TenuringThreshold being adaptive when UseAdaptiveSizePolicy is off
Jon Masamitsu
jon.masamitsu at oracle.com
Tue Mar 10 06:07:19 UTC 2015
On 3/9/2015 10:39 PM, Jungwoo Ha wrote:
> We were investigating some features and figured out that
> ParallelScavange and ParNew has different TenuringTreshold heuristics.
> We thought it would be nice to have a flag that can control the
> adaptiveness, so that we can fix it on purpose to isolate other
> performance factors.
Do you use UsePSAdaptiveSurvivorSizePolicy to turn off the
survivor space resizing and tenuring threshold adaptiveness
for ParallelGC?
Jon
> --Jungwoo
>
> On Mon, Mar 9, 2015 at 11:27 AM, Jon Masamitsu
> <jon.masamitsu at oracle.com <mailto:jon.masamitsu at oracle.com>> wrote:
>
> Jungwoo,
>
> On 03/06/2015 06:03 PM, Jungwoo Ha wrote:
>> I think it is the same for all JDK{7,8,9}.
>>
>> arguments.cpp disabled UseAdaptiveSizePolicy for CMS.
>> parallel scavange initializes _tenuring_threshold with
>> _tenuring_threshold = (UseAdaptiveSizePolicy) ?
>> InitialTenuringThreshold : MaxTenuringThreshold;
>> whereas CMS uses
>> _tenuring_threshold = MaxTenuringThreshold;
>>
>> adjust_desired_tenuring_threshold() is called inside
>> ParNewGeneration::collect(), which calls compute_tenuring_threshold.
>> It only uses MaxTenuringThreshold and TargetSurvivorRatio.
>> I don't see any other flags here.
>
> Yes, this is the intended behavior.
>
> You're saying we're sometimes wasting survivor space?
>
> Jon
>
>>
>> On Fri, Mar 6, 2015 at 4:28 PM, Jon Masamitsu
>> <jon.masamitsu at oracle.com <mailto:jon.masamitsu at oracle.com>> wrote:
>>
>> This is in jdk9?
>>
>> Jon
>>
>>
>> On 3/6/2015 4:21 PM, Jungwoo Ha wrote:
>>
>> On CMS when UseAdaptiveSizePolicy is off, still
>> tenuring_threshold is being changed.
>> Is this an intended behavior?
>> (yes. I know it is not "size" related heuristics)
>>
>> It would be nice to have a flag that can disable
>> adjusting tenuring threshold,
>> or at least set minimum threshold. When the default
>> heuristics doesn't work,
>> there are nothing much we can do other than changing the Max.
>>
>> --Jungwoo
>>
>>
>>
>
>
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