1 /*
2 * Copyright (c) 2021, Amazon.com, Inc. or its affiliates. All rights reserved.
3 *
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26
27 #include "precompiled.hpp"
28
29 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
30 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
31 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
32 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
33 #include "logging/log.hpp"
34
35 ShenandoahDirectCardMarkRememberedSet::ShenandoahDirectCardMarkRememberedSet(ShenandoahCardTable* card_table, size_t total_card_count) {
36 _heap = ShenandoahHeap::heap();
37 _card_table = card_table;
38 _total_card_count = total_card_count;
39 _cluster_count = total_card_count / ShenandoahCardCluster<ShenandoahDirectCardMarkRememberedSet>::CardsPerCluster;
40 _card_shift = CardTable::card_shift();
41
42 _byte_map = _card_table->byte_for_index(0);
43
44 _whole_heap_base = _card_table->addr_for(_byte_map);
45 _byte_map_base = _byte_map - (uintptr_t(_whole_heap_base) >> _card_shift);
46
47 assert(total_card_count % ShenandoahCardCluster<ShenandoahDirectCardMarkRememberedSet>::CardsPerCluster == 0, "Invalid card count.");
48 assert(total_card_count > 0, "Card count cannot be zero.");
49 }
50
51 ShenandoahScanRememberedTask::ShenandoahScanRememberedTask(ShenandoahObjToScanQueueSet* queue_set,
52 ShenandoahObjToScanQueueSet* old_queue_set,
53 ShenandoahReferenceProcessor* rp,
54 ShenandoahRegionChunkIterator* work_list, bool is_concurrent) :
55 WorkerTask("Scan Remembered Set"),
56 _queue_set(queue_set), _old_queue_set(old_queue_set), _rp(rp), _work_list(work_list), _is_concurrent(is_concurrent) {}
57
58 void ShenandoahScanRememberedTask::work(uint worker_id) {
59 if (_is_concurrent) {
60 // This sets up a thread local reference to the worker_id which is needed by the weak reference processor.
61 ShenandoahConcurrentWorkerSession worker_session(worker_id);
62 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
63 do_work(worker_id);
64 } else {
65 // This sets up a thread local reference to the worker_id which is needed by the weak reference processor.
66 ShenandoahParallelWorkerSession worker_session(worker_id);
67 do_work(worker_id);
68 }
69 }
70
71 void ShenandoahScanRememberedTask::do_work(uint worker_id) {
72 ShenandoahWorkerTimingsTracker x(ShenandoahPhaseTimings::init_scan_rset, ShenandoahPhaseTimings::ScanClusters, worker_id);
73
74 ShenandoahObjToScanQueue* q = _queue_set->queue(worker_id);
75 ShenandoahObjToScanQueue* old = _old_queue_set == NULL ? NULL : _old_queue_set->queue(worker_id);
76 ShenandoahMarkRefsClosure<YOUNG> cl(q, _rp, old);
77 ShenandoahHeap* heap = ShenandoahHeap::heap();
78 RememberedScanner* scanner = heap->card_scan();
79
80 // set up thread local closure for shen ref processor
81 _rp->set_mark_closure(worker_id, &cl);
82 struct ShenandoahRegionChunk assignment;
83 while (_work_list->next(&assignment)) {
84 ShenandoahHeapRegion* region = assignment._r;
85 log_debug(gc)("ShenandoahScanRememberedTask::do_work(%u), processing slice of region "
86 SIZE_FORMAT " at offset " SIZE_FORMAT ", size: " SIZE_FORMAT,
87 worker_id, region->index(), assignment._chunk_offset, assignment._chunk_size);
88 if (region->affiliation() == OLD_GENERATION) {
89 size_t cluster_size =
90 CardTable::card_size_in_words() * ShenandoahCardCluster<ShenandoahDirectCardMarkRememberedSet>::CardsPerCluster;
91 size_t clusters = assignment._chunk_size / cluster_size;
92 assert(clusters * cluster_size == assignment._chunk_size, "Chunk assignments must align on cluster boundaries");
93 HeapWord* end_of_range = region->bottom() + assignment._chunk_offset + assignment._chunk_size;
94
95 // During concurrent mark, region->top() equals TAMS with respect to the current young-gen pass.
