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/*
* Copyright (c) 2001, 2022, 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/g1BarrierSet.hpp"
#include "gc/g1/g1BatchedTask.hpp"
#include "gc/g1/g1BlockOffsetTable.inline.hpp"
#include "gc/g1/g1CardSet.inline.hpp"
#include "gc/g1/g1CardTable.inline.hpp"
#include "gc/g1/g1CardTableEntryClosure.hpp"
#include "gc/g1/g1CollectedHeap.inline.hpp"
#include "gc/g1/g1ConcurrentRefine.hpp"
#include "gc/g1/g1DirtyCardQueue.hpp"
#include "gc/g1/g1FromCardCache.hpp"
#include "gc/g1/g1GCParPhaseTimesTracker.hpp"
#include "gc/g1/g1GCPhaseTimes.hpp"
#include "gc/g1/g1HotCardCache.hpp"
#include "gc/g1/g1OopClosures.inline.hpp"
#include "gc/g1/g1Policy.hpp"
#include "gc/g1/g1RootClosures.hpp"
#include "gc/g1/g1RemSet.hpp"
#include "gc/g1/g1_globals.hpp"
#include "gc/g1/heapRegion.inline.hpp"
#include "gc/g1/heapRegionManager.inline.hpp"
#include "gc/g1/heapRegionRemSet.inline.hpp"
#include "gc/shared/bufferNodeList.hpp"
#include "gc/shared/gcTraceTime.inline.hpp"
#include "gc/shared/ptrQueue.hpp"
#include "jfr/jfrEvents.hpp"
#include "memory/iterator.hpp"
#include "memory/resourceArea.hpp"
#include "oops/access.inline.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/os.hpp"
#include "utilities/align.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/powerOfTwo.hpp"
#include "utilities/stack.inline.hpp"
#include "utilities/ticks.hpp"
#include CPU_HEADER(gc/g1/g1Globals)
// Collects information about the overall heap root scan progress during an evacuation.
//
// Scanning the remembered sets works by first merging all sources of cards to be
// scanned (log buffers, hcc, remembered sets) into a single data structure to remove
// duplicates and simplify work distribution.
//
// During the following card scanning we not only scan this combined set of cards, but
// also remember that these were completely scanned. The following evacuation passes
// do not scan these cards again, and so need to be preserved across increments.
//
// The representation for all the cards to scan is the card table: cards can have
// one of three states during GC:
// - clean: these cards will not be scanned in this pass
// - dirty: these cards will be scanned in this pass
// - scanned: these cards have already been scanned in a previous pass
//
// After all evacuation is done, we reset the card table to clean.
//
// Work distribution occurs on "chunk" basis, i.e. contiguous ranges of cards. As an
// additional optimization, during card merging we remember which regions and which
// chunks actually contain cards to be scanned. Threads iterate only across these
// regions, and only compete for chunks containing any cards.
//
// Within these chunks, a worker scans the card table on "blocks" of cards, i.e.
// contiguous ranges of dirty cards to be scanned. These blocks are converted to actual
// memory ranges and then passed on to actual scanning.
class G1RemSetScanState : public CHeapObj<mtGC> {
class G1DirtyRegions;
size_t _max_reserved_regions;
// Has this region that is part of the regions in the collection set been processed yet.
typedef bool G1RemsetIterState;
G1RemsetIterState volatile* _collection_set_iter_state;
// Card table iteration claim for each heap region, from 0 (completely unscanned)
// to (>=) HeapRegion::CardsPerRegion (completely scanned).
uint volatile* _card_table_scan_state;
uint _scan_chunks_per_region; // Number of chunks per region.
uint8_t _log_scan_chunks_per_region; // Log of number of chunks per region.
bool* _region_scan_chunks;
size_t _num_total_scan_chunks; // Total number of elements in _region_scan_chunks.
uint8_t _scan_chunks_shift; // For conversion between card index and chunk index.
public:
uint scan_chunk_size_in_cards() const { return (uint)1 << _scan_chunks_shift; }
// Returns whether the chunk corresponding to the given region/card in region contain a
// dirty card, i.e. actually needs scanning.
bool chunk_needs_scan(uint const region_idx, uint const card_in_region) const {
size_t const idx = ((size_t)region_idx << _log_scan_chunks_per_region) + (card_in_region >> _scan_chunks_shift);
assert(idx < _num_total_scan_chunks, "Index " SIZE_FORMAT " out of bounds " SIZE_FORMAT,
idx, _num_total_scan_chunks);
return _region_scan_chunks[idx];
}
private:
// The complete set of regions which card table needs to be cleared at the end
// of GC because we scribbled over these card tables.
//
// Regions may be added for two reasons:
// - they were part of the collection set: they may contain g1_young_card_val
// or regular card marks that we never scan so we must always clear their card
// table
// - or in case g1 does an optional evacuation pass, g1 marks the cards in there
// as g1_scanned_card_val. If G1 only did an initial evacuation pass, the
// scanning already cleared these cards. In that case they are not in this set
// at the end of the collection.
G1DirtyRegions* _all_dirty_regions;
// The set of regions which card table needs to be scanned for new dirty cards
// in the current evacuation pass.
G1DirtyRegions* _next_dirty_regions;
// Set of (unique) regions that can be added to concurrently.
class G1DirtyRegions : public CHeapObj<mtGC> {
uint* _buffer;
uint _cur_idx;
size_t _max_reserved_regions;
bool* _contains;
public:
G1DirtyRegions(size_t max_reserved_regions) :
_buffer(NEW_C_HEAP_ARRAY(uint, max_reserved_regions, mtGC)),
_cur_idx(0),
_max_reserved_regions(max_reserved_regions),
_contains(NEW_C_HEAP_ARRAY(bool, max_reserved_regions, mtGC)) {
reset();
}
static size_t chunk_size() { return M; }
~G1DirtyRegions() {
FREE_C_HEAP_ARRAY(uint, _buffer);
FREE_C_HEAP_ARRAY(bool, _contains);
}
void reset() {
_cur_idx = 0;
::memset(_contains, false, _max_reserved_regions * sizeof(bool));
}
uint size() const { return _cur_idx; }
uint at(uint idx) const {
assert(idx < _cur_idx, "Index %u beyond valid regions", idx);
return _buffer[idx];
}
void add_dirty_region(uint region) {
if (_contains[region]) {
return;
}
bool marked_as_dirty = Atomic::cmpxchg(&_contains[region], false, true) == false;
if (marked_as_dirty) {
uint allocated = Atomic::fetch_and_add(&_cur_idx, 1u);
_buffer[allocated] = region;
}
}
// Creates the union of this and the other G1DirtyRegions.
void merge(const G1DirtyRegions* other) {
for (uint i = 0; i < other->size(); i++) {
uint region = other->at(i);
if (!_contains[region]) {
_buffer[_cur_idx++] = region;
_contains[region] = true;
}
}
}
};
// 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;
class G1ClearCardTableTask : public G1AbstractSubTask {
G1CollectedHeap* _g1h;
G1DirtyRegions* _regions;
uint _chunk_length;
uint volatile _cur_dirty_regions;
G1RemSetScanState* _scan_state;
public:
G1ClearCardTableTask(G1CollectedHeap* g1h,
G1DirtyRegions* regions,
uint chunk_length,
G1RemSetScanState* scan_state) :
G1AbstractSubTask(G1GCPhaseTimes::ClearCardTable),
_g1h(g1h),
_regions(regions),
_chunk_length(chunk_length),
_cur_dirty_regions(0),
_scan_state(scan_state) {
assert(chunk_length > 0, "must be");
}
double worker_cost() const override {
uint num_regions = _regions->size();
if (num_regions == 0) {
// There is no card table clean work, only some cleanup of memory.
