1 /*
2 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26
27 #include "gc/shenandoah/shenandoahAsserts.hpp"
28 #include "gc/shenandoah/shenandoahFreeSet.hpp"
29 #include "gc/shenandoah/shenandoahGenerationalEvacuationTask.hpp"
30 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
31 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
32 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
33 #include "gc/shenandoah/shenandoahPacer.hpp"
34 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
35 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
36 #include "gc/shenandoah/shenandoahUtils.hpp"
37
38 class ShenandoahConcurrentEvacuator : public ObjectClosure {
39 private:
40 ShenandoahGenerationalHeap* const _heap;
41 Thread* const _thread;
42 public:
43 explicit ShenandoahConcurrentEvacuator(ShenandoahGenerationalHeap* heap) :
44 _heap(heap), _thread(Thread::current()) {}
45
46 void do_object(oop p) override {
47 shenandoah_assert_marked(nullptr, p);
48 if (!p->is_forwarded()) {
49 _heap->evacuate_object(p, _thread);
50 }
51 }
52 };
53
54 ShenandoahGenerationalEvacuationTask::ShenandoahGenerationalEvacuationTask(ShenandoahGenerationalHeap* heap,
55 ShenandoahRegionIterator* iterator,
56 bool concurrent) :
57 WorkerTask("Shenandoah Evacuation"),
58 _heap(heap),
59 _regions(iterator),
60 _concurrent(concurrent),
61 _tenuring_threshold(0)
62 {
63 shenandoah_assert_generational();
64 _tenuring_threshold = _heap->age_census()->tenuring_threshold();
65 }
66
67 void ShenandoahGenerationalEvacuationTask::work(uint worker_id) {
68 if (_concurrent) {
69 ShenandoahConcurrentWorkerSession worker_session(worker_id);
70 ShenandoahSuspendibleThreadSetJoiner stsj;
71 ShenandoahEvacOOMScope oom_evac_scope;
72 do_work();
73 } else {
74 ShenandoahParallelWorkerSession worker_session(worker_id);
75 ShenandoahEvacOOMScope oom_evac_scope;
76 do_work();
77 }
78 }
79
80 void ShenandoahGenerationalEvacuationTask::do_work() {
81 ShenandoahConcurrentEvacuator cl(_heap);
82 ShenandoahHeapRegion* r;
83
84 while ((r = _regions->next()) != nullptr) {
85 log_debug(gc)("GenerationalEvacuationTask do_work(), looking at %s region " SIZE_FORMAT ", (age: %d) [%s, %s, %s]",
86 r->is_old()? "old": r->is_young()? "young": "free", r->index(), r->age(),
87 r->is_active()? "active": "inactive",
88 r->is_humongous()? (r->is_humongous_start()? "humongous_start": "humongous_continuation"): "regular",
89 r->is_cset()? "cset": "not-cset");
90
91 if (r->is_cset()) {
92 assert(r->has_live(), "Region " SIZE_FORMAT " should have been reclaimed early", r->index());
93 _heap->marked_object_iterate(r, &cl);
94 if (ShenandoahPacing) {
95 _heap->pacer()->report_evac(r->used() >> LogHeapWordSize);
96 }
97 } else if (r->is_young() && r->is_active() && (r->age() >= _tenuring_threshold)) {
98 if (r->is_humongous_start()) {
99 // We promote humongous_start regions along with their affiliated continuations during evacuation rather than
100 // doing this work during a safepoint. We cannot put humongous regions into the collection set because that
101 // triggers the load-reference barrier (LRB) to copy on reference fetch.
102 promote_humongous(r);
103 } else if (r->is_regular() && (r->get_top_before_promote() != nullptr)) {
104 // Likewise, we cannot put promote-in-place regions into the collection set because that would also trigger
105 // the LRB to copy on reference fetch.
106 promote_in_place(r);
107 }
108 // Aged humongous continuation regions are handled with their start region. If an aged regular region has
109 // more garbage than ShenandoahOldGarbageThreshold, we'll promote by evacuation. If there is room for evacuation
110 // in this cycle, the region will be in the collection set. If there is not room, the region will be promoted
111 // by evacuation in some future GC cycle.
112
113 // If an aged regular region has received allocations during the current cycle, we do not promote because the
114 // newly allocated objects do not have appropriate age; this region's age will be reset to zero at end of cycle.
115 }
116 // else, region is free, or OLD, or not in collection set, or humongous_continuation,
117 // or is young humongous_start that is too young to be promoted
118 if (_heap->check_cancelled_gc_and_yield(_concurrent)) {
119 break;
120 }
121 }
122 }
123
124 // When we promote a region in place, we can continue to use the established marking context to guide subsequent remembered
125 // set scans of this region's content. The region will be coalesced and filled prior to the next old-gen marking effort.
126 // We identify the entirety of the region as DIRTY to force the next remembered set scan to identify the "interesting poitners"
127 // contained herein.
