1 /* 2 * Copyright (c) 2001, 2009, 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 "incls/_precompiled.incl" 26 # include "incls/_parGCAllocBuffer.cpp.incl" 27 28 ParGCAllocBuffer::ParGCAllocBuffer(size_t desired_plab_sz_) : 29 _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL), 30 _end(NULL), _hard_end(NULL), 31 _retained(false), _retained_filler(), 32 _allocated(0), _wasted(0) 33 { 34 assert (min_size() > AlignmentReserve, "Inconsistency!"); 35 // arrayOopDesc::header_size depends on command line initialization. 36 FillerHeaderSize = align_object_size(arrayOopDesc::header_size(T_INT)); 37 AlignmentReserve = oopDesc::header_size() > MinObjAlignment ? FillerHeaderSize : 0; 38 } 39 40 size_t ParGCAllocBuffer::FillerHeaderSize; 41 42 // If the minimum object size is greater than MinObjAlignment, we can 43 // end up with a shard at the end of the buffer that's smaller than 44 // the smallest object. We can't allow that because the buffer must 45 // look like it's full of objects when we retire it, so we make 46 // sure we have enough space for a filler int array object. 47 size_t ParGCAllocBuffer::AlignmentReserve; 48 49 void ParGCAllocBuffer::retire(bool end_of_gc, bool retain) { 50 assert(!retain || end_of_gc, "Can only retain at GC end."); 51 if (_retained) { 52 // If the buffer had been retained shorten the previous filler object. 53 assert(_retained_filler.end() <= _top, "INVARIANT"); 54 CollectedHeap::fill_with_object(_retained_filler); 55 // Wasted space book-keeping, otherwise (normally) done in invalidate() 56 _wasted += _retained_filler.word_size(); 57 _retained = false; 58 } 59 assert(!end_of_gc || !_retained, "At this point, end_of_gc ==> !_retained."); 60 if (_top < _hard_end) { 61 CollectedHeap::fill_with_object(_top, _hard_end); 62 if (!retain) { 63 invalidate(); 64 } else { 65 // Is there wasted space we'd like to retain for the next GC? 66 if (pointer_delta(_end, _top) > FillerHeaderSize) { 67 _retained = true; 68 _retained_filler = MemRegion(_top, FillerHeaderSize); 69 _top = _top + FillerHeaderSize; 70 } else { 71 invalidate(); 72 } 73 } 74 } 75 } 76 77 void ParGCAllocBuffer::flush_stats(PLABStats* stats) { 78 assert(ResizePLAB, "Wasted work"); 79 stats->add_allocated(_allocated); 80 stats->add_wasted(_wasted); 81 stats->add_unused(pointer_delta(_end, _top)); 82 } 83 84 // Compute desired plab size and latch result for later 85 // use. This should be called once at the end of parallel 86 // scavenge; it clears the sensor accumulators. 87 void PLABStats::adjust_desired_plab_sz() { 88 assert(ResizePLAB, "Not set"); 89 if (_allocated == 0) { 90 assert(_unused == 0, "Inconsistency in PLAB stats"); 91 _allocated = 1; 92 } 93 double wasted_frac = (double)_unused/(double)_allocated; 94 size_t target_refills = (size_t)((wasted_frac*TargetSurvivorRatio)/ 95 TargetPLABWastePct); 96 if (target_refills == 0) { 97 target_refills = 1; 98 } 99 _used = _allocated - _wasted - _unused; 100 size_t plab_sz = _used/(target_refills*ParallelGCThreads); 101 if (PrintPLAB) gclog_or_tty->print(" (plab_sz = %d ", plab_sz); 102 // Take historical weighted average 103 _filter.sample(plab_sz); 104 // Clip from above and below, and align to object boundary 105 plab_sz = MAX2(min_size(), (size_t)_filter.average()); 106 plab_sz = MIN2(max_size(), plab_sz); 107 plab_sz = align_object_size(plab_sz); 108 // Latch the result 109 if (PrintPLAB) gclog_or_tty->print(" desired_plab_sz = %d) ", plab_sz); 110 if (ResizePLAB) { 111 _desired_plab_sz = plab_sz; 112 } 113 // Now clear the accumulators for next round: 114 // note this needs to be fixed in the case where we 115 // are retaining across scavenges. FIX ME !!! XXX 116 _allocated = 0; 117 _wasted = 0; 118 _unused = 0; 119 } 120 121 #ifndef PRODUCT 122 void ParGCAllocBuffer::print() { 123 gclog_or_tty->print("parGCAllocBuffer: _bottom: %p _top: %p _end: %p _hard_end: %p" 124 "_retained: %c _retained_filler: [%p,%p)\n", 125 _bottom, _top, _end, _hard_end, 126 "FT"[_retained], _retained_filler.start(), _retained_filler.end()); 127 } 128 #endif // !PRODUCT 129 130 const size_t ParGCAllocBufferWithBOT::ChunkSizeInWords = 131 MIN2(CardTableModRefBS::par_chunk_heapword_alignment(), 132 ((size_t)Generation::GenGrain)/HeapWordSize); 133 const size_t ParGCAllocBufferWithBOT::ChunkSizeInBytes = 134 