1 /*
   2  * Copyright (c) 2015, 2019, 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/g1/g1CollectedHeap.inline.hpp"
  27 #include "gc/g1/g1CollectionSet.hpp"
  28 #include "gc/g1/g1ConcurrentMark.inline.hpp"
  29 #include "gc/g1/g1ConcurrentMarkThread.inline.hpp"
  30 #include "gc/g1/g1Policy.hpp"
  31 #include "gc/g1/g1YoungRemSetSamplingThread.hpp"
  32 #include "gc/g1/heapRegion.inline.hpp"
  33 #include "gc/g1/heapRegionRemSet.hpp"
  34 #include "gc/shared/suspendibleThreadSet.hpp"
  35 #include "memory/universe.hpp"
  36 #include "runtime/mutexLocker.hpp"
  37 
  38 G1YoungRemSetSamplingThread::G1YoungRemSetSamplingThread() :
  39     ConcurrentGCThread(),
  40     _monitor(Mutex::nonleaf,
  41              "G1YoungRemSetSamplingThread monitor",
  42              true,
  43              Monitor::_safepoint_check_never),
  44     _last_periodic_gc_attempt_s(os::elapsedTime()),
  45     _vtime_accum(0) {
  46   set_name("G1 Young RemSet Sampling");
  47   create_and_start();
  48 }
  49 
  50 void G1YoungRemSetSamplingThread::sleep_before_next_cycle() {
  51   MonitorLocker ml(&_monitor, Mutex::_no_safepoint_check_flag);
  52   if (!should_terminate()) {
  53     uintx waitms = G1ConcRefinementServiceIntervalMillis;
  54     ml.wait(waitms);
  55   }
  56 }
  57 
  58 bool G1YoungRemSetSamplingThread::should_start_periodic_gc() {
  59   // If we are currently in a concurrent mark we are going to uncommit memory soon.
  60   if (G1CollectedHeap::heap()->concurrent_mark()->cm_thread()->during_cycle()) {
  61     log_debug(gc, periodic)("Concurrent cycle in progress. Skipping.");
  62     return false;
  63   }
  64 
  65   // Check if enough time has passed since the last GC.
  66   uintx time_since_last_gc = (uintx)Universe::heap()->millis_since_last_gc();
  67   if ((time_since_last_gc < G1PeriodicGCInterval)) {
  68     log_debug(gc, periodic)("Last GC occurred " UINTX_FORMAT "ms before which is below threshold " UINTX_FORMAT "ms. Skipping.",
  69                             time_since_last_gc, G1PeriodicGCInterval);
  70     return false;
  71   }
  72 
  73   // Check if load is lower than max.
  74   double recent_load;
  75   if ((G1PeriodicGCSystemLoadThreshold > 0.0f) &&
  76       (os::loadavg(&recent_load, 1) == -1 || recent_load > G1PeriodicGCSystemLoadThreshold)) {
  77     log_debug(gc, periodic)("Load %1.2f is higher than threshold %1.2f. Skipping.",
  78                             recent_load, G1PeriodicGCSystemLoadThreshold);
  79     return false;
  80   }
  81 
  82   return true;
  83 }
  84 
  85 void G1YoungRemSetSamplingThread::check_for_periodic_gc(){
  86   // If disabled, just return.
  87   if (G1PeriodicGCInterval == 0) {
  88     return;
  89   }
  90   if ((os::elapsedTime() - _last_periodic_gc_attempt_s) > (G1PeriodicGCInterval / 1000.0)) {
  91     log_debug(gc, periodic)("Checking for periodic GC.");
  92     if (should_start_periodic_gc()) {
  93       if (!G1CollectedHeap::heap()->try_collect(GCCause::_g1_periodic_collection,
  94                                                     false /* retry_on_vmop_failure */)) {
  95         log_debug(gc, periodic)("GC request denied. Skipping.");
  96       }
  97     }
  98     _last_periodic_gc_attempt_s = os::elapsedTime();
  99   }
 100 }
 101 
 102 void G1YoungRemSetSamplingThread::run_service() {
 103   double vtime_start = os::elapsedVTime();
 104 
 105   // Print a message about periodic GC configuration.
 106   if (G1PeriodicGCInterval != 0) {
 107     log_info(gc)("Periodic GC enabled with interval " UINTX_FORMAT "ms", G1PeriodicGCInterval);
 108   } else {
 109     log_info(gc)("Periodic GC disabled");
 110   }
 111 
 112   while (!should_terminate()) {
 113     sample_young_list_rs_lengths();
 114 
 115     if (os::supports_vtime()) {
 116       _vtime_accum = (os::elapsedVTime() - vtime_start);
 117     } else {
 118       _vtime_accum = 0.0;
 119     }
 120 
 121     check_for_periodic_gc();
 122 
 123     sleep_before_next_cycle();
 124   }
 125 }
 126 
 127 void G1YoungRemSetSamplingThread::stop_service() {
 128   MutexLocker x(&_monitor, Mutex::_no_safepoint_check_flag);
 129   _monitor.notify();
 130 }
 131 
 132 class G1YoungRemSetSamplingClosure : public HeapRegionClosure {
 133   SuspendibleThreadSetJoiner* _sts;
 134   size_t _regions_visited;
 135   size_t _sampled_rs_lengths;
 136 public:
 137   G1YoungRemSetSamplingClosure(SuspendibleThreadSetJoiner* sts) :
 138     HeapRegionClosure(), _sts(sts), _regions_visited(0), _sampled_rs_lengths(0) { }
 139 
 140   virtual bool do_heap_region(HeapRegion* r) {
 141     size_t rs_length = r->rem_set()->occupied();
 142     _sampled_rs_lengths += rs_length;
 143 
 144     // Update the collection set policy information for this region
 145     G1CollectedHeap::heap()->collection_set()->update_young_region_prediction(r, rs_length);
 146 
 147     _regions_visited++;
 148 
 149     if (_regions_visited == 10) {
 150       if (_sts->should_yield()) {
 151         _sts->yield();
 152         // A gc may have occurred and our sampling data is stale and further
 153         // traversal of the collection set is unsafe
 154         return true;
 155       }
 156       _regions_visited = 0;
 157     }
 158     return false;
 159   }
 160 
 161   size_t sampled_rs_lengths() const { return _sampled_rs_lengths; }
 162 };
 163 
 164 void G1YoungRemSetSamplingThread::sample_young_list_rs_lengths() {
 165   SuspendibleThreadSetJoiner sts;
 166   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 167   G1Policy* policy = g1h->policy();
 168 
 169   if (policy->use_adaptive_young_list_length()) {
 170     G1YoungRemSetSamplingClosure cl(&sts);
 171 
 172     G1CollectionSet* g1cs = g1h->collection_set();
 173     g1cs->iterate(&cl);
 174 
 175     if (cl.is_complete()) {
 176       policy->revise_young_list_target_length_if_necessary(cl.sampled_rs_lengths());
 177     }
 178   }
 179 }