CRR (XXS): 7146246: G1: expose some of the -XX flags that drive which old regions to collect during mixed GCs

[Jesper Wilhelmsson]

OK, then I'm fine with the changes.
Ship it!
/Jesper

On 03/21/2012 05:56 PM, Tony Printezis wrote:
> Jesper,
>
> Inline.
>
> On 03/21/2012 12:25 PM, Jesper Wilhelmsson wrote:
>> Tony,
>>
>> You also changed the default value of G1OldCSetRegionLiveThresholdPercent
>> from 95% to 90%. Was this intentional?
>
> Actually, yes. And I forgot to document it. Thanks for pointing this out. In
> some of the logs that Charlie showed me there were a lot of regions with more
> than 90% live objects that we were considering for collection during mixed
> GCs. I thought I'd try to exclude them.
>
>> I interpret the explanation of G1HeapWastePercent as if it is 5% in total
>> over all regions. Is that correct?
>
> Yes.
>
>> I thought that was checked on a per region basis.
>
> G1OldCSetRegionLiveThresholdPercent is per-region (so basically, if a region
> has more live objects than that, it's not added to the CSet chooser at all).
>
> G1HeapWastePercent determines when we should stop mixed GCs, given that even
> if we do another one we won't get back that much.
>
> Tony
>
>>
>>
>> On 03/21/2012 04:13 PM, Tony Printezis wrote:
>>> Hi all,
>>>
>>> Can I have a couple of quick code review for this very small change?
>>>
>>> http://cr.openjdk.java.net/~tonyp/7146246/webrev.0/
>>>
>>> It turns the following two cmd line params into product params:
>>>
>>> G1HeapWastePercent (previously called: G1OldReclaimableThresholdPercent)
>>> G1MixedGCCountTarget (previous called: G1MaxMixedGCNum)
>>>
>>> These are helpful in allowing the user to fine-tune G1's behavior wrt which
>>> old regions to collect during mixed GCs, how many mixed GCs to do, etc.
>>>
>>> I also increased the default value of the former from 1% to 5%. Charlie ran
>>> some performance tests and found that the new default eliminated some very
>>> long mixed GCs that he was experiencing with the old default.
>>>
>>> Tony
>>>