8325673: GenShen: Share Reserves between Old and Young Collector #395
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Given that mixed evacuation will sometimes borrow up to this amount of memory from the young evacuation reserve for old evacuations, we reduce the default value to reduce the impact on normal young GC.
1. Always require that evacuation reserve quantities be established before rebuilding free set 2. Establish evacuation reserve quantities before initial rebuild of free set 3. Fix the calucation of old reserves during adjust generation sizes for next gc cycle
This reverts commit 7bb1d38.
When we round up, we introduce the risk that the new size exceeds the maximum LAB size, resulting in an assertion error.
This reverts commit 99cce53.
In the previous implementaiton, reserve quantities were only sometimes established.
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git fetch https://git.openjdk.org/shenandoah.git master
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# resolve conflicts and follow the instructions given by git merge
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1. Some debug instrumetnation which will eventually be removed 2. Disable assert_bounds for trashed OLD regions (until after they are recycled) 3. When a trashed old region is recycled, adjust the old empty interval immediately if assertions are enabled and the region is still in the OldCollector partition 4. When rebuild freeset transfers regions between OLD and YOUNG, log the transfer and clear the region balance so we do not redundantly adjust repeat the transfer 5. In compute_young_and_old_reserves(), adjust young_available by xfer_bytes if regions are being transferred between young and old generations
Limit the size of old-gen by memory available in the OldCollector set following find_regions_with_alloc_capacity() (rather than limiting the size of old-gen by the total capacity of the OldCollector set, which includes used memory).
Soft capacities are established, for example, by setting NewRatio or New size on the
JVM command line. GenShen, for now at least, does not honor these settings. Better
performance is obtained by allowing GenShen to expand and shrink generation sizes
according to application behavior.
This commit also tidies up various aspects of the implementation to make adjustments
to generation sizing more consistent:
1. ShenandoahGlobalHeuristics::choose_global_collection_set(): share the reserves
between young and old collection to maximize evacuation of garbage-first
regions, regardless of whether most garbage is found in old or young
2. ShenandoahConcurrentGC::entry_final_roots(): do not balance generations before
invoking finish_rebuild() because finish_rebuild will balance generations.
3. ShenandoahFreeSet::flip_to_old_gc(): invoke force_transfer_to_young() instead
of transfer_to_young() so we can override soft-capacity limits
4. ShenandoahFullGC::phase5_epilog(): Do not invoke compute_balances() or
balance_generations_after_rebuilding_free_set(). Allow the free-set
rebuild() implementation to do this work in a more consistent fashion.
5. ShenandoahGeneration::adjust_evacuation_budgets(): replace transfer_to_youn()
with force_transfer_to_young() to avoid enforcement of soft capacity limits.
6. ShenandoahGenerationSizer::force_transfer_to_young(): new method
7. ShenandoahGenerationalFullGC::balance_generations_after_gc(): establish
reserves() so that free-set rebuild() can adjust balance. Do not redundantly
force transfer of regions here.
8. ShenandoahGenerationalFullGC::balance_generations_after_rebuilding_free_set():
deprecate this method.
9. ShenandoahGenerationalFullGC::compute_balances(): deprecate this method.
10. ShenandoahGenerationaStatsClosure::validate_usage() (part of Shenandoah
Verification): add consistency check for generation capacities
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| void ShenandoahOldHeuristics::initialize_piggyback_evacs(ShenandoahCollectionSet* collection_set, |
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Can we continue using mixed instead of piggyback to describe collections that include young and old regions? I think mixed is an accepted term and piggyback feels a little bit too colloquial (also not sure if the phrase is commonly known outside of English).
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Good suggestion. Thanks. I'm replacing piggyback with mixed throughout (where piggyback means mixed evac). There are a few places where piggyback in Shenandoah where piggyback is used for other purposes and I'm leaving those as is.
src/hotspot/share/gc/shenandoah/heuristics/shenandoahOldHeuristics.cpp
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Left a few suggestions; would be great to take care of the re-order thing that confuses the github diffs. Not sure if restoring old order of those methods in shenandoahOldHeuritsics.cpp is possible/easy. See comments inline.
Flushing these for now, but will continue in that file and remaining ones in a subsequent session later today/tomorrow.
src/hotspot/share/gc/shenandoah/heuristics/shenandoahOldHeuristics.hpp
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src/hotspot/share/gc/shenandoah/heuristics/shenandoahOldHeuristics.hpp
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src/hotspot/share/gc/shenandoah/heuristics/shenandoahOldHeuristics.hpp
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src/hotspot/share/gc/shenandoah/heuristics/shenandoahOldHeuristics.cpp
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Most invocations do not need to resize generations between prepare_to_rebuild() and finish_rebuild(), so no need to make these two independent invocations.
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Allow young-gen Collector reserve to share memory with old-gen Collector reserve in order to support prompt processing of mixed evacuations, as constrained by ShenandoahOldEvacRatioPercent.
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