MIN2(CardTableModRefBS::par_chunk_heapword_alignment() * HeapWordSize, 135 (size_t)Generation::GenGrain); 136 137 ParGCAllocBufferWithBOT::ParGCAllocBufferWithBOT(size_t word_sz, 138 BlockOffsetSharedArray* bsa) : 139 ParGCAllocBuffer(word_sz), 140 _bsa(bsa), 141 _bt(bsa, MemRegion(_bottom, _hard_end)), 142 _true_end(_hard_end) 143 {} 144 145 // The buffer comes with its own BOT, with a shared (obviously) underlying 146 // BlockOffsetSharedArray. We manipulate this BOT in the normal way 147 // as we would for any contiguous space. However, on accasion we 148 // need to do some buffer surgery at the extremities before we 149 // start using the body of the buffer for allocations. Such surgery 150 // (as explained elsewhere) is to prevent allocation on a card that 151 // is in the process of being walked concurrently by another GC thread. 152 // When such surgery happens at a point that is far removed (to the 153 // right of the current allocation point, top), we use the "contig" 154 // parameter below to directly manipulate the shared array without 155 // modifying the _next_threshold state in the BOT. 156 void ParGCAllocBufferWithBOT::fill_region_with_block(MemRegion mr, 157 bool contig) { 158 CollectedHeap::fill_with_object(mr); 159 if (contig) { 160 _bt.alloc_block(mr.start(), mr.end()); 161 } else { 162 _bt.BlockOffsetArray::alloc_block(mr.start(), mr.end()); 163 } 164 } 165 166 HeapWord* ParGCAllocBufferWithBOT::allocate_slow(size_t word_sz) { 167 HeapWord* res = NULL; 168 if (_true_end > _hard_end) { 169 assert((HeapWord*)align_size_down(intptr_t(_hard_end), 170 ChunkSizeInBytes) == _hard_end, 171 "or else _true_end should be equal to _hard_end"); 172 assert(_retained, "or else _true_end should be equal to _hard_end"); 173 assert(_retained_filler.end() <= _top, "INVARIANT"); 174 CollectedHeap::fill_with_object(_retained_filler); 175 if (_top < _hard_end) { 176 fill_region_with_block(MemRegion(_top, _hard_end), true); 177 } 178 HeapWord* next_hard_end = MIN2(_true_end, _hard_end + ChunkSizeInWords); 179 _retained_filler = MemRegion(_hard_end, FillerHeaderSize); 180 _bt.alloc_block(_retained_filler.start(), _retained_filler.word_size()); 181 _top = _retained_filler.end(); 182 _hard_end = next_hard_end; 183 _end = _hard_end - AlignmentReserve; 184 res = ParGCAllocBuffer::allocate(word_sz); 185 if (res != NULL) { 186 _bt.alloc_block(res, word_sz); 187 } 188 } 189 return res; 190 } 191 192 void 193 ParGCAllocBufferWithBOT::undo_allocation(HeapWord* obj, size_t word_sz) { 194 ParGCAllocBuffer::undo_allocation(obj, word_sz); 195 // This may back us up beyond the previous threshold, so reset. 196 _bt.set_region(MemRegion(_top, _hard_end)); 197 _bt.initialize_threshold(); 198 } 199 200 void ParGCAllocBufferWithBOT::retire(bool end_of_gc, bool retain) { 201 assert(!retain || end_of_gc, "Can only retain at GC end."); 202 if (_retained) { 203 // We're about to make the retained_filler into a block. 204 _bt.BlockOffsetArray::alloc_block(_retained_filler.start(), 205 _retained_filler.end()); 206 } 207 // Reset _hard_end to _true_end (and update _end) 208 if (retain && _hard_end != NULL) { 209 assert(_hard_end <= _true_end, "Invariant."); 210 _hard_end = _true_end; 211 _end = MAX2(_top, _hard_end - AlignmentReserve); 212 assert(_end <= _hard_end, "Invariant."); 213 } 214 _true_end = _hard_end; 215 HeapWord* pre_top = _top; 216 217 ParGCAllocBuffer::retire(end_of_gc, retain); 218 // Now any old _retained_filler is cut back to size, the free part is 219 // filled with a filler object, and top is past the header of that 220 // object. 221 222 if (retain && _top < _end) { 223 assert(end_of_gc && retain, "Or else retain should be false."); 224 // If the lab does not start on a card boundary, we don't want to 225 // allocate onto that card, since that might lead to concurrent 226 // allocation and card scanning, which we don't support. So we fill 227 // the first card with a garbage object. 