return AlmostNoWork;
}
return ((double)align_up((size_t)num_regions << HeapRegion::LogCardsPerRegion, chunk_size()) / chunk_size());
}
virtual ~G1ClearCardTableTask() {
_scan_state->cleanup();
#ifndef PRODUCT
G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup();
#endif
}
static uint chunk_size() { return M; }
void do_work(uint worker_id) override {
while (_cur_dirty_regions < _regions->size()) {
uint next = Atomic::fetch_and_add(&_cur_dirty_regions, _chunk_length);
uint max = MIN2(next + _chunk_length, _regions->size());
for (uint i = next; i < max; i++) {
HeapRegion* r = _g1h->region_at(_regions->at(i));
if (!r->is_survivor()) {
r->clear_cardtable();
}
}
}
}
};
public:
G1RemSetScanState() :
_max_reserved_regions(0),
_collection_set_iter_state(NULL),
_card_table_scan_state(NULL),
_scan_chunks_per_region(G1CollectedHeap::get_chunks_per_region()),
_log_scan_chunks_per_region(log2i(_scan_chunks_per_region)),
_region_scan_chunks(NULL),
_num_total_scan_chunks(0),
_scan_chunks_shift(0),
_all_dirty_regions(NULL),
_next_dirty_regions(NULL),
_scan_top(NULL) {
}
~G1RemSetScanState() {
FREE_C_HEAP_ARRAY(G1RemsetIterState, _collection_set_iter_state);
FREE_C_HEAP_ARRAY(uint, _card_table_scan_state);
FREE_C_HEAP_ARRAY(bool, _region_scan_chunks);
FREE_C_HEAP_ARRAY(HeapWord*, _scan_top);
}
void initialize(size_t max_reserved_regions) {
assert(_collection_set_iter_state == NULL, "Must not be initialized twice");
_max_reserved_regions = max_reserved_regions;
_collection_set_iter_state = NEW_C_HEAP_ARRAY(G1RemsetIterState, max_reserved_regions, mtGC);
_card_table_scan_state = NEW_C_HEAP_ARRAY(uint, max_reserved_regions, mtGC);
_num_total_scan_chunks = max_reserved_regions * _scan_chunks_per_region;
_region_scan_chunks = NEW_C_HEAP_ARRAY(bool, _num_total_scan_chunks, mtGC);
_scan_chunks_shift = (uint8_t)log2i(HeapRegion::CardsPerRegion / _scan_chunks_per_region);
_scan_top = NEW_C_HEAP_ARRAY(HeapWord*, max_reserved_regions, mtGC);
}
void prepare() {
// Reset the claim and clear scan top for all regions, including
// regions currently not available or free. Since regions might
// become used during the collection these values must be valid
// for those regions as well.
for (size_t i = 0; i < _max_reserved_regions; i++) {
reset_region_claim((uint)i);
clear_scan_top((uint)i);
}
_all_dirty_regions = new G1DirtyRegions(_max_reserved_regions);
_next_dirty_regions = new G1DirtyRegions(_max_reserved_regions);
}
void prepare_for_merge_heap_roots() {
assert(_next_dirty_regions->size() == 0, "next dirty regions must be empty");
for (size_t i = 0; i < _max_reserved_regions; i++) {
_card_table_scan_state[i] = 0;
}
::memset(_region_scan_chunks, false, _num_total_scan_chunks * sizeof(*_region_scan_chunks));
}
void complete_evac_phase(bool merge_dirty_regions) {
if (merge_dirty_regions) {
_all_dirty_regions->merge(_next_dirty_regions);
}
_next_dirty_regions->reset();
}
// Returns whether the given region contains cards we need to scan. The remembered
// set and other sources may contain cards that
// - are in uncommitted regions
// - are located in the collection set
// - are located in free regions
// as we do not clean up remembered sets before merging heap roots.
bool contains_cards_to_process(uint const region_idx) const {
HeapRegion* hr = G1CollectedHeap::heap()->region_at_or_null(region_idx);
return (hr != NULL && !hr->in_collection_set() && hr->is_old_or_humongous_or_archive());
}
size_t num_visited_cards() const {
size_t result = 0;
for (uint i = 0; i < _num_total_scan_chunks; i++) {
if (_region_scan_chunks[i]) {
result++;
}
}
return result * (HeapRegion::CardsPerRegion / _scan_chunks_per_region);
}
size_t num_cards_in_dirty_regions() const {
return _next_dirty_regions->size() * HeapRegion::CardsPerRegion;
}
void set_chunk_range_dirty(size_t const region_card_idx, size_t const card_length) {
size_t chunk_idx = region_card_idx >> _scan_chunks_shift;
// Make sure that all chunks that contain the range are marked. Calculate the
// chunk of the last card that is actually marked.
size_t const end_chunk = (region_card_idx + card_length - 1) >> _scan_chunks_shift;
for (; chunk_idx <= end_chunk; chunk_idx++) {
_region_scan_chunks[chunk_idx] = true;
}
}
void set_chunk_dirty(size_t const card_idx) {
assert((card_idx >> _scan_chunks_shift) < _num_total_scan_chunks,
"Trying to access index " SIZE_FORMAT " out of bounds " SIZE_FORMAT,
card_idx >> _scan_chunks_shift, _num_total_scan_chunks);
size_t const chunk_idx = card_idx >> _scan_chunks_shift;
_region_scan_chunks[chunk_idx] = true;
}
G1AbstractSubTask* create_cleanup_after_scan_heap_roots_task() {
uint const chunk_length = G1ClearCardTableTask::chunk_size() / (uint)HeapRegion::CardsPerRegion;
return new G1ClearCardTableTask(G1CollectedHeap::heap(), _all_dirty_regions, chunk_length, this);
}
void cleanup() {
delete _all_dirty_regions;
_all_dirty_regions = NULL;
delete _next_dirty_regions;
_next_dirty_regions = NULL;
}
void iterate_dirty_regions_from(HeapRegionClosure* cl, uint worker_id) {
uint num_regions = _next_dirty_regions->size();
if (num_regions == 0) {
return;
}
G1CollectedHeap* g1h = G1CollectedHeap::heap();
WorkerThreads* workers = g1h->workers();
uint const max_workers = workers->active_workers();
uint const start_pos = num_regions * worker_id / max_workers;
uint cur = start_pos;
do {
bool result = cl->do_heap_region(g1h->region_at(_next_dirty_regions->at(cur)));
guarantee(!result, "Not allowed to ask for early termination.");
cur++;
if (cur == _next_dirty_regions->size()) {
cur = 0;
}
} while (cur != start_pos);
}
void reset_region_claim(uint region_idx) {
_collection_set_iter_state[region_idx] = false;
}
// Attempt to claim the given region in the collection set for iteration. Returns true
// if this call caused the transition from Unclaimed to Claimed.