128 void ShenandoahGenerationalEvacuationTask::promote_in_place(ShenandoahHeapRegion* region) {
129 ShenandoahMarkingContext* const marking_context = _heap->marking_context();
130 HeapWord* const tams = marking_context->top_at_mark_start(region);
131
132 {
133 const size_t old_garbage_threshold = (ShenandoahHeapRegion::region_size_bytes() * ShenandoahOldGarbageThreshold) / 100;
134 assert(_heap->active_generation()->is_mark_complete(), "sanity");
135 assert(!_heap->is_concurrent_old_mark_in_progress(), "Cannot promote in place during old marking");
136 assert(region->garbage_before_padded_for_promote() < old_garbage_threshold, "Region " SIZE_FORMAT " has too much garbage for promotion", region->index());
137 assert(region->is_young(), "Only young regions can be promoted");
138 assert(region->is_regular(), "Use different service to promote humongous regions");
139 assert(region->age() >= _heap->age_census()->tenuring_threshold(), "Only promote regions that are sufficiently aged");
140 assert(region->get_top_before_promote() == tams, "Region " SIZE_FORMAT " has been used for allocations before promotion", region->index());
141 }
142
143 // Rebuild the remembered set information and mark the entire range as DIRTY. We do NOT scan the content of this
144 // range to determine which cards need to be DIRTY. That would force us to scan the region twice, once now, and
145 // once during the subsequent remembered set scan. Instead, we blindly (conservatively) mark everything as DIRTY
146 // now and then sort out the CLEAN pages during the next remembered set scan.
147 //
148 // Rebuilding the remembered set consists of clearing all object registrations (reset_object_range()) here,
149 // then registering every live object and every coalesced range of free objects in the loop that follows.
150 _heap->card_scan()->reset_object_range(region->bottom(), region->end());
151 _heap->card_scan()->mark_range_as_dirty(region->bottom(), region->get_top_before_promote() - region->bottom());
152
153 // TODO: use an existing coalesce-and-fill function rather than replicating the code here.
154 HeapWord* obj_addr = region->bottom();
155 while (obj_addr < tams) {
156 oop obj = cast_to_oop(obj_addr);
157 if (marking_context->is_marked(obj)) {
158 assert(obj->klass() != nullptr, "klass should not be NULL");
159 // This thread is responsible for registering all objects in this region. No need for lock.
160 _heap->card_scan()->register_object_without_lock(obj_addr);
161 obj_addr += obj->size();
162 } else {
163 HeapWord* next_marked_obj = marking_context->get_next_marked_addr(obj_addr, tams);
164 assert(next_marked_obj <= tams, "next marked object cannot exceed tams");
165 size_t fill_size = next_marked_obj - obj_addr;
166 assert(fill_size >= ShenandoahHeap::min_fill_size(), "previously allocated objects known to be larger than min_size");
167 ShenandoahHeap::fill_with_object(obj_addr, fill_size);
168 _heap->card_scan()->register_object_without_lock(obj_addr);
169 obj_addr = next_marked_obj;
170 }
171 }
172 // We do not need to scan above TAMS because restored top equals tams
173 assert(obj_addr == tams, "Expect loop to terminate when obj_addr equals tams");
174
175 ShenandoahOldGeneration* const old_gen = _heap->old_generation();
176 ShenandoahYoungGeneration* const young_gen = _heap->young_generation();
177
178 {
179 ShenandoahHeapLocker locker(_heap->lock());
180
181 HeapWord* update_watermark = region->get_update_watermark();
182
183 // Now that this region is affiliated with old, we can allow it to receive allocations, though it may not be in the
184 // is_collector_free range.
185 region->restore_top_before_promote();
186
187 size_t region_used = region->used();
188
189 // The update_watermark was likely established while we had the artificially high value of top. Make it sane now.
190 assert(update_watermark >= region->top(), "original top cannot exceed preserved update_watermark");
191 region->set_update_watermark(region->top());
192
193 // Unconditionally transfer one region from young to old. This represents the newly promoted region.
194 // This expands old and shrinks new by the size of one region. Strictly, we do not "need" to expand old
195 // if there are already enough unaffiliated regions in old to account for this newly promoted region.
196 // However, if we do not transfer the capacities, we end up reducing the amount of memory that would have
197 // otherwise been available to hold old evacuations, because old available is max_capacity - used and now
198 // we would be trading a fully empty region for a partially used region.
