8227084: Add timing information for merge heap root preparation
Reviewed-by: sangheki, kbarrett
/*
* Copyright (c) 2001, 2019, 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
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*/
#include "precompiled.hpp"
#include "gc/g1/g1BarrierSet.hpp"
#include "gc/g1/g1BlockOffsetTable.inline.hpp"
#include "gc/g1/g1CardTable.inline.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/g1GCPhaseTimes.hpp"
#include "gc/g1/g1HotCardCache.hpp"
#include "gc/g1/g1OopClosures.inline.hpp"
#include "gc/g1/g1RootClosures.hpp"
#include "gc/g1/g1RemSet.hpp"
#include "gc/g1/g1SharedDirtyCardQueue.hpp"
#include "gc/g1/heapRegion.inline.hpp"
#include "gc/g1/heapRegionManager.inline.hpp"
#include "gc/g1/heapRegionRemSet.inline.hpp"
#include "gc/g1/sparsePRT.hpp"
#include "gc/shared/gcTraceTime.inline.hpp"
#include "gc/shared/suspendibleThreadSet.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/os.hpp"
#include "utilities/align.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/stack.inline.hpp"
#include "utilities/ticks.hpp"
// 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_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;
// Random power of two number of cards we want to claim per thread. This corresponds
// to a 64k of memory work chunk area for every thread.
// We use the same claim size as Parallel GC. No particular measurements have been
// performed to determine an optimal number.
static const uint CardsPerChunk = 128;
uint _scan_chunks_per_region;
bool* _region_scan_chunks;
uint8_t _scan_chunks_shift;
public:
uint scan_chunk_size() 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 * _scan_chunks_per_region + (card_in_region >> _scan_chunks_shift);
assert(idx < (_max_regions * _scan_chunks_per_region), "Index " SIZE_FORMAT " out of bounds " SIZE_FORMAT,
idx, _max_regions * _scan_chunks_per_region);
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 all over them.
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_regions;
bool* _contains;
public:
G1DirtyRegions(size_t max_regions) :
_buffer(NEW_C_HEAP_ARRAY(uint, max_regions, mtGC)),
_cur_idx(0),
_max_regions(max_regions),
_contains(NEW_C_HEAP_ARRAY(bool, max_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_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(true, &_contains[region], false) == false;
if (marked_as_dirty) {
uint allocated = Atomic::add(1u, &_cur_idx) - 1;
_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;
}
}
}
};
// 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 {
G1RemSetScanState* _scan_state;
public:
G1ResetScanTopClosure(G1RemSetScanState* scan_state) : _scan_state(scan_state) { }
virtual bool do_heap_region(HeapRegion* r) {
uint hrm_index = r->hrm_index();
if (r->in_collection_set()) {
// Young regions had their card table marked as young at their allocation;
// we need to make sure that these marks are cleared at the end of GC, *but*
// they should not be scanned for cards.
// So directly add them to the "all_dirty_regions".
// Same for regions in the (initial) collection set: they may contain cards from
// the log buffers, make sure they are cleaned.
_scan_state->add_all_dirty_region(hrm_index);
} else if (r->is_old_or_humongous_or_archive()) {
_scan_state->set_scan_top(hrm_index, r->top());
}
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;
class G1ClearCardTableTask : public AbstractGangTask {
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) :
AbstractGangTask("G1 Clear Card Table Task"),
_g1h(g1h),
_regions(regions),
_chunk_length(chunk_length),
_cur_dirty_regions(0),
_scan_state(scan_state) {
assert(chunk_length > 0, "must be");
}
static uint chunk_size() { return M; }
void work(uint worker_id) {
while (_cur_dirty_regions < _regions->size()) {
uint next = Atomic::add(_chunk_length, &_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();
}
}
}
}
};
// Clear the card table of "dirty" regions.
void clear_card_table(WorkGang* workers) {
uint num_regions = _all_dirty_regions->size();
if (num_regions == 0) {
return;
}
uint const num_chunks = (uint)(align_up((size_t)num_regions << HeapRegion::LogCardsPerRegion, G1ClearCardTableTask::chunk_size()) / G1ClearCardTableTask::chunk_size());
uint const num_workers = MIN2(num_chunks, workers->active_workers());
uint const chunk_length = G1ClearCardTableTask::chunk_size() / (uint)HeapRegion::CardsPerRegion;
// Iterate over the dirty cards region list.
