G1GC, Java8u40ea, Metaspace questions

[Wolfgang Pedot]

Hi,

the last log was with a MaxMetaspaceFreeRatio of 10% and that was quite 
well behaved. The log I have sent before (starting 
2015-02-13T20:04:43.512+0100) shows a slow but continuous increase of 
the "commited" value for Metaspace even though "used" after a collect is 
quite stable and "commited" is shrunk after every collect. Once a 
configured MaxMetaspaceSize is reached the FullGCs start. I do have a 
log showing that but that is with smaller sizes (Metaspace=300MB, 
MaxMetaspace=305MB, MinMetaspaceFreeRatio=0) so I dont know if it will 
be a good case. I have found out that I need to set Min and 
MaxMetaspaceFreeRatio really really low (like <=10%) to keep the 
high-water-mark in check and I dont quite see why in the numbers.

I can send you the 300/305MB log if it helps, otherwise do you want me 
to run another test with specific configuration-values?

Wolfgang


Am 17.02.2015 20:22, schrieb Yu Zhang:
> Jon,
>
> Here is the version:
> Java HotSpot(TM) 64-Bit Server VM (25.40-b25) for windows-amd64 JRE 
> (1.8.0_40-ea-b23), built on Jan 27 2015 19:35:49 by "java_re" with MS 
> VC++ 10.0 (VS2010)
>
> Wolfang,
> Thanks for the logs.  But the one you sent me seems pretty well 
> behaved.  There is no full gc.  The interval between initial-marking 
> for metesapce is not getting longer.  Do you have a log that you saw 
> the high-warter mark is getting higher, so the concurrent marking is 
> less frequent, then there is a full gc?
> Thanks,
> Jenny
> On 2/13/2015 11:46 AM, Jon Masamitsu wrote:
>>
>> On 2/13/2015 10:25 AM, Wolfgang Pedot wrote:
>>> Thanks for your reply,
>>>
>>> I was under the impression that the MetaspaceSize is only used as a 
>>> starting value for the high-water mark and 
>> That's correct.
>>
>>> adjusting it will only change the behaviour at startup. Correct me 
>>> if I am wrong but after the first collect ergonomics 
>>
>> If "at startup" includes the  first time the metaspace reaches 
>> MetaspaceSize, yes that is also correct.
>>
>>> would take over and adjust that mark according to 
>>> Min/MaxMetaspaceFreeRatio, right? My problem is that I have to 
>> Right.
>>
>>> deal with lots of short lived generated classes and it would be a 
>>> step back to have the garbage-collector set a low mark right before 
>>> a class-generation spike and then do a Full-GC before raising it 
>>> again (Full-GC currently takes ~10sec on the real system). Although 
>>> with MaxMetaSpaceFreeRation being 70% by default that would probably 
>>> not happen that often.
>>>
>>> As for my first question, it is still not clear to me why Metaspace 
>>> "capacity" never seemed to reach "commited" during my first tests. I 
>>> have checked the logs for the current instance and with the higher 
>>> maximum-setting "capacity" and "commited" actually can get quite 
>>> close now but both are nowhere near the allowed maximum even after I 
>>> have driven the JVM into multiple FullGCs by creating classes like 
>>> crazy. Can I assume that RAM that is not 
>>
>>