1 /*
   2  * Copyright (c) 2015, 2016, 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/g1Policy.hpp"
  29 #include "gc/g1/g1YoungRemSetSamplingThread.hpp"
  30 #include "gc/g1/heapRegion.inline.hpp"
  31 #include "gc/g1/heapRegionRemSet.hpp"
  32 #include "gc/g1/suspendibleThreadSet.hpp"
  33 #include "runtime/mutexLocker.hpp"
  34 
  35 G1YoungRemSetSamplingThread::G1YoungRemSetSamplingThread() :
  36     ConcurrentGCThread(),
  37     _monitor(Mutex::nonleaf,
  38              "G1YoungRemSetSamplingThread monitor",
  39              true,
  40              Monitor::_safepoint_check_never) {
  41   set_name("G1 Young RemSet Sampling");
  42   create_and_start();
  43 }
  44 
  45 void G1YoungRemSetSamplingThread::sleep_before_next_cycle() {
  46   MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);
  47   if (!should_terminate()) {
  48     uintx waitms = G1ConcRefinementServiceIntervalMillis; // 300, really should be?
  49     _monitor.wait(Mutex::_no_safepoint_check_flag, waitms);
  50   }
  51 }
  52 
  53 void G1YoungRemSetSamplingThread::run_service() {
  54   double vtime_start = os::elapsedVTime();
  55 
  56   while (!should_terminate()) {
  57     sample_young_list_rs_lengths();
  58 
  59     if (os::supports_vtime()) {
  60       _vtime_accum = (os::elapsedVTime() - vtime_start);
  61     } else {
  62       _vtime_accum = 0.0;
  63     }
  64 
  65     sleep_before_next_cycle();
  66   }
  67 }
  68 
  69 void G1YoungRemSetSamplingThread::stop_service() {
  70   MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);
  71   _monitor.notify();
  72 }
  73 
  74 void G1YoungRemSetSamplingThread::sample_young_list_rs_lengths() {
  75   SuspendibleThreadSetJoiner sts;
  76   G1CollectedHeap* g1h = G1CollectedHeap::heap();
  77   G1Policy* g1p = g1h->g1_policy();
  78   G1CollectionSet* g1cs = g1h->collection_set();
  79   if (g1p->adaptive_young_list_length()) {
  80     int regions_visited = 0;
  81     HeapRegion* hr = g1cs->inc_head();
  82     size_t sampled_rs_lengths = 0;
  83 
  84     while (hr != NULL) {
  85       size_t rs_length = hr->rem_set()->occupied();
  86       sampled_rs_lengths += rs_length;
  87 
  88       // Update the collection set policy information for this region
  89       g1cs->update_young_region_prediction(hr, rs_length);
  90 
  91       ++regions_visited;
  92 
  93       // we try to yield every time we visit 10 regions
  94       if (regions_visited == 10) {
  95         if (sts.should_yield()) {
  96           sts.yield();
  97           // A gc may have occurred and our sampling data is stale and further
  98           // traversal of the collection set is unsafe
  99           return;
 100         }
 101         regions_visited = 0;
 102       }
 103       assert(hr == g1cs->inc_tail() || hr->next_in_collection_set() != NULL, "next should only be null at tail of icset");
 104       hr = hr->next_in_collection_set();
 105     }
 106     g1p->revise_young_list_target_length_if_necessary(sampled_rs_lengths);
 107   }
 108 }