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 }