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8027959: Early reclamation of large objects in G1

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Try to reclaim humongous objects at every young collection after doing a conservative estimate of its liveness.

Reviewed-by: brutisso, mgerdin
This commit is contained in:
Thomas Schatzl 2014-07-23 09:03:32 +02:00
parent bc56e061ec
commit f161bd6d16
12 changed files with 537 additions and 32 deletions
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235
hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
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@ -1926,6 +1926,8 @@ G1CollectedHeap::G1CollectedHeap(G1CollectorPolicy* policy_) :
_secondary_free_list("Secondary Free List", new SecondaryFreeRegionListMtSafeChecker()),
_old_set("Old Set", false /* humongous */, new OldRegionSetMtSafeChecker()),
_humongous_set("Master Humongous Set", true /* humongous */, new HumongousRegionSetMtSafeChecker()),
_humongous_is_live(),
_has_humongous_reclaim_candidates(false),
_free_regions_coming(false),
_young_list(new YoungList(this)),
_gc_time_stamp(0),
@ -2082,6 +2084,7 @@ jint G1CollectedHeap::initialize() {
_g1h = this;
_in_cset_fast_test.initialize(_g1_reserved.start(), _g1_reserved.end(), HeapRegion::GrainBytes);
_humongous_is_live.initialize(_g1_reserved.start(), _g1_reserved.end(), HeapRegion::GrainBytes);
// Create the ConcurrentMark data structure and thread.
// (Must do this late, so that "max_regions" is defined.)
@ -2177,6 +2180,11 @@ void G1CollectedHeap::stop() {
}
}
void G1CollectedHeap::clear_humongous_is_live_table() {
guarantee(G1ReclaimDeadHumongousObjectsAtYoungGC, "Should only be called if true");
_humongous_is_live.clear();
}
size_t G1CollectedHeap::conservative_max_heap_alignment() {
return HeapRegion::max_region_size();
}
@ -3771,6 +3779,61 @@ size_t G1CollectedHeap::cards_scanned() {
return g1_rem_set()->cardsScanned();
}
bool G1CollectedHeap::humongous_region_is_always_live(uint index) {
HeapRegion* region = region_at(index);
assert(region->startsHumongous(), "Must start a humongous object");
return oop(region->bottom())->is_objArray() || !region->rem_set()->is_empty();
}
class RegisterHumongousWithInCSetFastTestClosure : public HeapRegionClosure {
private:
size_t _total_humongous;
size_t _candidate_humongous;
public:
RegisterHumongousWithInCSetFastTestClosure() : _total_humongous(0), _candidate_humongous(0) {
}
virtual bool doHeapRegion(HeapRegion* r) {
if (!r->startsHumongous()) {
return false;
}
G1CollectedHeap* g1h = G1CollectedHeap::heap();
uint region_idx = r->hrs_index();
bool is_candidate = !g1h->humongous_region_is_always_live(region_idx);
// Is_candidate already filters out humongous regions with some remembered set.
// This will not lead to humongous object that we mistakenly keep alive because
// during young collection the remembered sets will only be added to.
if (is_candidate) {
g1h->register_humongous_region_with_in_cset_fast_test(region_idx);
_candidate_humongous++;
}
_total_humongous++;
return false;
}
size_t total_humongous() const { return _total_humongous; }
size_t candidate_humongous() const { return _candidate_humongous; }
};
void G1CollectedHeap::register_humongous_regions_with_in_cset_fast_test() {
if (!G1ReclaimDeadHumongousObjectsAtYoungGC) {
g1_policy()->phase_times()->record_fast_reclaim_humongous_stats(0, 0);
return;
}
RegisterHumongousWithInCSetFastTestClosure cl;
heap_region_iterate(&cl);
g1_policy()->phase_times()->record_fast_reclaim_humongous_stats(cl.total_humongous(),
cl.candidate_humongous());
_has_humongous_reclaim_candidates = cl.candidate_humongous() > 0;
if (_has_humongous_reclaim_candidates) {
clear_humongous_is_live_table();
}
}
void
G1CollectedHeap::setup_surviving_young_words() {
assert(_surviving_young_words == NULL, "pre-condition");
@ -4058,6 +4121,8 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
g1_policy()->finalize_cset(target_pause_time_ms, evacuation_info);
register_humongous_regions_with_in_cset_fast_test();
_cm->note_start_of_gc();
// We should not verify the per-thread SATB buffers given that
// we have not filtered them yet (we'll do so during the
@ -4108,6 +4173,9 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
true /* verify_fingers */);
free_collection_set(g1_policy()->collection_set(), evacuation_info);
eagerly_reclaim_humongous_regions();
g1_policy()->clear_collection_set();
cleanup_surviving_young_words();
@ -4608,7 +4676,9 @@ void G1ParCopyClosure<barrier, do_mark_object>::do_oop_work(T* p) {
assert(_worker_id == _par_scan_state->queue_num(), "sanity");
if (_g1->in_cset_fast_test(obj)) {
G1CollectedHeap::in_cset_state_t state = _g1->in_cset_state(obj);
if (state == G1CollectedHeap::InCSet) {
oop forwardee;
if (obj->is_forwarded()) {
forwardee = obj->forwardee();
@ -4627,6 +4697,9 @@ void G1ParCopyClosure<barrier, do_mark_object>::do_oop_work(T* p) {
do_klass_barrier(p, forwardee);
}
} else {
if (state == G1CollectedHeap::IsHumongous) {
_g1->set_humongous_is_live(obj);
}
// The object is not in collection set. If we're a root scanning
// closure during an initial mark pause then attempt to mark the object.
