1 /*
2 * Copyright (c) 2021, Red Hat, Inc. All rights reserved.
3 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
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 "gc/shared/collectorCounters.hpp"
28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
29 #include "gc/shenandoah/shenandoahConcurrentMark.hpp"
30 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
31 #include "gc/shenandoah/shenandoahFullGC.hpp"
32 #include "gc/shenandoah/shenandoahGeneration.hpp"
33 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
35 #include "gc/shenandoah/shenandoahMetrics.hpp"
36 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
37 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
38 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
39 #include "gc/shenandoah/shenandoahStackWatermark.hpp"
40 #include "gc/shenandoah/shenandoahSTWMark.hpp"
41 #include "gc/shenandoah/shenandoahUtils.hpp"
42 #include "gc/shenandoah/shenandoahVerifier.hpp"
43 #include "gc/shenandoah/shenandoahVMOperations.hpp"
44 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
45 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
46 #include "runtime/vmThread.hpp"
47 #include "utilities/events.hpp"
48
49 ShenandoahDegenGC::ShenandoahDegenGC(ShenandoahDegenPoint degen_point, ShenandoahGeneration* generation) :
50 ShenandoahGC(generation),
51 _degen_point(degen_point),
52 _abbreviated(false) {
53 }
54
55 bool ShenandoahDegenGC::collect(GCCause::Cause cause) {
56 vmop_degenerated();
57 ShenandoahHeap* heap = ShenandoahHeap::heap();
58 if (heap->mode()->is_generational()) {
59 bool is_bootstrap_gc = heap->old_generation()->is_bootstrapping();
60 heap->mmu_tracker()->record_degenerated(GCId::current(), is_bootstrap_gc);
61 const char* msg = is_bootstrap_gc? "At end of Degenerated Bootstrap Old GC": "At end of Degenerated Young GC";
62 heap->log_heap_status(msg);
63 }
64 return true;
65 }
66
67 void ShenandoahDegenGC::vmop_degenerated() {
68 TraceCollectorStats tcs(ShenandoahHeap::heap()->monitoring_support()->full_stw_collection_counters());
69 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_gross);
70 VM_ShenandoahDegeneratedGC degenerated_gc(this);
71 VMThread::execute(°enerated_gc);
72 }
73
74 void ShenandoahDegenGC::entry_degenerated() {
75 const char* msg = degen_event_message(_degen_point);
76 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::degen_gc, true /* log_heap_usage */);
77 EventMark em("%s", msg);
78 ShenandoahHeap* const heap = ShenandoahHeap::heap();
79 ShenandoahWorkerScope scope(heap->workers(),
80 ShenandoahWorkerPolicy::calc_workers_for_stw_degenerated(),
81 "stw degenerated gc");
82
83 heap->set_degenerated_gc_in_progress(true);
84 op_degenerated();
85 heap->set_degenerated_gc_in_progress(false);
86 {
87 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_propagate_gc_state);
88 heap->propagate_gc_state_to_all_threads();
89 }
90 }
91
92 void ShenandoahDegenGC::op_degenerated() {
93 ShenandoahHeap* const heap = ShenandoahHeap::heap();
94 // Degenerated GC is STW, but it can also fail. Current mechanics communicates
95 // GC failure via cancelled_concgc() flag. So, if we detect the failure after
96 // some phase, we have to upgrade the Degenerate GC to Full GC.
97 heap->clear_cancelled_gc();
98
99 // If it's passive mode with ShenandoahCardBarrier turned on: clean the write table
100 // without swapping the tables since no scan happens in passive mode anyway
101 if (ShenandoahCardBarrier && !heap->mode()->is_generational()) {
102 heap->old_generation()->card_scan()->mark_write_table_as_clean();
103 }
104
105 if (heap->mode()->is_generational()) {
106 const ShenandoahOldGeneration* old_generation = heap->old_generation();
107 if (!heap->is_concurrent_old_mark_in_progress()) {
108 // If we are not marking the old generation, there should be nothing in the old mark queues
109 assert(old_generation->task_queues()->is_empty(), "Old gen task queues should be empty");
110 } else {
111 // This is still necessary for degenerated cycles because the degeneration point may occur
112 // after final mark of the young generation. See ShenandoahConcurrentGC::op_final_update_refs for
113 // a more detailed explanation.
114 old_generation->transfer_pointers_from_satb();
115 }
116
117 if (_generation->is_global()) {
118 // If we are in a global cycle, the old generation should not be marking. It is, however,
119 // allowed to be holding regions for evacuation or coalescing.
