1 /*
2 * Copyright (c) 2013, 2018, Red Hat, Inc. All rights reserved.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #include "precompiled.hpp"
25
26 #include "gc/shenandoah/shenandoahConcurrentMark.inline.hpp"
27 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
28 #include "gc/shenandoah/shenandoahFreeSet.hpp"
29 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
30 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
31 #include "gc/shenandoah/shenandoahHeuristics.hpp"
32 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
33 #include "gc/shenandoah/shenandoahControlThread.hpp"
34 #include "gc/shenandoah/shenandoahTraversalGC.hpp"
35 #include "gc/shenandoah/shenandoahUtils.hpp"
36 #include "gc/shenandoah/shenandoahVMOperations.hpp"
37 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
38 #include "memory/iterator.hpp"
39 #include "memory/universe.hpp"
40
41 ShenandoahControlThread::ShenandoahControlThread() :
42 ConcurrentGCThread(),
43 _alloc_failure_waiters_lock(Mutex::leaf, "ShenandoahAllocFailureGC_lock", true, Monitor::_safepoint_check_always),
44 _gc_waiters_lock(Mutex::leaf, "ShenandoahRequestedGC_lock", true, Monitor::_safepoint_check_always),
45 _periodic_task(this),
46 _requested_gc_cause(GCCause::_no_cause_specified),
47 _degen_point(ShenandoahHeap::_degenerated_outside_cycle),
48 _allocs_seen(0) {
49
50 create_and_start(ShenandoahCriticalControlThreadPriority ? CriticalPriority : NearMaxPriority);
51 _periodic_task.enroll();
52 _periodic_satb_flush_task.enroll();
53 }
54
55 ShenandoahControlThread::~ShenandoahControlThread() {
56 // This is here so that super is called.
57 }
58
59 void ShenandoahPeriodicTask::task() {
60 _thread->handle_force_counters_update();
61 _thread->handle_counters_update();
62 }
63
64 void ShenandoahPeriodicSATBFlushTask::task() {
65 ShenandoahHeap::heap()->force_satb_flush_all_threads();
66 }
67
68 void ShenandoahControlThread::run_service() {
69 ShenandoahHeap* heap = ShenandoahHeap::heap();
70
71 GCMode default_mode = heap->is_traversal_mode() ?
72 concurrent_traversal : concurrent_normal;
73 GCCause::Cause default_cause = heap->is_traversal_mode() ?
74 GCCause::_shenandoah_traversal_gc : GCCause::_shenandoah_concurrent_gc;
75 int sleep = ShenandoahControlIntervalMin;
76
77 double last_shrink_time = os::elapsedTime();
78 double last_sleep_adjust_time = os::elapsedTime();
79
80 // Shrink period avoids constantly polling regions for shrinking.
81 // Having a period 10x lower than the delay would mean we hit the
82 // shrinking with lag of less than 1/10-th of true delay.
83 // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
84 double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
85
86 ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
87 ShenandoahHeuristics* heuristics = heap->heuristics();
88 while (!in_graceful_shutdown() && !should_terminate()) {
89 // Figure out if we have pending requests.
90 bool alloc_failure_pending = _alloc_failure_gc.is_set();
91 bool explicit_gc_requested = _gc_requested.is_set() && is_explicit_gc(_requested_gc_cause);
92 bool implicit_gc_requested = _gc_requested.is_set() && !is_explicit_gc(_requested_gc_cause);
93
94 // This control loop iteration have seen this much allocations.
95 size_t allocs_seen = Atomic::xchg<size_t>(0, &_allocs_seen);
96
97 // Choose which GC mode to run in. The block below should select a single mode.
