/*
* Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#include "precompiled.hpp"
#include "gc/g1/dirtyCardQueue.hpp"
#include "gc/g1/g1BlockOffsetTable.inline.hpp"
#include "gc/g1/g1CollectedHeap.inline.hpp"
#include "gc/g1/g1ConcurrentRefine.hpp"
#include "gc/g1/g1FromCardCache.hpp"
#include "gc/g1/g1GCPhaseTimes.hpp"
#include "gc/g1/g1HotCardCache.hpp"
#include "gc/g1/g1OopClosures.inline.hpp"
#include "gc/g1/g1RemSet.hpp"
#include "gc/g1/g1SATBCardTableModRefBS.inline.hpp"
#include "gc/g1/heapRegion.inline.hpp"
#include "gc/g1/heapRegionManager.inline.hpp"
#include "gc/g1/heapRegionRemSet.hpp"
#include "gc/shared/gcTraceTime.inline.hpp"
#include "gc/shared/suspendibleThreadSet.hpp"
#include "memory/iterator.hpp"
#include "memory/resourceArea.hpp"
#include "oops/oop.inline.hpp"
#include "utilities/align.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/intHisto.hpp"
#include "utilities/stack.inline.hpp"
// Collects information about the overall remembered set scan progress during an evacuation.
class G1RemSetScanState : public CHeapObj<mtGC> {
private:
class G1ClearCardTableTask : public AbstractGangTask {
G1CollectedHeap* _g1h;
uint* _dirty_region_list;
size_t _num_dirty_regions;
size_t _chunk_length;
size_t volatile _cur_dirty_regions;
public:
G1ClearCardTableTask(G1CollectedHeap* g1h,
uint* dirty_region_list,
size_t num_dirty_regions,
size_t chunk_length) :
AbstractGangTask("G1 Clear Card Table Task"),
_g1h(g1h),
_dirty_region_list(dirty_region_list),
_num_dirty_regions(num_dirty_regions),
_chunk_length(chunk_length),
_cur_dirty_regions(0) {
assert(chunk_length > 0, "must be");
}
static size_t chunk_size() { return M; }
void work(uint worker_id) {
G1SATBCardTableModRefBS* ct_bs = _g1h->g1_barrier_set();
while (_cur_dirty_regions < _num_dirty_regions) {
size_t next = Atomic::add(_chunk_length, &_cur_dirty_regions) - _chunk_length;
size_t max = MIN2(next + _chunk_length, _num_dirty_regions);
for (size_t i = next; i < max; i++) {
HeapRegion* r = _g1h->region_at(_dirty_region_list[i]);
if (!r->is_survivor()) {
ct_bs->clear(MemRegion(r->bottom(), r->end()));
}
}
}
}
};
size_t _max_regions;
// Scan progress for the remembered set of a single region. Transitions from
// Unclaimed -> Claimed -> Complete.
// At each of the transitions the thread that does the transition needs to perform
// some special action once. This is the reason for the extra "Claimed" state.
typedef jint G1RemsetIterState;
static const G1RemsetIterState Unclaimed = 0; // The remembered set has not been scanned yet.
static const G1RemsetIterState Claimed = 1; // The remembered set is currently being scanned.
static const G1RemsetIterState Complete = 2; // The remembered set has been completely scanned.
G1RemsetIterState volatile* _iter_states;
// The current location where the next thread should continue scanning in a region's
// remembered set.
size_t volatile* _iter_claims;
// Temporary buffer holding the regions we used to store remembered set scan duplicate
// information. These are also called "dirty". Valid entries are from [0.._cur_dirty_region)
uint* _dirty_region_buffer;
typedef jbyte IsDirtyRegionState;
static const IsDirtyRegionState Clean = 0;
static const IsDirtyRegionState Dirty = 1;
// Holds a flag for every region whether it is in the _dirty_region_buffer already
// to avoid duplicates. Uses jbyte since there are no atomic instructions for bools.
