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 #include "precompiled.hpp"
27
28 #include "gc/shared/collectorCounters.hpp"
29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
30 #include "gc/shenandoah/shenandoahConcurrentMark.hpp"
31 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
32 #include "gc/shenandoah/shenandoahFullGC.hpp"
33 #include "gc/shenandoah/shenandoahGeneration.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/shenandoahOopClosures.inline.hpp"
39 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
40 #include "gc/shenandoah/shenandoahSTWMark.hpp"
41 #include "gc/shenandoah/shenandoahUtils.hpp"
42 #include "gc/shenandoah/shenandoahVerifier.hpp"
43 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
44 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
45 #include "gc/shenandoah/shenandoahVMOperations.hpp"
46 #include "runtime/vmThread.hpp"
47 #include "utilities/events.hpp"
48
49 ShenandoahDegenGC::ShenandoahDegenGC(ShenandoahDegenPoint degen_point, ShenandoahGeneration* generation) :
50 ShenandoahGC(),
51 _degen_point(degen_point),
52 _generation(generation),
53 _upgraded_to_full(false) {
54 }
55
56 bool ShenandoahDegenGC::collect(GCCause::Cause cause) {
57 vmop_degenerated();
58 ShenandoahHeap* heap = ShenandoahHeap::heap();
59 if (heap->mode()->is_generational()) {
60 bool is_bootstrap_gc = heap->is_concurrent_old_mark_in_progress() && _generation->is_young();
61 heap->mmu_tracker()->record_degenerated(_generation, GCId::current(), is_bootstrap_gc,
62 !heap->collection_set()->has_old_regions());
63 const char* msg = is_bootstrap_gc? "At end of Degenerated Boostrap Old GC": "At end of Degenerated GC";
64 heap->log_heap_status(msg);
65 }
66 return true;
67 }
68
69 void ShenandoahDegenGC::vmop_degenerated() {
70 TraceCollectorStats tcs(ShenandoahHeap::heap()->monitoring_support()->full_stw_collection_counters());
71 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_gross);
72 VM_ShenandoahDegeneratedGC degenerated_gc(this);
73 VMThread::execute(°enerated_gc);
74 }
75
76 void ShenandoahDegenGC::entry_degenerated() {
77 const char* msg = degen_event_message(_degen_point);
78 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::degen_gc, true /* log_heap_usage */);
79 EventMark em("%s", msg);
80 ShenandoahHeap* const heap = ShenandoahHeap::heap();
81 ShenandoahWorkerScope scope(heap->workers(),
82 ShenandoahWorkerPolicy::calc_workers_for_stw_degenerated(),
83 "stw degenerated gc");
84
85 heap->set_degenerated_gc_in_progress(true);
86 op_degenerated();
87 heap->set_degenerated_gc_in_progress(false);
88 }
89
90 void ShenandoahDegenGC::op_degenerated() {
91 ShenandoahHeap* const heap = ShenandoahHeap::heap();
92 // Degenerated GC is STW, but it can also fail. Current mechanics communicates
93 // GC failure via cancelled_concgc() flag. So, if we detect the failure after
94 // some phase, we have to upgrade the Degenerate GC to Full GC.
95 heap->clear_cancelled_gc(true /* clear oom handler */);
96
97 #ifdef ASSERT
98 if (heap->mode()->is_generational()) {
99 if (_generation->is_global()) {
100 // We can only get to a degenerated global cycle _after_ a concurrent global cycle
101 // has been cancelled. In which case, we expect the concurrent global cycle to have
102 // cancelled the old gc already.
103 assert(!heap->is_old_gc_active(), "Old GC should not be active during global cycle");
104 }
105
106 if (!heap->is_concurrent_old_mark_in_progress()) {
107 // If we are not marking the old generation, there should be nothing in the old mark queues
108 assert(heap->old_generation()->task_queues()->is_empty(), "Old gen task queues should be empty");
109 }
110 }
111 #endif
112
113 ShenandoahMetricsSnapshot metrics;
114 metrics.snap_before();
115
116 switch (_degen_point) {
117 // The cases below form the Duff's-like device: it describes the actual GC cycle,
118 // but enters it at different points, depending on which concurrent phase had
119 // degenerated.
120
121 case _degenerated_outside_cycle:
122 // We have degenerated from outside the cycle, which means something is bad with
123 // the heap, most probably heavy humongous fragmentation, or we are very low on free
124 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when
125 // we can do the most aggressive degen cycle, which includes processing references and
126 // class unloading, unless those features are explicitly disabled.
