-XX:-CMSClassUnloadingEnabled

Jon Masamitsu jon.masamitsu at oracle.com
Fri Mar 11 17:29:23 UTC 2016



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.

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 
>> <tprintezis at twitter.com <mailto: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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