IsDirtyRegionState* _in_dirty_region_buffer;
size_t _cur_dirty_region;
// Creates a snapshot of the current _top values at the start of collection to
// filter out card marks that we do not want to scan.
class G1ResetScanTopClosure : public HeapRegionClosure {
private:
HeapWord** _scan_top;
public:
G1ResetScanTopClosure(HeapWord** scan_top) : _scan_top(scan_top) { }
virtual bool do_heap_region(HeapRegion* r) {
uint hrm_index = r->hrm_index();
if (!r->in_collection_set() && r->is_old_or_humongous()) {
_scan_top[hrm_index] = r->top();
} else {
_scan_top[hrm_index] = r->bottom();
}
return false;
}
};
// For each region, contains the maximum top() value to be used during this garbage
// collection. Subsumes common checks like filtering out everything but old and
// humongous regions outside the collection set.
// This is valid because we are not interested in scanning stray remembered set
// entries from free or archive regions.
HeapWord** _scan_top;
public:
G1RemSetScanState() :
_max_regions(0),
_iter_states(NULL),
_iter_claims(NULL),
_dirty_region_buffer(NULL),
_in_dirty_region_buffer(NULL),
_cur_dirty_region(0),
_scan_top(NULL) {
}
~G1RemSetScanState() {
if (_iter_states != NULL) {
FREE_C_HEAP_ARRAY(G1RemsetIterState, _iter_states);
}
if (_iter_claims != NULL) {
FREE_C_HEAP_ARRAY(size_t, _iter_claims);
}
if (_dirty_region_buffer != NULL) {
FREE_C_HEAP_ARRAY(uint, _dirty_region_buffer);
}
if (_in_dirty_region_buffer != NULL) {
FREE_C_HEAP_ARRAY(IsDirtyRegionState, _in_dirty_region_buffer);
}
if (_scan_top != NULL) {
FREE_C_HEAP_ARRAY(HeapWord*, _scan_top);
}
}
void initialize(uint max_regions) {
assert(_iter_states == NULL, "Must not be initialized twice");
assert(_iter_claims == NULL, "Must not be initialized twice");
_max_regions = max_regions;
_iter_states = NEW_C_HEAP_ARRAY(G1RemsetIterState, max_regions, mtGC);
_iter_claims = NEW_C_HEAP_ARRAY(size_t, max_regions, mtGC);
_dirty_region_buffer = NEW_C_HEAP_ARRAY(uint, max_regions, mtGC);
_in_dirty_region_buffer = NEW_C_HEAP_ARRAY(IsDirtyRegionState, max_regions, mtGC);
_scan_top = NEW_C_HEAP_ARRAY(HeapWord*, max_regions, mtGC);
}
void reset() {
for (uint i = 0; i < _max_regions; i++) {
_iter_states[i] = Unclaimed;
}
G1ResetScanTopClosure cl(_scan_top);
G1CollectedHeap::heap()->heap_region_iterate(&cl);
memset((void*)_iter_claims, 0, _max_regions * sizeof(size_t));
memset(_in_dirty_region_buffer, Clean, _max_regions * sizeof(IsDirtyRegionState));
_cur_dirty_region = 0;
}
// Attempt to claim the remembered set of the region for iteration. Returns true
// if this call caused the transition from Unclaimed to Claimed.
inline bool claim_iter(uint region) {
assert(region < _max_regions, "Tried to access invalid region %u", region);
if (_iter_states[region] != Unclaimed) {
return false;
}
G1RemsetIterState res = Atomic::cmpxchg(Claimed, &_iter_states[region], Unclaimed);
return (res == Unclaimed);
}
// Try to atomically sets the iteration state to "complete". Returns true for the
// thread that caused the transition.
inline bool set_iter_complete(uint region) {
if (iter_is_complete(region)) {
return false;
}
G1RemsetIterState res = Atomic::cmpxchg(Complete, &_iter_states[region], Claimed);
return (res == Claimed);
}
// Returns true if the region's iteration is complete.