127
128 if (heap->is_concurrent_old_mark_in_progress()) {
129 // We have come straight into a degenerated cycle without running a concurrent cycle
130 // first and the SATB barrier is enabled to support concurrent old marking. The SATB buffer
131 // may hold a mix of old and young pointers. The old pointers need to be transferred
132 // to the old generation mark queues and the young pointers are _not_ part of this
133 // snapshot, so they must be dropped here.
134 heap->transfer_old_pointers_from_satb();
135 }
136
137 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk
138 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover.
139 heap->set_unload_classes(_generation->heuristics()->can_unload_classes() &&
140 (!heap->mode()->is_generational() || _generation->is_global()));
141
142 if (heap->mode()->is_generational() &&
143 (_generation->is_young() || (_generation->is_global() && ShenandoahVerify))) {
144 // Swap remembered sets for young, or if the verifier will run during a global collect
145 // TODO: This path should not depend on ShenandoahVerify
146 _generation->swap_remembered_set();
147 }
148
149 case _degenerated_roots:
150 // Degenerated from concurrent root mark, reset the flag for STW mark
151 if (!heap->mode()->is_generational()) {
152 if (heap->is_concurrent_mark_in_progress()) {
153 heap->cancel_concurrent_mark();
154 }
155 } else {
156 if (_generation->is_concurrent_mark_in_progress()) {
157 // We want to allow old generation marking to be punctuated by young collections
158 // (even if they have degenerated). If this is a global cycle, we'd have cancelled
159 // the entire old gc before coming into this switch.
160 _generation->cancel_marking();
161 }
162 }
163
164 if (_degen_point == ShenandoahDegenPoint::_degenerated_roots) {
165 // We only need this if the concurrent cycle has already swapped the card tables.
166 // Marking will use the 'read' table, but interesting pointers may have been
167 // recorded in the 'write' table in the time between the cancelled concurrent cycle
168 // and this degenerated cycle. These pointers need to be included the 'read' table
169 // used to scan the remembered set during the STW mark which follows here.
170 _generation->merge_write_table();
171 }
172
173 op_reset();
174
175 // STW mark
176 op_mark();
177
178 case _degenerated_mark:
179 // No fallthrough. Continue mark, handed over from concurrent mark if
180 // concurrent mark has yet completed
181 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark &&
182 heap->is_concurrent_mark_in_progress()) {
183 op_finish_mark();
184 }
185 assert(!heap->cancelled_gc(), "STW mark can not OOM");
186
187 /* Degen select Collection Set. etc. */
188 op_prepare_evacuation();
189
190 op_cleanup_early();
191
192 case _degenerated_evac:
193
194 if (heap->mode()->is_generational() && _generation->is_global()) {
195 op_global_coalesce_and_fill();
196 }
197
198 // If heuristics thinks we should do the cycle, this flag would be set,
199 // and we can do evacuation. Otherwise, it would be the shortcut cycle.
200 if (heap->is_evacuation_in_progress()) {
201
202 if (_degen_point == _degenerated_evac) {
203 // Degeneration under oom-evac protocol allows the mutator LRB to expose
204 // references to from-space objects. This is okay, in theory, because we
205 // will come to the safepoint here to complete the evacuations and update
206 // the references. However, if the from-space reference is written to a
207 // region that was EC during final mark or was recycled after final mark
208 // it will not have TAMS or UWM updated. Such a region is effectively
209 // skipped during update references which can lead to crashes and corruption
210 // if the from-space reference is accessed.
211 if (UseTLAB) {
212 heap->labs_make_parsable();
213 }
214
215 for (size_t i = 0; i < heap->num_regions(); i++) {
216 ShenandoahHeapRegion* r = heap->get_region(i);
217 if (r->is_active() && r->top() > r->get_update_watermark()) {
218 r->set_update_watermark_at_safepoint(r->top());
219 }
220 }
221 }
222
223 // Degeneration under oom-evac protocol might have left some objects in
224 // collection set un-evacuated. Restart evacuation from the beginning to
225 // capture all objects. For all the objects that are already evacuated,
226 // it would be a simple check, which is supposed to be fast. This is also
227 // safe to do even without degeneration, as CSet iterator is at beginning
228 // in preparation for evacuation anyway.
229 //
230 // Before doing that, we need to make sure we never had any cset-pinned
231 // regions. This may happen if allocation failure happened when evacuating
232 // the about-to-be-pinned object, oom-evac protocol left the object in
233 // the collection set, and then the pin reached the cset region. If we continue
234 // the cycle here, we would trash the cset and alive objects in it. To avoid
235 // it, we fail degeneration right away and slide into Full GC to recover.
