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8379020: GenShen: Promote all objects when whitebox full GC is requested

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Reviewed-by: ysr, kdnilsen
This commit is contained in:
William Kemper 2026-03-25 00:23:41 +00:00
parent 4e79015768
commit e8ce930e28
2 changed files with 35 additions and 0 deletions
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28
src/hotspot/share/gc/shenandoah/shenandoahAgeCensus.hpp
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@ -97,6 +97,8 @@ struct ShenandoahNoiseStats {
// once the per-worker data is consolidated into the appropriate population vector
// per minor collection. The _local_age_table is thus C x N, for N GC workers.
class ShenandoahAgeCensus: public CHeapObj<mtGC> {
friend class ShenandoahTenuringOverride;
AgeTable** _global_age_tables; // Global age tables used for adapting tenuring threshold, one per snapshot
AgeTable** _local_age_tables; // Local scratch age tables to track object ages, one per worker
@ -148,6 +150,10 @@ class ShenandoahAgeCensus: public CHeapObj<mtGC> {
return _tenuring_threshold[prev];
}
// Override the tenuring threshold for the current epoch. This is used to
// cause everything to be promoted for a whitebox full gc request.
void set_tenuring_threshold(uint threshold) { _tenuring_threshold[_epoch] = threshold; }
#ifndef PRODUCT
// Return the sum of size of objects of all ages recorded in the
// census at snapshot indexed by snap.
@ -232,4 +238,26 @@ class ShenandoahAgeCensus: public CHeapObj<mtGC> {
void print();
};
// RAII object that temporarily overrides the tenuring threshold for the
// duration of a scope, restoring the original value on destruction.
// Used to force promotion of all young objects during whitebox full GCs.
class ShenandoahTenuringOverride : public StackObj {
ShenandoahAgeCensus* _census;
uint _saved_threshold;
bool _active;
public:
ShenandoahTenuringOverride(bool active, ShenandoahAgeCensus* census) :
_census(census), _saved_threshold(0), _active(active) {
if (_active) {
_saved_threshold = _census->tenuring_threshold();
_census->set_tenuring_threshold(0);
}
}
~ShenandoahTenuringOverride() {
if (_active) {
_census->set_tenuring_threshold(_saved_threshold);
}
}
};
#endif // SHARE_GC_SHENANDOAH_SHENANDOAHAGECENSUS_HPP

7
src/hotspot/share/gc/shenandoah/shenandoahGenerationalControlThread.cpp
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@ -24,6 +24,7 @@
*
*/
#include "gc/shenandoah/shenandoahAgeCensus.hpp"
#include "gc/shenandoah/shenandoahAsserts.hpp"
#include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
#include "gc/shenandoah/shenandoahConcurrentGC.hpp"
@ -271,6 +272,12 @@ void ShenandoahGenerationalControlThread::run_gc_cycle(const ShenandoahGCRequest
// Cannot uncommit bitmap slices during concurrent reset
ShenandoahNoUncommitMark forbid_region_uncommit(_heap);
// When a whitebox full GC is requested, set the tenuring threshold to zero
// so that all young objects are promoted to old. This ensures that tests
// using WB.fullGC() to promote objects to old gen will not loop forever.
ShenandoahTenuringOverride tenuring_override(request.cause == GCCause::_wb_full_gc,
_heap->age_census());
_heap->print_before_gc();
switch (gc_mode()) {
case concurrent_normal: {