96 if (end_of_range > region->top()) {
97 end_of_range = region->top();
98 }
99 scanner->process_region_slice(region, assignment._chunk_offset, clusters, end_of_range, &cl, false, _is_concurrent, worker_id);
100 }
101 #ifdef ENABLE_REMEMBERED_SET_CANCELLATION
102 // This check is currently disabled to avoid crashes that occur
103 // when we try to cancel remembered set scanning; it should be re-enabled
104 // after the issues are fixed, as it would allow more prompt cancellation and
105 // transition to degenerated / full GCs. Note that work that has been assigned/
106 // claimed above must be completed before we return here upon cancellation.
107 if (heap->check_cancelled_gc_and_yield(_is_concurrent)) {
108 return;
109 }
110 #endif
111 }
112 }
113
114 size_t ShenandoahRegionChunkIterator::calc_regular_group_size() {
115 // The group size is calculated from the number of regions. Suppose the entire heap size is N. The first group processes
116 // N/2 of total heap size. The second group processes N/4 of total heap size. The third group processes N/2 of total heap
117 // size, and so on. Note that N/2 + N/4 + N/8 + N/16 + ... sums to N if expanded to infinite terms.
118 //
119 // The normal group size is the number of regions / 2.
120 //
121 // In the case that the region_size_words is greater than _maximum_chunk_size_words, the first group_size is
122 // larger than the normal group size because each chunk in the group will be smaller than the region size.
123 //
124 // The last group also has more than the normal entries because it finishes the total scanning effort. The chunk sizes are
125 // different for each group. The intention is that the first group processes roughly half of the heap, the second processes
126 // a quarter of the remaining heap, the third processes an eight of what remains and so on. The smallest chunk size
127 // is represented by _smallest_chunk_size_words. We do not divide work any smaller than this.
128 //
129
130 size_t group_size = _heap->num_regions() / 2;
131 return group_size;
132 }
133
134 size_t ShenandoahRegionChunkIterator::calc_first_group_chunk_size_b4_rebalance() {
135 size_t words_in_first_chunk = ShenandoahHeapRegion::region_size_words();
136 return words_in_first_chunk;
137 }
138
139 size_t ShenandoahRegionChunkIterator::calc_num_groups() {
140 size_t total_heap_size = _heap->num_regions() * ShenandoahHeapRegion::region_size_words();
141 size_t num_groups = 0;
142 size_t cumulative_group_span = 0;
143 size_t current_group_span = _first_group_chunk_size_b4_rebalance * _regular_group_size;
144 size_t smallest_group_span = smallest_chunk_size_words() * _regular_group_size;
145 while ((num_groups < _maximum_groups) && (cumulative_group_span + current_group_span <= total_heap_size)) {
146 num_groups++;
147 cumulative_group_span += current_group_span;
148 if (current_group_span <= smallest_group_span) {
149 break;
150 } else {
151 current_group_span /= 2; // Each group spans half of what the preceding group spanned.
152 }
153 }
154 // Loop post condition:
155 // num_groups <= _maximum_groups
156 // cumulative_group_span is the memory spanned by num_groups
157 // current_group_span is the span of the last fully populated group (assuming loop iterates at least once)
158 // each of num_groups is fully populated with _regular_group_size chunks in each
159 // Non post conditions:
160 // cumulative_group_span may be less than total_heap size for one or more of the folowing reasons
161 // a) The number of regions remaining to be spanned is smaller than a complete group, or
162 // b) We have filled up all groups through _maximum_groups and still have not spanned all regions
163
164 if (cumulative_group_span < total_heap_size) {
165 // We've got more regions to span
166 if ((num_groups < _maximum_groups) && (current_group_span > smallest_group_span)) {
167 num_groups++; // Place all remaining regions into a new not-full group (chunk_size half that of previous group)
168 }
169 // Else we are unable to create a new group because we've exceed the number of allowed groups or have reached the
170 // minimum chunk size.