236
237 {
238 heap->sync_pinned_region_status();
239 heap->collection_set()->clear_current_index();
240 ShenandoahHeapRegion* r;
241 while ((r = heap->collection_set()->next()) != nullptr) {
242 if (r->is_pinned()) {
243 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
244 op_degenerated_fail();
245 return;
246 }
247 }
248
249 heap->collection_set()->clear_current_index();
250 }
251 op_evacuate();
252 if (heap->cancelled_gc()) {
253 op_degenerated_fail();
254 return;
255 }
256 }
257
258 // If heuristics thinks we should do the cycle, this flag would be set,
259 // and we need to do update-refs. Otherwise, it would be the shortcut cycle.
260 if (heap->has_forwarded_objects()) {
261 op_init_updaterefs();
262 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
263 }
264
265 case _degenerated_updaterefs:
266 if (heap->has_forwarded_objects()) {
267 op_updaterefs();
268 op_update_roots();
269 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
270 }
271
272 if (ClassUnloading) {
273 // Disarm nmethods that armed in concurrent cycle.
274 // In above case, update roots should disarm them
275 ShenandoahCodeRoots::disarm_nmethods();
276 }
277
278 op_cleanup_complete();
279 // We defer generation resizing actions until after cset regions have been recycled.
280 if (heap->mode()->is_generational()) {
281 size_t old_region_surplus = heap->get_old_region_surplus();
282 size_t old_region_deficit = heap->get_old_region_deficit();
283 bool success;
284 size_t region_xfer;
285 const char* region_destination;
286 if (old_region_surplus) {
287 region_xfer = old_region_surplus;
288 region_destination = "young";
289 success = heap->generation_sizer()->transfer_to_young(old_region_surplus);
290 } else if (old_region_deficit) {
291 region_xfer = old_region_surplus;
292 region_destination = "old";
293 success = heap->generation_sizer()->transfer_to_old(old_region_deficit);
294 if (!success) {
295 ((ShenandoahOldHeuristics *) heap->old_generation()->heuristics())->trigger_cannot_expand();
296 }
297 } else {
298 region_destination = "none";
299 region_xfer = 0;
300 success = true;
301 }
302
303 size_t young_available = heap->young_generation()->available();
304 size_t old_available = heap->old_generation()->available();
305 log_info(gc, ergo)("After cleanup, %s " SIZE_FORMAT " regions to %s to prepare for next gc, old available: "
306 SIZE_FORMAT "%s, young_available: " SIZE_FORMAT "%s",
307 success? "successfully transferred": "failed to transfer", region_xfer, region_destination,
308 byte_size_in_proper_unit(old_available), proper_unit_for_byte_size(old_available),
309 byte_size_in_proper_unit(young_available), proper_unit_for_byte_size(young_available));
310
311 heap->set_old_region_surplus(0);
312 heap->set_old_region_deficit(0);
313 }
314 break;
315 default:
316 ShouldNotReachHere();
317 }
318
319 if (heap->mode()->is_generational()) {
320 // In case degeneration interrupted concurrent evacuation or update references, we need to clean up transient state.
321 // Otherwise, these actions have no effect.
322 heap->set_young_evac_reserve(0);
323 heap->set_old_evac_reserve(0);
324 heap->reset_old_evac_expended();
325 heap->set_promoted_reserve(0);
326 }
327
328 if (ShenandoahVerify) {
329 heap->verifier()->verify_after_degenerated();
330 }
331
332 if (VerifyAfterGC) {
333 Universe::verify();
334 }
335
336 metrics.snap_after();
337
338 // Check for futility and fail. There is no reason to do several back-to-back Degenerated cycles,
339 // because that probably means the heap is overloaded and/or fragmented.
340 if (!metrics.is_good_progress()) {
341 heap->notify_gc_no_progress();
342 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
343 op_degenerated_futile();
344 } else {
345 heap->notify_gc_progress();
346 }
347 }
348
349 void ShenandoahDegenGC::op_reset() {
350 _generation->prepare_gc();
351 }
352
353 void ShenandoahDegenGC::op_mark() {
354 assert(!_generation->is_concurrent_mark_in_progress(), "Should be reset");
355 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark);
356 ShenandoahSTWMark mark(_generation, false /*full gc*/);
357 mark.mark();
358 }
359
360 void ShenandoahDegenGC::op_finish_mark() {
361 ShenandoahConcurrentMark mark(_generation);
362 mark.finish_mark();
363 }
364
365 void ShenandoahDegenGC::op_prepare_evacuation() {
366 ShenandoahHeap* const heap = ShenandoahHeap::heap();
367 if (ShenandoahVerify) {
368 heap->verifier()->verify_roots_no_forwarded();
369 }
370
371 // STW cleanup weak roots and unload classes
372 heap->parallel_cleaning(false /*full gc*/);
373
374 // Prepare regions and collection set
375 _generation->prepare_regions_and_collection_set(false /*concurrent*/);
376
377 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause.