inline bool claim_collection_set_region(uint region) {
assert(region < _max_reserved_regions, "Tried to access invalid region %u", region);
if (_collection_set_iter_state[region]) {
return false;
}
return !Atomic::cmpxchg(&_collection_set_iter_state[region], false, true);
}
bool has_cards_to_scan(uint region) {
assert(region < _max_reserved_regions, "Tried to access invalid region %u", region);
return _card_table_scan_state[region] < HeapRegion::CardsPerRegion;
}
uint claim_cards_to_scan(uint region, uint increment) {
assert(region < _max_reserved_regions, "Tried to access invalid region %u", region);
return Atomic::fetch_and_add(&_card_table_scan_state[region], increment);
}
void add_dirty_region(uint const region) {
#ifdef ASSERT
HeapRegion* hr = G1CollectedHeap::heap()->region_at(region);
assert(!hr->in_collection_set() && hr->is_old_or_humongous_or_archive(),
"Region %u is not suitable for scanning, is %sin collection set or %s",
hr->hrm_index(), hr->in_collection_set() ? "" : "not ", hr->get_short_type_str());
#endif
_next_dirty_regions->add_dirty_region(region);
}
void add_all_dirty_region(uint region) {
#ifdef ASSERT
HeapRegion* hr = G1CollectedHeap::heap()->region_at(region);
assert(hr->in_collection_set(),
"Only add collection set regions to all dirty regions directly but %u is %s",
hr->hrm_index(), hr->get_short_type_str());
#endif
_all_dirty_regions->add_dirty_region(region);
}
void set_scan_top(uint region_idx, HeapWord* value) {
_scan_top[region_idx] = value;
}
HeapWord* scan_top(uint region_idx) const {
return _scan_top[region_idx];
}
void clear_scan_top(uint region_idx) {
set_scan_top(region_idx, NULL);
}
};
G1RemSet::G1RemSet(G1CollectedHeap* g1h,
G1CardTable* ct,
G1HotCardCache* hot_card_cache) :
_scan_state(new G1RemSetScanState()),
_prev_period_summary(false),
_g1h(g1h),
_ct(ct),
_g1p(_g1h->policy()),
_hot_card_cache(hot_card_cache) {
}
G1RemSet::~G1RemSet() {
delete _scan_state;
}
void G1RemSet::initialize(uint max_reserved_regions) {
_scan_state->initialize(max_reserved_regions);
}
// Helper class to scan and detect ranges of cards that need to be scanned on the
// card table.
class G1CardTableScanner : public StackObj {
public:
typedef CardTable::CardValue CardValue;
private:
CardValue* const _base_addr;
CardValue* _cur_addr;
CardValue* const _end_addr;
static const size_t ToScanMask = G1CardTable::g1_card_already_scanned;
static const size_t ExpandedToScanMask = G1CardTable::WordAlreadyScanned;
bool cur_addr_aligned() const {
return ((uintptr_t)_cur_addr) % sizeof(size_t) == 0;
}
bool cur_card_is_dirty() const {
CardValue value = *_cur_addr;
return (value & ToScanMask) == 0;
}
bool cur_word_of_cards_contains_any_dirty_card() const {
assert(cur_addr_aligned(), "Current address should be aligned");
size_t const value = *(size_t*)_cur_addr;
return (~value & ExpandedToScanMask) != 0;
}
bool cur_word_of_cards_all_dirty_cards() const {
size_t const value = *(size_t*)_cur_addr;
return value == G1CardTable::WordAllDirty;
}
size_t get_and_advance_pos() {
_cur_addr++;
return pointer_delta(_cur_addr, _base_addr, sizeof(CardValue)) - 1;
}
public:
G1CardTableScanner(CardValue* start_card, size_t size) :
_base_addr(start_card),
_cur_addr(start_card),
_end_addr(start_card + size) {
assert(is_aligned(start_card, sizeof(size_t)), "Unaligned start addr " PTR_FORMAT, p2i(start_card));
assert(is_aligned(size, sizeof(size_t)), "Unaligned size " SIZE_FORMAT, size);
}
size_t find_next_dirty() {
while (!cur_addr_aligned()) {
if (cur_card_is_dirty()) {
return get_and_advance_pos();
}
_cur_addr++;
}
assert(cur_addr_aligned(), "Current address should be aligned now.");
while (_cur_addr != _end_addr) {
if (cur_word_of_cards_contains_any_dirty_card()) {
for (size_t i = 0; i < sizeof(size_t); i++) {
if (cur_card_is_dirty()) {
return get_and_advance_pos();
}
_cur_addr++;
}
assert(false, "Should not reach here given we detected a dirty card in the word.");
}
_cur_addr += sizeof(size_t);
}
return get_and_advance_pos();
}
size_t find_next_non_dirty() {
assert(_cur_addr <= _end_addr, "Not allowed to search for marks after area.");
while (!cur_addr_aligned()) {
if (!cur_card_is_dirty()) {
return get_and_advance_pos();
}
_cur_addr++;
}
assert(cur_addr_aligned(), "Current address should be aligned now.");
while (_cur_addr != _end_addr) {
if (!cur_word_of_cards_all_dirty_cards()) {
for (size_t i = 0; i < sizeof(size_t); i++) {
if (!cur_card_is_dirty()) {
return get_and_advance_pos();
}
_cur_addr++;
}
assert(false, "Should not reach here given we detected a non-dirty card in the word.");
}
_cur_addr += sizeof(size_t);
}
return get_and_advance_pos();
}
};
// Helper class to claim dirty chunks within the card table.
class G1CardTableChunkClaimer {
G1RemSetScanState* _scan_state;
uint _region_idx;
uint _cur_claim;
public:
G1CardTableChunkClaimer(G1RemSetScanState* scan_state, uint region_idx) :
_scan_state(scan_state),
_region_idx(region_idx),
_cur_claim(0) {
guarantee(size() <= HeapRegion::CardsPerRegion, "Should not claim more space than possible.");
}
bool has_next() {
while (true) {
_cur_claim = _scan_state->claim_cards_to_scan(_region_idx, size());
if (_cur_claim >= HeapRegion::CardsPerRegion) {
return false;
}
if (_scan_state->chunk_needs_scan(_region_idx, _cur_claim)) {
return true;
}
}
}
uint value() const { return _cur_claim; }
uint size() const { return _scan_state->scan_chunk_size_in_cards(); }
};
// Scans a heap region for dirty cards.
class G1ScanHRForRegionClosure : public HeapRegionClosure {
G1CollectedHeap* _g1h;
G1CardTable* _ct;
G1BlockOffsetTable* _bot;
G1ParScanThreadState* _pss;
G1RemSetScanState* _scan_state;
G1GCPhaseTimes::GCParPhases _phase;
uint _worker_id;
size_t _cards_scanned;
size_t _blocks_scanned;
size_t _chunks_claimed;
size_t _heap_roots_found;
Tickspan _rem_set_root_scan_time;
Tickspan _rem_set_trim_partially_time;
// The address to which this thread already scanned (walked the heap) up to during
// card scanning (exclusive).