98 GCMode mode = none;
99 GCCause::Cause cause = GCCause::_last_gc_cause;
100 ShenandoahHeap::ShenandoahDegenPoint degen_point = ShenandoahHeap::_degenerated_unset;
101
102 if (alloc_failure_pending) {
103 // Allocation failure takes precedence: we have to deal with it first thing
104 log_info(gc)("Trigger: Handle Allocation Failure");
105
106 cause = GCCause::_allocation_failure;
107
108 // Consume the degen point, and seed it with default value
109 degen_point = _degen_point;
110 _degen_point = ShenandoahHeap::_degenerated_outside_cycle;
111
112 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle()) {
113 heuristics->record_allocation_failure_gc();
114 policy->record_alloc_failure_to_degenerated(degen_point);
115 mode = stw_degenerated;
116 } else {
117 heuristics->record_allocation_failure_gc();
118 policy->record_alloc_failure_to_full();
119 mode = stw_full;
120 }
121
122 } else if (explicit_gc_requested) {
123 cause = _requested_gc_cause;
124 log_info(gc)("Trigger: Explicit GC request (%s)", GCCause::to_string(cause));
125
126 heuristics->record_requested_gc();
127
128 if (ExplicitGCInvokesConcurrent) {
129 policy->record_explicit_to_concurrent();
130 mode = default_mode;
131 // Unload and clean up everything
132 heap->set_process_references(heuristics->can_process_references());
133 heap->set_unload_classes(heuristics->can_unload_classes());
134 } else {
135 policy->record_explicit_to_full();
136 mode = stw_full;
137 }
138 } else if (implicit_gc_requested) {
139 cause = _requested_gc_cause;
140 log_info(gc)("Trigger: Implicit GC request (%s)", GCCause::to_string(cause));
141
142 heuristics->record_requested_gc();
143
144 if (ShenandoahImplicitGCInvokesConcurrent) {
145 policy->record_implicit_to_concurrent();
146 mode = default_mode;
147
148 // Unload and clean up everything
149 heap->set_process_references(heuristics->can_process_references());
150 heap->set_unload_classes(heuristics->can_unload_classes());
151 } else {
152 policy->record_implicit_to_full();
153 mode = stw_full;
154 }
155 } else {
156 // Potential normal cycle: ask heuristics if it wants to act
157 if (heuristics->should_start_gc()) {
158 mode = default_mode;
159 cause = default_cause;
160 }
161
162 // Ask policy if this cycle wants to process references or unload classes
163 heap->set_process_references(heuristics->should_process_references());
164 heap->set_unload_classes(heuristics->should_unload_classes());
165 }
166
167 // Blow all soft references on this cycle, if handling allocation failure,
168 // or we are requested to do so unconditionally.
169 if (alloc_failure_pending || ShenandoahAlwaysClearSoftRefs) {
170 heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
171 }
172
173 bool gc_requested = (mode != none);
174 assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
175
176 if (gc_requested) {
177 heap->reset_bytes_allocated_since_gc_start();
178
179 // If GC was requested, we are sampling the counters even without actual triggers
180 // from allocation machinery. This captures GC phases more accurately.
181 set_forced_counters_update(true);
182
183 // If GC was requested, we better dump freeset data for performance debugging
184 {
185 ShenandoahHeapLocker locker(heap->lock());
186 heap->free_set()->log_status();
187 }
188 }
189
190 switch (mode) {
191 case none:
192 break;
193 case concurrent_traversal:
194 service_concurrent_traversal_cycle(cause);
195 break;
196 case concurrent_normal:
197 service_concurrent_normal_cycle(cause);
198 break;
199 case stw_degenerated:
200 service_stw_degenerated_cycle(cause, degen_point);
201 break;
202 case stw_full:
203 service_stw_full_cycle(cause);
204 break;
205 default:
206 ShouldNotReachHere();
207 }
208
209 if (gc_requested) {
210 // If this was the requested GC cycle, notify waiters about it
211 if (explicit_gc_requested || implicit_gc_requested) {
212 notify_gc_waiters();
213 }
214
215 // If this was the allocation failure GC cycle, notify waiters about it
216 if (alloc_failure_pending) {
217 notify_alloc_failure_waiters();
218 }
219
220 // Report current free set state at the end of cycle, whether
221 // it is a normal completion, or the abort.
222 {
223 ShenandoahHeapLocker locker(heap->lock());
224 heap->free_set()->log_status();
225
226 // Notify Universe about new heap usage. This has implications for
227 // global soft refs policy, and we better report it every time heap
228 // usage goes down.
229 Universe::update_heap_info_at_gc();
230 }
231
232 // Disable forced counters update, and update counters one more time
233 // to capture the state at the end of GC session.