120 assert(old_generation->is_idle()
121 || old_generation->is_doing_mixed_evacuations()
122 || old_generation->is_preparing_for_mark(),
123 "Old generation cannot be in state: %s", old_generation->state_name());
124 }
125 }
126
127 ShenandoahMetricsSnapshot metrics(heap->free_set());
128
129 switch (_degen_point) {
130 // The cases below form the Duff's-like device: it describes the actual GC cycle,
131 // but enters it at different points, depending on which concurrent phase had
132 // degenerated.
133
134 case _degenerated_outside_cycle:
135 // We have degenerated from outside the cycle, which means something is bad with
136 // the heap, most probably heavy humongous fragmentation, or we are very low on free
137 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when
138 // we can do the most aggressive degen cycle, which includes processing references and
139 // class unloading, unless those features are explicitly disabled.
140
141 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk
142 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover.
143 heap->set_unload_classes(_generation->heuristics()->can_unload_classes() &&
144 (!heap->mode()->is_generational() || _generation->is_global()));
145
146 if (heap->mode()->is_generational()) {
147 // Clean the read table before swapping it. The end goal here is to have a clean
148 // write table, and to have the read table updated with the previous write table.
149 heap->old_generation()->card_scan()->mark_read_table_as_clean();
150
151 if (_generation->is_young()) {
152 // Swap remembered sets for young
153 _generation->swap_card_tables();
154 }
155 }
156
157 case _degenerated_roots:
158 // Degenerated from concurrent root mark, reset the flag for STW mark
159 if (!heap->mode()->is_generational()) {
160 if (heap->is_concurrent_mark_in_progress()) {
161 heap->cancel_concurrent_mark();
162 }
163 } else {
164 if (_generation->is_concurrent_mark_in_progress()) {
165 // We want to allow old generation marking to be punctuated by young collections
166 // (even if they have degenerated). If this is a global cycle, we'd have cancelled
167 // the entire old gc before coming into this switch. Note that cancel_marking on
168 // the generation does NOT abandon incomplete SATB buffers as cancel_concurrent_mark does.
169 // We need to separate out the old pointers which is done below.
170 _generation->cancel_marking();
171 }
172
173 if (_degen_point == ShenandoahDegenPoint::_degenerated_roots) {
174 // We only need this if the concurrent cycle has already swapped the card tables.
175 // Marking will use the 'read' table, but interesting pointers may have been
176 // recorded in the 'write' table in the time between the cancelled concurrent cycle
177 // and this degenerated cycle. These pointers need to be included in the 'read' table
178 // used to scan the remembered set during the STW mark which follows here.
179 _generation->merge_write_table();
180 }
181 }
182
183 op_reset();
184
185 // STW mark
186 op_mark();
187
188 case _degenerated_mark:
189 // No fallthrough. Continue mark, handed over from concurrent mark if
190 // concurrent mark has yet completed
191 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark && heap->is_concurrent_mark_in_progress()) {
192 assert(!ShenandoahBarrierSet::satb_mark_queue_set().get_filter_out_young(),
193 "Should not be filtering out young pointers when concurrent mark degenerates");
194 op_finish_mark();
195 }
196 assert(!heap->cancelled_gc(), "STW mark can not OOM");
197
198 /* Degen select Collection Set. etc. */
199 op_prepare_evacuation();
200
201 op_cleanup_early();
202
203 case _degenerated_evac:
204 // If heuristics thinks we should do the cycle, this flag would be set,
205 // and we can do evacuation. Otherwise, it would be the shortcut cycle.
206 if (heap->is_evacuation_in_progress()) {
207
208 if (_degen_point == _degenerated_evac) {
209 // Degeneration under oom-evac protocol allows the mutator LRB to expose
210 // references to from-space objects. This is okay, in theory, because we
211 // will come to the safepoint here to complete the evacuations and update
212 // the references. However, if the from-space reference is written to a
213 // region that was EC during final mark or was recycled after final mark
214 // it will not have TAMS or UWM updated. Such a region is effectively
215 // skipped during update references which can lead to crashes and corruption
216 // if the from-space reference is accessed.
