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/heuristics/shenandoahGenerationalHeuristics.hpp"
 28 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
 29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
 30 #include "gc/shenandoah/shenandoahGeneration.hpp"
 31 #include "gc/shenandoah/shenandoahGenerationalHeap.inline.hpp"
 32 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
 33 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
 34 #include "gc/shenandoah/shenandoahEvacInfo.hpp"
 35 #include "gc/shenandoah/shenandoahTrace.hpp"
 36 
 37 #include "logging/log.hpp"
 38 
 39 ShenandoahGenerationalHeuristics::ShenandoahGenerationalHeuristics(ShenandoahGeneration* generation)
 40         : ShenandoahAdaptiveHeuristics(generation), _generation(generation) {
 41 }
 42 
 43 void ShenandoahGenerationalHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
 44   assert(collection_set->is_empty(), "Must be empty");
 45 
 46   auto heap = ShenandoahGenerationalHeap::heap();
 47   size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
 48 
 49 
 50   // Check all pinned regions have updated status before choosing the collection set.
 51   heap->assert_pinned_region_status();
 52 
 53   // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
 54 
 55   size_t num_regions = heap->num_regions();
 56 
 57   RegionData* candidates = _region_data;
 58 
 59   size_t cand_idx = 0;
 60   size_t preselected_candidates = 0;
 61 
 62   size_t total_garbage = 0;
 63 
 64   size_t immediate_garbage = 0;
 65   size_t immediate_regions = 0;
 66 
 67   size_t free = 0;
 68   size_t free_regions = 0;
 69 
 70   // This counts number of humongous regions that we intend to promote in this cycle.
 71   size_t humongous_regions_promoted = 0;
 72   // This counts number of regular regions that will be promoted in place.
 73   size_t regular_regions_promoted_in_place = 0;
 74   // This counts bytes of memory used by regular regions to be promoted in place.
 75   size_t regular_regions_promoted_usage = 0;
 76   // This counts bytes of memory free in regular regions to be promoted in place.
 77   size_t regular_regions_promoted_free = 0;
 78   // This counts bytes of garbage memory in regular regions to be promoted in place.
 79   size_t regular_regions_promoted_garbage = 0;
 80 
 81   for (size_t i = 0; i < num_regions; i++) {
 82     ShenandoahHeapRegion* region = heap->get_region(i);
 83     if (!_generation->contains(region)) {
 84       continue;
 85     }
 86     size_t garbage = region->garbage();
 87     total_garbage += garbage;
 88     if (region->is_empty()) {
 89       free_regions++;
 90       free += region_size_bytes;
 91     } else if (region->is_regular()) {
 92       if (!region->has_live()) {
 93         // We can recycle it right away and put it in the free set.
 94         immediate_regions++;
 95         immediate_garbage += garbage;
 96         region->make_trash_immediate();
 97       } else {
 98         bool is_candidate;
 99         // This is our candidate for later consideration.
100         if (collection_set->is_preselected(i)) {
101           assert(heap->is_tenurable(region), "Preselection filter");
102           is_candidate = true;
103           preselected_candidates++;
104           // Set garbage value to maximum value to force this into the sorted collection set.
105           garbage = region_size_bytes;
106         } else if (region->is_young() && heap->is_tenurable(region)) {
107           // Note that for GLOBAL GC, region may be OLD, and OLD regions do not qualify for pre-selection
108 
109           // This region is old enough to be promoted but it was not preselected, either because its garbage is below
110           // ShenandoahOldGarbageThreshold so it will be promoted in place, or because there is not sufficient room
111           // in old gen to hold the evacuated copies of this region's live data.  In both cases, we choose not to
112           // place this region into the collection set.
