1 /*
   2  * Copyright (c) 2004, 2014, Oracle and/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 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
  27 #include "gc_interface/gcCause.hpp"
  28 #include "memory/collectorPolicy.hpp"
  29 #include "runtime/timer.hpp"
  30 #include "utilities/ostream.hpp"
  31 #include "utilities/workgroup.hpp"
  32 elapsedTimer AdaptiveSizePolicy::_minor_timer;
  33 elapsedTimer AdaptiveSizePolicy::_major_timer;
  34 bool AdaptiveSizePolicy::_debug_perturbation = false;
  35 
  36 // The throughput goal is implemented as
  37 //      _throughput_goal = 1 - ( 1 / (1 + gc_cost_ratio))
  38 // gc_cost_ratio is the ratio
  39 //      application cost / gc cost
  40 // For example a gc_cost_ratio of 4 translates into a
  41 // throughput goal of .80
  42 
  43 AdaptiveSizePolicy::AdaptiveSizePolicy(size_t init_eden_size,
  44                                        size_t init_promo_size,
  45                                        size_t init_survivor_size,
  46                                        double gc_pause_goal_sec,
  47                                        uint gc_cost_ratio) :
  48     _eden_size(init_eden_size),
  49     _promo_size(init_promo_size),
  50     _survivor_size(init_survivor_size),
  51     _gc_pause_goal_sec(gc_pause_goal_sec),
  52     _throughput_goal(1.0 - double(1.0 / (1.0 + (double) gc_cost_ratio))),
  53     _gc_overhead_limit_exceeded(false),
  54     _print_gc_overhead_limit_would_be_exceeded(false),
  55     _gc_overhead_limit_count(0),
  56     _latest_minor_mutator_interval_seconds(0),
  57     _threshold_tolerance_percent(1.0 + ThresholdTolerance/100.0),
  58     _young_gen_change_for_minor_throughput(0),
  59     _old_gen_change_for_major_throughput(0) {
  60   assert(AdaptiveSizePolicyGCTimeLimitThreshold > 0,
  61     "No opportunity to clear SoftReferences before GC overhead limit");
  62   _avg_minor_pause    =
  63     new AdaptivePaddedAverage(AdaptiveTimeWeight, PausePadding);
  64   _avg_minor_interval = new AdaptiveWeightedAverage(AdaptiveTimeWeight);
  65   _avg_minor_gc_cost  = new AdaptiveWeightedAverage(AdaptiveTimeWeight);
  66   _avg_major_gc_cost  = new AdaptiveWeightedAverage(AdaptiveTimeWeight);
  67 
  68   _avg_young_live     = new AdaptiveWeightedAverage(AdaptiveSizePolicyWeight);
  69   _avg_old_live       = new AdaptiveWeightedAverage(AdaptiveSizePolicyWeight);
  70   _avg_eden_live      = new AdaptiveWeightedAverage(AdaptiveSizePolicyWeight);
  71 
  72   _avg_survived       = new AdaptivePaddedAverage(AdaptiveSizePolicyWeight,
  73                                                   SurvivorPadding);
  74   _avg_pretenured     = new AdaptivePaddedNoZeroDevAverage(
  75                                                   AdaptiveSizePolicyWeight,
  76                                                   SurvivorPadding);
  77 
  78   _minor_pause_old_estimator =
  79     new LinearLeastSquareFit(AdaptiveSizePolicyWeight);
  80   _minor_pause_young_estimator =
  81     new LinearLeastSquareFit(AdaptiveSizePolicyWeight);
  82   _minor_collection_estimator =
  83     new LinearLeastSquareFit(AdaptiveSizePolicyWeight);
  84   _major_collection_estimator =
  85     new LinearLeastSquareFit(AdaptiveSizePolicyWeight);
  86 
  87   // Start the timers
  88   _minor_timer.start();
  89 
  90   _young_gen_policy_is_ready = false;
  91 }
  92 
  93 //  If the number of GC threads was set on the command line,
  94 // use it.
  95 //  Else
  96 //    Calculate the number of GC threads based on the number of Java threads.
  97 //    Calculate the number of GC threads based on the size of the heap.
  98 //    Use the larger.
  99 
 100 int AdaptiveSizePolicy::calc_default_active_workers(uintx total_workers,
 101                                             const uintx min_workers,
 102                                             uintx active_workers,
 103                                             uintx application_workers) {
 104   // If the user has specifically set the number of
 105   // GC threads, use them.