217 if (UseTLAB) {
218 heap->labs_make_parsable();
219 }
220
221 for (size_t i = 0; i < heap->num_regions(); i++) {
222 ShenandoahHeapRegion* r = heap->get_region(i);
223 if (r->is_active() && r->top() > r->get_update_watermark()) {
224 r->set_update_watermark_at_safepoint(r->top());
225 }
226 }
227 }
228
229 // Degeneration under oom-evac protocol might have left some objects in
230 // collection set un-evacuated. Restart evacuation from the beginning to
231 // capture all objects. For all the objects that are already evacuated,
232 // it would be a simple check, which is supposed to be fast. This is also
233 // safe to do even without degeneration, as CSet iterator is at beginning
234 // in preparation for evacuation anyway.
235 //
236 // Before doing that, we need to make sure we never had any cset-pinned
237 // regions. This may happen if allocation failure happened when evacuating
238 // the about-to-be-pinned object, oom-evac protocol left the object in
239 // the collection set, and then the pin reached the cset region. If we continue
240 // the cycle here, we would trash the cset and alive objects in it. To avoid
241 // it, we fail degeneration right away and slide into Full GC to recover.
242
243 {
244 heap->sync_pinned_region_status();
245 heap->collection_set()->clear_current_index();
246 ShenandoahHeapRegion* r;
247 while ((r = heap->collection_set()->next()) != nullptr) {
248 if (r->is_pinned()) {
249 op_degenerated_fail();
250 return;
251 }
252 }
253
254 heap->collection_set()->clear_current_index();
255 }
256 op_evacuate();
257 if (heap->cancelled_gc()) {
258 op_degenerated_fail();
259 return;
260 }
261 } else if (has_in_place_promotions(heap)) {
262 // We have nothing to evacuate, but there are still regions to promote in place.
263 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_promote_regions);
264 ShenandoahGenerationalHeap::heap()->promote_regions_in_place(_generation, false /* concurrent*/);
265 }
266
267 // Update collector state regardless of whether there are forwarded objects
268 heap->set_evacuation_in_progress(false);
269 heap->set_concurrent_weak_root_in_progress(false);
270 heap->set_concurrent_strong_root_in_progress(false);
271
272 // If heuristics thinks we should do the cycle, this flag would be set,
273 // and we need to do update-refs. Otherwise, it would be the shortcut cycle.
274 if (heap->has_forwarded_objects()) {
275 op_init_update_refs();
276 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
277 } else {
278 _abbreviated = true;
279 }
280
281 case _degenerated_update_refs:
282 if (heap->has_forwarded_objects()) {
283 op_update_refs();
284 op_update_roots();
285 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
286 }
287
288 if (ShenandoahGCStateCheckHotpatch) {
289 // Leaving degenerated GC, we need to flip barriers back to idle.
290 ShenandoahCodeRoots::arm_nmethods();
291 ShenandoahStackWatermark::change_epoch_id();
292 } else {
293 // Disarm nmethods that armed in concurrent cycle.
294 // In above case, update roots should disarm them
295 ShenandoahCodeRoots::disarm_nmethods();
296 }
297
298 op_cleanup_complete();
299
300 if (heap->mode()->is_generational()) {
301 ShenandoahGenerationalHeap::heap()->complete_degenerated_cycle();
302 }
303
304 break;
305 default:
306 ShouldNotReachHere();
307 }
308
309 if (ShenandoahVerify) {
310 heap->verifier()->verify_after_degenerated(_generation);
311 }
312
313 if (VerifyAfterGC) {
314 Universe::verify();
315 }
316
317 // Decide if this cycle made good progress, and, if not, should it upgrade to a full GC.
318 const bool progress = metrics.is_good_progress();
319 ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
320 policy->record_degenerated(_generation->is_young(), _abbreviated, progress);
321 if (progress) {
322 heap->notify_gc_progress();
323 _generation->heuristics()->record_degenerated();
324 heap->start_idle_span();
325 } else if (policy->should_upgrade_degenerated_gc()) {
326 // Upgrade to full GC, register full-GC impact on heuristics.
327 op_degenerated_futile();
328 } else {
329 _generation->heuristics()->record_degenerated();
330 }
331 }
332
333 void ShenandoahDegenGC::op_reset() {
334 _generation->prepare_gc();
335 }
336
337 void ShenandoahDegenGC::op_mark() {
338 assert(!_generation->is_concurrent_mark_in_progress(), "Should be reset");
339 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark);
340 ShenandoahSTWMark mark(_generation, false /*full gc*/);
341 mark.mark();
342 }
343
344 void ShenandoahDegenGC::op_finish_mark() {
345 ShenandoahConcurrentMark mark(_generation);
346 mark.finish_mark();
347 }
348
349 void ShenandoahDegenGC::op_prepare_evacuation() {
350 ShenandoahHeap* const heap = ShenandoahHeap::heap();
351 if (ShenandoahVerify) {
352 heap->verifier()->verify_roots_no_forwarded(_generation);
353 }
354
355 // STW cleanup weak roots and unload classes
356 heap->parallel_cleaning(_generation, false /*full gc*/);
357
358 // Prepare regions and collection set
359 _generation->prepare_regions_and_collection_set(false /*concurrent*/);
360
361 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause.