inline bool iter_is_complete(uint region) const {
assert(region < _max_regions, "Tried to access invalid region %u", region);
return _iter_states[region] == Complete;
}
// The current position within the remembered set of the given region.
inline size_t iter_claimed(uint region) const {
assert(region < _max_regions, "Tried to access invalid region %u", region);
return _iter_claims[region];
}
// Claim the next block of cards within the remembered set of the region with
// step size.
inline size_t iter_claimed_next(uint region, size_t step) {
return Atomic::add(step, &_iter_claims[region]) - step;
}
void add_dirty_region(uint region) {
if (_in_dirty_region_buffer[region] == Dirty) {
return;
}
bool marked_as_dirty = Atomic::cmpxchg(Dirty, &_in_dirty_region_buffer[region], Clean) == Clean;
if (marked_as_dirty) {
size_t allocated = Atomic::add(1u, &_cur_dirty_region) - 1;
_dirty_region_buffer[allocated] = region;
}
}
HeapWord* scan_top(uint region_idx) const {
return _scan_top[region_idx];
}
// Clear the card table of "dirty" regions.
void clear_card_table(WorkGang* workers) {
if (_cur_dirty_region == 0) {
return;
}
size_t const num_chunks = align_up(_cur_dirty_region * HeapRegion::CardsPerRegion, G1ClearCardTableTask::chunk_size()) / G1ClearCardTableTask::chunk_size();
uint const num_workers = (uint)MIN2(num_chunks, (size_t)workers->active_workers());
size_t const chunk_length = G1ClearCardTableTask::chunk_size() / HeapRegion::CardsPerRegion;
// Iterate over the dirty cards region list.
G1ClearCardTableTask cl(G1CollectedHeap::heap(), _dirty_region_buffer, _cur_dirty_region, chunk_length);
log_debug(gc, ergo)("Running %s using %u workers for " SIZE_FORMAT " "
"units of work for " SIZE_FORMAT " regions.",
cl.name(), num_workers, num_chunks, _cur_dirty_region);
workers->run_task(&cl, num_workers);
#ifndef PRODUCT
// Need to synchronize with concurrent cleanup since it needs to
// finish its card table clearing before we can verify.
G1CollectedHeap::heap()->wait_while_free_regions_coming();
G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup();
#endif
}
};
G1RemSet::G1RemSet(G1CollectedHeap* g1,
CardTableModRefBS* ct_bs,
G1HotCardCache* hot_card_cache) :
_g1(g1),
_scan_state(new G1RemSetScanState()),
_num_conc_refined_cards(0),
_ct_bs(ct_bs),
_g1p(_g1->g1_policy()),
_hot_card_cache(hot_card_cache),
_prev_period_summary() {
}
G1RemSet::~G1RemSet() {
if (_scan_state != NULL) {
delete _scan_state;
}
}
uint G1RemSet::num_par_rem_sets() {
return MAX2(DirtyCardQueueSet::num_par_ids() + G1ConcurrentRefine::max_num_threads(), ParallelGCThreads);
}
void G1RemSet::initialize(size_t capacity, uint max_regions) {
G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
_scan_state->initialize(max_regions);
{
GCTraceTime(Debug, gc, marking)("Initialize Card Live Data");
_card_live_data.initialize(capacity, max_regions);
}
if (G1PretouchAuxiliaryMemory) {
GCTraceTime(Debug, gc, marking)("Pre-Touch Card Live Data");
_card_live_data.pretouch();
}
}
G1ScanRSForRegionClosure::G1ScanRSForRegionClosure(G1RemSetScanState* scan_state,
G1ScanObjsDuringScanRSClosure* scan_obj_on_card,
CodeBlobClosure* code_root_cl,
uint worker_i) :
_scan_state(scan_state),
_scan_objs_on_card_cl(scan_obj_on_card),
_code_root_cl(code_root_cl),
_strong_code_root_scan_time_sec(0.0),
_cards_claimed(0),
_cards_scanned(0),
_cards_skipped(0),
_worker_i(worker_i) {
_g1h = G1CollectedHeap::heap();
_bot = _g1h->bot();
_ct_bs = _g1h->g1_barrier_set();
}
void G1ScanRSForRegionClosure::scan_card(MemRegion mr, uint region_idx_for_card) {
HeapRegion* const card_region = _g1h->region_at(region_idx_for_card);
_scan_objs_on_card_cl->set_region(card_region);
card_region->oops_on_card_seq_iterate_careful<true>(mr, _scan_objs_on_card_cl);