G1ClearCardTableTask cl(G1CollectedHeap::heap(), _all_dirty_regions, chunk_length, this);
log_debug(gc, ergo)("Running %s using %u workers for %u "
"units of work for %u regions.",
cl.name(), num_workers, num_chunks, num_regions);
workers->run_task(&cl, num_workers);
#ifndef PRODUCT
G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup();
#endif
}
public:
G1RemSetScanState() :
_max_regions(0),
_collection_set_iter_state(NULL),
_card_table_scan_state(NULL),
_scan_chunks_per_region((uint)(HeapRegion::CardsPerRegion / CardsPerChunk)),
_region_scan_chunks(NULL),
_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_regions) {
assert(_collection_set_iter_state == NULL, "Must not be initialized twice");
_max_regions = max_regions;
_collection_set_iter_state = NEW_C_HEAP_ARRAY(G1RemsetIterState, max_regions, mtGC);
_card_table_scan_state = NEW_C_HEAP_ARRAY(uint, max_regions, mtGC);
_region_scan_chunks = NEW_C_HEAP_ARRAY(bool, max_regions * _scan_chunks_per_region, mtGC);
_scan_chunks_shift = (uint8_t)log2_intptr(HeapRegion::CardsPerRegion / _scan_chunks_per_region);
_scan_top = NEW_C_HEAP_ARRAY(HeapWord*, max_regions, mtGC);
}
void prepare() {
for (size_t i = 0; i < _max_regions; i++) {
_collection_set_iter_state[i] = false;
clear_scan_top((uint)i);
}
_all_dirty_regions = new G1DirtyRegions(_max_regions);
_next_dirty_regions = new G1DirtyRegions(_max_regions);
G1ResetScanTopClosure cl(this);
G1CollectedHeap::heap()->heap_region_iterate(&cl);
}
void prepare_for_merge_heap_roots() {
_all_dirty_regions->merge(_next_dirty_regions);
_next_dirty_regions->reset();
for (size_t i = 0; i < _max_regions; i++) {
_card_table_scan_state[i] = 0;
}
::memset(_region_scan_chunks, false, _max_regions * _scan_chunks_per_region * sizeof(*_region_scan_chunks));
}
// 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 < _max_regions * _scan_chunks_per_region; i++) {
if (_region_scan_chunks[i]) {
result++;
}
}
return result * CardsPerChunk;
}
size_t num_cards_in_dirty_regions() const {
return _next_dirty_regions->size() * HeapRegion::CardsPerRegion;
}
void set_chunk_region_dirty(size_t const region_card_idx) {
size_t chunk_idx = region_card_idx >> _scan_chunks_shift;
for (uint i = 0; i < _scan_chunks_per_region; i++) {
_region_scan_chunks[chunk_idx++] = true;
}
}
void set_chunk_dirty(size_t const card_idx) {
assert((card_idx >> _scan_chunks_shift) < (_max_regions * _scan_chunks_per_region),
"Trying to access index " SIZE_FORMAT " out of bounds " SIZE_FORMAT,
card_idx >> _scan_chunks_shift, _max_regions * _scan_chunks_per_region);
size_t const chunk_idx = card_idx >> _scan_chunks_shift;
if (!_region_scan_chunks[chunk_idx]) {
_region_scan_chunks[chunk_idx] = true;
}
}
void cleanup(WorkGang* workers) {
_all_dirty_regions->merge(_next_dirty_regions);
clear_card_table(workers);
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();
WorkGang* 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);
}
// 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_regions, "Tried to access invalid region %u", region);
if (_collection_set_iter_state[region]) {
return false;
}
return !Atomic::cmpxchg(true, &_collection_set_iter_state[region], false);
}
bool has_cards_to_scan(uint region) {
assert(region < _max_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_regions, "Tried to access invalid region %u", region);