HeapWord* _scanned_to;
G1CardTable::CardValue _scanned_card_value;
HeapWord* scan_memregion(uint region_idx_for_card, MemRegion mr) {
HeapRegion* const card_region = _g1h->region_at(region_idx_for_card);
G1ScanCardClosure card_cl(_g1h, _pss, _heap_roots_found);
HeapWord* const scanned_to = card_region->oops_on_memregion_seq_iterate_careful<true>(mr, &card_cl);
assert(scanned_to != NULL, "Should be able to scan range");
assert(scanned_to >= mr.end(), "Scanned to " PTR_FORMAT " less than range " PTR_FORMAT, p2i(scanned_to), p2i(mr.end()));
_pss->trim_queue_partially();
return scanned_to;
}
void do_claimed_block(uint const region_idx_for_card, size_t const first_card, size_t const num_cards) {
HeapWord* const card_start = _bot->address_for_index_raw(first_card);
#ifdef ASSERT
HeapRegion* hr = _g1h->region_at_or_null(region_idx_for_card);
assert(hr == NULL || hr->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());
#endif
HeapWord* const top = _scan_state->scan_top(region_idx_for_card);
if (card_start >= top) {
return;
}
HeapWord* scan_end = MIN2(card_start + (num_cards << BOTConstants::log_card_size_in_words()), top);
if (_scanned_to >= scan_end) {
return;
}
MemRegion mr(MAX2(card_start, _scanned_to), scan_end);
_scanned_to = scan_memregion(region_idx_for_card, mr);
_cards_scanned += num_cards;
}
ALWAYSINLINE void do_card_block(uint const region_idx, size_t const first_card, size_t const num_cards) {
_ct->change_dirty_cards_to(first_card, num_cards, _scanned_card_value);
do_claimed_block(region_idx, first_card, num_cards);
_blocks_scanned++;
}
void scan_heap_roots(HeapRegion* r) {
uint const region_idx = r->hrm_index();
ResourceMark rm;
G1CardTableChunkClaimer claim(_scan_state, region_idx);
// Set the current scan "finger" to NULL for every heap region to scan. Since
// the claim value is monotonically increasing, the check to not scan below this
// will filter out objects spanning chunks within the region too then, as opposed
// to resetting this value for every claim.
_scanned_to = NULL;
while (claim.has_next()) {
size_t const region_card_base_idx = ((size_t)region_idx << HeapRegion::LogCardsPerRegion) + claim.value();
CardTable::CardValue* const base_addr = _ct->byte_for_index(region_card_base_idx);
G1CardTableScanner scan(base_addr, claim.size());
size_t first_scan_idx = scan.find_next_dirty();
while (first_scan_idx != claim.size()) {
#ifdef ASSERT
{
CardTable::CardValue value = *_ct->byte_for_index(region_card_base_idx + first_scan_idx);
assert(value == CardTable::dirty_card_val(), "is %d at region %u idx " SIZE_FORMAT, value, region_idx, first_scan_idx);
}
#endif
size_t const last_scan_idx = scan.find_next_non_dirty();
size_t const len = last_scan_idx - first_scan_idx;
do_card_block(region_idx, region_card_base_idx + first_scan_idx, len);
if (last_scan_idx == claim.size()) {
break;
}
first_scan_idx = scan.find_next_dirty();
}
_chunks_claimed++;
}
}
public:
G1ScanHRForRegionClosure(G1RemSetScanState* scan_state,
G1ParScanThreadState* pss,
uint worker_id,
G1GCPhaseTimes::GCParPhases phase,
bool remember_already_scanned_cards) :
_g1h(G1CollectedHeap::heap()),
_ct(_g1h->card_table()),
_bot(_g1h->bot()),
_pss(pss),
_scan_state(scan_state),
_phase(phase),
_worker_id(worker_id),
_cards_scanned(0),
_blocks_scanned(0),
_chunks_claimed(0),
_heap_roots_found(0),
_rem_set_root_scan_time(),
_rem_set_trim_partially_time(),
_scanned_to(NULL),
_scanned_card_value(remember_already_scanned_cards ? G1CardTable::g1_scanned_card_val()
: G1CardTable::clean_card_val()) {
}
bool do_heap_region(HeapRegion* r) {
assert(!r->in_collection_set() && r->is_old_or_humongous_or_archive(),
"Should only be called on old gen non-collection set regions but region %u is not.",
r->hrm_index());
uint const region_idx = r->hrm_index();
if (_scan_state->has_cards_to_scan(region_idx)) {
G1EvacPhaseWithTrimTimeTracker timer(_pss, _rem_set_root_scan_time, _rem_set_trim_partially_time);
scan_heap_roots(r);
}
return false;
}
Tickspan rem_set_root_scan_time() const { return _rem_set_root_scan_time; }
Tickspan rem_set_trim_partially_time() const { return _rem_set_trim_partially_time; }
size_t cards_scanned() const { return _cards_scanned; }
size_t blocks_scanned() const { return _blocks_scanned; }
size_t chunks_claimed() const { return _chunks_claimed; }
size_t heap_roots_found() const { return _heap_roots_found; }
};
void G1RemSet::scan_heap_roots(G1ParScanThreadState* pss,
uint worker_id,
G1GCPhaseTimes::GCParPhases scan_phase,
G1GCPhaseTimes::GCParPhases objcopy_phase,
bool remember_already_scanned_cards) {
EventGCPhaseParallel event;
G1ScanHRForRegionClosure cl(_scan_state, pss, worker_id, scan_phase, remember_already_scanned_cards);
_scan_state->iterate_dirty_regions_from(&cl, worker_id);
event.commit(GCId::current(), worker_id, G1GCPhaseTimes::phase_name(scan_phase));
G1GCPhaseTimes* p = _g1p->phase_times();
p->record_or_add_time_secs(objcopy_phase, worker_id, cl.rem_set_trim_partially_time().seconds());
p->record_or_add_time_secs(scan_phase, worker_id, cl.rem_set_root_scan_time().seconds());
p->record_or_add_thread_work_item(scan_phase, worker_id, cl.cards_scanned(), G1GCPhaseTimes::ScanHRScannedCards);
p->record_or_add_thread_work_item(scan_phase, worker_id, cl.blocks_scanned(), G1GCPhaseTimes::ScanHRScannedBlocks);
p->record_or_add_thread_work_item(scan_phase, worker_id, cl.chunks_claimed(), G1GCPhaseTimes::ScanHRClaimedChunks);
p->record_or_add_thread_work_item(scan_phase, worker_id, cl.heap_roots_found(), G1GCPhaseTimes::ScanHRFoundRoots);
}
// Heap region closure to be applied to all regions in the current collection set
// increment to fix up non-card related roots.
class G1ScanCollectionSetRegionClosure : public HeapRegionClosure {
G1ParScanThreadState* _pss;
G1RemSetScanState* _scan_state;
G1GCPhaseTimes::GCParPhases _scan_phase;
G1GCPhaseTimes::GCParPhases _code_roots_phase;
uint _worker_id;
size_t _opt_roots_scanned;
size_t _opt_refs_scanned;
size_t _opt_refs_memory_used;
Tickspan _code_root_scan_time;
Tickspan _code_trim_partially_time;
Tickspan _rem_set_opt_root_scan_time;
Tickspan _rem_set_opt_trim_partially_time;
void scan_opt_rem_set_roots(HeapRegion* r) {
G1OopStarChunkedList* opt_rem_set_list = _pss->oops_into_optional_region(r);
G1ScanCardClosure scan_cl(G1CollectedHeap::heap(), _pss, _opt_roots_scanned);
G1ScanRSForOptionalClosure cl(G1CollectedHeap::heap(), &scan_cl);
_opt_refs_scanned += opt_rem_set_list->oops_do(&cl, _pss->closures()->strong_oops());
_opt_refs_memory_used += opt_rem_set_list->used_memory();
}
public:
G1ScanCollectionSetRegionClosure(G1RemSetScanState* scan_state,
G1ParScanThreadState* pss,
uint worker_id,
G1GCPhaseTimes::GCParPhases scan_phase,
G1GCPhaseTimes::GCParPhases code_roots_phase) :
_pss(pss),
_scan_state(scan_state),
_scan_phase(scan_phase),
_code_roots_phase(code_roots_phase),
_worker_id(worker_id),
_opt_roots_scanned(0),
_opt_refs_scanned(0),
_opt_refs_memory_used(0),
_code_root_scan_time(),
_code_trim_partially_time(),
_rem_set_opt_root_scan_time(),
_rem_set_opt_trim_partially_time() { }
bool do_heap_region(HeapRegion* r) {
uint const region_idx = r->hrm_index();
// The individual references for the optional remembered set are per-worker, so we
// always need to scan them.
