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0
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1 /*
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2 * Copyright 2001-2006 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 # include "incls/_precompiled.incl"
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26 # include "incls/_parGCAllocBuffer.cpp.incl"
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27
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28 ParGCAllocBuffer::ParGCAllocBuffer(size_t desired_plab_sz_) :
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29 _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL),
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30 _end(NULL), _hard_end(NULL),
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31 _retained(false), _retained_filler(),
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32 _allocated(0), _wasted(0)
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33 {
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34 assert (min_size() > AlignmentReserve, "Inconsistency!");
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35 }
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36
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37 const size_t ParGCAllocBuffer::FillerHeaderSize =
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38 align_object_size(arrayOopDesc::header_size(T_INT));
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39
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40 // If the minimum object size is greater than MinObjAlignment, we can
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41 // end up with a shard at the end of the buffer that's smaller than
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42 // the smallest object. We can't allow that because the buffer must
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43 // look like it's full of objects when we retire it, so we make
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44 // sure we have enough space for a filler int array object.
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45 const size_t ParGCAllocBuffer::AlignmentReserve =
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46 oopDesc::header_size() > MinObjAlignment ? FillerHeaderSize : 0;
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47
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48 void ParGCAllocBuffer::retire(bool end_of_gc, bool retain) {
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49 assert(!retain || end_of_gc, "Can only retain at GC end.");
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50 if (_retained) {
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51 // If the buffer had been retained shorten the previous filler object.
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52 assert(_retained_filler.end() <= _top, "INVARIANT");
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53 SharedHeap::fill_region_with_object(_retained_filler);
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54 // Wasted space book-keeping, otherwise (normally) done in invalidate()
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55 _wasted += _retained_filler.word_size();
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56 _retained = false;
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57 }
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58 assert(!end_of_gc || !_retained, "At this point, end_of_gc ==> !_retained.");
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59 if (_top < _hard_end) {
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60 SharedHeap::fill_region_with_object(MemRegion(_top, _hard_end));
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61 if (!retain) {
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62 invalidate();
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63 } else {
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64 // Is there wasted space we'd like to retain for the next GC?
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65 if (pointer_delta(_end, _top) > FillerHeaderSize) {
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66 _retained = true;
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67 _retained_filler = MemRegion(_top, FillerHeaderSize);
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68 _top = _top + FillerHeaderSize;
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69 } else {
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70 invalidate();
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71 }
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72 }
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73 }
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74 }
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75
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76 void ParGCAllocBuffer::flush_stats(PLABStats* stats) {
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77 assert(ResizePLAB, "Wasted work");
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78 stats->add_allocated(_allocated);
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79 stats->add_wasted(_wasted);
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80 stats->add_unused(pointer_delta(_end, _top));
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81 }
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82
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83 // Compute desired plab size and latch result for later
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84 // use. This should be called once at the end of parallel
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85 // scavenge; it clears the sensor accumulators.