234 handle_force_counters_update();
235 set_forced_counters_update(false);
236
237 // Retract forceful part of soft refs policy
238 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
239
240 // Clear metaspace oom flag, if current cycle unloaded classes
241 if (heap->unload_classes()) {
242 heuristics->clear_metaspace_oom();
243 }
244
245 // GC is over, we are at idle now
246 if (ShenandoahPacing) {
247 heap->pacer()->setup_for_idle();
248 }
249 } else {
250 // Allow allocators to know we have seen this much regions
251 if (ShenandoahPacing && (allocs_seen > 0)) {
252 heap->pacer()->report_alloc(allocs_seen);
253 }
254 }
255
256 double current = os::elapsedTime();
257
258 if (ShenandoahUncommit && (explicit_gc_requested || (current - last_shrink_time > shrink_period))) {
259 // Try to uncommit enough stale regions. Explicit GC tries to uncommit everything.
260 // Regular paths uncommit only occasionally.
261 double shrink_before = explicit_gc_requested ?
262 current :
263 current - (ShenandoahUncommitDelay / 1000.0);
264 service_uncommit(shrink_before);
265 last_shrink_time = current;
266 }
267
268 // Wait before performing the next action. If allocation happened during this wait,
269 // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
270 // back off exponentially.
271 if (_heap_changed.try_unset()) {
272 sleep = ShenandoahControlIntervalMin;
273 } else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
274 sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
275 last_sleep_adjust_time = current;
276 }
277 os::naked_short_sleep(sleep);
278 }
279
280 // Wait for the actual stop(), can't leave run_service() earlier.
281 while (!should_terminate()) {
282 os::naked_short_sleep(ShenandoahControlIntervalMin);
283 }
284 }
285
286 void ShenandoahControlThread::service_concurrent_traversal_cycle(GCCause::Cause cause) {
287 GCIdMark gc_id_mark;
288 ShenandoahGCSession session(cause);
289
290 ShenandoahHeap* heap = ShenandoahHeap::heap();
291 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
292
293 // Reset for upcoming cycle
294 heap->entry_reset();
295
296 heap->vmop_entry_init_traversal();
297
298 if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_traversal)) return;
299
300 heap->entry_traversal();
301 if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_traversal)) return;
302
303 heap->vmop_entry_final_traversal();
304
305 heap->entry_cleanup();
306
307 heap->heuristics()->record_success_concurrent();
308 heap->shenandoah_policy()->record_success_concurrent();
309 }
310
311 void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
312 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
313 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
314 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
315 // tries to evac something and no memory is available), cycle degrades to Full GC.
316 //
317 // There are also two shortcuts through the normal cycle: a) immediate garbage shortcut, when
318 // heuristics says there are no regions to compact, and all the collection comes from immediately
319 // reclaimable regions; b) coalesced UR shortcut, when heuristics decides to coalesce UR with the
320 // mark from the next cycle.
321 //
322 // ................................................................................................
323 //
324 // (immediate garbage shortcut) Concurrent GC
325 // /-------------------------------------------\
326 // | (coalesced UR) v
327 // | /----------------------->o
328 // | | |
329 // | | v
330 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
331 // | | | ^
332 // | (af) | (af) | (af) |
333 // ..................|....................|.................|..............|.......................
334 // | | | |
335 // | | | | Degenerated GC
336 // v v v |
337 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
338 // | | | ^
339 // | (af) | (af) | (af) |
340 // ..................|....................|.................|..............|.......................
341 // | | | |
342 // | v | | Full GC
343 // \------------------->o<----------------/ |
344 // | |
345 // v |
346 // Full GC --------------------------/
347 //
348 ShenandoahHeap* heap = ShenandoahHeap::heap();
349
350 if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_outside_cycle)) return;
351
352 GCIdMark gc_id_mark;
353 ShenandoahGCSession session(cause);
354
355 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
356
357 // Reset for upcoming marking
358 heap->entry_reset();
359
360 // Start initial mark under STW
361 heap->vmop_entry_init_mark();
362
363 // Continue concurrent mark
364 heap->entry_mark();
365 if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_mark)) return;
366
367 // If not cancelled, can try to concurrently pre-clean
368 heap->entry_preclean();
369
370 // Complete marking under STW, and start evacuation
371 heap->vmop_entry_final_mark();
372
373 // Final mark might have reclaimed some immediate garbage, kick cleanup to reclaim
374 // the space. This would be the last action if there is nothing to evacuate.
375 heap->entry_cleanup();
376
377 {
378 ShenandoahHeapLocker locker(heap->lock());
379 heap->free_set()->log_status();
380 }
381
382 // Continue the cycle with evacuation and optional update-refs.