362 // This is needed for two reasons. Strong one: new allocations would be with new freeset,
363 // which would be outside the collection set, so no cset writes would happen there.
364 // Weaker one: new allocations would happen past update watermark, and so less work would
365 // be needed for reference updates (would update the large filler instead).
366 if (UseTLAB) {
367 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs);
368 heap->tlabs_retire(false);
369 }
370
371 if (!heap->collection_set()->is_empty()) {
372 if (ShenandoahVerify) {
373 heap->verifier()->verify_before_evacuation(_generation);
374 }
375
376 heap->set_evacuation_in_progress(true);
377 heap->set_has_forwarded_objects(true);
378 } else {
379 if (ShenandoahVerify) {
380 if (has_in_place_promotions(heap)) {
381 heap->verifier()->verify_after_concmark_with_promotions(_generation);
382 } else {
383 heap->verifier()->verify_after_concmark(_generation);
384 }
385 }
386
387 if (VerifyAfterGC) {
388 Universe::verify();
389 }
390 }
391 }
392
393 bool ShenandoahDegenGC::has_in_place_promotions(const ShenandoahHeap* heap) const {
394 return heap->mode()->is_generational() && heap->old_generation()->has_in_place_promotions();
395 }
396
397 void ShenandoahDegenGC::op_cleanup_early() {
398 ShenandoahHeap::heap()->recycle_trash();
399 }
400
401 void ShenandoahDegenGC::op_evacuate() {
402 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
403 ShenandoahHeap::heap()->evacuate_collection_set(_generation, false /* concurrent*/);
404 }
405
406 void ShenandoahDegenGC::op_init_update_refs() {
407 // Evacuation has completed
408 ShenandoahHeap* const heap = ShenandoahHeap::heap();
409 heap->prepare_update_heap_references();
410 heap->set_update_refs_in_progress(true);
411 }
412
413 void ShenandoahDegenGC::op_update_refs() {
414 ShenandoahHeap* const heap = ShenandoahHeap::heap();
415 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_update_refs);
416 // Handed over from concurrent update references phase
417 heap->update_heap_references(_generation, false /*concurrent*/);
418
419 heap->set_update_refs_in_progress(false);
420 heap->set_has_forwarded_objects(false);
421 }
422
423 void ShenandoahDegenGC::op_update_roots() {
424 ShenandoahHeap* const heap = ShenandoahHeap::heap();
425
426 update_roots(false /*full_gc*/);
427
428 heap->update_heap_region_states(false /*concurrent*/);
429
430 if (ShenandoahVerify) {
431 heap->verifier()->verify_after_update_refs(_generation);
432 }
433
434 if (VerifyAfterGC) {
435 Universe::verify();
436 }
437
438 heap->rebuild_free_set(false /*concurrent*/);
439 }
440
441 void ShenandoahDegenGC::op_cleanup_complete() {
442 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
443 ShenandoahHeap::heap()->recycle_trash();
444 }
445
446 void ShenandoahDegenGC::op_degenerated_fail() {
447 upgrade_to_full();
448 }
449
450 void ShenandoahDegenGC::op_degenerated_futile() {
451 upgrade_to_full();
452 }
453
454 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const {
455 switch (point) {
456 case _degenerated_unset:
457 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (<UNSET>)");
458 case _degenerated_outside_cycle:
459 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Outside of Cycle)");
460 case _degenerated_roots:
461 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Roots)");
462 case _degenerated_mark:
463 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Mark)");
464 case _degenerated_evac:
465 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Evacuation)");
466 case _degenerated_update_refs:
467 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Update Refs)");
468 default:
469 ShouldNotReachHere();
470 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (?)");
471 }
472 }
473
474 void ShenandoahDegenGC::upgrade_to_full() {
475 log_info(gc)("Degenerated GC upgrading to Full GC");
476 ShenandoahHeap* heap = ShenandoahHeap::heap();
477 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
478 heap->increment_total_collections(true);
479 heap->shenandoah_policy()->record_degenerated_upgrade_to_full();
480 ShenandoahFullGC full_gc;
481 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
482 }