228 size_t first_card_index = _bsa->index_for(pre_top); 229 HeapWord* first_card_start = _bsa->address_for_index(first_card_index); 230 if (first_card_start < pre_top) { 231 HeapWord* second_card_start = 232 _bsa->inc_by_region_size(first_card_start); 233 234 // Ensure enough room to fill with the smallest block 235 second_card_start = MAX2(second_card_start, pre_top + AlignmentReserve); 236 237 // If the end is already in the first card, don't go beyond it! 238 // Or if the remainder is too small for a filler object, gobble it up. 239 if (_hard_end < second_card_start || 240 pointer_delta(_hard_end, second_card_start) < AlignmentReserve) { 241 second_card_start = _hard_end; 242 } 243 if (pre_top < second_card_start) { 244 MemRegion first_card_suffix(pre_top, second_card_start); 245 fill_region_with_block(first_card_suffix, true); 246 } 247 pre_top = second_card_start; 248 _top = pre_top; 249 _end = MAX2(_top, _hard_end - AlignmentReserve); 250 } 251 252 // If the lab does not end on a card boundary, we don't want to 253 // allocate onto that card, since that might lead to concurrent 254 // allocation and card scanning, which we don't support. So we fill 255 // the last card with a garbage object. 256 size_t last_card_index = _bsa->index_for(_hard_end); 257 HeapWord* last_card_start = _bsa->address_for_index(last_card_index); 258 if (last_card_start < _hard_end) { 259 260 // Ensure enough room to fill with the smallest block 261 last_card_start = MIN2(last_card_start, _hard_end - AlignmentReserve); 262 263 // If the top is already in the last card, don't go back beyond it! 264 // Or if the remainder is too small for a filler object, gobble it up. 265 if (_top > last_card_start || 266 pointer_delta(last_card_start, _top) < AlignmentReserve) { 267 last_card_start = _top; 268 } 269 if (last_card_start < _hard_end) { 270 MemRegion last_card_prefix(last_card_start, _hard_end); 271 fill_region_with_block(last_card_prefix, false); 272 } 273 _hard_end = last_card_start; 274 _end = MAX2(_top, _hard_end - AlignmentReserve); 275 _true_end = _hard_end; 276 assert(_end <= _hard_end, "Invariant."); 277 } 278 279 // At this point: 280 // 1) we had a filler object from the original top to hard_end. 281 // 2) We've filled in any partial cards at the front and back. 282 if (pre_top < _hard_end) { 283 // Now we can reset the _bt to do allocation in the given area. 284 MemRegion new_filler(pre_top, _hard_end); 285 fill_region_with_block(new_filler, false); 286 _top = pre_top + ParGCAllocBuffer::FillerHeaderSize; 287 // If there's no space left, don't retain. 288 if (_top >= _end) { 289 _retained = false; 290 invalidate(); 291 return; 292 } 293 _retained_filler = MemRegion(pre_top, _top); 294 _bt.set_region(MemRegion(_top, _hard_end)); 295 _bt.initialize_threshold(); 296 assert(_bt.threshold() > _top, "initialize_threshold failed!"); 297 298 // There may be other reasons for queries into the middle of the 299 // filler object. When such queries are done in parallel with 300 // allocation, bad things can happen, if the query involves object 301 // iteration. So we ensure that such queries do not involve object 302 // iteration, by putting another filler object on the boundaries of 303 // such queries. One such is the object spanning a parallel card 304 // chunk boundary. 305 306 // "chunk_boundary" is the address of the first chunk boundary less 307 // than "hard_end". 308 HeapWord* chunk_boundary = 309 (HeapWord*)align_size_down(intptr_t(_hard_end-1), ChunkSizeInBytes); 310 assert(chunk_boundary < _hard_end, "Or else above did not work."); 311 assert(pointer_delta(_true_end, chunk_boundary) >= AlignmentReserve, 312 "Consequence of last card handling above."); 313 314 if (_top <= chunk_boundary) { 315 assert(_true_end == _hard_end, "Invariant."); 316 while (_top <= chunk_boundary) { 317 assert(pointer_delta(_hard_end, chunk_boundary) >= AlignmentReserve, 318 "Consequence of last card handling above."); 319 _bt.BlockOffsetArray::alloc_block(chunk_boundary, _hard_end); 320 CollectedHeap::fill_with_object(chunk_boundary, _hard_end); 321 _hard_end = chunk_boundary; 322 chunk_boundary -= ChunkSizeInWords; 323 } 324 _end = _hard_end - AlignmentReserve; 325 assert(_top <= _end, "Invariant."); 326 // Now reset the initial filler chunk so it doesn't overlap with 327 // the one(s) inserted above. 328 MemRegion new_filler(pre_top, _hard_end); 329 fill_region_with_block(new_filler, false); 330 } 331 } else { 332 _retained = false; 333 invalidate(); 334 } 335 } else { 336 assert(!end_of_gc || 337 (!_retained && _true_end == _hard_end), "Checking."); 338 } 339 assert(_end <= _hard_end, "Invariant."); 340 assert(_top < _end || _top == _hard_end, "Invariant"); 341 }