1 /*
   2  * Copyright (c) 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/shared/gcCause.hpp"
  27 #include "gc/shenandoah/shenandoahBrooksPointer.hpp"
  28 #include "gc/shenandoah/shenandoahCollectionSet.inline.hpp"
  29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
  30 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  31 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
  32 #include "gc/shenandoah/shenandoahHeuristics.hpp"
  33 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
  34 #include "logging/log.hpp"
  35 #include "logging/logTag.hpp"
  36 
  37 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
  38   if (a._garbage > b._garbage)
  39     return -1;
  40   else if (a._garbage < b._garbage)
  41     return 1;
  42   else return 0;
  43 }
  44 
  45 int ShenandoahHeuristics::compare_by_garbage_then_alloc_seq_ascending(RegionData a, RegionData b) {
  46   int r = compare_by_garbage(a, b);
  47   if (r != 0) {
  48     return r;
  49   }
  50   return compare_by_alloc_seq_ascending(a, b);
  51 }
  52 
  53 int ShenandoahHeuristics::compare_by_alloc_seq_ascending(RegionData a, RegionData b) {
  54   if (a._seqnum_last_alloc == b._seqnum_last_alloc)
  55     return 0;
  56   else if (a._seqnum_last_alloc < b._seqnum_last_alloc)
  57     return -1;
  58   else return 1;
  59 }
  60 
  61 int ShenandoahHeuristics::compare_by_alloc_seq_descending(RegionData a, RegionData b) {
  62   return -compare_by_alloc_seq_ascending(a, b);
  63 }
  64 
  65 ShenandoahHeuristics::ShenandoahHeuristics() :
  66   _update_refs_early(false),
  67   _update_refs_adaptive(false),
  68   _region_data(NULL),
  69   _region_data_size(0),
  70   _degenerated_cycles_in_a_row(0),
  71   _successful_cycles_in_a_row(0),
  72   _bytes_in_cset(0),
  73   _cycle_start(os::elapsedTime()),
  74   _last_cycle_end(0),
  75   _gc_times_learned(0),
  76   _gc_time_penalties(0),
  77   _gc_time_history(new TruncatedSeq(5)),
  78   _metaspace_oom()
  79 {
  80   if (strcmp(ShenandoahUpdateRefsEarly, "on") == 0 ||
  81       strcmp(ShenandoahUpdateRefsEarly, "true") == 0 ) {
  82     _update_refs_early = true;
  83   } else if (strcmp(ShenandoahUpdateRefsEarly, "off") == 0 ||
  84              strcmp(ShenandoahUpdateRefsEarly, "false") == 0 ) {
  85     _update_refs_early = false;
  86   } else if (strcmp(ShenandoahUpdateRefsEarly, "adaptive") == 0) {
  87     _update_refs_adaptive = true;
  88     _update_refs_early = true;
  89   } else {
  90     vm_exit_during_initialization("Unknown -XX:ShenandoahUpdateRefsEarly option: %s", ShenandoahUpdateRefsEarly);
  91   }
  92 
  93   // No unloading during concurrent mark? Communicate that to heuristics
  94   if (!ClassUnloadingWithConcurrentMark) {
  95     FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
  96   }
  97 }
  98 
  99 ShenandoahHeuristics::~ShenandoahHeuristics() {
 100   if (_region_data != NULL) {
 101     FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
 102   }
 103 }
 104 
 105 ShenandoahHeuristics::RegionData* ShenandoahHeuristics::get_region_data_cache(size_t num) {
 106   RegionData* res = _region_data;
 107   if (res == NULL) {
 108     res = NEW_C_HEAP_ARRAY(RegionData, num, mtGC);
 109     _region_data = res;
 110     _region_data_size = num;
 111   } else if (_region_data_size < num) {
 112     res = REALLOC_C_HEAP_ARRAY(RegionData, _region_data, num, mtGC);
 113     _region_data = res;
 114     _region_data_size = num;
 115   }
 116   return res;
 117 }
 118 
 119 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
 120   assert(collection_set->count() == 0, "Must be empty");
 121 
 122   ShenandoahHeap* heap = ShenandoahHeap::heap();
 123 
 124   // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
 125 
 126   size_t num_regions = heap->num_regions();
 127 
 128   RegionData* candidates = get_region_data_cache(num_regions);
 129 
 130   size_t cand_idx = 0;
 131 
 132   size_t total_garbage = 0;
 133 
 134   size_t immediate_garbage = 0;
 135   size_t immediate_regions = 0;
 136 
 137   size_t free = 0;
 138   size_t free_regions = 0;
 139 
 140   ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
 141 
 142   for (size_t i = 0; i < num_regions; i++) {
 143     ShenandoahHeapRegion* region = heap->get_region(i);
 144 
 145     size_t garbage = region->garbage();
 146     total_garbage += garbage;
 147 
 148     if (region->is_empty()) {
 149       free_regions++;
 150       free += ShenandoahHeapRegion::region_size_bytes();
 151     } else if (region->is_regular()) {
 152       if (!region->has_live()) {
 153         // We can recycle it right away and put it in the free set.