if (do_mark_object == G1MarkFromRoot) {
@ -5450,12 +5523,21 @@ class G1KeepAliveClosure: public OopClosure {
public:
G1KeepAliveClosure(G1CollectedHeap* g1) : _g1(g1) {}
void do_oop(narrowOop* p) { guarantee(false, "Not needed"); }
void do_oop( oop* p) {
void do_oop(oop* p) {
oop obj = *p;
if (_g1->obj_in_cs(obj)) {
G1CollectedHeap::in_cset_state_t cset_state = _g1->in_cset_state(obj);
if (obj == NULL || cset_state == G1CollectedHeap::InNeither) {
return;
}
if (cset_state == G1CollectedHeap::InCSet) {
assert( obj->is_forwarded(), "invariant" );
*p = obj->forwardee();
} else {
assert(!obj->is_forwarded(), "invariant" );
assert(cset_state == G1CollectedHeap::IsHumongous,
err_msg("Only allowed InCSet state is IsHumongous, but is %d", cset_state));
_g1->set_humongous_is_live(obj);
}
}
};
@ -5485,7 +5567,7 @@ public:
template <class T> void do_oop_work(T* p) {
oop obj = oopDesc::load_decode_heap_oop(p);
if (_g1h->obj_in_cs(obj)) {
if (_g1h->is_in_cset_or_humongous(obj)) {
// If the referent object has been forwarded (either copied
// to a new location or to itself in the event of an
// evacuation failure) then we need to update the reference
@ -5510,10 +5592,10 @@ public:
assert(!Metaspace::contains((const void*)p),
err_msg("Unexpectedly found a pointer from metadata: "
PTR_FORMAT, p));
_copy_non_heap_obj_cl->do_oop(p);
}
_copy_non_heap_obj_cl->do_oop(p);
}
}
}
};
// Serial drain queue closure. Called as the 'complete_gc'
@ -6435,6 +6517,147 @@ void G1CollectedHeap::free_collection_set(HeapRegion* cs_head, EvacuationInfo& e
policy->phase_times()->record_non_young_free_cset_time_ms(non_young_time_ms);
}
class G1FreeHumongousRegionClosure : public HeapRegionClosure {
private:
FreeRegionList* _free_region_list;
HeapRegionSet* _proxy_set;
HeapRegionSetCount _humongous_regions_removed;
size_t _freed_bytes;
public:
G1FreeHumongousRegionClosure(FreeRegionList* free_region_list) :
_free_region_list(free_region_list), _humongous_regions_removed(), _freed_bytes(0) {
}
virtual bool doHeapRegion(HeapRegion* r) {
if (!r->startsHumongous()) {
return false;
}
G1CollectedHeap* g1h = G1CollectedHeap::heap();
// The following checks whether the humongous object is live are sufficient.
// The main additional check (in addition to having a reference from the roots
// or the young gen) is whether the humongous object has a remembered set entry.
//
// A humongous object cannot be live if there is no remembered set for it
// because:
// - there can be no references from within humongous starts regions referencing
// the object because we never allocate other objects into them.