if (r->has_index_in_opt_cset()) {
EventGCPhaseParallel event;
G1EvacPhaseWithTrimTimeTracker timer(_pss, _rem_set_opt_root_scan_time, _rem_set_opt_trim_partially_time);
scan_opt_rem_set_roots(r);
event.commit(GCId::current(), _worker_id, G1GCPhaseTimes::phase_name(_scan_phase));
}
if (_scan_state->claim_collection_set_region(region_idx)) {
EventGCPhaseParallel event;
G1EvacPhaseWithTrimTimeTracker timer(_pss, _code_root_scan_time, _code_trim_partially_time);
// Scan the code root list attached to the current region
r->code_roots_do(_pss->closures()->weak_codeblobs());
event.commit(GCId::current(), _worker_id, G1GCPhaseTimes::phase_name(_code_roots_phase));
}
return false;
}
Tickspan code_root_scan_time() const { return _code_root_scan_time; }
Tickspan code_root_trim_partially_time() const { return _code_trim_partially_time; }
Tickspan rem_set_opt_root_scan_time() const { return _rem_set_opt_root_scan_time; }
Tickspan rem_set_opt_trim_partially_time() const { return _rem_set_opt_trim_partially_time; }
size_t opt_roots_scanned() const { return _opt_roots_scanned; }
size_t opt_refs_scanned() const { return _opt_refs_scanned; }
size_t opt_refs_memory_used() const { return _opt_refs_memory_used; }
};
void G1RemSet::scan_collection_set_regions(G1ParScanThreadState* pss,
uint worker_id,
G1GCPhaseTimes::GCParPhases scan_phase,
G1GCPhaseTimes::GCParPhases coderoots_phase,
G1GCPhaseTimes::GCParPhases objcopy_phase) {
G1ScanCollectionSetRegionClosure cl(_scan_state, pss, worker_id, scan_phase, coderoots_phase);
_g1h->collection_set_iterate_increment_from(&cl, worker_id);
G1GCPhaseTimes* p = _g1h->phase_times();
p->record_or_add_time_secs(scan_phase, worker_id, cl.rem_set_opt_root_scan_time().seconds());
p->record_or_add_time_secs(scan_phase, worker_id, cl.rem_set_opt_trim_partially_time().seconds());
p->record_or_add_time_secs(coderoots_phase, worker_id, cl.code_root_scan_time().seconds());
p->add_time_secs(objcopy_phase, worker_id, cl.code_root_trim_partially_time().seconds());
// At this time we record some metrics only for the evacuations after the initial one.
if (scan_phase == G1GCPhaseTimes::OptScanHR) {
p->record_or_add_thread_work_item(scan_phase, worker_id, cl.opt_roots_scanned(), G1GCPhaseTimes::ScanHRFoundRoots);
p->record_or_add_thread_work_item(scan_phase, worker_id, cl.opt_refs_scanned(), G1GCPhaseTimes::ScanHRScannedOptRefs);
p->record_or_add_thread_work_item(scan_phase, worker_id, cl.opt_refs_memory_used(), G1GCPhaseTimes::ScanHRUsedMemory);
}
}
#ifdef ASSERT
void G1RemSet::assert_scan_top_is_null(uint hrm_index) {
assert(_scan_state->scan_top(hrm_index) == NULL,
"scan_top of region %u is unexpectedly " PTR_FORMAT,
hrm_index, p2i(_scan_state->scan_top(hrm_index)));
}
#endif
void G1RemSet::prepare_region_for_scan(HeapRegion* r) {
uint hrm_index = r->hrm_index();
r->prepare_remset_for_scan();
// Only update non-collection set old regions, others must have already been set
// to NULL (don't scan) in the initialization.
if (r->in_collection_set()) {
assert_scan_top_is_null(hrm_index);
} else if (r->is_old_or_humongous_or_archive()) {
_scan_state->set_scan_top(hrm_index, r->top());
} else {
assert_scan_top_is_null(hrm_index);
assert(r->is_free(),
"Region %u should be free region but is %s", hrm_index, r->get_type_str());
}
}
void G1RemSet::prepare_for_scan_heap_roots() {
_scan_state->prepare();
}
// Small ring buffer used for prefetching cards for write from the card
// table during GC.
template <class T>
class G1MergeHeapRootsPrefetchCache {
public:
static const uint CacheSize = G1MergeHeapRootsPrefetchCacheSize;
static_assert(is_power_of_2(CacheSize), "Cache size must be power of 2");
private:
T* _cache[CacheSize];
uint _cur_cache_idx;
NONCOPYABLE(G1MergeHeapRootsPrefetchCache);
protected:
// Initial content of all elements in the cache. It's value should be
// "neutral", i.e. no work done on it when processing it.
G1CardTable::CardValue _dummy_card;
~G1MergeHeapRootsPrefetchCache() = default;
public:
G1MergeHeapRootsPrefetchCache(G1CardTable::CardValue dummy_card_value) :
_cur_cache_idx(0),
_dummy_card(dummy_card_value) {
for (uint i = 0; i < CacheSize; i++) {
push(&_dummy_card);
}
}
T* push(T* elem) {
Prefetch::write(elem, 0);
T* result = _cache[_cur_cache_idx];
_cache[_cur_cache_idx++] = elem;
_cur_cache_idx &= (CacheSize - 1);
return result;
}
};
class G1MergeHeapRootsTask : public WorkerTask {
class G1MergeCardSetStats {
size_t _merged[G1GCPhaseTimes::MergeRSContainersSentinel];
public:
G1MergeCardSetStats() {
for (uint i = 0; i < ARRAY_SIZE(_merged); i++) {
_merged[i] = 0;
}
}
void inc_card_set_merged(uint tag) {
assert(tag < ARRAY_SIZE(_merged), "tag out of bounds %u", tag);
_merged[tag]++;
}
void inc_remset_cards(size_t increment = 1) {
_merged[G1GCPhaseTimes::MergeRSCards] += increment;
}
size_t merged(uint i) const { return _merged[i]; }
};
// Visitor for remembered sets. Several methods of it are called by a region's
// card set iterator to drop card set remembered set entries onto the card.
// table. This is in addition to being the HeapRegionClosure to iterate over
// all region's remembered sets.
