OpenJDK / amber / amber
changeset 34134:d4fd14f628fb
8138684: G1 decision about taking regions into the collection set is too aggressive
Summary: Factor in expected waste and uncertainty of our guess in the decision whether to take another region into the collection set.
Reviewed-by: mgerdin, jmasa
| author | tschatzl |
|---|---|
| date | Fri, 13 Nov 2015 09:12:06 +0100 |
| parents | 5d761539ac2c |
| children | 317af749634b 7e08409e5935 |
| files | hotspot/src/share/vm/gc/g1/g1CollectorPolicy.cpp |
| diffstat | 1 files changed, 13 insertions(+), 2 deletions(-) [+] |
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--- a/hotspot/src/share/vm/gc/g1/g1CollectorPolicy.cpp Tue Nov 03 13:03:04 2015 -0800 +++ b/hotspot/src/share/vm/gc/g1/g1CollectorPolicy.cpp Fri Nov 13 09:12:06 2015 +0100 @@ -467,8 +467,19 @@ } size_t free_bytes = (base_free_regions - young_length) * HeapRegion::GrainBytes; - if ((2.0 /* magic */ * _predictor.sigma()) * bytes_to_copy > free_bytes) { - // end condition 3: out-of-space (conservatively!) + + // When copying, we will likely need more bytes free than is live in the region. + // Add some safety margin to factor in the confidence of our guess, and the + // natural expected waste. + // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty + // of the calculation: the lower the confidence, the more headroom. + // (100 + TargetPLABWastePct) represents the increase in expected bytes during + // copying due to anticipated waste in the PLABs. + double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0; + size_t expected_bytes_to_copy = safety_factor * bytes_to_copy; + + if (expected_bytes_to_copy > free_bytes) { + // end condition 3: out-of-space return false; }