 106 
 107   // If the user has turned off using a dynamic number of GC threads
 108   // or the users has requested a specific number, set the active
 109   // number of workers to all the workers.
 110 
 111   uintx new_active_workers = total_workers;
 112   uintx prev_active_workers = active_workers;
 113   uintx active_workers_by_JT = 0;
 114   uintx active_workers_by_heap_size = 0;
 115 
 116   // Always use at least min_workers but use up to
 117   // GCThreadsPerJavaThreads * application threads.
 118   active_workers_by_JT =
 119     MAX2((uintx) GCWorkersPerJavaThread * application_workers,
 120          min_workers);
 121 
 122   // Choose a number of GC threads based on the current size
 123   // of the heap.  This may be complicated because the size of
 124   // the heap depends on factors such as the thoughput goal.
 125   // Still a large heap should be collected by more GC threads.
 126   active_workers_by_heap_size =
 127       MAX2((size_t) 2U, Universe::heap()->capacity() / HeapSizePerGCThread);
 128 
 129   uintx max_active_workers =
 130     MAX2(active_workers_by_JT, active_workers_by_heap_size);
 131 
 132   // Limit the number of workers to the the number created,
 133   // (workers()).
 134   new_active_workers = MIN2(max_active_workers,
 135                                 (uintx) total_workers);
 136 
 137   // Increase GC workers instantly but decrease them more
 138   // slowly.
 139   if (new_active_workers < prev_active_workers) {
 140     new_active_workers =
 141       MAX2(min_workers, (prev_active_workers + new_active_workers) / 2);
 142   }
 143 
 144   // Check once more that the number of workers is within the limits.
 145   assert(min_workers <= total_workers, "Minimum workers not consistent with total workers");
 146   assert(new_active_workers >= min_workers, "Minimum workers not observed");
 147   assert(new_active_workers <= total_workers, "Total workers not observed");
 148 
 149   if (ForceDynamicNumberOfGCThreads) {
 150     // Assume this is debugging and jiggle the number of GC threads.
 151     if (new_active_workers == prev_active_workers) {
 152       if (new_active_workers < total_workers) {
 153         new_active_workers++;
 154       } else if (new_active_workers > min_workers) {
 155         new_active_workers--;
 156       }
 157     }
 158     if (new_active_workers == total_workers) {
 159       if (_debug_perturbation) {
 160         new_active_workers =  min_workers;
 161       }
 162       _debug_perturbation = !_debug_perturbation;
 163     }
 164     assert((new_active_workers <= (uintx) ParallelGCThreads) &&
 165            (new_active_workers >= min_workers),
 166       "Jiggled active workers too much");
 167   }
 168 
 169   if (TraceDynamicGCThreads) {
 170      gclog_or_tty->print_cr("GCTaskManager::calc_default_active_workers() : "
 171        "active_workers(): %d  new_acitve_workers: %d  "
 172        "prev_active_workers: %d\n"
 173        " active_workers_by_JT: %d  active_workers_by_heap_size: %d",
 174        (int) active_workers, (int) new_active_workers, (int) prev_active_workers,
 175        (int) active_workers_by_JT, (int) active_workers_by_heap_size);
 176   }
 177   assert(new_active_workers > 0, "Always need at least 1");
 178   return new_active_workers;
 179 }
 180 
 181 int AdaptiveSizePolicy::calc_active_workers(uintx total_workers,
 182                                             uintx active_workers,
 183                                             uintx application_workers) {
 184   // If the user has specifically set the number of
 185   // GC threads, use them.
 186 
 187   // If the user has turned off using a dynamic number of GC threads
 188   // or the users has requested a specific number, set the active
 189   // number of workers to all the workers.