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86 void PLABStats::adjust_desired_plab_sz() {
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87 assert(ResizePLAB, "Not set");
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88 if (_allocated == 0) {
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89 assert(_unused == 0, "Inconsistency in PLAB stats");
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90 _allocated = 1;
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91 }
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92 double wasted_frac = (double)_unused/(double)_allocated;
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93 size_t target_refills = (size_t)((wasted_frac*TargetSurvivorRatio)/
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94 TargetPLABWastePct);
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95 if (target_refills == 0) {
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96 target_refills = 1;
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97 }
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98 _used = _allocated - _wasted - _unused;
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99 size_t plab_sz = _used/(target_refills*ParallelGCThreads);
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100 if (PrintPLAB) gclog_or_tty->print(" (plab_sz = %d ", plab_sz);
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101 // Take historical weighted average
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102 _filter.sample(plab_sz);
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103 // Clip from above and below, and align to object boundary
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104 plab_sz = MAX2(min_size(), (size_t)_filter.average());
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105 plab_sz = MIN2(max_size(), plab_sz);
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106 plab_sz = align_object_size(plab_sz);
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107 // Latch the result
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108 if (PrintPLAB) gclog_or_tty->print(" desired_plab_sz = %d) ", plab_sz);
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109 if (ResizePLAB) {
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110 _desired_plab_sz = plab_sz;
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111 }
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112 // Now clear the accumulators for next round:
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113 // note this needs to be fixed in the case where we
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114 // are retaining across scavenges. FIX ME !!! XXX
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115 _allocated = 0;
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116 _wasted = 0;
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117 _unused = 0;
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118 }
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119
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120 #ifndef PRODUCT
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121 void ParGCAllocBuffer::print() {
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122 gclog_or_tty->print("parGCAllocBuffer: _bottom: %p _top: %p _end: %p _hard_end: %p"
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123 "_retained: %c _retained_filler: [%p,%p)\n",
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124 _bottom, _top, _end, _hard_end,
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125 "FT"[_retained], _retained_filler.start(), _retained_filler.end());
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126 }
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127 #endif // !PRODUCT
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128
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129 const size_t ParGCAllocBufferWithBOT::ChunkSizeInWords =
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130 MIN2(CardTableModRefBS::par_chunk_heapword_alignment(),
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131 ((size_t)Generation::GenGrain)/HeapWordSize);
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132 const size_t ParGCAllocBufferWithBOT::ChunkSizeInBytes =
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133 MIN2(CardTableModRefBS::par_chunk_heapword_alignment() * HeapWordSize,
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134 (size_t)Generation::GenGrain);
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135
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136 ParGCAllocBufferWithBOT::ParGCAllocBufferWithBOT(size_t word_sz,
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137 BlockOffsetSharedArray* bsa) :
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138 ParGCAllocBuffer(word_sz),
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139 _bsa(bsa),
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140 _bt(bsa, MemRegion(_bottom, _hard_end)),
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141 _true_end(_hard_end)
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142 {}
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143
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144 // The buffer comes with its own BOT, with a shared (obviously) underlying
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145 // BlockOffsetSharedArray. We manipulate this BOT in the normal way
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146 // as we would for any contiguous space. However, on accasion we
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147 // need to do some buffer surgery at the extremities before we
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148 // start using the body of the buffer for allocations. Such surgery
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149 // (as explained elsewhere) is to prevent allocation on a card that
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150 // is in the process of being walked concurrently by another GC thread.
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151 // When such surgery happens at a point that is far removed (to the
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152 // right of the current allocation point, top), we use the "contig"
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153 // parameter below to directly manipulate the shared array without
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154 // modifying the _next_threshold state in the BOT.
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155 void ParGCAllocBufferWithBOT::fill_region_with_block(MemRegion mr,
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156 bool contig) {
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157 SharedHeap::fill_region_with_object(mr);
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158 if (contig) {
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159 _bt.alloc_block(mr.start(), mr.end());
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160 } else {
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161 _bt.BlockOffsetArray::alloc_block(mr.start(), mr.end());
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162 }
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163 }
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164
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165 HeapWord* ParGCAllocBufferWithBOT::allocate_slow(size_t word_sz) {
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166 HeapWord* res = NULL;
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167 if (_true_end > _hard_end) {
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168 assert((HeapWord*)align_size_down(intptr_t(_hard_end),
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169 ChunkSizeInBytes) == _hard_end,
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170 "or else _true_end should be equal to _hard_end");
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171 assert(_retained, "or else _true_end should be equal to _hard_end");
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172 assert(_retained_filler.end() <= _top, "INVARIANT");
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173 SharedHeap::fill_region_with_object(_retained_filler);
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174 if (_top < _hard_end) {
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175 fill_region_with_block(MemRegion(_top, _hard_end), true);
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176 }
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177 HeapWord* next_hard_end = MIN2(_true_end, _hard_end + ChunkSizeInWords);
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178 _retained_filler = MemRegion(_hard_end, FillerHeaderSize);
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179 _bt.alloc_block(_retained_filler.start(), _retained_filler.word_size());
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180 _top = _retained_filler.end();
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181 _hard_end = next_hard_end;
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182 _end = _hard_end - AlignmentReserve;
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183 res = ParGCAllocBuffer::allocate(word_sz);
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184 if (res != NULL) {
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185 _bt.alloc_block(res, word_sz);
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186 }
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187 }
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188 return res;
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189 }
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190
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191 void
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192 ParGCAllocBufferWithBOT::undo_allocation(HeapWord* obj, size_t word_sz) {
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193 ParGCAllocBuffer::undo_allocation(obj, word_sz);
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194 // This may back us up beyond the previous threshold, so reset.