return Atomic::add(increment, &_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 young 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(),
_g1h(g1h),
_num_conc_refined_cards(0),
_ct(ct),
_g1p(_g1h->policy()),
_hot_card_cache(hot_card_cache) {
}
G1RemSet::~G1RemSet() {
delete _scan_state;
}
uint G1RemSet::num_par_rem_sets() {
return G1DirtyCardQueueSet::num_par_ids() + G1ConcurrentRefine::max_num_threads() + MAX2(ConcGCThreads, ParallelGCThreads);
}
void G1RemSet::initialize(size_t capacity, uint max_regions) {
G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
_scan_state->initialize(max_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(); }
};
// 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;
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;
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);
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::LogN_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->mark_as_scanned(first_card, num_cards);
do_claimed_block(region_idx, first_card, num_cards);
_blocks_scanned++;
}
void scan_heap_roots(HeapRegion* r) {
EventGCPhaseParallel event;
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()) {
assert(*_ct->byte_for_index(region_card_base_idx + first_scan_idx) <= 0x1, "is %d at region %u idx " SIZE_FORMAT, *_ct->byte_for_index(region_card_base_idx + first_scan_idx), region_idx, first_scan_idx);
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++;
}
event.commit(GCId::current(), _worker_id, G1GCPhaseTimes::phase_name(G1GCPhaseTimes::ScanHR));
}
public:
G1ScanHRForRegionClosure(G1RemSetScanState* scan_state,
G1ParScanThreadState* pss,
uint worker_id,
G1GCPhaseTimes::GCParPhases phase) :
_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),
_rem_set_root_scan_time(),
_rem_set_trim_partially_time(),
_scanned_to(NULL) {
}
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; }
};
void G1RemSet::scan_heap_roots(G1ParScanThreadState* pss,
uint worker_id,
G1GCPhaseTimes::GCParPhases scan_phase,
G1GCPhaseTimes::GCParPhases objcopy_phase) {
G1ScanHRForRegionClosure cl(_scan_state, pss, worker_id, scan_phase);
_scan_state->iterate_dirty_regions_from(&cl, worker_id);
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);
}
// 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_refs_scanned;
size_t _opt_refs_memory_used;
Tickspan _strong_code_root_scan_time;
Tickspan _strong_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) {
EventGCPhaseParallel event;
G1OopStarChunkedList* opt_rem_set_list = _pss->oops_into_optional_region(r);
G1ScanCardClosure scan_cl(G1CollectedHeap::heap(), _pss);
G1ScanRSForOptionalClosure cl(G1CollectedHeap::heap(), &scan_cl);
_opt_refs_scanned += opt_rem_set_list->oops_do(&cl, _pss->closures()->raw_strong_oops());
_opt_refs_memory_used += opt_rem_set_list->used_memory();
event.commit(GCId::current(), _worker_id, G1GCPhaseTimes::phase_name(_scan_phase));
}
public:
G1ScanCollectionSetRegionClosure(G1RemSetScanState* scan_state,
G1ParScanThreadState* pss,
uint worker_i,
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_i),
_opt_refs_scanned(0),
_opt_refs_memory_used(0),
_strong_code_root_scan_time(),
_strong_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()) {
G1EvacPhaseWithTrimTimeTracker timer(_pss, _rem_set_opt_root_scan_time, _rem_set_opt_trim_partially_time);