 190 
 191   int new_active_workers;
 192   if (!UseDynamicNumberOfGCThreads ||
 193      (!FLAG_IS_DEFAULT(ParallelGCThreads) && !ForceDynamicNumberOfGCThreads)) {
 194     new_active_workers = total_workers;
 195   } else {
 196     new_active_workers = calc_default_active_workers(total_workers,
 197                                                      2, /* Minimum number of workers */
 198                                                      active_workers,
 199                                                      application_workers);
 200   }
 201   assert(new_active_workers > 0, "Always need at least 1");
 202   return new_active_workers;
 203 }
 204 
 205 int AdaptiveSizePolicy::calc_active_conc_workers(uintx total_workers,
 206                                                  uintx active_workers,
 207                                                  uintx application_workers) {
 208   if (!UseDynamicNumberOfGCThreads ||
 209      (!FLAG_IS_DEFAULT(ConcGCThreads) && !ForceDynamicNumberOfGCThreads)) {
 210     return ConcGCThreads;
 211   } else {
 212     int no_of_gc_threads = calc_default_active_workers(
 213                              total_workers,
 214                              1, /* Minimum number of workers */
 215                              active_workers,
 216                              application_workers);
 217     return no_of_gc_threads;
 218   }
 219 }
 220 
 221 bool AdaptiveSizePolicy::tenuring_threshold_change() const {
 222   return decrement_tenuring_threshold_for_gc_cost() ||
 223          increment_tenuring_threshold_for_gc_cost() ||
 224          decrement_tenuring_threshold_for_survivor_limit();
 225 }
 226 
 227 void AdaptiveSizePolicy::minor_collection_begin() {
 228   // Update the interval time
 229   _minor_timer.stop();
 230   // Save most recent collection time
 231   _latest_minor_mutator_interval_seconds = _minor_timer.seconds();
 232   _minor_timer.reset();
 233   _minor_timer.start();
 234 }
 235 
 236 void AdaptiveSizePolicy::update_minor_pause_young_estimator(
 237     double minor_pause_in_ms) {
 238   double eden_size_in_mbytes = ((double)_eden_size)/((double)M);
 239   _minor_pause_young_estimator->update(eden_size_in_mbytes,
 240     minor_pause_in_ms);
 241 }
 242 
 243 void AdaptiveSizePolicy::minor_collection_end(GCCause::Cause gc_cause) {
 244   // Update the pause time.
 245   _minor_timer.stop();
 246 
 247   if (gc_cause != GCCause::_java_lang_system_gc ||
 248       UseAdaptiveSizePolicyWithSystemGC) {
 249     double minor_pause_in_seconds = _minor_timer.seconds();
 250     double minor_pause_in_ms = minor_pause_in_seconds * MILLIUNITS;
 251 
 252     // Sample for performance counter
 253     _avg_minor_pause->sample(minor_pause_in_seconds);
 254 
 255     // Cost of collection (unit-less)
 256     double collection_cost = 0.0;
 257     if ((_latest_minor_mutator_interval_seconds > 0.0) &&
 258         (minor_pause_in_seconds > 0.0)) {
 259       double interval_in_seconds =
 260         _latest_minor_mutator_interval_seconds + minor_pause_in_seconds;
 261       collection_cost =
 262         minor_pause_in_seconds / interval_in_seconds;
 263       _avg_minor_gc_cost->sample(collection_cost);
 264       // Sample for performance counter
 265       _avg_minor_interval->sample(interval_in_seconds);
 266     }
 267 
 268     // The policy does not have enough data until at least some
 269     // minor collections have been done.
 270     _young_gen_policy_is_ready =
 271       (_avg_minor_gc_cost->count() >= AdaptiveSizePolicyReadyThreshold);
 272 
 273     // Calculate variables used to estimate pause time vs. gen sizes
 274     double eden_size_in_mbytes = ((double)_eden_size)/((double)M);
 275     update_minor_pause_young_estimator(minor_pause_in_ms);
 276     update_minor_pause_old_estimator(minor_pause_in_ms);
 277 
 278     if (PrintAdaptiveSizePolicy && Verbose) {
 279       gclog_or_tty->print("AdaptiveSizePolicy::minor_collection_end: "
 280         "minor gc cost: %f  average: %f", collection_cost,
 281         _avg_minor_gc_cost->average());
 282       gclog_or_tty->print_cr("  minor pause: %f minor period %f",
 283         minor_pause_in_ms,
 284         _latest_minor_mutator_interval_seconds * MILLIUNITS);
 285     }
 286 
 287     // Calculate variable used to estimate collection cost vs. gen sizes
 288     assert(collection_cost >= 0.0, "Expected to be non-negative");
 289     _minor_collection_estimator->update(eden_size_in_mbytes, collection_cost);
 290   }
 291 
 292   // Interval times use this timer to measure the mutator time.
 293   // Reset the timer after the GC pause.