_cards_scanned++;
}
void G1ScanRSForRegionClosure::scan_strong_code_roots(HeapRegion* r) {
double scan_start = os::elapsedTime();
r->strong_code_roots_do(_code_root_cl);
_strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
}
void G1ScanRSForRegionClosure::claim_card(size_t card_index, const uint region_idx_for_card){
_ct_bs->set_card_claimed(card_index);
_scan_state->add_dirty_region(region_idx_for_card);
}
bool G1ScanRSForRegionClosure::do_heap_region(HeapRegion* r) {
assert(r->in_collection_set(), "should only be called on elements of CS.");
uint region_idx = r->hrm_index();
if (_scan_state->iter_is_complete(region_idx)) {
return false;
}
if (_scan_state->claim_iter(region_idx)) {
// If we ever free the collection set concurrently, we should also
// clear the card table concurrently therefore we won't need to
// add regions of the collection set to the dirty cards region.
_scan_state->add_dirty_region(region_idx);
}
// We claim cards in blocks so as to reduce the contention.
size_t const block_size = G1RSetScanBlockSize;
HeapRegionRemSetIterator iter(r->rem_set());
size_t card_index;
size_t claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
if (current_card >= claimed_card_block + block_size) {
claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
}
if (current_card < claimed_card_block) {
_cards_skipped++;
continue;
}
_cards_claimed++;
// If the card is dirty, then G1 will scan it during Update RS.
if (_ct_bs->is_card_claimed(card_index) || _ct_bs->is_card_dirty(card_index)) {
continue;
}
HeapWord* const card_start = _g1h->bot()->address_for_index(card_index);
uint const region_idx_for_card = _g1h->addr_to_region(card_start);
assert(_g1h->region_at(region_idx_for_card)->is_in_reserved(card_start),
"Card start " PTR_FORMAT " to scan outside of region %u", p2i(card_start), _g1h->region_at(region_idx_for_card)->hrm_index());
HeapWord* const top = _scan_state->scan_top(region_idx_for_card);
if (card_start >= top) {
continue;
}
// We claim lazily (so races are possible but they're benign), which reduces the
// number of duplicate scans (the rsets of the regions in the cset can intersect).
// Claim the card after checking bounds above: the remembered set may contain
// random cards into current survivor, and we would then have an incorrectly
// claimed card in survivor space. Card table clear does not reset the card table
// of survivor space regions.
claim_card(card_index, region_idx_for_card);
MemRegion const mr(card_start, MIN2(card_start + BOTConstants::N_words, top));
scan_card(mr, region_idx_for_card);
}
if (_scan_state->set_iter_complete(region_idx)) {
// Scan the strong code root list attached to the current region
scan_strong_code_roots(r);
}
return false;
}
void G1RemSet::scan_rem_set(G1ParScanThreadState* pss,
CodeBlobClosure* heap_region_codeblobs,
uint worker_i) {
double rs_time_start = os::elapsedTime();
G1ScanObjsDuringScanRSClosure scan_cl(_g1, pss);
G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, heap_region_codeblobs, worker_i);
_g1->collection_set_iterate_from(&cl, worker_i);
double scan_rs_time_sec = (os::elapsedTime() - rs_time_start) -
cl.strong_code_root_scan_time_sec();
G1GCPhaseTimes* p = _g1p->phase_times();
p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, scan_rs_time_sec);
p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScanRSScannedCards);
p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ScanRSClaimedCards);
p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::ScanRSSkippedCards);
p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, cl.strong_code_root_scan_time_sec());
}
// Closure used for updating rem sets. Only called during an evacuation pause.