scan_opt_rem_set_roots(r);
}
if (_scan_state->claim_collection_set_region(region_idx)) {
EventGCPhaseParallel event;
G1EvacPhaseWithTrimTimeTracker timer(_pss, _strong_code_root_scan_time, _strong_code_trim_partially_time);
// Scan the strong code root list attached to the current region
r->strong_code_roots_do(_pss->closures()->weak_codeblobs());
event.commit(GCId::current(), _worker_id, G1GCPhaseTimes::phase_name(_code_roots_phase));
}
return false;
}
Tickspan strong_code_root_scan_time() const { return _strong_code_root_scan_time; }
Tickspan strong_code_root_trim_partially_time() const { return _strong_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_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.strong_code_root_scan_time().seconds());
p->add_time_secs(objcopy_phase, worker_id, cl.strong_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_refs_scanned(), G1GCPhaseTimes::ScanHRScannedOptRefs);
p->record_or_add_thread_work_item(scan_phase, worker_id, cl.opt_refs_memory_used(), G1GCPhaseTimes::ScanHRUsedMemory);
}
}
void G1RemSet::prepare_for_scan_heap_roots() {
G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
dcqs.concatenate_logs();
_scan_state->prepare();
}
class G1MergeHeapRootsTask : public AbstractGangTask {
// Visitor for remembered sets, dropping entries onto the card table.
class G1MergeCardSetClosure : public HeapRegionClosure {
G1RemSetScanState* _scan_state;
G1CardTable* _ct;
uint _merged_sparse;
uint _merged_fine;
uint _merged_coarse;
// Returns if 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;
}
public:
G1MergeCardSetClosure(G1RemSetScanState* scan_state) :
_scan_state(scan_state),
_ct(G1CollectedHeap::heap()->card_table()),
_merged_sparse(0),
_merged_fine(0),
_merged_coarse(0) { }
void next_coarse_prt(uint const region_idx) {
if (!remember_if_interesting(region_idx)) {
return;
}
_merged_coarse++;
size_t region_base_idx = (size_t)region_idx << HeapRegion::LogCardsPerRegion;
_ct->mark_region_dirty(region_base_idx, HeapRegion::CardsPerRegion);
_scan_state->set_chunk_region_dirty(region_base_idx);
}
void next_fine_prt(uint const region_idx, BitMap* bm) {
if (!remember_if_interesting(region_idx)) {
return;
}
_merged_fine++;
size_t const region_base_idx = (size_t)region_idx << HeapRegion::LogCardsPerRegion;
BitMap::idx_t cur = bm->get_next_one_offset(0);
while (cur != bm->size()) {
_ct->mark_clean_as_dirty(region_base_idx + cur);
_scan_state->set_chunk_dirty(region_base_idx + cur);
cur = bm->get_next_one_offset(cur + 1);
}
}
void next_sparse_prt(uint const region_idx, SparsePRTEntry::card_elem_t* cards, uint const num_cards) {
if (!remember_if_interesting(region_idx)) {
return;
}
_merged_sparse++;
size_t const region_base_idx = (size_t)region_idx << HeapRegion::LogCardsPerRegion;
for (uint i = 0; i < num_cards; i++) {
size_t card_idx = region_base_idx + cards[i];
_ct->mark_clean_as_dirty(card_idx);
_scan_state->set_chunk_dirty(card_idx);
}
}
virtual bool do_heap_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_prts(*this);
}
return false;
}
size_t merged_sparse() const { return _merged_sparse; }
size_t merged_fine() const { return _merged_fine; }
size_t merged_coarse() const { return _merged_coarse; }
};
// Visitor for the remembered sets of humongous candidate regions to merge their
// remembered set into the card table.