 294   _minor_timer.reset();
 295   _minor_timer.start();
 296 }
 297 
 298 size_t AdaptiveSizePolicy::eden_increment(size_t cur_eden,
 299                                             uint percent_change) {
 300   size_t eden_heap_delta;
 301   eden_heap_delta = cur_eden / 100 * percent_change;
 302   return eden_heap_delta;
 303 }
 304 
 305 size_t AdaptiveSizePolicy::eden_increment(size_t cur_eden) {
 306   return eden_increment(cur_eden, YoungGenerationSizeIncrement);
 307 }
 308 
 309 size_t AdaptiveSizePolicy::eden_decrement(size_t cur_eden) {
 310   size_t eden_heap_delta = eden_increment(cur_eden) /
 311     AdaptiveSizeDecrementScaleFactor;
 312   return eden_heap_delta;
 313 }
 314 
 315 size_t AdaptiveSizePolicy::promo_increment(size_t cur_promo,
 316                                              uint percent_change) {
 317   size_t promo_heap_delta;
 318   promo_heap_delta = cur_promo / 100 * percent_change;
 319   return promo_heap_delta;
 320 }
 321 
 322 size_t AdaptiveSizePolicy::promo_increment(size_t cur_promo) {
 323   return promo_increment(cur_promo, TenuredGenerationSizeIncrement);
 324 }
 325 
 326 size_t AdaptiveSizePolicy::promo_decrement(size_t cur_promo) {
 327   size_t promo_heap_delta = promo_increment(cur_promo);
 328   promo_heap_delta = promo_heap_delta / AdaptiveSizeDecrementScaleFactor;
 329   return promo_heap_delta;
 330 }
 331 
 332 double AdaptiveSizePolicy::time_since_major_gc() const {
 333   _major_timer.stop();
 334   double result = _major_timer.seconds();
 335   _major_timer.start();
 336   return result;
 337 }
 338 
 339 // Linear decay of major gc cost
 340 double AdaptiveSizePolicy::decaying_major_gc_cost() const {
 341   double major_interval = major_gc_interval_average_for_decay();
 342   double major_gc_cost_average = major_gc_cost();
 343   double decayed_major_gc_cost = major_gc_cost_average;
 344   if(time_since_major_gc() > 0.0) {
 345     decayed_major_gc_cost = major_gc_cost() *
 346       (((double) AdaptiveSizeMajorGCDecayTimeScale) * major_interval)
 347       / time_since_major_gc();
 348   }
 349 
 350   // The decayed cost should always be smaller than the
 351   // average cost but the vagaries of finite arithmetic could
 352   // produce a larger value in decayed_major_gc_cost so protect
 353   // against that.
 354   return MIN2(major_gc_cost_average, decayed_major_gc_cost);
 355 }
 356 
 357 // Use a value of the major gc cost that has been decayed
 358 // by the factor
 359 //
 360 //      average-interval-between-major-gc * AdaptiveSizeMajorGCDecayTimeScale /
 361 //        time-since-last-major-gc
 362 //
 363 // if the average-interval-between-major-gc * AdaptiveSizeMajorGCDecayTimeScale
 364 // is less than time-since-last-major-gc.
 365 //
 366 // In cases where there are initial major gc's that
 367 // are of a relatively high cost but no later major
 368 // gc's, the total gc cost can remain high because
 369 // the major gc cost remains unchanged (since there are no major
 370 // gc's).  In such a situation the value of the unchanging
 371 // major gc cost can keep the mutator throughput below
 372 // the goal when in fact the major gc cost is becoming diminishingly
 373 // small.  Use the decaying gc cost only to decide whether to
 374 // adjust for throughput.  Using it also to determine the adjustment
 375 // to be made for throughput also seems reasonable but there is
 376 // no test case to use to decide if it is the right thing to do
 377 // don't do it yet.
 378 
 379 double AdaptiveSizePolicy::decaying_gc_cost() const {
 380   double decayed_major_gc_cost = major_gc_cost();
 381   double avg_major_interval = major_gc_interval_average_for_decay();
 382   if (UseAdaptiveSizeDecayMajorGCCost &&
 383       (AdaptiveSizeMajorGCDecayTimeScale > 0) &&
 384       (avg_major_interval > 0.00)) {
 385     double time_since_last_major_gc = time_since_major_gc();
 386 
 387     // Decay the major gc cost?