171
172 // Any remaining regions will be treated as if they are part of the most recently created group. This group will
173 // have more than _regular_group_size chunks within it.
174 }
175 return num_groups;
176 }
177
178 size_t ShenandoahRegionChunkIterator::calc_total_chunks() {
179 size_t region_size_words = ShenandoahHeapRegion::region_size_words();
180 size_t unspanned_heap_size = _heap->num_regions() * region_size_words;
181 size_t num_chunks = 0;
182 size_t cumulative_group_span = 0;
183 size_t current_group_span = _first_group_chunk_size_b4_rebalance * _regular_group_size;
184 size_t smallest_group_span = smallest_chunk_size_words() * _regular_group_size;
185
186 // The first group gets special handling because the first chunk size can be no larger than _largest_chunk_size_words
187 if (region_size_words > _maximum_chunk_size_words) {
188 // In the case that we shrink the first group's chunk size, certain other groups will also be subsumed within the first group
189 size_t effective_chunk_size = _first_group_chunk_size_b4_rebalance;
190 while (effective_chunk_size >= _maximum_chunk_size_words) {
191 num_chunks += current_group_span / _maximum_chunk_size_words;
192 unspanned_heap_size -= current_group_span;
193 effective_chunk_size /= 2;
194 current_group_span /= 2;
195 }
196 } else {
197 num_chunks = _regular_group_size;
198 unspanned_heap_size -= current_group_span;
199 current_group_span /= 2;
200 }
201 size_t spanned_groups = 1;
202 while (unspanned_heap_size > 0) {
203 if (current_group_span <= unspanned_heap_size) {
204 unspanned_heap_size -= current_group_span;
205 num_chunks += _regular_group_size;
206 spanned_groups++;
207
208 // _num_groups is the number of groups required to span the configured heap size. We are not allowed
209 // to change the number of groups. The last group is responsible for spanning all chunks not spanned
210 // by previously processed groups.
211 if (spanned_groups >= _num_groups) {
212 // The last group has more than _regular_group_size entries.
213 size_t chunk_span = current_group_span / _regular_group_size;
214 size_t extra_chunks = unspanned_heap_size / chunk_span;
215 assert (extra_chunks * chunk_span == unspanned_heap_size, "Chunks must precisely span regions");
216 num_chunks += extra_chunks;
217 return num_chunks;
218 } else if (current_group_span <= smallest_group_span) {
219 // We cannot introduce new groups because we've reached the lower bound on group size. So this last
220 // group may hold extra chunks.
221 size_t chunk_span = smallest_chunk_size_words();
222 size_t extra_chunks = unspanned_heap_size / chunk_span;
223 assert (extra_chunks * chunk_span == unspanned_heap_size, "Chunks must precisely span regions");
224 num_chunks += extra_chunks;
225 return num_chunks;
226 } else {
227 current_group_span /= 2;
228 }
229 } else {
230 // This last group has fewer than _regular_group_size entries.