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195 _bt.set_region(MemRegion(_top, _hard_end));
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196 _bt.initialize_threshold();
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197 }
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198
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199 void ParGCAllocBufferWithBOT::retire(bool end_of_gc, bool retain) {
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200 assert(!retain || end_of_gc, "Can only retain at GC end.");
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201 if (_retained) {
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202 // We're about to make the retained_filler into a block.
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203 _bt.BlockOffsetArray::alloc_block(_retained_filler.start(),
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204 _retained_filler.end());
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205 }
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206 // Reset _hard_end to _true_end (and update _end)
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207 if (retain && _hard_end != NULL) {
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208 assert(_hard_end <= _true_end, "Invariant.");
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209 _hard_end = _true_end;
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210 _end = MAX2(_top, _hard_end - AlignmentReserve);
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211 assert(_end <= _hard_end, "Invariant.");
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212 }
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213 _true_end = _hard_end;
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214 HeapWord* pre_top = _top;
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215
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216 ParGCAllocBuffer::retire(end_of_gc, retain);
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217 // Now any old _retained_filler is cut back to size, the free part is
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218 // filled with a filler object, and top is past the header of that
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219 // object.
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220
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221 if (retain && _top < _end) {
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222 assert(end_of_gc && retain, "Or else retain should be false.");
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223 // If the lab does not start on a card boundary, we don't want to
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224 // allocate onto that card, since that might lead to concurrent
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225 // allocation and card scanning, which we don't support. So we fill
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226 // the first card with a garbage object.
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227 size_t first_card_index = _bsa->index_for(pre_top);
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228 HeapWord* first_card_start = _bsa->address_for_index(first_card_index);
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229 if (first_card_start < pre_top) {
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230 HeapWord* second_card_start =
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231 _bsa->address_for_index(first_card_index + 1);
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232
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233 // Ensure enough room to fill with the smallest block
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234 second_card_start = MAX2(second_card_start, pre_top + AlignmentReserve);
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235
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236 // If the end is already in the first card, don't go beyond it!
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237 // Or if the remainder is too small for a filler object, gobble it up.
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238 if (_hard_end < second_card_start ||
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239 pointer_delta(_hard_end, second_card_start) < AlignmentReserve) {
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240 second_card_start = _hard_end;
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241 }
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242 if (pre_top < second_card_start) {
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243 MemRegion first_card_suffix(pre_top, second_card_start);
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244 fill_region_with_block(first_card_suffix, true);
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245 }
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246 pre_top = second_card_start;
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247 _top = pre_top;
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248 _end = MAX2(_top, _hard_end - AlignmentReserve);
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249 }
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250
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251 // If the lab does not end on a card boundary, we don't want to
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252 // allocate onto that card, since that might lead to concurrent
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253 // allocation and card scanning, which we don't support. So we fill
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254 // the last card with a garbage object.
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255 size_t last_card_index = _bsa->index_for(_hard_end);
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256 HeapWord* last_card_start = _bsa->address_for_index(last_card_index);
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257 if (last_card_start < _hard_end) {
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258
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259 // Ensure enough room to fill with the smallest block
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260 last_card_start = MIN2(last_card_start, _hard_end - AlignmentReserve);
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261
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262 // If the top is already in the last card, don't go back beyond it!