113           if (region->get_top_before_promote() != nullptr) {
114             // Region was included for promotion-in-place
115             regular_regions_promoted_in_place++;
116             regular_regions_promoted_usage += region->used_before_promote();
117             regular_regions_promoted_free += region->free();
118             regular_regions_promoted_garbage += region->garbage();
119           }
120           is_candidate = false;
121         } else {
122           is_candidate = true;
123         }
124         if (is_candidate) {
125           candidates[cand_idx].set_region_and_garbage(region, garbage);
126           cand_idx++;
127         }
128       }
129     } else if (region->is_humongous_start()) {
130       // Reclaim humongous regions here, and count them as the immediate garbage
131 #ifdef ASSERT
132       bool reg_live = region->has_live();
133       bool bm_live = heap->active_generation()->complete_marking_context()->is_marked(cast_to_oop(region->bottom()));
134       assert(reg_live == bm_live,
135              "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
136              BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
137 #endif
138       if (!region->has_live()) {
139         heap->trash_humongous_region_at(region);
140 
141         // Count only the start. Continuations would be counted on "trash" path
142         immediate_regions++;
143         immediate_garbage += garbage;
144       } else {
145         if (region->is_young() && heap->is_tenurable(region)) {
146           oop obj = cast_to_oop(region->bottom());
147           size_t humongous_regions = ShenandoahHeapRegion::required_regions(obj->size() * HeapWordSize);
148           humongous_regions_promoted += humongous_regions;
149         }
150       }
151     } else if (region->is_trash()) {
152       // Count in just trashed collection set, during coalesced CM-with-UR
153       immediate_regions++;
154       immediate_garbage += garbage;
155     }
156   }
157   heap->old_generation()->set_expected_humongous_region_promotions(humongous_regions_promoted);
158   heap->old_generation()->set_expected_regular_region_promotions(regular_regions_promoted_in_place);
159   log_info(gc, ergo)("Planning to promote in place " SIZE_FORMAT " humongous regions and " SIZE_FORMAT
160                      " regular regions, spanning a total of " SIZE_FORMAT " used bytes",
161                      humongous_regions_promoted, regular_regions_promoted_in_place,
162                      humongous_regions_promoted * ShenandoahHeapRegion::region_size_bytes() +
163                      regular_regions_promoted_usage);
164 
165   // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
166   // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
167 
168   assert (immediate_garbage <= total_garbage,
169           "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
170           byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
171           byte_size_in_proper_unit(total_garbage), proper_unit_for_byte_size(total_garbage));
172 
173   size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
174 
175   bool doing_promote_in_place = (humongous_regions_promoted + regular_regions_promoted_in_place > 0);
176   if (doing_promote_in_place || (preselected_candidates > 0) || (immediate_percent <= ShenandoahImmediateThreshold)) {
177     // Only young collections need to prime the collection set.
178     if (_generation->is_young()) {
179       heap->old_generation()->heuristics()->prime_collection_set(collection_set);
180     }
181 
182     // Call the subclasses to add young-gen regions into the collection set.
183     choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
184   }
185 
186   if (collection_set->has_old_regions()) {
187     heap->shenandoah_policy()->record_mixed_cycle();
188   }
189 
190   size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
191   size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
192   size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
193 
194   log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
195                      "Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), " SIZE_FORMAT " regions, "
196                      "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), " SIZE_FORMAT " regions",
197 
198                      byte_size_in_proper_unit(collectable_garbage),
199                      proper_unit_for_byte_size(collectable_garbage),
200                      collectable_garbage_percent,
201 
202                      byte_size_in_proper_unit(immediate_garbage),
203                      proper_unit_for_byte_size(immediate_garbage),
204                      immediate_percent,
205                      immediate_regions,
206 
207                      byte_size_in_proper_unit(collection_set->garbage()),