 388     if (time_since_last_major_gc >
 389         ((double) AdaptiveSizeMajorGCDecayTimeScale) * avg_major_interval) {
 390 
 391       // Decay using the time-since-last-major-gc
 392       decayed_major_gc_cost = decaying_major_gc_cost();
 393       if (PrintGCDetails && Verbose) {
 394         gclog_or_tty->print_cr("\ndecaying_gc_cost: major interval average:"
 395           " %f  time since last major gc: %f",
 396           avg_major_interval, time_since_last_major_gc);
 397         gclog_or_tty->print_cr("  major gc cost: %f  decayed major gc cost: %f",
 398           major_gc_cost(), decayed_major_gc_cost);
 399       }
 400     }
 401   }
 402   double result = MIN2(1.0, decayed_major_gc_cost + minor_gc_cost());
 403   return result;
 404 }
 405 
 406 
 407 void AdaptiveSizePolicy::clear_generation_free_space_flags() {
 408   set_change_young_gen_for_min_pauses(0);
 409   set_change_old_gen_for_maj_pauses(0);
 410 
 411   set_change_old_gen_for_throughput(0);
 412   set_change_young_gen_for_throughput(0);
 413   set_decrease_for_footprint(0);
 414   set_decide_at_full_gc(0);
 415 }
 416 
 417 void AdaptiveSizePolicy::check_gc_overhead_limit(
 418                                           size_t young_live,
 419                                           size_t eden_live,
 420                                           size_t max_old_gen_size,
 421                                           size_t max_eden_size,
 422                                           bool   is_full_gc,
 423                                           GCCause::Cause gc_cause,
 424                                           CollectorPolicy* collector_policy) {
 425 
 426   // Ignore explicit GC's.  Exiting here does not set the flag and
 427   // does not reset the count.  Updating of the averages for system
 428   // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC.
 429   if (GCCause::is_user_requested_gc(gc_cause) ||
 430       GCCause::is_serviceability_requested_gc(gc_cause)) {
 431     return;
 432   }
 433   // eden_limit is the upper limit on the size of eden based on
 434   // the maximum size of the young generation and the sizes
 435   // of the survivor space.
 436   // The question being asked is whether the gc costs are high
 437   // and the space being recovered by a collection is low.
 438   // free_in_young_gen is the free space in the young generation
 439   // after a collection and promo_live is the free space in the old
 440   // generation after a collection.
 441   //
 442   // Use the minimum of the current value of the live in the
 443   // young gen or the average of the live in the young gen.
 444   // If the current value drops quickly, that should be taken
 445   // into account (i.e., don't trigger if the amount of free
 446   // space has suddenly jumped up).  If the current is much
 447   // higher than the average, use the average since it represents
 448   // the longer term behavor.
 449   const size_t live_in_eden =
 450     MIN2(eden_live, (size_t) avg_eden_live()->average());
 451   const size_t free_in_eden = max_eden_size > live_in_eden ?
 452     max_eden_size - live_in_eden : 0;
 453   const size_t free_in_old_gen = (size_t)(max_old_gen_size - avg_old_live()->average());
 454   const size_t total_free_limit = free_in_old_gen + free_in_eden;
 455   const size_t total_mem = max_old_gen_size + max_eden_size;
 456   const double mem_free_limit = total_mem * (GCHeapFreeLimit/100.0);
 457   const double mem_free_old_limit = max_old_gen_size * (GCHeapFreeLimit/100.0);
 458   const double mem_free_eden_limit = max_eden_size * (GCHeapFreeLimit/100.0);
 459   const double gc_cost_limit = GCTimeLimit/100.0;
 460   size_t promo_limit = (size_t)(max_old_gen_size - avg_old_live()->average());
 461   // But don't force a promo size below the current promo size. Otherwise,
 462   // the promo size will shrink for no good reason.
 463   promo_limit = MAX2(promo_limit, _promo_size);
 464 
 465 
 466   if (PrintAdaptiveSizePolicy && (Verbose ||
 467       (free_in_old_gen < (size_t) mem_free_old_limit &&
 468        free_in_eden < (size_t) mem_free_eden_limit))) {
 469     gclog_or_tty->print_cr(
 470           "PSAdaptiveSizePolicy::check_gc_overhead_limit:"
 471           " promo_limit: " SIZE_FORMAT
 472           " max_eden_size: " SIZE_FORMAT
 473           " total_free_limit: " SIZE_FORMAT
 474           " max_old_gen_size: " SIZE_FORMAT
 475           " max_eden_size: " SIZE_FORMAT
 476           " mem_free_limit: " SIZE_FORMAT,
 477           promo_limit, max_eden_size, total_free_limit,
 478           max_old_gen_size, max_eden_size,
 479           (size_t) mem_free_limit);
 480   }
 481 
 482   bool print_gc_overhead_limit_would_be_exceeded = false;
 483   if (is_full_gc) {
 484     if (gc_cost() > gc_cost_limit &&
 485       free_in_old_gen < (size_t) mem_free_old_limit &&
 486       free_in_eden < (size_t) mem_free_eden_limit) {
 487       // Collections, on average, are taking too much time, and
 488       //      gc_cost() > gc_cost_limit
 489       // we have too little space available after a full gc.
