RFR(S): 8007036: G1: Too many old regions added to last mixed GC

Vitaly Davidovich vitalyd at gmail.com
Wed Jan 30 14:19:03 UTC 2013


Hi John,

This nicely addresses my comments - thanks.

Vitaly

Sent from my phone
On Jan 29, 2013 4:36 PM, "John Cuthbertson" <john.cuthbertson at oracle.com>
wrote:

> Hi Everyone,
>
> Here's a new webrev based upon feedback from Vitaly:
> http://cr.openjdk.java.net/~**johnc/8007036/webrev.1/<http://cr.openjdk.java.net/~johnc/8007036/webrev.1/>
>
> JohnC
>
>
> On 1/28/2013 1:59 PM, John Cuthbertson wrote:
>
>> Hi Everyone,
>>
>> Can I have a couple of volunteers look over the changes for this CR? The
>> webrev is at: http://cr.openjdk.java.net/~**johnc/8007036/webrev.0/<http://cr.openjdk.java.net/~johnc/8007036/webrev.0/>
>>
>> Summary:
>> When adding old regions to the collection set we don't take into account
>> whether the old regions added so far take us below the G1HeapWastePercent.
>> As a result we could end up adding (and collecting) many more regions than
>> we needed to. The actual number added was the minimum between the number of
>> candidate regions / G1MixedGCCountTarget and 10% of the heap.
>>
>> Currently the calculation of the reclaimable bytes as a percentage of the
>> uses exact arithmetic. It might make sense, at some point in the future, to
>> use inexact arithmetic (rounding) in the decision on whether to continue
>> mixed GCs and use exact arithmetic when adding regions.
>>
>> As part of this change I've also moved a couple routines from
>> CollectionSetChooser to G1CollectorPolicy. I think they "fit" better in
>> G1CollectorPolicy.
>>
>> Testing:
>> GCOld with tenuring threshold = 1 and a marking threshold = 10.
>>
>> Many thanks to Monica for identifying the issue.
>>
>> Thanks,
>>
>> JohnC
>>
>
>
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