199 young_gen->decrease_used(region_used);
200 young_gen->decrement_affiliated_region_count();
201
202 // transfer_to_old() increases capacity of old and decreases capacity of young
203 _heap->generation_sizer()->force_transfer_to_old(1);
204 region->set_affiliation(OLD_GENERATION);
205
206 old_gen->increment_affiliated_region_count();
207 old_gen->increase_used(region_used);
208
209 // add_old_collector_free_region() increases promoted_reserve() if available space exceeds plab_min_size()
210 _heap->free_set()->add_old_collector_free_region(region);
211 }
212 }
213
214 void ShenandoahGenerationalEvacuationTask::promote_humongous(ShenandoahHeapRegion* region) {
215 ShenandoahMarkingContext* marking_context = _heap->marking_context();
216 oop obj = cast_to_oop(region->bottom());
217 assert(_heap->active_generation()->is_mark_complete(), "sanity");
218 assert(region->is_young(), "Only young regions can be promoted");
219 assert(region->is_humongous_start(), "Should not promote humongous continuation in isolation");
220 assert(region->age() >= _heap->age_census()->tenuring_threshold(), "Only promote regions that are sufficiently aged");
221 assert(marking_context->is_marked(obj), "promoted humongous object should be alive");
222
223 // TODO: Consider not promoting humongous objects that represent primitive arrays. Leaving a primitive array
224 // (obj->is_typeArray()) in young-gen is harmless because these objects are never relocated and they are not
225 // scanned. Leaving primitive arrays in young-gen memory allows their memory to be reclaimed more quickly when
226 // it becomes garbage. Better to not make this change until sizes of young-gen and old-gen are completely
227 // adaptive, as leaving primitive arrays in young-gen might be perceived as an "astonishing result" by someone
228 // has carefully analyzed the required sizes of an application's young-gen and old-gen.
229 const size_t used_bytes = obj->size() * HeapWordSize;
230 const size_t spanned_regions = ShenandoahHeapRegion::required_regions(used_bytes);
231 const size_t humongous_waste = spanned_regions * ShenandoahHeapRegion::region_size_bytes() - obj->size() * HeapWordSize;
232 const size_t index_limit = region->index() + spanned_regions;
233
234 ShenandoahGeneration* const old_generation = _heap->old_generation();
235 ShenandoahGeneration* const young_generation = _heap->young_generation();
236 {
237 // We need to grab the heap lock in order to avoid a race when changing the affiliations of spanned_regions from
238 // young to old.
239 ShenandoahHeapLocker locker(_heap->lock());
240
241 // We promote humongous objects unconditionally, without checking for availability. We adjust
242 // usage totals, including humongous waste, after evacuation is done.
243 log_debug(gc)("promoting humongous region " SIZE_FORMAT ", spanning " SIZE_FORMAT, region->index(), spanned_regions);
244
245 young_generation->decrease_used(used_bytes);
246 young_generation->decrease_humongous_waste(humongous_waste);
247 young_generation->decrease_affiliated_region_count(spanned_regions);
248
249 // transfer_to_old() increases capacity of old and decreases capacity of young
250 _heap->generation_sizer()->force_transfer_to_old(spanned_regions);
251
252 // For this region and each humongous continuation region spanned by this humongous object, change
253 // affiliation to OLD_GENERATION and adjust the generation-use tallies. The remnant of memory
254 // in the last humongous region that is not spanned by obj is currently not used.
255 for (size_t i = region->index(); i < index_limit; i++) {
256 ShenandoahHeapRegion* r = _heap->get_region(i);
257 log_debug(gc)("promoting humongous region " SIZE_FORMAT ", from " PTR_FORMAT " to " PTR_FORMAT,
258 r->index(), p2i(r->bottom()), p2i(r->top()));
259 // We mark the entire humongous object's range as dirty after loop terminates, so no need to dirty the range here
260 r->set_affiliation(OLD_GENERATION);
261 }
262
263 old_generation->increase_affiliated_region_count(spanned_regions);
264 old_generation->increase_used(used_bytes);
265 old_generation->increase_humongous_waste(humongous_waste);
266 }
267
268 // Since this region may have served previously as OLD, it may hold obsolete object range info.
269 HeapWord* const humongous_bottom = region->bottom();
270 _heap->card_scan()->reset_object_range(humongous_bottom, humongous_bottom + spanned_regions * ShenandoahHeapRegion::region_size_words());
271 // Since the humongous region holds only one object, no lock is necessary for this register_object() invocation.
272 _heap->card_scan()->register_object_without_lock(humongous_bottom);
273
274 if (obj->is_typeArray()) {
275 // Primitive arrays don't need to be scanned.
276 log_debug(gc)("Clean cards for promoted humongous object (Region " SIZE_FORMAT ") from " PTR_FORMAT " to " PTR_FORMAT,
277 region->index(), p2i(humongous_bottom), p2i(humongous_bottom + obj->size()));
278 _heap->card_scan()->mark_range_as_clean(humongous_bottom, obj->size());
279 } else {
280 log_debug(gc)("Dirty cards for promoted humongous object (Region " SIZE_FORMAT ") from " PTR_FORMAT " to " PTR_FORMAT,
281 region->index(), p2i(humongous_bottom), p2i(humongous_bottom + obj->size()));
282 _heap->card_scan()->mark_range_as_dirty(humongous_bottom, obj->size());
283 }
284 }