TenuringThreshold being adaptive when UseAdaptiveSizePolicy is off

Jungwoo Ha jwha at google.com
Tue Mar 10 05:39:58 UTC 2015


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.
--Jungwoo

On Mon, Mar 9, 2015 at 11:27 AM, Jon Masamitsu <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>
> 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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