-XX:-CMSClassUnloadingEnabled (original) (raw)
Mikael Gerdin mikael.gerdin at oracle.com
Fri Mar 11 18:32:34 UTC 2016
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On 2016-03-11 18:29, Jon Masamitsu wrote:
On 3/11/2016 8:12 AM, Tony Printezis wrote: Thanks for the heads up Jungwoo. I think it should be straightforward to decide whether to unload classes for a particular CMS cycle based on the rate at which the meatspace occupancy is growing. Has anyone considered / looked into this? No one has looked at this to my knowledge.
Another, perhaps simpler, alternative would be to enable class unloading for a single CMS cycle at if (MetaspaceGC::should_concurrent_collect()) { log_trace(gc)("CMSCollector: collect for metadata allocation "); return true; }
This would cause metaspace allocation triggered CMS cycles to unload classes at least.
/Mikael
Jon
Tony On March 10, 2016 at 7:07:00 PM, Jungwoo Ha (jwha at google.com <mailto:jwha at google.com>) wrote: We've been disabled CMSClassUnloading for a long time and had no issues. We recently turned it back on by default with CMSClassUnloadingMaxInterval=5, which amortizes the increased remark cost.
On Thu, Mar 10, 2016 at 1:32 PM, Tony Printezis <<mailto:tprintezis at twitter.com>tprintezis at twitter.com> wrote: Hi all, CMSClassUnloadingEnabled is enabled by default in JDK 8. Most of our services do not require class unloading (they load a bunch of classes up-front and that’s it) so we’re thinking of turning it off by default in our JDK as it increases our remark times by a non-trivial amount (40-90ms depending on the service). Any known issues with running with -XX:-CMSClassUnloadingEnabled? (This is a veiled way to ask: is anyone testing with that flag off?) Thanks, Tony ----- Tony Printezis | JVM/GC Engineer / VM Team | Twitter @TonyPrintezis tprintezis at twitter.com <mailto:tprintezis at twitter.com>
-- Jungwoo Ha | Java Platform Team | jwha at google.com <mailto:jwha at google.com> ----- Tony Printezis | JVM/GC Engineer / VM Team | Twitter @TonyPrintezis tprintezis at twitter.com <mailto:tprintezis at twitter.com>
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