383 // This may be skipped if there is nothing to evacuate.
384 // If so, evac_in_progress would be unset by collection set preparation code.
385 if (heap->is_evacuation_in_progress()) {
386 // Concurrently evacuate
387 heap->entry_evac();
388 if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_evac)) return;
389
390 // Perform update-refs phase, if required. This phase can be skipped if heuristics
391 // decides to piggy-back the update-refs on the next marking cycle. On either path,
392 // we need to turn off evacuation: either in init-update-refs, or in final-evac.
393 if (heap->heuristics()->should_start_update_refs()) {
394 heap->vmop_entry_init_updaterefs();
395 heap->entry_updaterefs();
396 if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_updaterefs)) return;
397
398 heap->vmop_entry_final_updaterefs();
399
400 // Update references freed up collection set, kick the cleanup to reclaim the space.
401 heap->entry_cleanup();
402
403 } else {
404 heap->vmop_entry_final_evac();
405 }
406 }
407
408 // Cycle is complete
409 heap->heuristics()->record_success_concurrent();
410 heap->shenandoah_policy()->record_success_concurrent();
411 }
412
413 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahHeap::ShenandoahDegenPoint point) {
414 ShenandoahHeap* heap = ShenandoahHeap::heap();
415 if (heap->cancelled_gc()) {
416 assert (is_alloc_failure_gc() || in_graceful_shutdown(), "Cancel GC either for alloc failure GC, or gracefully exiting");
417 if (!in_graceful_shutdown()) {
418 assert (_degen_point == ShenandoahHeap::_degenerated_outside_cycle,
419 "Should not be set yet: %s", ShenandoahHeap::degen_point_to_string(_degen_point));
420 _degen_point = point;
421 }
422 return true;
423 }
424 return false;
425 }
426
427 void ShenandoahControlThread::stop_service() {
428 // Nothing to do here.
429 }
430
431 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
432 GCIdMark gc_id_mark;
433 ShenandoahGCSession session(cause);
434
435 ShenandoahHeap* heap = ShenandoahHeap::heap();
436 heap->vmop_entry_full(cause);
437
438 heap->heuristics()->record_success_full();
439 heap->shenandoah_policy()->record_success_full();
440 }
441
442 void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahHeap::ShenandoahDegenPoint point) {
443 assert (point != ShenandoahHeap::_degenerated_unset, "Degenerated point should be set");
444
445 GCIdMark gc_id_mark;
446 ShenandoahGCSession session(cause);
447
448 ShenandoahHeap* heap = ShenandoahHeap::heap();
449 heap->vmop_degenerated(point);
450
451 heap->heuristics()->record_success_degenerated();
452 heap->shenandoah_policy()->record_success_degenerated();
453 }
454
455 void ShenandoahControlThread::service_uncommit(double shrink_before) {
456 ShenandoahHeap* heap = ShenandoahHeap::heap();
457
458 // Determine if there is work to do. This avoids taking heap lock if there is
459 // no work available, avoids spamming logs with superfluous logging messages,
460 // and minimises the amount of work while locks are taken.
461
462 if (heap->committed() <= heap->min_capacity()) return;
463
464 bool has_work = false;
465 for (size_t i = 0; i < heap->num_regions(); i++) {
466 ShenandoahHeapRegion *r = heap->get_region(i);
467 if (r->is_empty_committed() && (r->empty_time() < shrink_before)) {
468 has_work = true;
469 break;
470 }
471 }
472
473 if (has_work) {
474 heap->entry_uncommit(shrink_before);
475 }
476 }
477
478 bool ShenandoahControlThread::is_explicit_gc(GCCause::Cause cause) const {
479 return GCCause::is_user_requested_gc(cause) ||
480 GCCause::is_serviceability_requested_gc(cause);
481 }
482
483 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
484 assert(GCCause::is_user_requested_gc(cause) ||
485 GCCause::is_serviceability_requested_gc(cause) ||
486 cause == GCCause::_metadata_GC_clear_soft_refs ||
487 cause == GCCause::_full_gc_alot ||
488 cause == GCCause::_wb_full_gc ||
489 cause == GCCause::_scavenge_alot,
490 "only requested GCs here");
