1 #ifdef USE_PRAGMA_IDENT_SRC 2 #pragma ident "@(#)parGCAllocBuffer.cpp 1.28 07/05/29 09:44:12 JVM" 3 #endif 4 /* 5 * Copyright 2001-2008 Sun Microsystems, Inc. All Rights Reserved. 6 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 7 * 8 * This code is free software; you can redistribute it and/or modify it 9 * under the terms of the GNU General Public License version 2 only, as 10 * published by the Free Software Foundation. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, 23 * CA 95054 USA or visit www.sun.com if you need additional information or 24 * have any questions. 25 * 26 */ 27 28 # include "incls/_precompiled.incl" 29 # include "incls/_parGCAllocBuffer.cpp.incl" 30 31 ParGCAllocBuffer::ParGCAllocBuffer(size_t desired_plab_sz_) : 32 _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL), 33 _end(NULL), _hard_end(NULL), 34 _retained(false), _retained_filler(), 35 _allocated(0), _wasted(0) 36 { 37 assert (min_size() > AlignmentReserve, "Inconsistency!"); 38 // arrayOopDesc::header_size depends on command line initialization. 39 FillerHeaderSize = align_object_size(arrayOopDesc::header_size(T_INT)); 40 AlignmentReserve = oopDesc::header_size() > MinObjAlignment ? FillerHeaderSize : 0; 41 } 42 43 size_t ParGCAllocBuffer::FillerHeaderSize; 44 45 // If the minimum object size is greater than MinObjAlignment, we can 46 // end up with a shard at the end of the buffer that's smaller than 47 // the smallest object. We can't allow that because the buffer must 48 // look like it's full of objects when we retire it, so we make 49 // sure we have enough space for a filler int array object. 50 size_t ParGCAllocBuffer::AlignmentReserve; 51 52 void ParGCAllocBuffer::retire(bool end_of_gc, bool retain) { 53 assert(!retain || end_of_gc, "Can only retain at GC end."); 54 if (_retained) { 55 // If the buffer had been retained shorten the previous filler object. 56 assert(_retained_filler.end() <= _top, "INVARIANT"); 57 CollectedHeap::fill_with_object(_retained_filler); 58 // Wasted space book-keeping, otherwise (normally) done in invalidate() 59 _wasted += _retained_filler.word_size(); 60 _retained = false; 61 } 62 assert(!end_of_gc || !_retained, "At this point, end_of_gc ==> !_retained."); 63 if (_top < _hard_end) { 64 CollectedHeap::fill_with_object(_top, _hard_end); 65 if (!retain) { 66 invalidate(); 67 } else { 68 // Is there wasted space we'd like to retain for the next GC? 69 if (pointer_delta(_end, _top) > FillerHeaderSize) { 70 _retained = true; 71 _retained_filler = MemRegion(_top, FillerHeaderSize); 72 _top = _top + FillerHeaderSize; 73 } else { 74 invalidate(); 75 } 76 } 77 } 78 } 79 80 void ParGCAllocBuffer::flush_stats(PLABStats* stats) { 81 assert(ResizePLAB, "Wasted work"); 82 stats->add_allocated(_allocated); 83 stats->add_wasted(_wasted); 84 stats->add_unused(pointer_delta(_end, _top)); 85 } 86 87 // Compute desired plab size and latch result for later 88 // use. This should be called once at the end of parallel 89 // scavenge; it clears the sensor accumulators. 90 void PLABStats::adjust_desired_plab_sz() { 91 assert(ResizePLAB, "Not set"); 92 if (_allocated == 0) { 93 assert(_unused == 0, "Inconsistency in PLAB stats"); 94 _allocated = 1; 95 } 96 double wasted_frac = (double)_unused/(double)_allocated; 97 size_t target_refills = (size_t)((wasted_frac*TargetSurvivorRatio)/ 98 TargetPLABWastePct); 99 if (target_refills == 0) { 100 target_refills = 1; 101 } 102 _used = _allocated - _wasted - _unused; 103 size_t plab_sz = _used/(target_refills*ParallelGCThreads); 104 if (PrintPLAB) gclog_or_tty->print(" (plab_sz = %d ", plab_sz); 105 // Take historical weighted average 106 _filter.sample(plab_sz); 107 // Clip from above and below, and align to object boundary 108 plab_sz = MAX2(min_size(), (size_t)_filter.average()); 109 plab_sz = MIN2(max_size(), plab_sz); 110 plab_sz = align_object_size(plab_sz); 111 // Latch the result 112 if (PrintPLAB) gclog_or_tty->print(" desired_plab_sz = %d) ", plab_sz); 113 if (ResizePLAB) { 114 _desired_plab_sz = plab_sz; 115 } 116 // Now clear the accumulators for next round: 117 // note this needs to be fixed in the case where we 118 // are retaining across scavenges. FIX ME !!! XXX 119 _allocated = 0; 120 _wasted = 0; 121 _unused = 0; 122 } 123 124 #ifndef PRODUCT 125 void ParGCAllocBuffer::print() { 126 gclog_or_tty->print("parGCAllocBuffer: _bottom: %p _top: %p _end: %p _hard_end: %p" 127 "_retained: %c _retained_filler: [%p,%p)\n", 128 _bottom, _top, _end, _hard_end, 