1 /*
  2  * Copyright (c) 2018, 2020, 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 #include "gc/shared/gcCause.hpp"
 28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
 29 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
 30 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
 31 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
 32 #include "logging/log.hpp"
 33 #include "logging/logTag.hpp"
 34 #include "runtime/globals_extension.hpp"
 35 #include "utilities/quickSort.hpp"
 36 
 37 // sort by decreasing garbage (so most garbage comes first)
 38 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
 39   if (a._u._garbage > b._u._garbage)
 40     return -1;
 41   else if (a._u._garbage < b._u._garbage)
 42     return 1;
 43   else return 0;
 44 }
 45 
 46 ShenandoahHeuristics::ShenandoahHeuristics(ShenandoahSpaceInfo* space_info) :
 47   _space_info(space_info),
 48   _region_data(nullptr),
 49   _guaranteed_gc_interval(0),
 50   _cycle_start(os::elapsedTime()),
 51   _last_cycle_end(0),
 52   _gc_times_learned(0),
 53   _gc_time_penalties(0),
 54   _gc_cycle_time_history(new TruncatedSeq(Moving_Average_Samples, ShenandoahAdaptiveDecayFactor)),
 55   _metaspace_oom()
 56 {
 57   // No unloading during concurrent mark? Communicate that to heuristics
 58   if (!ClassUnloadingWithConcurrentMark) {
 59     FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
 60   }
 61 
 62   size_t num_regions = ShenandoahHeap::heap()->num_regions();
 63   assert(num_regions > 0, "Sanity");
 64 
 65   _region_data = NEW_C_HEAP_ARRAY(RegionData, num_regions, mtGC);
 66 }
 67 
 68 ShenandoahHeuristics::~ShenandoahHeuristics() {
 69   FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
 70 }
 71 
 72 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
 73   assert(collection_set->is_empty(), "Must be empty");
 74 
 75   ShenandoahHeap* heap = ShenandoahHeap::heap();
 76 
 77   // Check all pinned regions have updated status before choosing the collection set.
 78   heap->assert_pinned_region_status();
 79 
 80   // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
 81 
 82   size_t num_regions = heap->num_regions();
 83 
 84   RegionData* candidates = _region_data;
 85 
 86   size_t cand_idx = 0;
 87 
 88   size_t total_garbage = 0;
 89 
 90   size_t immediate_garbage = 0;
 91   size_t immediate_regions = 0;
 92 
 93   size_t free = 0;
 94   size_t free_regions = 0;
 95 
 96   ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
 97 
 98   for (size_t i = 0; i < num_regions; i++) {
 99     ShenandoahHeapRegion* region = heap->get_region(i);
100 
101     size_t garbage = region->garbage();
102     total_garbage += garbage;
103 
104     if (region->is_empty()) {
105       free_regions++;
106       free += ShenandoahHeapRegion::region_size_bytes();
107     } else if (region->is_regular()) {
108       if (!region->has_live()) {
109         // We can recycle it right away and put it in the free set.
110         immediate_regions++;
111         immediate_garbage += garbage;
112         region->make_trash_immediate();
113       } else {
114         // This is our candidate for later consideration.
115         candidates[cand_idx]._region = region;
116         candidates[cand_idx]._u._garbage = garbage;
117         cand_idx++;
118       }
119     } else if (region->is_humongous_start()) {
120       // Reclaim humongous regions here, and count them as the immediate garbage
121 #ifdef ASSERT
122       bool reg_live = region->has_live();
123       bool bm_live = ctx->is_marked(cast_to_oop(region->bottom()));
124       assert(reg_live == bm_live,
125              "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
126              BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
127 #endif
128       if (!region->has_live()) {
129         heap->trash_humongous_region_at(region);
130 
131         // Count only the start. Continuations would be counted on "trash" path
132         immediate_regions++;
133         immediate_garbage += garbage;
134       }
135     } else if (region->is_trash()) {
136       // Count in just trashed collection set, during coalesced CM-with-UR
137       immediate_regions++;
138       immediate_garbage += garbage;
139     }
140   }
141 
142   // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
143   // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
144 
145   assert (immediate_garbage <= total_garbage,
146           "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
147           byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
148           byte_size_in_proper_unit(total_garbage),     proper_unit_for_byte_size(total_garbage));
149 
150   size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
151 
152   if (immediate_percent <= ShenandoahImmediateThreshold) {
153     choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
154   }
155 
156   size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