378 // This is needed for two reasons. Strong one: new allocations would be with new freeset,
379 // which would be outside the collection set, so no cset writes would happen there.
380 // Weaker one: new allocations would happen past update watermark, and so less work would
381 // be needed for reference updates (would update the large filler instead).
382 if (UseTLAB) {
383 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs);
384 heap->tlabs_retire(false);
385 }
386
387 size_t humongous_regions_promoted = heap->get_promotable_humongous_regions();
388 size_t regular_regions_promoted_in_place = heap->get_regular_regions_promoted_in_place();
389 if (!heap->collection_set()->is_empty() || (humongous_regions_promoted + regular_regions_promoted_in_place > 0)) {
390 // Even if the collection set is empty, we need to do evacuation if there are regions to be promoted in place.
391 // Degenerated evacuation takes responsibility for registering objects and setting the remembered set cards to dirty.
392
393 if (ShenandoahVerify) {
394 heap->verifier()->verify_before_evacuation();
395 }
396
397 heap->set_evacuation_in_progress(true);
398 heap->set_has_forwarded_objects(true);
399
400 if(ShenandoahVerify) {
401 heap->verifier()->verify_during_evacuation();
402 }
403 } else {
404 if (ShenandoahVerify) {
405 heap->verifier()->verify_after_concmark();
406 }
407
408 if (VerifyAfterGC) {
409 Universe::verify();
410 }
411 }
412 }
413
414 void ShenandoahDegenGC::op_cleanup_early() {
415 ShenandoahHeap::heap()->recycle_trash();
416 }
417
418 void ShenandoahDegenGC::op_global_coalesce_and_fill() {
419 ShenandoahHeap::heap()->coalesce_and_fill_old_regions();
420 }
421
422 void ShenandoahDegenGC::op_evacuate() {
423 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
424 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/);
425 }
426
427 void ShenandoahDegenGC::op_init_updaterefs() {
428 // Evacuation has completed
429 ShenandoahHeap* const heap = ShenandoahHeap::heap();
430 heap->set_evacuation_in_progress(false);
431 heap->set_concurrent_weak_root_in_progress(false);
432 heap->set_concurrent_strong_root_in_progress(false);
433
434 heap->prepare_update_heap_references(false /*concurrent*/);
435 heap->set_update_refs_in_progress(true);
436 }
437
438 void ShenandoahDegenGC::op_updaterefs() {
439 ShenandoahHeap* const heap = ShenandoahHeap::heap();
440 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs);
441 // Handed over from concurrent update references phase
442 heap->update_heap_references(false /*concurrent*/);
443
444 heap->set_update_refs_in_progress(false);
445 heap->set_has_forwarded_objects(false);
446 }
447
448 void ShenandoahDegenGC::op_update_roots() {
449 ShenandoahHeap* const heap = ShenandoahHeap::heap();
450
451 update_roots(false /*full_gc*/);
452
453 heap->update_heap_region_states(false /*concurrent*/);
454
455 if (ShenandoahVerify) {
456 heap->verifier()->verify_after_updaterefs();
457 }
458
459 if (VerifyAfterGC) {
460 Universe::verify();
461 }
462
463 heap->rebuild_free_set(false /*concurrent*/);
464 }
465
466 void ShenandoahDegenGC::op_cleanup_complete() {
467 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
468 ShenandoahHeap::heap()->recycle_trash();
469 }
470
471 void ShenandoahDegenGC::op_degenerated_fail() {
472 upgrade_to_full();
473 ShenandoahFullGC full_gc;
474 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
475 }
476
477 void ShenandoahDegenGC::op_degenerated_futile() {
478 upgrade_to_full();
479 ShenandoahFullGC full_gc;
480 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
481 }
482
483 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const {
484 const ShenandoahHeap* heap = ShenandoahHeap::heap();
485 switch (point) {
486 case _degenerated_unset:
487 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (<UNSET>)");
488 case _degenerated_outside_cycle:
489 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Outside of Cycle)");
490 case _degenerated_roots:
491 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Roots)");
492 case _degenerated_mark:
493 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Mark)");
494 case _degenerated_evac:
495 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Evacuation)");
496 case _degenerated_updaterefs:
497 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Update Refs)");
498 default:
499 ShouldNotReachHere();
500 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (?)");
501 }
502 }
503
504 void ShenandoahDegenGC::upgrade_to_full() {
505 log_info(gc)("Degenerate GC upgrading to Full GC");
506 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full();
507 _upgraded_to_full = true;
508 }
509
510 bool ShenandoahDegenGC::upgraded_to_full() {
511 return _upgraded_to_full;
512 }