129 "FT"[_retained], _retained_filler.start(), _retained_filler.end()); 130 } 131 #endif // !PRODUCT 132 133 const size_t ParGCAllocBufferWithBOT::ChunkSizeInWords = 134 MIN2(CardTableModRefBS::par_chunk_heapword_alignment(), 135 ((size_t)Generation::GenGrain)/HeapWordSize); 136 const size_t ParGCAllocBufferWithBOT::ChunkSizeInBytes = 137 MIN2(CardTableModRefBS::par_chunk_heapword_alignment() * HeapWordSize, 138 (size_t)Generation::GenGrain); 139 140 ParGCAllocBufferWithBOT::ParGCAllocBufferWithBOT(size_t word_sz, 141 BlockOffsetSharedArray* bsa) : 142 ParGCAllocBuffer(word_sz), 143 _bsa(bsa), 144 _bt(bsa, MemRegion(_bottom, _hard_end)), 145 _true_end(_hard_end) 146 {} 147 148 // The buffer comes with its own BOT, with a shared (obviously) underlying 149 // BlockOffsetSharedArray. We manipulate this BOT in the normal way 150 // as we would for any contiguous space. However, on accasion we 151 // need to do some buffer surgery at the extremities before we 152 // start using the body of the buffer for allocations. Such surgery 153 // (as explained elsewhere) is to prevent allocation on a card that 154 // is in the process of being walked concurrently by another GC thread. 155 // When such surgery happens at a point that is far removed (to the 156 // right of the current allocation point, top), we use the "contig" 157 // parameter below to directly manipulate the shared array without 158 // modifying the _next_threshold state in the BOT. 159 void ParGCAllocBufferWithBOT::fill_region_with_block(MemRegion mr, 160 bool contig) { 161 CollectedHeap::fill_with_object(mr); 162 if (contig) { 163 _bt.alloc_block(mr.start(), mr.end()); 164 } else { 165 _bt.BlockOffsetArray::alloc_block(mr.start(), mr.end()); 166 } 167 } 168 169 HeapWord* ParGCAllocBufferWithBOT::allocate_slow(size_t word_sz) { 170 HeapWord* res = NULL; 171 if (_true_end > _hard_end) { 172 assert((HeapWord*)align_size_down(intptr_t(_hard_end), 173 ChunkSizeInBytes) == _hard_end, 174 "or else _true_end should be equal to _hard_end"); 175 assert(_retained, "or else _true_end should be equal to _hard_end"); 176 assert(_retained_filler.end() <= _top, "INVARIANT"); 177 CollectedHeap::fill_with_object(_retained_filler); 178 if (_top < _hard_end) { 179 fill_region_with_block(MemRegion(_top, _hard_end), true); 180 } 181 HeapWord* next_hard_end = MIN2(_true_end, _hard_end + ChunkSizeInWords); 182 _retained_filler = MemRegion(_hard_end, FillerHeaderSize); 183 _bt.alloc_block(_retained_filler.start(), _retained_filler.word_size()); 184 _top = _retained_filler.end(); 185 _hard_end = next_hard_end; 186 _end = _hard_end - AlignmentReserve; 187 res = ParGCAllocBuffer::allocate(word_sz); 188 if (res != NULL) { 189 _bt.alloc_block(res, word_sz); 190 } 191 } 192 return res; 193 } 194 195 void 196 ParGCAllocBufferWithBOT::undo_allocation(HeapWord* obj, size_t word_sz) { 197 ParGCAllocBuffer::undo_allocation(obj, word_sz); 198 // This may back us up beyond the previous threshold, so reset. 199 _bt.set_region(MemRegion(_top, _hard_end)); 200 _bt.initialize_threshold(); 201 } 202 203 void ParGCAllocBufferWithBOT::retire(bool end_of_gc, bool retain) { 204 assert(!retain || end_of_gc, "Can only retain at GC end."); 205 if (_retained) { 206 // We're about to make the retained_filler into a block. 207 _bt.BlockOffsetArray::alloc_block(_retained_filler.start(), 208 _retained_filler.end()); 209 } 210 // Reset _hard_end to _true_end (and update _end) 211 if (retain && _hard_end != NULL) { 212 assert(_hard_end <= _true_end, "Invariant."); 213 _hard_end = _true_end; 214 _end = MAX2(_top, _hard_end - AlignmentReserve); 215 assert(_end <= _hard_end, "Invariant."); 216 } 217 _true_end = _hard_end; 218 HeapWord* pre_top = _top; 219 220 ParGCAllocBuffer::retire(end_of_gc, retain); 221 // Now any old _retained_filler is cut back to size, the free part is 222 // filled with a filler object, and top is past the header of that 223 // object. 224 225 if (retain && _top < _end) { 226 assert(end_of_gc && retain, "Or else retain should be false."); 227 // If the lab does not start on a card boundary, we don't want to 228 // allocate onto that card, since that might lead to concurrent 229 // allocation and card scanning, which we don't support. So we fill 230 // the first card with a garbage object. 