157   size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
158   size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
159 
160   log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
161                      "Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), " SIZE_FORMAT " regions, "
162                      "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), " SIZE_FORMAT " regions",
163 
164                      byte_size_in_proper_unit(collectable_garbage),
165                      proper_unit_for_byte_size(collectable_garbage),
166                      collectable_garbage_percent,
167 
168                      byte_size_in_proper_unit(immediate_garbage),
169                      proper_unit_for_byte_size(immediate_garbage),
170                      immediate_percent,
171                      immediate_regions,
172 
173                      byte_size_in_proper_unit(collection_set->garbage()),
174                      proper_unit_for_byte_size(collection_set->garbage()),
175                      cset_percent,
176                      collection_set->count());
177 }
178 
179 void ShenandoahHeuristics::record_cycle_start() {
180   _cycle_start = os::elapsedTime();
181 }
182 
183 void ShenandoahHeuristics::record_cycle_end() {
184   _last_cycle_end = os::elapsedTime();
185 }
186 
187 bool ShenandoahHeuristics::should_start_gc() {
188   // Perform GC to cleanup metaspace
189   if (has_metaspace_oom()) {
190     // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
191     log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
192     return true;
193   }
194 
195   if (_guaranteed_gc_interval > 0) {
196     double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
197     if (last_time_ms > _guaranteed_gc_interval) {
198       log_info(gc)("Trigger (%s): Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
199                    _space_info->name(), last_time_ms, _guaranteed_gc_interval);
200       return true;
201     }
202   }
203 
204   return false;
205 }
206 
207 bool ShenandoahHeuristics::should_degenerate_cycle() {
208   return ShenandoahHeap::heap()->shenandoah_policy()->consecutive_degenerated_gc_count() <= ShenandoahFullGCThreshold;
209 }
210 
211 void ShenandoahHeuristics::adjust_penalty(intx step) {
212   assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
213          "In range before adjustment: " INTX_FORMAT, _gc_time_penalties);
214 
215   intx new_val = _gc_time_penalties + step;
216   if (new_val < 0) {
217     new_val = 0;
218   }
219   if (new_val > 100) {
220     new_val = 100;
221   }
222   _gc_time_penalties = new_val;
223 
224   assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
225          "In range after adjustment: " INTX_FORMAT, _gc_time_penalties);
226 }
227 
228 void ShenandoahHeuristics::record_success_concurrent(bool abbreviated) {
229   _gc_times_learned++;
230 
231   adjust_penalty(Concurrent_Adjust);
232 
233   if (_gc_times_learned <= ShenandoahLearningSteps || !(abbreviated && ShenandoahAdaptiveIgnoreShortCycles)) {
234     _gc_cycle_time_history->add(elapsed_cycle_time());
235   }
236 }
237 
238 void ShenandoahHeuristics::record_success_degenerated() {
239   adjust_penalty(Degenerated_Penalty);
240 }
241 
242 void ShenandoahHeuristics::record_success_full() {
243   adjust_penalty(Full_Penalty);
244 }
245 
246 void ShenandoahHeuristics::record_allocation_failure_gc() {
247   // Do nothing.
248 }
249 
250 void ShenandoahHeuristics::record_requested_gc() {
251   // Assume users call System.gc() when external state changes significantly,
252   // which forces us to re-learn the GC timings and allocation rates.
253   _gc_times_learned = 0;
254 }
255 
256 bool ShenandoahHeuristics::can_unload_classes() {
257   if (!ClassUnloading) return false;
258   return true;
259 }
260 
261 bool ShenandoahHeuristics::can_unload_classes_normal() {
262   if (!can_unload_classes()) return false;
263   if (has_metaspace_oom()) return true;
264   if (!ClassUnloadingWithConcurrentMark) return false;
265   if (ShenandoahUnloadClassesFrequency == 0) return false;
266   return true;
267 }
268 
269 bool ShenandoahHeuristics::should_unload_classes() {
270   if (!can_unload_classes_normal()) return false;
271   if (has_metaspace_oom()) return true;
272   size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
273   // Unload classes every Nth GC cycle.
274   // This should not happen in the same cycle as process_references to amortize costs.
275   // Offsetting by one is enough to break the rendezvous when periods are equal.
276   // When periods are not equal, offsetting by one is just as good as any other guess.
277   return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
278 }
279 
280 void ShenandoahHeuristics::initialize() {
281   // Nothing to do by default.
282 }
283 
284 double ShenandoahHeuristics::elapsed_cycle_time() const {
285   return os::elapsedTime() - _cycle_start;
286 }