class G1RefineCardClosure: public CardTableEntryClosure {
G1RemSet* _g1rs;
G1ScanObjsDuringUpdateRSClosure* _update_rs_cl;
size_t _cards_scanned;
size_t _cards_skipped;
public:
G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) :
_g1rs(g1h->g1_rem_set()), _update_rs_cl(update_rs_cl), _cards_scanned(0), _cards_skipped(0)
{}
bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
// The only time we care about recording cards that
// contain references that point into the collection set
// is during RSet updating within an evacuation pause.
// In this case worker_i should be the id of a GC worker thread.
assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
bool card_scanned = _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl);
if (card_scanned) {
_cards_scanned++;
} else {
_cards_skipped++;
}
return true;
}
size_t cards_scanned() const { return _cards_scanned; }
size_t cards_skipped() const { return _cards_skipped; }
};
void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) {
G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1, pss, worker_i);
G1RefineCardClosure refine_card_cl(_g1, &update_rs_cl);
G1GCParPhaseTimesTracker x(_g1p->phase_times(), G1GCPhaseTimes::UpdateRS, worker_i);
if (G1HotCardCache::default_use_cache()) {
// Apply the closure to the entries of the hot card cache.
G1GCParPhaseTimesTracker y(_g1p->phase_times(), G1GCPhaseTimes::ScanHCC, worker_i);
_g1->iterate_hcc_closure(&refine_card_cl, worker_i);
}
// Apply the closure to all remaining log entries.
_g1->iterate_dirty_card_closure(&refine_card_cl, worker_i);
G1GCPhaseTimes* p = _g1p->phase_times();
p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_scanned(), G1GCPhaseTimes::UpdateRSScannedCards);
p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_skipped(), G1GCPhaseTimes::UpdateRSSkippedCards);
}
void G1RemSet::cleanupHRRS() {
HeapRegionRemSet::cleanup();
}
void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss,
CodeBlobClosure* heap_region_codeblobs,
uint worker_i) {
update_rem_set(pss, worker_i);
scan_rem_set(pss, heap_region_codeblobs, worker_i);;
}
void G1RemSet::prepare_for_oops_into_collection_set_do() {
DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
dcqs.concatenate_logs();
_scan_state->reset();
}
void G1RemSet::cleanup_after_oops_into_collection_set_do() {
G1GCPhaseTimes* phase_times = _g1->g1_policy()->phase_times();
// Set all cards back to clean.
double start = os::elapsedTime();
_scan_state->clear_card_table(_g1->workers());
phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
}
class G1ScrubRSClosure: public HeapRegionClosure {
G1CollectedHeap* _g1h;
G1CardLiveData* _live_data;
public:
G1ScrubRSClosure(G1CardLiveData* live_data) :
_g1h(G1CollectedHeap::heap()),
_live_data(live_data) { }
bool do_heap_region(HeapRegion* r) {
if (!r->is_continues_humongous()) {
r->rem_set()->scrub(_live_data);
}
return false;
}
};
void G1RemSet::scrub(uint worker_num, HeapRegionClaimer *hrclaimer) {
G1ScrubRSClosure scrub_cl(&_card_live_data);
_g1->heap_region_par_iterate_from_worker_offset(&scrub_cl, hrclaimer, worker_num);
}
inline void check_card_ptr(jbyte* card_ptr, CardTableModRefBS* ct_bs) {
#ifdef ASSERT
G1CollectedHeap* g1 = G1CollectedHeap::heap();
assert(g1->is_in_exact(ct_bs->addr_for(card_ptr)),
"Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
p2i(card_ptr),
ct_bs->index_for(ct_bs->addr_for(card_ptr)),
p2i(ct_bs->addr_for(card_ptr)),
g1->addr_to_region(ct_bs->addr_for(card_ptr)));
#endif
}
void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
uint worker_i) {
assert(!_g1->is_gc_active(), "Only call concurrently");
check_card_ptr(card_ptr, _ct_bs);
// If the card is no longer dirty, nothing to do.
if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
return;
}
// Construct the region representing the card.