//
// We add a small prefetching cache in front of the actual work as dropping
// onto the card table is basically random memory access. This improves
// performance of this operation significantly.
class G1MergeCardSetClosure : public HeapRegionClosure {
friend class G1MergeCardSetCache;
G1RemSetScanState* _scan_state;
G1CardTable* _ct;
G1MergeCardSetStats _stats;
// Cached card table index of the currently processed region to avoid constant
// recalculation as our remembered set containers are per region.
size_t _region_base_idx;
class G1MergeCardSetCache : public G1MergeHeapRootsPrefetchCache<G1CardTable::CardValue> {
G1MergeCardSetClosure* const _merge_card_cl;
public:
G1MergeCardSetCache(G1MergeCardSetClosure* const merge_card_cl) :
// Initially set dummy card value to Dirty to avoid any actual mark work if we
// try to process it.
G1MergeHeapRootsPrefetchCache<G1CardTable::CardValue>(G1CardTable::dirty_card_val()),
_merge_card_cl(merge_card_cl) { }
void flush() {
for (uint i = 0; i < CacheSize; i++) {
_merge_card_cl->mark_card(push(&_dummy_card));
}
}
} _merge_card_set_cache;
// Returns whether the region contains cards we need to scan. If so, remember that
// region in the current set of dirty regions.
bool remember_if_interesting(uint const region_idx) {
if (!_scan_state->contains_cards_to_process(region_idx)) {
return false;
}
_scan_state->add_dirty_region(region_idx);
return true;
}
void mark_card(G1CardTable::CardValue* value) {
if (_ct->mark_clean_as_dirty(value)) {
_scan_state->set_chunk_dirty(_ct->index_for_cardvalue(value));
}
_stats.inc_remset_cards();
}
public:
G1MergeCardSetClosure(G1RemSetScanState* scan_state) :
_scan_state(scan_state),
_ct(G1CollectedHeap::heap()->card_table()),
_stats(),
_region_base_idx(0),
_merge_card_set_cache(this) { }
void do_card(uint const card_idx) {
G1CardTable::CardValue* to_prefetch = _ct->byte_for_index(_region_base_idx + card_idx);
G1CardTable::CardValue* to_process = _merge_card_set_cache.push(to_prefetch);
mark_card(to_process);
}
// Returns whether the given region actually needs iteration.
bool start_iterate(uint const tag, uint const region_idx) {
assert(tag < G1GCPhaseTimes::MergeRSCards, "invalid tag %u", tag);
if (remember_if_interesting(region_idx)) {
_region_base_idx = (size_t)region_idx << HeapRegion::LogCardsPerRegion;
_stats.inc_card_set_merged(tag);
return true;
}
return false;
}
void do_card_range(uint const start_card_idx, uint const length) {
_ct->mark_range_dirty(_region_base_idx + start_card_idx, length);
_stats.inc_remset_cards(length);
_scan_state->set_chunk_range_dirty(_region_base_idx + start_card_idx, length);
}
// Helper to merge the cards in the card set for the given region onto the card
// table.
//
// Called directly for humongous starts regions because we should not add
// humongous eager reclaim candidates to the "all" list of regions to
// clear the card table by default as we do not know yet whether this region
// will be reclaimed (and reused).
// If the humongous region contains dirty cards, g1 will scan them
// because dumping the remembered set entries onto the card table will add
// the humongous region to the "dirty" region list to scan. Then scanning
// either clears the card during scan (if there is only an initial evacuation
// pass) or the "dirty" list will be merged with the "all" list later otherwise.
// (And there is no problem either way if the region does not contain dirty
// cards).
void merge_card_set_for_region(HeapRegion* r) {
assert(r->in_collection_set() || r->is_starts_humongous(), "must be");
HeapRegionRemSet* rem_set = r->rem_set();
if (!rem_set->is_empty()) {
rem_set->iterate_for_merge(*this);
}
}
virtual bool do_heap_region(HeapRegion* r) {
assert(r->in_collection_set(), "must be");
_scan_state->add_all_dirty_region(r->hrm_index());
merge_card_set_for_region(r);
return false;
}
G1MergeCardSetStats stats() {
_merge_card_set_cache.flush();
return _stats;
}
};
// Closure to make sure that the marking bitmap is clear for any old region in
// the collection set.
// This is needed to be able to use the bitmap for evacuation failure handling.
class G1ClearBitmapClosure : public HeapRegionClosure {
G1CollectedHeap* _g1h;
void assert_bitmap_clear(HeapRegion* hr, const G1CMBitMap* bitmap) {
assert(bitmap->get_next_marked_addr(hr->bottom(), hr->end()) == hr->end(),
"Bitmap should have no mark for region %u (%s)", hr->hrm_index(), hr->get_short_type_str());
}
bool should_clear_region(HeapRegion* hr) const {
// The bitmap for young regions must obviously be clear as we never mark through them;
// old regions are only in the collection set after the concurrent cycle completed,
// so their bitmaps must also be clear except when the pause occurs during the
// Concurrent Cleanup for Next Mark phase. Only at that point the region's bitmap may
// contain marks while being in the collection set at the same time.
//
// There is one exception: shutdown might have aborted the Concurrent Cleanup for Next
// Mark phase midway, which might have also left stale marks in old generation regions.
// There might actually have been scheduled multiple collections, but at that point we do
// not care that much about performance and just do the work multiple times if needed.
return (_g1h->collector_state()->clearing_bitmap() ||
_g1h->concurrent_mark_is_terminating()) &&
hr->is_old();
}
public:
G1ClearBitmapClosure(G1CollectedHeap* g1h) : _g1h(g1h) { }
bool do_heap_region(HeapRegion* hr) {
assert(_g1h->is_in_cset(hr), "Should only be used iterating the collection set");
// Evacuation failure uses the bitmap to record evacuation failed objects,
// so the bitmap for the regions in the collection set must be cleared if not already.
if (should_clear_region(hr)) {
_g1h->clear_bitmap_for_region(hr);
hr->reset_top_at_mark_start();
} else {
assert_bitmap_clear(hr, _g1h->concurrent_mark()->mark_bitmap());
}
return false;
}
};
// Helper to allow two closure to be applied when
// iterating through the collection set.
class G1CombinedClosure : public HeapRegionClosure {
HeapRegionClosure* _closure1;
HeapRegionClosure* _closure2;
public:
G1CombinedClosure(HeapRegionClosure* cl1, HeapRegionClosure* cl2) :
_closure1(cl1),
_closure2(cl2) { }
bool do_heap_region(HeapRegion* hr) {
return _closure1->do_heap_region(hr) ||
_closure2->do_heap_region(hr);
}
};
// Visitor for the remembered sets of humongous candidate regions to merge their
// remembered set into the card table.
class G1FlushHumongousCandidateRemSets : public HeapRegionIndexClosure {
G1MergeCardSetClosure _cl;
public:
G1FlushHumongousCandidateRemSets(G1RemSetScanState* scan_state) : _cl(scan_state) { }
bool do_heap_region_index(uint region_index) override {
G1CollectedHeap* g1h = G1CollectedHeap::heap();
if (!g1h->region_attr(region_index).is_humongous_candidate()) {
return false;
}
HeapRegion* r = g1h->region_at(region_index);
if (r->rem_set()->is_empty()) {
return false;
}
guarantee(r->rem_set()->occupancy_less_or_equal_than(G1EagerReclaimRemSetThreshold),
"Found a not-small remembered set here. This is inconsistent with previous assumptions.");
_cl.merge_card_set_for_region(r);
// We should only clear the card based remembered set here as we will not
// implicitly rebuild anything else during eager reclaim. Note that at the moment
// (and probably never) we do not enter this path if there are other kind of
// remembered sets for this region.
