactly same problems regarding the support of
> proprietary changes in a downstream version of the OpenJDK. That was
> actually the main reason why we started contributing to the OpenJDK.
> What we want to kindly ask you is to make your changes and extensions
> more transparently visible to the community if you intend to integrate
> them into the OpenJDK. If Hiroshi had posted his changes directly to
> the hotspot mailing lists instead of sending them privately to Jon I'm
> pretty sure we would have picked them up. And maybe together we would
> have managed to push them through (we have some reviewers as well :).
> After all, there are already quite a lot of features in the OpenJDK
> which are supported and maintained by the community (i.e. RedHat, IBM,
> SAP, ...) and not by Oracle.
>
Volker,
With regards to integrating such a change as discussed here, how do you
see "supported and maintained by the community" working? I really
don't know what to expect.
Jon
PS. I actually never saw the patch from Hiroshi.
> I don't have much experience with other Open Source projects, but with
> OpenJDK and especially HotSpot it's pretty pointless to try to
> contribute something by writing mails like "..I've implemented this
> cool feature XXX. If somebody is interested I can post more
> details..". You'll almost never get any feedback to such kind of
> requests. You'll at least have to post a complete buildabel and
> runnable patch against the head revision. I know that's a lot of
> overhead and we're having this very same discussion if it is worth
> doing it nearly every day for most of the features/additions we are
> implementing. Nevertheless, I think it is worth doing it although it
> sometimes may take years until you get your changes back in the
> version you are using productively.
>
> So coming back to Ivan's initial request, we would kindly ask you to
> just publish your changes in their current form against your current
> version (8u45 or whatsoever). We'll take a look at them an may invest
> some time and effort (also jointly with you if desired) to forward
> port them to 9 and propose them for integration into the head revision
> if that makes sense. Thus that sound reasonable to you?
>
> Thank you and best regards,
> Volker
>
>
> On Tue, Jun 2, 2015 at 5:00 PM, Jeremy Manson <jeremymanson at google.com
> <mailto:jeremymanson at google.com>> wrote:
>
> We'd much rather it be part of OpenJDK, because it is large and
> fairly complicated, so that would save us time and energy forward
> porting it every year or so. It's pretty large (for 8u45, it is a
> 2600 line change and touches 20 files), so it tends to be a
> lengthy and complicated forward port. We would much rather spend
> that time doing something more interesting.
>
> Just posting an updated patch whenever we need to update it would
> be a little annoying (although not impossible).
>
> Hiroshi Yamauchi tried to offer it to (I think it was) Jon
> Masamitsu a few years ago, and Jon didn't know anyone with the
> bandwidth to review it. (It was around the same time we
> contributed the parallel initial mark). I believe that was when
> CMS was unowned for a while. Perhaps there's a different story
> now? Oracle volunteers?
>
> (Procedural: One problem is that Hotspot reviews have to go
> through someone at Oracle. We had it written by an OpenJDK author
> and reviewed by a reviewer. We've been using it in production for
> years without too many headaches (although we have yet to
> inflict^Wlaunch 8u45, which has the latest updates, widely). I
> totally understand that Oracle folks are the ones who have to pay
> the price for a bad check-in, but it's a pretty big hurdle for us.)
>
> Jeremy
>
> On Tue, Jun 2, 2015 at 6:12 AM, Galkin, Ivan <ivan.galkin at sap.com
> <mailto:ivan.galkin at sap.com>> wrote:
>
> Hi,
>
> in the thread „JEP 248: Make G1 the Default Garbage Collector”
> [1] there is an email from Jeremy Manson, who mentions the
> enhancements made by Google to improve CMS.
>
> Especially the parallelizing of full compaction is a great
> improvement and we at SAP see the strong demand of it.
>
> @Jeremy: Are these changes published somewhere? May we have
> insight into the diffs you've made? We could collaborate in
> order to try to bring your changes into OpenJDK.
>
> Kind regards and thank you in advance,
>
> Ivan
>
> [1]
> http://mail.openjdk.java.net/pipermail/hotspot-dev/2015-June/018740.html
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/hotspot-gc-dev/attachments/20150603/85319609/attachment.htm>
More information about the hotspot-gc-dev
mailing list