class G1FlushHumongousCandidateRemSets : public HeapRegionClosure {
G1MergeCardSetClosure _cl;
public:
G1FlushHumongousCandidateRemSets(G1RemSetScanState* scan_state) : _cl(scan_state) { }
virtual bool do_heap_region(HeapRegion* r) {
G1CollectedHeap* g1h = G1CollectedHeap::heap();
if (!r->is_starts_humongous() ||
!g1h->region_attr(r->hrm_index()).is_humongous() ||
r->rem_set()->is_empty()) {
return false;
}
guarantee(r->rem_set()->occupancy_less_or_equal_than(G1RSetSparseRegionEntries),
"Found a not-small remembered set here. This is inconsistent with previous assumptions.");
_cl.do_heap_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(r->hrm_index());
assert(region_attr.needs_remset_update(), "must be");
#endif
assert(r->rem_set()->is_empty(), "At this point any humongous candidate remembered set must be empty.");
return false;
}
size_t merged_sparse() const { return _cl.merged_sparse(); }
size_t merged_fine() const { return _cl.merged_fine(); }
size_t merged_coarse() const { return _cl.merged_coarse(); }
};
// 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;
public:
G1MergeLogBufferCardsClosure(G1CollectedHeap* g1h, G1RemSetScanState* scan_state) :
_scan_state(scan_state), _ct(g1h->card_table()), _cards_dirty(0), _cards_skipped(0)
{}
bool do_card_ptr(CardValue* 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_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 uncommited
// 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) && (*card_ptr == G1CardTable::dirty_card_val())) {
_scan_state->add_dirty_region(region_idx);
_scan_state->set_chunk_dirty(_ct->index_for_cardvalue(card_ptr));
_cards_dirty++;
} 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++;
}
return true;
}
size_t cards_dirty() const { return _cards_dirty; }
size_t cards_skipped() const { return _cards_skipped; }
};
HeapRegionClaimer _hr_claimer;
G1RemSetScanState* _scan_state;
bool _initial_evacuation;
volatile bool _fast_reclaim_handled;
public:
G1MergeHeapRootsTask(G1RemSetScanState* scan_state, uint num_workers, bool initial_evacuation) :
AbstractGangTask("G1 Merge Heap Roots"),
_hr_claimer(num_workers),
_scan_state(scan_state),
_initial_evacuation(initial_evacuation),
_fast_reclaim_handled(false) { }
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;
// We schedule flushing the remembered sets of humongous fast reclaim candidates
// onto the card table first to allow the remaining parallelized tasks hide it.
if (_initial_evacuation &&
p->fast_reclaim_humongous_candidates() > 0 &&
!_fast_reclaim_handled &&
!Atomic::cmpxchg(true, &_fast_reclaim_handled, false)) {
G1FlushHumongousCandidateRemSets cl(_scan_state);
g1h->heap_region_iterate(&cl);
p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_sparse(), G1GCPhaseTimes::MergeRSMergedSparse);
p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_fine(), G1GCPhaseTimes::MergeRSMergedFine);
p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_coarse(), G1GCPhaseTimes::MergeRSMergedCoarse);
}
// Merge remembered sets of current candidates.
{
G1GCParPhaseTimesTracker x(p, merge_remset_phase, worker_id, _initial_evacuation /* must_record */);
G1MergeCardSetClosure cl(_scan_state);
g1h->collection_set_iterate_increment_from(&cl, &_hr_claimer, worker_id);
p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_sparse(), G1GCPhaseTimes::MergeRSMergedSparse);
p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_fine(), G1GCPhaseTimes::MergeRSMergedFine);
p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_coarse(), G1GCPhaseTimes::MergeRSMergedCoarse);
}
// Apply closure to log entries in the HCC.
if (_initial_evacuation && G1HotCardCache::default_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);
}
// 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);
g1h->iterate_dirty_card_closure(&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() {
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;
log_debug(gc,remset)("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);
}
}
WorkGang* 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);
}
if (log_is_enabled(Debug, gc, remset)) {
print_merge_heap_roots_stats();
}
}
void G1RemSet::prepare_for_scan_heap_roots(uint region_idx) {
_scan_state->clear_scan_top(region_idx);
}
void G1RemSet::cleanup_after_scan_heap_roots() {
G1GCPhaseTimes* phase_times = _g1h->phase_times();
// Set all cards back to clean.