208                      proper_unit_for_byte_size(collection_set->garbage()),
209                      cset_percent,
210                      collection_set->count());
211 
212   if (collection_set->garbage() > 0) {
213     size_t young_evac_bytes = collection_set->get_young_bytes_reserved_for_evacuation();
214     size_t promote_evac_bytes = collection_set->get_young_bytes_to_be_promoted();
215     size_t old_evac_bytes = collection_set->get_old_bytes_reserved_for_evacuation();
216     size_t total_evac_bytes = young_evac_bytes + promote_evac_bytes + old_evac_bytes;
217     log_info(gc, ergo)("Evacuation Targets: YOUNG: " SIZE_FORMAT "%s, "
218                        "PROMOTE: " SIZE_FORMAT "%s, "
219                        "OLD: " SIZE_FORMAT "%s, "
220                        "TOTAL: " SIZE_FORMAT "%s",
221                        byte_size_in_proper_unit(young_evac_bytes), proper_unit_for_byte_size(young_evac_bytes),
222                        byte_size_in_proper_unit(promote_evac_bytes), proper_unit_for_byte_size(promote_evac_bytes),
223                        byte_size_in_proper_unit(old_evac_bytes), proper_unit_for_byte_size(old_evac_bytes),
224                        byte_size_in_proper_unit(total_evac_bytes), proper_unit_for_byte_size(total_evac_bytes));
225 
226     ShenandoahEvacuationInformation evacInfo;
227     evacInfo.set_collection_set_regions(collection_set->count());
228     evacInfo.set_collection_set_used_before(collection_set->used());
229     evacInfo.set_collection_set_used_after(collection_set->live());
230     evacInfo.set_collected_old(old_evac_bytes);
231     evacInfo.set_collected_promoted(promote_evac_bytes);
232     evacInfo.set_collected_young(young_evac_bytes);
233     evacInfo.set_regions_promoted_humongous(humongous_regions_promoted);
234     evacInfo.set_regions_promoted_regular(regular_regions_promoted_in_place);
235     evacInfo.set_regular_promoted_garbage(regular_regions_promoted_garbage);
236     evacInfo.set_regular_promoted_free(regular_regions_promoted_free);
237     evacInfo.set_regions_immediate(immediate_regions);
238     evacInfo.set_immediate_size(immediate_garbage);
239     evacInfo.set_free_regions(free_regions);
240 
241     ShenandoahTracer().report_evacuation_info(&evacInfo);
242   }
243 }
244 
245 
246 size_t ShenandoahGenerationalHeuristics::add_preselected_regions_to_collection_set(ShenandoahCollectionSet* cset,
247                                                                                    const RegionData* data,
248                                                                                    size_t size) const {
249   // cur_young_garbage represents the amount of memory to be reclaimed from young-gen.  In the case that live objects
250   // are known to be promoted out of young-gen, we count this as cur_young_garbage because this memory is reclaimed
251   // from young-gen and becomes available to serve future young-gen allocation requests.
252   size_t cur_young_garbage = 0;
253   for (size_t idx = 0; idx < size; idx++) {
254     ShenandoahHeapRegion* r = data[idx].get_region();
255     if (cset->is_preselected(r->index())) {
256       assert(ShenandoahGenerationalHeap::heap()->is_tenurable(r), "Preselected regions must have tenure age");
257       // Entire region will be promoted, This region does not impact young-gen or old-gen evacuation reserve.
258       // This region has been pre-selected and its impact on promotion reserve is already accounted for.
259 
260       // r->used() is r->garbage() + r->get_live_data_bytes()
261       // Since all live data in this region is being evacuated from young-gen, it is as if this memory
262       // is garbage insofar as young-gen is concerned.  Counting this as garbage reduces the need to
263       // reclaim highly utilized young-gen regions just for the sake of finding min_garbage to reclaim
264       // within young-gen memory.
265 
266       cur_young_garbage += r->garbage();
267       cset->add_region(r);
268     }
269   }
270   return cur_young_garbage;
271 }
272 
273 void ShenandoahGenerationalHeuristics::log_cset_composition(ShenandoahCollectionSet* cset) const {
274   size_t collected_old = cset->get_old_bytes_reserved_for_evacuation();
275   size_t collected_promoted = cset->get_young_bytes_to_be_promoted();
276   size_t collected_young = cset->get_young_bytes_reserved_for_evacuation();
277 
278   log_info(gc, ergo)(
279           "Chosen CSet evacuates young: " SIZE_FORMAT "%s (of which at least: " SIZE_FORMAT "%s are to be promoted), "
280           "old: " SIZE_FORMAT "%s",
281           byte_size_in_proper_unit(collected_young), proper_unit_for_byte_size(collected_young),
282           byte_size_in_proper_unit(collected_promoted), proper_unit_for_byte_size(collected_promoted),
283           byte_size_in_proper_unit(collected_old), proper_unit_for_byte_size(collected_old));
284 }