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263 // Or if the remainder is too small for a filler object, gobble it up.
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264 if (_top > last_card_start ||
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265 pointer_delta(last_card_start, _top) < AlignmentReserve) {
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266 last_card_start = _top;
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267 }
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268 if (last_card_start < _hard_end) {
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269 MemRegion last_card_prefix(last_card_start, _hard_end);
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270 fill_region_with_block(last_card_prefix, false);
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271 }
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272 _hard_end = last_card_start;
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273 _end = MAX2(_top, _hard_end - AlignmentReserve);
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274 _true_end = _hard_end;
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275 assert(_end <= _hard_end, "Invariant.");
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276 }
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277
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278 // At this point:
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279 // 1) we had a filler object from the original top to hard_end.
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280 // 2) We've filled in any partial cards at the front and back.
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281 if (pre_top < _hard_end) {
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282 // Now we can reset the _bt to do allocation in the given area.
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283 MemRegion new_filler(pre_top, _hard_end);
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284 fill_region_with_block(new_filler, false);
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285 _top = pre_top + ParGCAllocBuffer::FillerHeaderSize;
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286 // If there's no space left, don't retain.
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287 if (_top >= _end) {
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288 _retained = false;
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289 invalidate();
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290 return;
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291 }
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292 _retained_filler = MemRegion(pre_top, _top);
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293 _bt.set_region(MemRegion(_top, _hard_end));
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294 _bt.initialize_threshold();
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295 assert(_bt.threshold() > _top, "initialize_threshold failed!");
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296
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297 // There may be other reasons for queries into the middle of the
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298 // filler object. When such queries are done in parallel with
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299 // allocation, bad things can happen, if the query involves object
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300 // iteration. So we ensure that such queries do not involve object
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301 // iteration, by putting another filler object on the boundaries of
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302 // such queries. One such is the object spanning a parallel card
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303 // chunk boundary.
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304
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305 // "chunk_boundary" is the address of the first chunk boundary less
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306 // than "hard_end".
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307 HeapWord* chunk_boundary =
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308 (HeapWord*)align_size_down(intptr_t(_hard_end-1), ChunkSizeInBytes);
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309 assert(chunk_boundary < _hard_end, "Or else above did not work.");
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310 assert(pointer_delta(_true_end, chunk_boundary) >= AlignmentReserve,
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311 "Consequence of last card handling above.");
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312
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313 if (_top <= chunk_boundary) {
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314 assert(_true_end == _hard_end, "Invariant.");
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315 while (_top <= chunk_boundary) {
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316 assert(pointer_delta(_hard_end, chunk_boundary) >= AlignmentReserve,
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317 "Consequence of last card handling above.");
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318 MemRegion chunk_portion(chunk_boundary, _hard_end);
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319 _bt.BlockOffsetArray::alloc_block(chunk_portion.start(),
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320 chunk_portion.end());
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321 SharedHeap::fill_region_with_object(chunk_portion);
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322 _hard_end = chunk_portion.start();
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323 chunk_boundary -= ChunkSizeInWords;
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324 }
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325 _end = _hard_end - AlignmentReserve;
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326 assert(_top <= _end, "Invariant.");
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327 // Now reset the initial filler chunk so it doesn't overlap with
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328 // the one(s) inserted above.
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329 MemRegion new_filler(pre_top, _hard_end);
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330 fill_region_with_block(new_filler, false);
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331 }
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332 } else {
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333 _retained = false;
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334 invalidate();
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335 }
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336 } else {
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337 assert(!end_of_gc ||
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338 (!_retained && _true_end == _hard_end), "Checking.");
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339 }
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340 assert(_end <= _hard_end, "Invariant.");
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341 assert(_top < _end || _top == _hard_end, "Invariant");
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342 }
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