// (I.e. there are no intra-region references that may be missed by the
// remembered set)
// - as soon there is a remembered set entry to the humongous starts region
// (i.e. it has "escaped" to an old object) this remembered set entry will stay
// until the end of a concurrent mark.
//
// It is not required to check whether the object has been found dead by marking
// or not, in fact it would prevent reclamation within a concurrent cycle, as
// all objects allocated during that time are considered live.
// SATB marking is even more conservative than the remembered set.
// So if at this point in the collection there is no remembered set entry,
// nobody has a reference to it.
// At the start of collection we flush all refinement logs, and remembered sets
// are completely up-to-date wrt to references to the humongous object.
//
// Other implementation considerations:
// - never consider object arrays: while they are a valid target, they have not
// been observed to be used as temporary objects.
// - they would also pose considerable effort for cleaning up the the remembered
// sets.
// While this cleanup is not strictly necessary to be done (or done instantly),
// given that their occurrence is very low, this saves us this additional
// complexity.
uint region_idx = r->hrs_index();
if (g1h->humongous_is_live(region_idx) ||
g1h->humongous_region_is_always_live(region_idx)) {
if (G1TraceReclaimDeadHumongousObjectsAtYoungGC) {
gclog_or_tty->print_cr("Live humongous %d region %d with remset "SIZE_FORMAT" code roots "SIZE_FORMAT" is dead-bitmap %d live-other %d obj array %d",
r->isHumongous(),
region_idx,
r->rem_set()->occupied(),
r->rem_set()->strong_code_roots_list_length(),
g1h->mark_in_progress() && !g1h->g1_policy()->during_initial_mark_pause(),
g1h->humongous_is_live(region_idx),
oop(r->bottom())->is_objArray()
);
}
return false;
}
guarantee(!((oop)(r->bottom()))->is_objArray(),
err_msg("Eagerly reclaiming object arrays is not supported, but the object "PTR_FORMAT" is.",
r->bottom()));
if (G1TraceReclaimDeadHumongousObjectsAtYoungGC) {
gclog_or_tty->print_cr("Reclaim humongous region %d start "PTR_FORMAT" region %d length "UINT32_FORMAT" with remset "SIZE_FORMAT" code roots "SIZE_FORMAT" is dead-bitmap %d live-other %d obj array %d",
r->isHumongous(),
r->bottom(),
region_idx,
r->region_num(),
r->rem_set()->occupied(),
r->rem_set()->strong_code_roots_list_length(),
g1h->mark_in_progress() && !g1h->g1_policy()->during_initial_mark_pause(),
g1h->humongous_is_live(region_idx),
oop(r->bottom())->is_objArray()
);
}
_freed_bytes += r->used();
r->set_containing_set(NULL);
_humongous_regions_removed.increment(1u, r->capacity());
g1h->free_humongous_region(r, _free_region_list, false);
return false;
}
HeapRegionSetCount& humongous_free_count() {
return _humongous_regions_removed;
}
size_t bytes_freed() const {
return _freed_bytes;
}
size_t humongous_reclaimed() const {
return _humongous_regions_removed.length();
}
};
void G1CollectedHeap::eagerly_reclaim_humongous_regions() {
assert_at_safepoint(true);
if (!G1ReclaimDeadHumongousObjectsAtYoungGC || !_has_humongous_reclaim_candidates) {
g1_policy()->phase_times()->record_fast_reclaim_humongous_time_ms(0.0, 0);
return;
}
double start_time = os::elapsedTime();
FreeRegionList local_cleanup_list("Local Humongous Cleanup List");
G1FreeHumongousRegionClosure cl(&local_cleanup_list);
heap_region_iterate(&cl);
HeapRegionSetCount empty_set;
remove_from_old_sets(empty_set, cl.humongous_free_count());
G1HRPrinter* hr_printer = _g1h->hr_printer();
if (hr_printer->is_active()) {
FreeRegionListIterator iter(&local_cleanup_list);
while (iter.more_available()) {
HeapRegion* hr = iter.get_next();
hr_printer->cleanup(hr);
}
}
prepend_to_freelist(&local_cleanup_list);
decrement_summary_bytes(cl.bytes_freed());
g1_policy()->phase_times()->record_fast_reclaim_humongous_time_ms((os::elapsedTime() - start_time) * 1000.0,
cl.humongous_reclaimed());
}
// This routine is similar to the above but does not record
// any policy statistics or update free lists; we are abandoning
// the current incremental collection set in preparation of a