HeapWord* start = _ct_bs->addr_for(card_ptr);
// And find the region containing it.
HeapRegion* r = _g1->heap_region_containing(start);
// This check is needed for some uncommon cases where we should
// ignore the card.
//
// The region could be young. Cards for young regions are
// distinctly marked (set to g1_young_gen), so the post-barrier will
// filter them out. However, that marking is performed
// concurrently. A write to a young object could occur before the
// card has been marked young, slipping past the filter.
//
// The card could be stale, because the region has been freed since
// the card was recorded. In this case the region type could be
// anything. If (still) free or (reallocated) young, just ignore
// it. If (reallocated) old or humongous, the later card trimming
// and additional checks in iteration may detect staleness. At
// worst, we end up processing a stale card unnecessarily.
//
// In the normal (non-stale) case, the synchronization between the
// enqueueing of the card and processing it here will have ensured
// we see the up-to-date region type here.
if (!r->is_old_or_humongous()) {
return;
}
// The result from the hot card cache insert call is either:
// * pointer to the current card
// (implying that the current card is not 'hot'),
// * null
// (meaning we had inserted the card ptr into the "hot" card cache,
// which had some headroom),
// * a pointer to a "hot" card that was evicted from the "hot" cache.
//
if (_hot_card_cache->use_cache()) {
assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
const jbyte* orig_card_ptr = card_ptr;
card_ptr = _hot_card_cache->insert(card_ptr);
if (card_ptr == NULL) {
// There was no eviction. Nothing to do.
return;
} else if (card_ptr != orig_card_ptr) {
// Original card was inserted and an old card was evicted.
start = _ct_bs->addr_for(card_ptr);
r = _g1->heap_region_containing(start);
// Check whether the region formerly in the cache should be
// ignored, as discussed earlier for the original card. The
// region could have been freed while in the cache.
if (!r->is_old_or_humongous()) {
return;
}
} // Else we still have the original card.
}
// Trim the region designated by the card to what's been allocated
// in the region. The card could be stale, or the card could cover
// (part of) an object at the end of the allocated space and extend
// beyond the end of allocation.
// Non-humongous objects are only allocated in the old-gen during
// GC, so if region is old then top is stable. Humongous object
// allocation sets top last; if top has not yet been set, this is
// a stale card and we'll end up with an empty intersection. If
// this is not a stale card, the synchronization between the
// enqueuing of the card and processing it here will have ensured
// we see the up-to-date top here.
HeapWord* scan_limit = r->top();
if (scan_limit <= start) {
// If the trimmed region is empty, the card must be stale.
return;
}
// Okay to clean and process the card now. There are still some
// stale card cases that may be detected by iteration and dealt with
// as iteration failure.
*const_cast<volatile jbyte*>(card_ptr) = CardTableModRefBS::clean_card_val();
// This fence serves two purposes. First, the card must be cleaned
// before processing the contents. Second, we can't proceed with
// processing until after the read of top, for synchronization with
// possibly concurrent humongous object allocation. It's okay that
// reading top and reading type were racy wrto each other. We need
// both set, in any order, to proceed.
OrderAccess::fence();
// Don't use addr_for(card_ptr + 1) which can ask for
// a card beyond the heap.