231 size_t first_card_index = _bsa->index_for(pre_top); 232 HeapWord* first_card_start = _bsa->address_for_index(first_card_index); 233 if (first_card_start < pre_top) { 234 HeapWord* second_card_start = 235 _bsa->inc_by_region_size(first_card_start); 236 237 // Ensure enough room to fill with the smallest block 238 second_card_start = MAX2(second_card_start, pre_top + AlignmentReserve); 239 240 // If the end is already in the first card, don't go beyond it! 241 // Or if the remainder is too small for a filler object, gobble it up. 242 if (_hard_end < second_card_start || 243 pointer_delta(_hard_end, second_card_start) < AlignmentReserve) { 244 second_card_start = _hard_end; 245 } 246 if (pre_top < second_card_start) { 247 MemRegion first_card_suffix(pre_top, second_card_start); 248 fill_region_with_block(first_card_suffix, true); 249 } 250 pre_top = second_card_start; 251 _top = pre_top; 252 _end = MAX2(_top, _hard_end - AlignmentReserve); 253 } 254 255 // If the lab does not end on a card boundary, we don't want to 256 // allocate onto that card, since that might lead to concurrent 257 // allocation and card scanning, which we don't support. So we fill 258 // the last card with a garbage object. 259 size_t last_card_index = _bsa->index_for(_hard_end); 260 HeapWord* last_card_start = _bsa->address_for_index(last_card_index); 261 if (last_card_start < _hard_end) { 262 263 // Ensure enough room to fill with the smallest block 264 last_card_start = MIN2(last_card_start, _hard_end - AlignmentReserve); 265 266 // If the top is already in the last card, don't go back beyond it! 267 // Or if the remainder is too small for a filler object, gobble it up. 268 if (_top > last_card_start || 269 pointer_delta(last_card_start, _top) < AlignmentReserve) { 270 last_card_start = _top; 271 } 272 if (last_card_start < _hard_end) { 273 MemRegion last_card_prefix(last_card_start, _hard_end); 274 fill_region_with_block(last_card_prefix, false); 275 } 276 _hard_end = last_card_start; 277 _end = MAX2(_top, _hard_end - AlignmentReserve); 278 _true_end = _hard_end; 279 assert(_end <= _hard_end, "Invariant."); 280 } 281 282 // At this point: 283 // 1) we had a filler object from the original top to hard_end. 284 // 2) We've filled in any partial cards at the front and back. 285 if (pre_top < _hard_end) { 286 // Now we can reset the _bt to do allocation in the given area. 287 MemRegion new_filler(pre_top, _hard_end); 288 fill_region_with_block(new_filler, false); 289 _top = pre_top + ParGCAllocBuffer::FillerHeaderSize; 290 // If there's no space left, don't retain. 291 if (_top >= _end) { 292 _retained = false; 293 invalidate(); 294 return; 295 } 296 _retained_filler = MemRegion(pre_top, _top); 297 _bt.set_region(MemRegion(_top, _hard_end)); 298 _bt.initialize_threshold(); 299 assert(_bt.threshold() > _top, "initialize_threshold failed!"); 300 301 // There may be other reasons for queries into the middle of the 302 // filler object. When such queries are done in parallel with 303 // allocation, bad things can happen, if the query involves object 304 // iteration. So we ensure that such queries do not involve object 305 // iteration, by putting another filler object on the boundaries of 306 // such queries. One such is the object spanning a parallel card 307 // chunk boundary. 308 309 // "chunk_boundary" is the address of the first chunk boundary less 310 // than "hard_end". 311 HeapWord* chunk_boundary = 312 (HeapWord*)align_size_down(intptr_t(_hard_end-1), ChunkSizeInBytes); 313 assert(chunk_boundary < _hard_end, "Or else above did not work."); 314 assert(pointer_delta(_true_end, chunk_boundary) >= AlignmentReserve, 315 "Consequence of last card handling above."); 316 317 if (_top <= chunk_boundary) { 318 assert(_true_end == _hard_end, "Invariant."); 319 while (_top <= chunk_boundary) { 320 assert(pointer_delta(_hard_end, chunk_boundary) >= AlignmentReserve, 321 "Consequence of last card handling above."); 322 _bt.BlockOffsetArray::alloc_block(chunk_boundary, _hard_end); 323 CollectedHeap::fill_with_object(chunk_boundary, _hard_end); 324 _hard_end = chunk_boundary; 325 chunk_boundary -= ChunkSizeInWords; 326 } 327 _end = _hard_end - AlignmentReserve; 328 assert(_top <= _end, "Invariant."); 329 // Now reset the initial filler chunk so it doesn't overlap with 330 // the one(s) inserted above. 331 MemRegion new_filler(pre_top, _hard_end); 332 fill_region_with_block(new_filler, false); 333 } 334 } else { 335 _retained = false; 336 invalidate(); 337 } 338 } else { 339 assert(!end_of_gc || 340 (!_retained && _true_end == _hard_end), "Checking."); 341 } 342 assert(_end <= _hard_end, "Invariant."); 343 assert(_top < _end || _top == _hard_end, "Invariant"); 344 }