 154         immediate_regions++;
 155         immediate_garbage += garbage;
 156         region->make_trash_immediate();
 157       } else {
 158         // This is our candidate for later consideration.
 159         candidates[cand_idx]._region = region;
 160         candidates[cand_idx]._garbage = garbage;
 161         cand_idx++;
 162       }
 163     } else if (region->is_humongous_start()) {
 164       // Reclaim humongous regions here, and count them as the immediate garbage
 165 #ifdef ASSERT
 166       bool reg_live = region->has_live();
 167       bool bm_live = ctx->is_marked(oop(region->bottom() + ShenandoahBrooksPointer::word_size()));
 168       assert(reg_live == bm_live,
 169              "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
 170              BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
 171 #endif
 172       if (!region->has_live()) {
 173         heap->trash_humongous_region_at(region);
 174 
 175         // Count only the start. Continuations would be counted on "trash" path
 176         immediate_regions++;
 177         immediate_garbage += garbage;
 178       }
 179     } else if (region->is_trash()) {
 180       // Count in just trashed collection set, during coalesced CM-with-UR
 181       immediate_regions++;
 182       immediate_garbage += garbage;
 183     }
 184   }
 185 
 186   // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
 187   // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
 188 
 189   assert (immediate_garbage <= total_garbage,
 190           "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "M vs " SIZE_FORMAT "M",
 191           immediate_garbage / M, total_garbage / M);
 192 
 193   size_t immediate_percent = total_garbage == 0 ? 0 : (immediate_garbage * 100 / total_garbage);
 194 
 195   if (immediate_percent <= ShenandoahImmediateThreshold) {
 196     choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
 197     collection_set->update_region_status();
 198 
 199     size_t cset_percent = total_garbage == 0 ? 0 : (collection_set->garbage() * 100 / total_garbage);
 200     log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "M (" SIZE_FORMAT "%% of total), " SIZE_FORMAT "M CSet, " SIZE_FORMAT " CSet regions",
 201                        collection_set->garbage() / M, cset_percent, collection_set->live_data() / M, collection_set->count());
 202   }
 203 
 204   log_info(gc, ergo)("Immediate Garbage: " SIZE_FORMAT "M (" SIZE_FORMAT "%% of total), " SIZE_FORMAT " regions",
 205                      immediate_garbage / M, immediate_percent, immediate_regions);
 206 }
 207 
 208 void ShenandoahHeuristics::record_gc_start() {
 209   // Do nothing
 210 }
 211 
 212 void ShenandoahHeuristics::record_gc_end() {
 213   // Do nothing
 214 }
 215 
 216 void ShenandoahHeuristics::record_cycle_start() {
 217   _cycle_start = os::elapsedTime();
 218 }
 219 
 220 void ShenandoahHeuristics::record_cycle_end() {
 221   _last_cycle_end = os::elapsedTime();
 222 }
 223 
 224 void ShenandoahHeuristics::record_phase_time(ShenandoahPhaseTimings::Phase phase, double secs) {
 225   // Do nothing
 226 }
 227 
 228 bool ShenandoahHeuristics::should_start_update_refs() {
 229   return _update_refs_early;
 230 }
 231 
 232 bool ShenandoahHeuristics::should_start_normal_gc() const {
 233   // Perform GC to cleanup metaspace
 234   if (has_metaspace_oom()) {
 235     // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
 236     log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
 237     return true;
 238   }
