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/g1CollectorPolicy.hpp"
  28 #include "gc/g1/g1CollectionSet.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   G1CollectorPolicy* g1p = g1h->g1_policy();
  78   if (g1p->adaptive_young_list_length()) {
  79     int regions_visited = 0;
  80     HeapRegion* hr = g1h->young_list()->first_region();
  81     size_t sampled_rs_lengths = 0;
  82 
  83     while (hr != NULL) {
  84       size_t rs_length = hr->rem_set()->occupied();
  85       sampled_rs_lengths += rs_length;
  86 
  87       // The current region may not yet have been added to the
  88       // incremental collection set (it gets added when it is
  89       // retired as the current allocation region).
  90       if (hr->in_collection_set()) {
  91         // Update the collection set policy information for this region
  92         g1h->collection_set()->update_young_region_prediction(hr, rs_length);
  93       }
  94 
  95       ++regions_visited;
  96 
  97       // we try to yield every time we visit 10 regions
  98       if (regions_visited == 10) {
  99         if (sts.should_yield()) {
 100           sts.yield();
 101           // A gc may have occurred and our sampling data is stale and further
 102           // traversal of the young list is unsafe
 103           return;
 104         }
 105         regions_visited = 0;
 106       }
 107       hr = hr->get_next_young_region();
 108     }
 109     g1p->revise_young_list_target_length_if_necessary(sampled_rs_lengths);
 110   }
 111 }