491
492 if (is_explicit_gc(cause)) {
493 if (!DisableExplicitGC) {
494 handle_requested_gc(cause);
495 }
496 } else {
497 handle_requested_gc(cause);
498 }
499 }
500
501 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
502 _requested_gc_cause = cause;
503 _gc_requested.set();
504 MonitorLockerEx ml(&_gc_waiters_lock);
505 while (_gc_requested.is_set()) {
506 ml.wait();
507 }
508 }
509
510 void ShenandoahControlThread::handle_alloc_failure(size_t words) {
511 ShenandoahHeap* heap = ShenandoahHeap::heap();
512
513 assert(current()->is_Java_thread(), "expect Java thread here");
514
515 if (try_set_alloc_failure_gc()) {
516 // Only report the first allocation failure
517 log_info(gc)("Failed to allocate " SIZE_FORMAT "%s",
518 byte_size_in_proper_unit(words * HeapWordSize), proper_unit_for_byte_size(words * HeapWordSize));
519
520 // Now that alloc failure GC is scheduled, we can abort everything else
521 heap->cancel_gc(GCCause::_allocation_failure);
522 }
523
524 MonitorLockerEx ml(&_alloc_failure_waiters_lock);
525 while (is_alloc_failure_gc()) {
526 ml.wait();
527 }
528 }
529
530 void ShenandoahControlThread::handle_alloc_failure_evac(size_t words) {
531 ShenandoahHeap* heap = ShenandoahHeap::heap();
532
533 if (try_set_alloc_failure_gc()) {
534 // Only report the first allocation failure
535 log_info(gc)("Failed to allocate " SIZE_FORMAT "%s for evacuation",
536 byte_size_in_proper_unit(words * HeapWordSize), proper_unit_for_byte_size(words * HeapWordSize));
537 }
538
539 // Forcefully report allocation failure
540 heap->cancel_gc(GCCause::_shenandoah_allocation_failure_evac);
541 }
542
543 void ShenandoahControlThread::notify_alloc_failure_waiters() {
544 _alloc_failure_gc.unset();
545 MonitorLockerEx ml(&_alloc_failure_waiters_lock);
546 ml.notify_all();
547 }
548
549 bool ShenandoahControlThread::try_set_alloc_failure_gc() {
550 return _alloc_failure_gc.try_set();
551 }
552
553 bool ShenandoahControlThread::is_alloc_failure_gc() {
554 return _alloc_failure_gc.is_set();
555 }
556
557 void ShenandoahControlThread::notify_gc_waiters() {
558 _gc_requested.unset();
559 MonitorLockerEx ml(&_gc_waiters_lock);
560 ml.notify_all();
561 }
562
563 void ShenandoahControlThread::handle_counters_update() {
564 if (_do_counters_update.is_set()) {
565 _do_counters_update.unset();
566 ShenandoahHeap::heap()->monitoring_support()->update_counters();
567 }
568 }
569
570 void ShenandoahControlThread::handle_force_counters_update() {
571 if (_force_counters_update.is_set()) {
572 _do_counters_update.unset(); // reset these too, we do update now!
573 ShenandoahHeap::heap()->monitoring_support()->update_counters();
574 }
575 }
576
577 void ShenandoahControlThread::notify_heap_changed() {
578 // This is called from allocation path, and thus should be fast.
579
580 // Update monitoring counters when we took a new region. This amortizes the
581 // update costs on slow path.
582 if (_do_counters_update.is_unset()) {
583 _do_counters_update.set();
584 }
585 // Notify that something had changed.
586 if (_heap_changed.is_unset()) {
587 _heap_changed.set();
588 }
589 }
590
591 void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
592 assert(ShenandoahPacing, "should only call when pacing is enabled");
593 Atomic::add(words, &_allocs_seen);
594 }
595
596 void ShenandoahControlThread::set_forced_counters_update(bool value) {
597 _force_counters_update.set_cond(value);
598 }
599
600 void ShenandoahControlThread::print() const {
601 print_on(tty);
602 }
603
604 void ShenandoahControlThread::print_on(outputStream* st) const {
605 st->print("Shenandoah Concurrent Thread");
606 Thread::print_on(st);
607 st->cr();
608 }
609
610 void ShenandoahControlThread::start() {
611 create_and_start();
612 }
613
614 void ShenandoahControlThread::prepare_for_graceful_shutdown() {
615 _graceful_shutdown.set();
616 }
617
618 bool ShenandoahControlThread::in_graceful_shutdown() {
619 return _graceful_shutdown.is_set();
620 }