r->rem_set()->clear_locked(true /* only_cardset */);
// Clear_locked() above sets the state to Empty. However we want to continue
// collecting remembered set entries for humongous regions that were not
// reclaimed.
r->rem_set()->set_state_complete();
#ifdef ASSERT
G1HeapRegionAttr region_attr = g1h->region_attr(region_index);
assert(region_attr.remset_is_tracked(), "must be");
#endif
assert(r->rem_set()->is_empty(), "At this point any humongous candidate remembered set must be empty.");
return false;
}
G1MergeCardSetStats stats() {
return _cl.stats();
}
};
// Visitor for the log buffer entries to merge them into the card table.
class G1MergeLogBufferCardsClosure : public G1CardTableEntryClosure {
G1RemSetScanState* _scan_state;
G1CardTable* _ct;
size_t _cards_dirty;
size_t _cards_skipped;
void process_card(CardValue* card_ptr) {
if (*card_ptr == G1CardTable::dirty_card_val()) {
uint const region_idx = _ct->region_idx_for(card_ptr);
_scan_state->add_dirty_region(region_idx);
_scan_state->set_chunk_dirty(_ct->index_for_cardvalue(card_ptr));
_cards_dirty++;
}
}
public:
G1MergeLogBufferCardsClosure(G1CollectedHeap* g1h, G1RemSetScanState* scan_state) :
_scan_state(scan_state),
_ct(g1h->card_table()),
_cards_dirty(0),
_cards_skipped(0)
{}
void do_card_ptr(CardValue* card_ptr, uint worker_id) {
// 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_id should be the id of a GC worker thread.
assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
uint const region_idx = _ct->region_idx_for(card_ptr);
// The second clause must come after - the log buffers might contain cards to uncommitted
// regions.
// This code may count duplicate entries in the log buffers (even if rare) multiple
// times.
if (_scan_state->contains_cards_to_process(region_idx)) {
process_card(card_ptr);
} else {
// We may have had dirty cards in the (initial) collection set (or the
// young regions which are always in the initial collection set). We do
// not fix their cards here: we already added these regions to the set of
// regions to clear the card table at the end during the prepare() phase.
_cards_skipped++;
}
}
size_t cards_dirty() const { return _cards_dirty; }
size_t cards_skipped() const { return _cards_skipped; }
};
HeapRegionClaimer _hr_claimer;
G1RemSetScanState* _scan_state;
BufferNode::Stack _dirty_card_buffers;
bool _initial_evacuation;
volatile bool _fast_reclaim_handled;
void apply_closure_to_dirty_card_buffers(G1MergeLogBufferCardsClosure* cl, uint worker_id) {
G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
size_t buffer_size = dcqs.buffer_size();
while (BufferNode* node = _dirty_card_buffers.pop()) {
cl->apply_to_buffer(node, buffer_size, worker_id);
dcqs.deallocate_buffer(node);
}
}
public:
G1MergeHeapRootsTask(G1RemSetScanState* scan_state, uint num_workers, bool initial_evacuation) :
WorkerTask("G1 Merge Heap Roots"),
_hr_claimer(num_workers),
_scan_state(scan_state),
_dirty_card_buffers(),
_initial_evacuation(initial_evacuation),
_fast_reclaim_handled(false)
{
if (initial_evacuation) {
G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
BufferNodeList buffers = dcqs.take_all_completed_buffers();
if (buffers._entry_count != 0) {
_dirty_card_buffers.prepend(*buffers._head, *buffers._tail);
}
}
}
virtual void work(uint worker_id) {
G1CollectedHeap* g1h = G1CollectedHeap::heap();
G1GCPhaseTimes* p = g1h->phase_times();
G1GCPhaseTimes::GCParPhases merge_remset_phase = _initial_evacuation ?
G1GCPhaseTimes::MergeRS :
G1GCPhaseTimes::OptMergeRS;
{
// Merge remset of ...
G1GCParPhaseTimesTracker x(p, merge_remset_phase, worker_id, !_initial_evacuation /* allow_multiple_record */);
{
// 1. eager-reclaim candidates
if (_initial_evacuation &&
g1h->has_humongous_reclaim_candidates() &&
!_fast_reclaim_handled &&
!Atomic::cmpxchg(&_fast_reclaim_handled, false, true)) {
G1GCParPhaseTimesTracker subphase_x(p, G1GCPhaseTimes::MergeER, worker_id);
G1FlushHumongousCandidateRemSets cl(_scan_state);
g1h->heap_region_iterate(&cl);
G1MergeCardSetStats stats = cl.stats();
for (uint i = 0; i < G1GCPhaseTimes::MergeRSContainersSentinel; i++) {
p->record_or_add_thread_work_item(merge_remset_phase, worker_id, stats.merged(i), i);
}
}
}
{
// 2. collection set
G1MergeCardSetClosure merge(_scan_state);
G1ClearBitmapClosure clear(g1h);
G1CombinedClosure combined(&merge, &clear);
g1h->collection_set_iterate_increment_from(&combined, nullptr, worker_id);
G1MergeCardSetStats stats = merge.stats();
for (uint i = 0; i < G1GCPhaseTimes::MergeRSContainersSentinel; i++) {
p->record_or_add_thread_work_item(merge_remset_phase, worker_id, stats.merged(i), i);
}
}
}
// Apply closure to log entries in the HCC.
if (_initial_evacuation && G1HotCardCache::use_cache()) {
assert(merge_remset_phase == G1GCPhaseTimes::MergeRS, "Wrong merge phase");
G1GCParPhaseTimesTracker x(p, G1GCPhaseTimes::MergeHCC, worker_id);
G1MergeLogBufferCardsClosure cl(g1h, _scan_state);
g1h->iterate_hcc_closure(&cl, worker_id);
p->record_thread_work_item(G1GCPhaseTimes::MergeHCC, worker_id, cl.cards_dirty(), G1GCPhaseTimes::MergeHCCDirtyCards);
p->record_thread_work_item(G1GCPhaseTimes::MergeHCC, worker_id, cl.cards_skipped(), G1GCPhaseTimes::MergeHCCSkippedCards);
}
// Now apply the closure to all remaining log entries.