 490       //      total_free_limit < mem_free_limit
 491       // where
 492       //   total_free_limit is the free space available in
 493       //     both generations
 494       //   total_mem is the total space available for allocation
 495       //     in both generations (survivor spaces are not included
 496       //     just as they are not included in eden_limit).
 497       //   mem_free_limit is a fraction of total_mem judged to be an
 498       //     acceptable amount that is still unused.
 499       // The heap can ask for the value of this variable when deciding
 500       // whether to thrown an OutOfMemory error.
 501       // Note that the gc time limit test only works for the collections
 502       // of the young gen + tenured gen and not for collections of the
 503       // permanent gen.  That is because the calculation of the space
 504       // freed by the collection is the free space in the young gen +
 505       // tenured gen.
 506       // At this point the GC overhead limit is being exceeded.
 507       inc_gc_overhead_limit_count();
 508       if (UseGCOverheadLimit) {
 509         if (gc_overhead_limit_count() >=
 510             AdaptiveSizePolicyGCTimeLimitThreshold){
 511           // All conditions have been met for throwing an out-of-memory
 512           set_gc_overhead_limit_exceeded(true);
 513           // Avoid consecutive OOM due to the gc time limit by resetting
 514           // the counter.
 515           reset_gc_overhead_limit_count();
 516         } else {
 517           // The required consecutive collections which exceed the
 518           // GC time limit may or may not have been reached. We
 519           // are approaching that condition and so as not to
 520           // throw an out-of-memory before all SoftRef's have been
 521           // cleared, set _should_clear_all_soft_refs in CollectorPolicy.
 522           // The clearing will be done on the next GC.
 523           bool near_limit = gc_overhead_limit_near();
 524           if (near_limit) {
 525             collector_policy->set_should_clear_all_soft_refs(true);
 526             if (PrintGCDetails && Verbose) {
 527               gclog_or_tty->print_cr("  Nearing GC overhead limit, "
 528                 "will be clearing all SoftReference");
 529             }
 530           }
 531         }
 532       }
 533       // Set this even when the overhead limit will not
 534       // cause an out-of-memory.  Diagnostic message indicating
 535       // that the overhead limit is being exceeded is sometimes
 536       // printed.
 537       print_gc_overhead_limit_would_be_exceeded = true;
 538 
 539     } else {
 540       // Did not exceed overhead limits
 541       reset_gc_overhead_limit_count();
 542     }
 543   }
 544 
 545   if (UseGCOverheadLimit && PrintGCDetails && Verbose) {
 546     if (gc_overhead_limit_exceeded()) {
 547       gclog_or_tty->print_cr("      GC is exceeding overhead limit "
 548         "of %d%%", (int) GCTimeLimit);
 549       reset_gc_overhead_limit_count();
 550     } else if (print_gc_overhead_limit_would_be_exceeded) {
 551       assert(gc_overhead_limit_count() > 0, "Should not be printing");
 552       gclog_or_tty->print_cr("      GC would exceed overhead limit "
 553         "of %d%% %d consecutive time(s)",
 554         (int) GCTimeLimit, gc_overhead_limit_count());
 555     }
 556   }
 557 }
 558 // Printing
 559 
 560 bool AdaptiveSizePolicy::print_adaptive_size_policy_on(outputStream* st) const {
 561 
 562   //  Should only be used with adaptive size policy turned on.
 563   // Otherwise, there may be variables that are undefined.
 564   if (!UseAdaptiveSizePolicy) return false;
 565 
 566   // Print goal for which action is needed.