double start = os::elapsedTime();
_scan_state->cleanup(_g1h->workers());
phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
}
inline void check_card_ptr(CardTable::CardValue* card_ptr, G1CardTable* ct) {
#ifdef ASSERT
G1CollectedHeap* g1h = G1CollectedHeap::heap();
assert(g1h->is_in_exact(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
}
void G1RemSet::refine_card_concurrently(CardValue* card_ptr,
uint worker_i) {
assert(!_g1h->is_gc_active(), "Only call concurrently");
// Construct the region representing 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;
}
check_card_ptr(card_ptr, _ct);
// If the card is no longer dirty, nothing to do.
if (*card_ptr != G1CardTable::dirty_card_val()) {
return;
}
// 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;
}
// 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 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;
} 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(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_or_archive()) {
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 CardValue*>(card_ptr) = G1CardTable::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 + 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_i);
if (r->oops_on_memregion_seq_iterate_careful<false>(dirty_region, &conc_refine_cl) != NULL) {
_num_conc_refined_cards++; // Unsynchronized update, only used for logging.
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;
}
// Re-dirty the card and enqueue in the *shared* queue. 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.
*card_ptr = G1CardTable::dirty_card_val();
G1BarrierSet::shared_dirty_card_queue().enqueue(card_ptr);
}
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);
}
}
class G1RebuildRemSetTask: public AbstractGangTask {
// Aggregate the counting data that was constructed concurrently
// with marking.
class G1RebuildRemSetHeapRegionClosure : public HeapRegionClosure {
G1ConcurrentMark* _cm;
G1RebuildRemSetClosure _update_cl;
// Applies _update_cl to the references of the given object, limiting objArrays
// to the given MemRegion. Returns the amount of words actually scanned.
size_t scan_for_references(oop const obj, MemRegion mr) {
size_t const obj_size = obj->size();
// All non-objArrays and objArrays completely within the mr
// can be scanned without passing the mr.
if (!obj->is_objArray() || mr.contains(MemRegion((HeapWord*)obj, obj_size))) {
obj->oop_iterate(&_update_cl);
return obj_size;
}
// This path is for objArrays crossing the given MemRegion. Only scan the
// area within the MemRegion.
obj->oop_iterate(&_update_cl, mr);
return mr.intersection(MemRegion((HeapWord*)obj, obj_size)).word_size();
}
// A humongous object is live (with respect to the scanning) either
// a) it is marked on the bitmap as such
// b) its TARS is larger than TAMS, i.e. has been allocated during marking.
bool is_humongous_live(oop const humongous_obj, const G1CMBitMap* const bitmap, HeapWord* tams, HeapWord* tars) const {
return bitmap->is_marked(humongous_obj) || (tars > tams);
}
// Iterator over the live objects within the given MemRegion.
class LiveObjIterator : public StackObj {
const G1CMBitMap* const _bitmap;
const HeapWord* _tams;
const MemRegion _mr;
HeapWord* _current;
bool is_below_tams() const {
return _current < _tams;
}
bool is_live(HeapWord* obj) const {
return !is_below_tams() || _bitmap->is_marked(obj);
}
HeapWord* bitmap_limit() const {
return MIN2(const_cast<HeapWord*>(_tams), _mr.end());
}
void move_if_below_tams() {
if (is_below_tams() && has_next()) {
_current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
}
}
public:
LiveObjIterator(const G1CMBitMap* const bitmap, const HeapWord* tams, const MemRegion mr, HeapWord* first_oop_into_mr) :
_bitmap(bitmap),
_tams(tams),
_mr(mr),
_current(first_oop_into_mr) {
assert(_current <= _mr.start(),
"First oop " PTR_FORMAT " should extend into mr [" PTR_FORMAT ", " PTR_FORMAT ")",
p2i(first_oop_into_mr), p2i(mr.start()), p2i(mr.end()));
// Step to the next live object within the MemRegion if needed.
if (is_live(_current)) {
// Non-objArrays were scanned by the previous part of that region.
if (_current < mr.start() && !oop(_current)->is_objArray()) {
_current += oop(_current)->size();
// We might have positioned _current on a non-live object. Reposition to the next
// live one if needed.
move_if_below_tams();
}
} else {
// The object at _current can only be dead if below TAMS, so we can use the bitmap.