 239 
 240   double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
 241   bool periodic_gc = (last_time_ms > ShenandoahGuaranteedGCInterval);
 242   if (periodic_gc) {
 243     log_info(gc)("Trigger: Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
 244                   last_time_ms, ShenandoahGuaranteedGCInterval);
 245   }
 246   return periodic_gc;
 247 }
 248 
 249 bool ShenandoahHeuristics::should_start_traversal_gc() {
 250   return false;
 251 }
 252 
 253 bool ShenandoahHeuristics::can_do_traversal_gc() {
 254   return false;
 255 }
 256 
 257 bool ShenandoahHeuristics::should_degenerate_cycle() {
 258   return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
 259 }
 260 
 261 void ShenandoahHeuristics::record_success_concurrent() {
 262   _degenerated_cycles_in_a_row = 0;
 263   _successful_cycles_in_a_row++;
 264 
 265   _gc_time_history->add(time_since_last_gc());
 266   _gc_times_learned++;
 267   _gc_time_penalties -= MIN2<size_t>(_gc_time_penalties, Concurrent_Adjust);
 268 }
 269 
 270 void ShenandoahHeuristics::record_success_degenerated() {
 271   _degenerated_cycles_in_a_row++;
 272   _successful_cycles_in_a_row = 0;
 273   _gc_time_penalties += Degenerated_Penalty;
 274 }
 275 
 276 void ShenandoahHeuristics::record_success_full() {
 277   _degenerated_cycles_in_a_row = 0;
 278   _successful_cycles_in_a_row++;
 279   _gc_time_penalties += Full_Penalty;
 280 }
 281 
 282 void ShenandoahHeuristics::record_allocation_failure_gc() {
 283   _bytes_in_cset = 0;
 284 }
 285 
 286 void ShenandoahHeuristics::record_requested_gc() {
 287   _bytes_in_cset = 0;
 288 
 289   // Assume users call System.gc() when external state changes significantly,
 290   // which forces us to re-learn the GC timings and allocation rates.
 291   _gc_times_learned = 0;
 292 }
 293 
 294 bool ShenandoahHeuristics::can_process_references() {
 295   if (ShenandoahRefProcFrequency == 0) return false;
 296   return true;
 297 }
 298 
 299 bool ShenandoahHeuristics::should_process_references() {
 300   if (!can_process_references()) return false;
 301   size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
 302   // Process references every Nth GC cycle.
 303   return cycle % ShenandoahRefProcFrequency == 0;
 304 }
 305 
 306 bool ShenandoahHeuristics::can_unload_classes() {
 307   if (!ClassUnloading) return false;
 308   return true;
 309 }
 310 
 311 bool ShenandoahHeuristics::can_unload_classes_normal() {
 312   if (!can_unload_classes()) return false;
 313   if (has_metaspace_oom()) return true;
 314   if (!ClassUnloadingWithConcurrentMark) return false;
 315   if (ShenandoahUnloadClassesFrequency == 0) return false;
 316   return true;
 317 }
 318 
 319 bool ShenandoahHeuristics::should_unload_classes() {
 320   if (!can_unload_classes_normal()) return false;
 321   if (has_metaspace_oom()) return true;
 322   size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
 323   // Unload classes every Nth GC cycle.
 324   // This should not happen in the same cycle as process_references to amortize costs.
 325   // Offsetting by one is enough to break the rendezvous when periods are equal.
 326   // When periods are not equal, offsetting by one is just as good as any other guess.
 327   return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
 328 }
 329 
 330 void ShenandoahHeuristics::initialize() {
 331   // Nothing to do by default.
 332 }
 333 
 334 double ShenandoahHeuristics::time_since_last_gc() const {
 335   return os::elapsedTime() - _cycle_start;
 336 }