 567   char* action = NULL;
 568   bool change_for_pause = false;
 569   if ((change_old_gen_for_maj_pauses() ==
 570          decrease_old_gen_for_maj_pauses_true) ||
 571       (change_young_gen_for_min_pauses() ==
 572          decrease_young_gen_for_min_pauses_true)) {
 573     action = (char*) " *** pause time goal ***";
 574     change_for_pause = true;
 575   } else if ((change_old_gen_for_throughput() ==
 576                increase_old_gen_for_throughput_true) ||
 577             (change_young_gen_for_throughput() ==
 578                increase_young_gen_for_througput_true)) {
 579     action = (char*) " *** throughput goal ***";
 580   } else if (decrease_for_footprint()) {
 581     action = (char*) " *** reduced footprint ***";
 582   } else {
 583     // No actions were taken.  This can legitimately be the
 584     // situation if not enough data has been gathered to make
 585     // decisions.
 586     return false;
 587   }
 588 
 589   // Pauses
 590   // Currently the size of the old gen is only adjusted to
 591   // change the major pause times.
 592   char* young_gen_action = NULL;
 593   char* tenured_gen_action = NULL;
 594 
 595   char* shrink_msg = (char*) "(attempted to shrink)";
 596   char* grow_msg = (char*) "(attempted to grow)";
 597   char* no_change_msg = (char*) "(no change)";
 598   if (change_young_gen_for_min_pauses() ==
 599       decrease_young_gen_for_min_pauses_true) {
 600     young_gen_action = shrink_msg;
 601   } else if (change_for_pause) {
 602     young_gen_action = no_change_msg;
 603   }
 604 
 605   if (change_old_gen_for_maj_pauses() == decrease_old_gen_for_maj_pauses_true) {
 606     tenured_gen_action = shrink_msg;
 607   } else if (change_for_pause) {
 608     tenured_gen_action = no_change_msg;
 609   }
 610 
 611   // Throughput
 612   if (change_old_gen_for_throughput() == increase_old_gen_for_throughput_true) {
 613     assert(change_young_gen_for_throughput() ==
 614            increase_young_gen_for_througput_true,
 615            "Both generations should be growing");
 616     young_gen_action = grow_msg;
 617     tenured_gen_action = grow_msg;
 618   } else if (change_young_gen_for_throughput() ==
 619              increase_young_gen_for_througput_true) {
 620     // Only the young generation may grow at start up (before
 621     // enough full collections have been done to grow the old generation).
 622     young_gen_action = grow_msg;
 623     tenured_gen_action = no_change_msg;
 624   }
 625 
 626   // Minimum footprint
 627   if (decrease_for_footprint() != 0) {
 628     young_gen_action = shrink_msg;
 629     tenured_gen_action = shrink_msg;
 630   }
 631 
 632   st->print_cr("    UseAdaptiveSizePolicy actions to meet %s", action);
 633   st->print_cr("                       GC overhead (%%)");
 634   st->print_cr("    Young generation:     %7.2f\t  %s",
 635     100.0 * avg_minor_gc_cost()->average(),
 636     young_gen_action);
 637   st->print_cr("    Tenured generation:   %7.2f\t  %s",
 638     100.0 * avg_major_gc_cost()->average(),
 639     tenured_gen_action);
 640   return true;
 641 }
 642 
 643 bool AdaptiveSizePolicy::print_adaptive_size_policy_on(
 644                                             outputStream* st,
 645                                             uint tenuring_threshold_arg) const {
 646   if (!AdaptiveSizePolicy::print_adaptive_size_policy_on(st)) {
 647     return false;
 648   }
 649 
 650   // Tenuring threshold
 651   bool tenuring_threshold_changed = true;
 652   if (decrement_tenuring_threshold_for_survivor_limit()) {
 653     st->print("    Tenuring threshold:    (attempted to decrease to avoid"
 654               " survivor space overflow) = ");
 655   } else if (decrement_tenuring_threshold_for_gc_cost()) {
 656     st->print("    Tenuring threshold:    (attempted to decrease to balance"
 657               " GC costs) = ");
 658   } else if (increment_tenuring_threshold_for_gc_cost()) {
 659     st->print("    Tenuring threshold:    (attempted to increase to balance"
 660               " GC costs) = ");
 661   } else {
 662     tenuring_threshold_changed = false;
 663     assert(!tenuring_threshold_change(), "(no change was attempted)");
 664   }
 665   if (tenuring_threshold_changed) {
 666     st->print_cr("%u", tenuring_threshold_arg);
 667   }
 668   return true;
 669 }