// immediately.
_current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
assert(_current == _mr.end() || is_live(_current),
"Current " PTR_FORMAT " should be live (%s) or beyond the end of the MemRegion (" PTR_FORMAT ")",
p2i(_current), BOOL_TO_STR(is_live(_current)), p2i(_mr.end()));
}
}
void move_to_next() {
_current += next()->size();
move_if_below_tams();
}
oop next() const {
oop result = oop(_current);
assert(is_live(_current),
"Object " PTR_FORMAT " must be live TAMS " PTR_FORMAT " below %d mr " PTR_FORMAT " " PTR_FORMAT " outside %d",
p2i(_current), p2i(_tams), _tams > _current, p2i(_mr.start()), p2i(_mr.end()), _mr.contains(result));
return result;
}
bool has_next() const {
return _current < _mr.end();
}
};
// Rebuild remembered sets in the part of the region specified by mr and hr.
// Objects between the bottom of the region and the TAMS are checked for liveness
// using the given bitmap. Objects between TAMS and TARS are assumed to be live.
// Returns the number of live words between bottom and TAMS.
size_t rebuild_rem_set_in_region(const G1CMBitMap* const bitmap,
HeapWord* const top_at_mark_start,
HeapWord* const top_at_rebuild_start,
HeapRegion* hr,
MemRegion mr) {
size_t marked_words = 0;
if (hr->is_humongous()) {
oop const humongous_obj = oop(hr->humongous_start_region()->bottom());
if (is_humongous_live(humongous_obj, bitmap, top_at_mark_start, top_at_rebuild_start)) {
// We need to scan both [bottom, TAMS) and [TAMS, top_at_rebuild_start);
// however in case of humongous objects it is sufficient to scan the encompassing
// area (top_at_rebuild_start is always larger or equal to TAMS) as one of the
// two areas will be zero sized. I.e. TAMS is either
// the same as bottom or top(_at_rebuild_start). There is no way TAMS has a different
// value: this would mean that TAMS points somewhere into the object.
assert(hr->top() == top_at_mark_start || hr->top() == top_at_rebuild_start,
"More than one object in the humongous region?");
humongous_obj->oop_iterate(&_update_cl, mr);
return top_at_mark_start != hr->bottom() ? mr.intersection(MemRegion((HeapWord*)humongous_obj, humongous_obj->size())).byte_size() : 0;
} else {
return 0;
}
}
for (LiveObjIterator it(bitmap, top_at_mark_start, mr, hr->block_start(mr.start())); it.has_next(); it.move_to_next()) {
oop obj = it.next();
size_t scanned_size = scan_for_references(obj, mr);
if ((HeapWord*)obj < top_at_mark_start) {
marked_words += scanned_size;
}
}
return marked_words * HeapWordSize;
}
public:
G1RebuildRemSetHeapRegionClosure(G1CollectedHeap* g1h,
G1ConcurrentMark* cm,
uint worker_id) :
HeapRegionClosure(),
_cm(cm),
_update_cl(g1h, worker_id) { }
bool do_heap_region(HeapRegion* hr) {
if (_cm->has_aborted()) {
return true;
}
uint const region_idx = hr->hrm_index();
DEBUG_ONLY(HeapWord* const top_at_rebuild_start_check = _cm->top_at_rebuild_start(region_idx);)
assert(top_at_rebuild_start_check == NULL ||
top_at_rebuild_start_check > hr->bottom(),
"A TARS (" PTR_FORMAT ") == bottom() (" PTR_FORMAT ") indicates the old region %u is empty (%s)",
p2i(top_at_rebuild_start_check), p2i(hr->bottom()), region_idx, hr->get_type_str());
size_t total_marked_bytes = 0;
size_t const chunk_size_in_words = G1RebuildRemSetChunkSize / HeapWordSize;
HeapWord* const top_at_mark_start = hr->prev_top_at_mark_start();
HeapWord* cur = hr->bottom();
while (cur < hr->end()) {
// After every iteration (yield point) we need to check whether the region's
// TARS changed due to e.g. eager reclaim.
HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);
if (top_at_rebuild_start == NULL) {
return false;
}
MemRegion next_chunk = MemRegion(hr->bottom(), top_at_rebuild_start).intersection(MemRegion(cur, chunk_size_in_words));
if (next_chunk.is_empty()) {
break;
}
const Ticks start = Ticks::now();
size_t marked_bytes = rebuild_rem_set_in_region(_cm->prev_mark_bitmap(),
top_at_mark_start,
top_at_rebuild_start,
hr,
next_chunk);
Tickspan time = Ticks::now() - start;
log_trace(gc, remset, tracking)("Rebuilt region %u "
"live " SIZE_FORMAT " "
"time %.3fms "
"marked bytes " SIZE_FORMAT " "
"bot " PTR_FORMAT " "
"TAMS " PTR_FORMAT " "
"TARS " PTR_FORMAT,
region_idx,
_cm->liveness(region_idx) * HeapWordSize,
time.seconds() * 1000.0,
marked_bytes,
p2i(hr->bottom()),
p2i(top_at_mark_start),
p2i(top_at_rebuild_start));
if (marked_bytes > 0) {
total_marked_bytes += marked_bytes;
}
cur += chunk_size_in_words;
_cm->do_yield_check();
if (_cm->has_aborted()) {
return true;
}
}
// In the final iteration of the loop the region might have been eagerly reclaimed.
// Simply filter out those regions. We can not just use region type because there
// might have already been new allocations into these regions.
DEBUG_ONLY(HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);)
assert(top_at_rebuild_start == NULL ||
total_marked_bytes == hr->marked_bytes(),
"Marked bytes " SIZE_FORMAT " for region %u (%s) in [bottom, TAMS) do not match calculated marked bytes " SIZE_FORMAT " "
"(" PTR_FORMAT " " PTR_FORMAT " " PTR_FORMAT ")",
total_marked_bytes, hr->hrm_index(), hr->get_type_str(), hr->marked_bytes(),
p2i(hr->bottom()), p2i(top_at_mark_start), p2i(top_at_rebuild_start));
// Abort state may have changed after the yield check.
return _cm->has_aborted();
}
};
HeapRegionClaimer _hr_claimer;
G1ConcurrentMark* _cm;
uint _worker_id_offset;
public:
G1RebuildRemSetTask(G1ConcurrentMark* cm,
uint n_workers,
uint worker_id_offset) :
AbstractGangTask("G1 Rebuild Remembered Set"),
_hr_claimer(n_workers),
_cm(cm),
_worker_id_offset(worker_id_offset) {
}
void work(uint worker_id) {
SuspendibleThreadSetJoiner sts_join;
G1CollectedHeap* g1h = G1CollectedHeap::heap();
G1RebuildRemSetHeapRegionClosure cl(g1h, _cm, _worker_id_offset + worker_id);
g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hr_claimer, worker_id);
}
};
void G1RemSet::rebuild_rem_set(G1ConcurrentMark* cm,
WorkGang* workers,
uint worker_id_offset) {
uint num_workers = workers->active_workers();
G1RebuildRemSetTask cl(cm,
num_workers,
worker_id_offset);
workers->run_task(&cl, num_workers);
}