231 size_t chunk_span = current_group_span / _regular_group_size;
232 size_t last_group_size = unspanned_heap_size / chunk_span;
233 assert (last_group_size * chunk_span == unspanned_heap_size, "Chunks must precisely span regions");
234 num_chunks += last_group_size;
235 return num_chunks;
236 }
237 }
238 return num_chunks;
239 }
240
241 ShenandoahRegionChunkIterator::ShenandoahRegionChunkIterator(size_t worker_count) :
242 ShenandoahRegionChunkIterator(ShenandoahHeap::heap(), worker_count)
243 {
244 }
245
246 ShenandoahRegionChunkIterator::ShenandoahRegionChunkIterator(ShenandoahHeap* heap, size_t worker_count) :
247 _heap(heap),
248 _regular_group_size(calc_regular_group_size()),
249 _first_group_chunk_size_b4_rebalance(calc_first_group_chunk_size_b4_rebalance()),
250 _num_groups(calc_num_groups()),
251 _total_chunks(calc_total_chunks()),
252 _index(0)
253 {
254 #ifdef ASSERT
255 size_t expected_chunk_size_words = _clusters_in_smallest_chunk * CardTable::card_size_in_words() * ShenandoahCardCluster<ShenandoahDirectCardMarkRememberedSet>::CardsPerCluster;
256 assert(smallest_chunk_size_words() == expected_chunk_size_words, "_smallest_chunk_size (" SIZE_FORMAT") is not valid because it does not equal (" SIZE_FORMAT ")",
257 smallest_chunk_size_words(), expected_chunk_size_words);
258 #endif
259 assert(_num_groups <= _maximum_groups,
260 "The number of remembered set scanning groups must be less than or equal to maximum groups");
261 assert(smallest_chunk_size_words() << (_maximum_groups - 1) == _maximum_chunk_size_words,
262 "Maximum number of groups needs to span maximum chunk size to smallest chunk size");
263
264 size_t words_in_region = ShenandoahHeapRegion::region_size_words();
265 _region_index[0] = 0;
266 _group_offset[0] = 0;
267 if (words_in_region > _maximum_chunk_size_words) {
268 // In the case that we shrink the first group's chunk size, certain other groups will also be subsumed within the first group
269 size_t num_chunks = 0;
270 size_t effective_chunk_size = _first_group_chunk_size_b4_rebalance;
271 size_t current_group_span = effective_chunk_size * _regular_group_size;
272 while (effective_chunk_size >= _maximum_chunk_size_words) {
273 num_chunks += current_group_span / _maximum_chunk_size_words;
274 effective_chunk_size /= 2;
275 current_group_span /= 2;
276 }
277 _group_entries[0] = num_chunks;
278 _group_chunk_size[0] = _maximum_chunk_size_words;
279 } else {
280 _group_entries[0] = _regular_group_size;
281 _group_chunk_size[0] = _first_group_chunk_size_b4_rebalance;
282 }
283
284 size_t previous_group_span = _group_entries[0] * _group_chunk_size[0];
285 for (size_t i = 1; i < _num_groups; i++) {
286 size_t previous_group_entries = (i == 1)? _group_entries[0]: (_group_entries[i-1] - _group_entries[i-2]);
287 _group_chunk_size[i] = _group_chunk_size[i-1] / 2;
288 size_t chunks_in_group = _regular_group_size;
289 size_t this_group_span = _group_chunk_size[i] * chunks_in_group;
290 size_t total_span_of_groups = previous_group_span + this_group_span;
291 _region_index[i] = previous_group_span / words_in_region;
292 _group_offset[i] = previous_group_span % words_in_region;
293 _group_entries[i] = _group_entries[i-1] + _regular_group_size;
294 previous_group_span = total_span_of_groups;
295 }
296 if (_group_entries[_num_groups-1] < _total_chunks) {
297 assert((_total_chunks - _group_entries[_num_groups-1]) * _group_chunk_size[_num_groups-1] + previous_group_span ==
298 heap->num_regions() * words_in_region, "Total region chunks (" SIZE_FORMAT
299 ") do not span total heap regions (" SIZE_FORMAT ")", _total_chunks, _heap->num_regions());
300 previous_group_span += (_total_chunks - _group_entries[_num_groups-1]) * _group_chunk_size[_num_groups-1];
301 _group_entries[_num_groups-1] = _total_chunks;
302 }
303 assert(previous_group_span == heap->num_regions() * words_in_region, "Total region chunks (" SIZE_FORMAT
304 ") do not span total heap regions (" SIZE_FORMAT "): " SIZE_FORMAT " does not equal " SIZE_FORMAT,
305 _total_chunks, _heap->num_regions(), previous_group_span, heap->num_regions() * words_in_region);
306
307 // Not necessary, but keeps things tidy
308 for (size_t i = _num_groups; i < _maximum_groups; i++) {
309 _region_index[i] = 0;
310 _group_offset[i] = 0;
311 _group_entries[i] = _group_entries[i-1];
312 _group_chunk_size[i] = 0;
313 }
314 }
315
316 void ShenandoahRegionChunkIterator::reset() {
317 _index = 0;
318 }