if (_initial_evacuation) {
assert(merge_remset_phase == G1GCPhaseTimes::MergeRS, "Wrong merge phase");
G1GCParPhaseTimesTracker x(p, G1GCPhaseTimes::MergeLB, worker_id);
G1MergeLogBufferCardsClosure cl(g1h, _scan_state);
apply_closure_to_dirty_card_buffers(&cl, worker_id);
p->record_thread_work_item(G1GCPhaseTimes::MergeLB, worker_id, cl.cards_dirty(), G1GCPhaseTimes::MergeLBDirtyCards);
p->record_thread_work_item(G1GCPhaseTimes::MergeLB, worker_id, cl.cards_skipped(), G1GCPhaseTimes::MergeLBSkippedCards);
}
}
};
void G1RemSet::print_merge_heap_roots_stats() {
LogTarget(Debug, gc, remset) lt;
if (lt.is_enabled()) {
LogStream ls(lt);
size_t num_visited_cards = _scan_state->num_visited_cards();
size_t total_dirty_region_cards = _scan_state->num_cards_in_dirty_regions();
G1CollectedHeap* g1h = G1CollectedHeap::heap();
size_t total_old_region_cards =
(g1h->num_regions() - (g1h->num_free_regions() - g1h->collection_set()->cur_length())) * HeapRegion::CardsPerRegion;
ls.print_cr("Visited cards " SIZE_FORMAT " Total dirty " SIZE_FORMAT " (%.2lf%%) Total old " SIZE_FORMAT " (%.2lf%%)",
num_visited_cards,
total_dirty_region_cards,
percent_of(num_visited_cards, total_dirty_region_cards),
total_old_region_cards,
percent_of(num_visited_cards, total_old_region_cards));
}
}
void G1RemSet::merge_heap_roots(bool initial_evacuation) {
G1CollectedHeap* g1h = G1CollectedHeap::heap();
{
Ticks start = Ticks::now();
_scan_state->prepare_for_merge_heap_roots();
Tickspan total = Ticks::now() - start;
if (initial_evacuation) {
g1h->phase_times()->record_prepare_merge_heap_roots_time(total.seconds() * 1000.0);
} else {
g1h->phase_times()->record_or_add_optional_prepare_merge_heap_roots_time(total.seconds() * 1000.0);
}
}
WorkerThreads* workers = g1h->workers();
size_t const increment_length = g1h->collection_set()->increment_length();
uint const num_workers = initial_evacuation ? workers->active_workers() :
MIN2(workers->active_workers(), (uint)increment_length);
{
G1MergeHeapRootsTask cl(_scan_state, num_workers, initial_evacuation);
log_debug(gc, ergo)("Running %s using %u workers for " SIZE_FORMAT " regions",
cl.name(), num_workers, increment_length);
workers->run_task(&cl, num_workers);
}
print_merge_heap_roots_stats();
}
void G1RemSet::complete_evac_phase(bool has_more_than_one_evacuation_phase) {
_scan_state->complete_evac_phase(has_more_than_one_evacuation_phase);
}
void G1RemSet::exclude_region_from_scan(uint region_idx) {
_scan_state->clear_scan_top(region_idx);
}
G1AbstractSubTask* G1RemSet::create_cleanup_after_scan_heap_roots_task() {
return _scan_state->create_cleanup_after_scan_heap_roots_task();
}
void G1RemSet::print_coarsen_stats() {
LogTarget(Debug, gc, remset) lt;
if (lt.is_enabled()) {
LogStream ls(lt);
G1CardSet::print_coarsen_stats(&ls);
}
}
inline void check_card_ptr(CardTable::CardValue* card_ptr, G1CardTable* ct) {
#ifdef ASSERT
G1CollectedHeap* g1h = G1CollectedHeap::heap();
assert(g1h->is_in(ct->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->index_for(ct->addr_for(card_ptr)),
p2i(ct->addr_for(card_ptr)),
g1h->addr_to_region(ct->addr_for(card_ptr)));
#endif
}
bool G1RemSet::clean_card_before_refine(CardValue** const card_ptr_addr) {
assert(!SafepointSynchronize::is_at_safepoint(), "Only call concurrently");
CardValue* card_ptr = *card_ptr_addr;
// Find the start address represented by the card.
HeapWord* start = _ct->addr_for(card_ptr);
// And find the region containing it.
HeapRegion* r = _g1h->heap_region_containing_or_null(start);
// If this is a (stale) card into an uncommitted region, exit.
if (r == NULL) {
return false;
}
check_card_ptr(card_ptr, _ct);
// If the card is no longer dirty, nothing to do.
// We cannot load the card value before the "r == NULL" check, because G1
// could uncommit parts of the card table covering uncommitted regions.
if (*card_ptr != G1CardTable::dirty_card_val()) {
return false;
}
// 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_or_archive()) {
return false;
}
// 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 (G1HotCardCache::use_cache()) {
const CardValue* 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 false;
} else if (card_ptr != orig_card_ptr) {
// Original card was inserted and an old card was evicted.
start = _ct->addr_for(card_ptr);
r = _g1h->heap_region_containing_or_null(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 (or even uncommitted) while
// in the cache.
if (r == nullptr || !r->is_old_or_humongous_or_archive()) {
return false;
}
*card_ptr_addr = card_ptr;
} // 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 either allocated in the old regions during GC,
// or mapped in archive regions during startup. So if region is old or
// archive 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 false;
}
// 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 CardValue*>(card_ptr) = G1CardTable::clean_card_val();
return true;
}
void G1RemSet::refine_card_concurrently(CardValue* const card_ptr,
const uint worker_id) {
assert(!_g1h->is_gc_active(), "Only call concurrently");
check_card_ptr(card_ptr, _ct);
// Construct the MemRegion representing the card.
HeapWord* start = _ct->addr_for(card_ptr);
// And find the region containing it.
HeapRegion* r = _g1h->heap_region_containing(start);
// This reload of the top is safe even though it happens after the full
// fence, because top is stable for old, archive and unfiltered humongous
// regions, so it must return the same value as the previous load when
// cleaning the card. Also cleaning the card and refinement of the card
// cannot span across safepoint, so we don't need to worry about top being
// changed during safepoint.
HeapWord* scan_limit = r->top();
assert(scan_limit > start, "sanity");
// Don't use addr_for(card_ptr + 1) which can ask for
// a card beyond the heap.
HeapWord* end = start + G1CardTable::card_size_in_words();
MemRegion dirty_region(start, MIN2(scan_limit, end));
assert(!dirty_region.is_empty(), "sanity");
G1ConcurrentRefineOopClosure conc_refine_cl(_g1h, worker_id);
if (r->oops_on_memregion_seq_iterate_careful<false>(dirty_region, &conc_refine_cl) != NULL) {
return;
}
// If unable to process the card then we encountered an unparsable
// part of the heap (e.g. a partially allocated object, so only
// temporarily a problem) while processing a stale card. Despite
// the card being stale, we can't simply ignore it, because we've
// already marked the card cleaned, so taken responsibility for
// ensuring the card gets scanned.
//
// However, the card might have gotten re-dirtied and re-enqueued
// while we worked. (In fact, it's pretty likely.)
if (*card_ptr == G1CardTable::dirty_card_val()) {
return;
}
enqueue_for_reprocessing(card_ptr);
}
// Re-dirty and re-enqueue the card to retry refinement later.
// This is used to deal with a rare race condition in concurrent refinement.
void G1RemSet::enqueue_for_reprocessing(CardValue* card_ptr) {
// We can't use the thread-local queue, because that might be the queue
// that is being processed by us; we could be a Java thread conscripted to
// perform refinement on our queue's current buffer. This situation only
// arises from rare race condition, so it's not worth any significant
// development effort or clever lock-free queue implementation. Instead
// we use brute force, allocating and enqueuing an entire buffer for just
// this card. Since buffers are processed in FIFO order and we try to
// keep some in the queue, it is likely that the racing state will have
// resolved by the time this card comes up for reprocessing.
*card_ptr = G1CardTable::dirty_card_val();
G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
void** buffer = dcqs.allocate_buffer();
size_t index = dcqs.buffer_size() - 1;
buffer[index] = card_ptr;
dcqs.enqueue_completed_buffer(BufferNode::make_node_from_buffer(buffer, index));
}
void G1RemSet::print_periodic_summary_info(const char* header, uint period_count, bool show_thread_times) {
if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
(period_count % G1SummarizeRSetStatsPeriod == 0)) {
G1RemSetSummary current;
_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, show_thread_times);
_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;
ResourceMark rm;
LogStream ls(log.trace());
current.print_on(&ls, true /* show_thread_times*/);
}
}
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