HeapWord* end = start + CardTableModRefBS::card_size_in_words;
MemRegion dirty_region(start, MIN2(scan_limit, end));
assert(!dirty_region.is_empty(), "sanity");
G1ConcurrentRefineOopClosure conc_refine_cl(_g1, worker_i);
bool card_processed =
r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
// If unable to process the card then we encountered an unparsable
// part of the heap (e.g. a partially allocated object) while
// processing a stale card. Despite the card being stale, redirty
// and re-enqueue, because we've already cleaned the card. Without
// this we could incorrectly discard a non-stale card.
if (!card_processed) {
// The card might have gotten re-dirtied and re-enqueued while we
// worked. (In fact, it's pretty likely.)
if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
*card_ptr = CardTableModRefBS::dirty_card_val();
MutexLockerEx x(Shared_DirtyCardQ_lock,
Mutex::_no_safepoint_check_flag);
DirtyCardQueue* sdcq =
JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
sdcq->enqueue(card_ptr);
}
} else {
_num_conc_refined_cards++; // Unsynchronized update, only used for logging.
}
}
bool G1RemSet::refine_card_during_gc(jbyte* card_ptr,
G1ScanObjsDuringUpdateRSClosure* update_rs_cl) {
assert(_g1->is_gc_active(), "Only call during GC");
check_card_ptr(card_ptr, _ct_bs);
// If the card is no longer dirty, nothing to do. This covers cards that were already
// scanned as parts of the remembered sets.
if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
return false;
}
// We claim lazily (so races are possible but they're benign), which reduces the
// number of potential duplicate scans (multiple threads may enqueue the same card twice).
*card_ptr = CardTableModRefBS::clean_card_val() | CardTableModRefBS::claimed_card_val();
// Construct the region representing the card.
HeapWord* card_start = _ct_bs->addr_for(card_ptr);
// And find the region containing it.
uint const card_region_idx = _g1->addr_to_region(card_start);
_scan_state->add_dirty_region(card_region_idx);
HeapWord* scan_limit = _scan_state->scan_top(card_region_idx);
if (scan_limit <= card_start) {
// If the card starts above the area in the region containing objects to scan, skip it.
return false;
}
// Don't use addr_for(card_ptr + 1) which can ask for
// a card beyond the heap.
HeapWord* card_end = card_start + CardTableModRefBS::card_size_in_words;
MemRegion dirty_region(card_start, MIN2(scan_limit, card_end));
assert(!dirty_region.is_empty(), "sanity");
HeapRegion* const card_region = _g1->region_at(card_region_idx);
update_rs_cl->set_region(card_region);
bool card_processed = card_region->oops_on_card_seq_iterate_careful<true>(dirty_region, update_rs_cl);
assert(card_processed, "must be");
return true;
}
void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) {
if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
(period_count % G1SummarizeRSetStatsPeriod == 0)) {
G1RemSetSummary current(this);
_prev_period_summary.subtract_from(¤t);
Log(gc, remset) log;
log.trace("%s", header);
ResourceMark rm;
LogStream ls(log.trace());
_prev_period_summary.print_on(&ls);
_prev_period_summary.set(¤t);
}
}
void G1RemSet::print_summary_info() {
Log(gc, remset, exit) log;
if (log.is_trace()) {
log.trace(" Cumulative RS summary");
G1RemSetSummary current(this);
ResourceMark rm;
LogStream ls(log.trace());
current.print_on(&ls);
}
}
void G1RemSet::create_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
_card_live_data.create(workers, mark_bitmap);
}
void G1RemSet::finalize_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
_card_live_data.finalize(workers, mark_bitmap);
}
void G1RemSet::verify_card_live_data(WorkGang* workers, G1CMBitMap* bitmap) {
_card_live_data.verify(workers, bitmap);
}
void G1RemSet::clear_card_live_data(WorkGang* workers) {
_card_live_data.clear(workers);
}
#ifdef ASSERT
void G1RemSet::verify_card_live_data_is_clear() {
_card_live_data.verify_is_clear();
}
#endif