1 #ifdef USE_PRAGMA_IDENT_SRC
2 #pragma ident "@(#)compactibleFreeListSpace.cpp 1.144 08/09/06 09:20:55 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/_compactibleFreeListSpace.cpp.incl"
30
31 /////////////////////////////////////////////////////////////////////////
32 //// CompactibleFreeListSpace
33 /////////////////////////////////////////////////////////////////////////
34
35 // highest ranked free list lock rank
36 int CompactibleFreeListSpace::_lockRank = Mutex::leaf + 3;
37
38 // Constructor
39 CompactibleFreeListSpace::CompactibleFreeListSpace(BlockOffsetSharedArray* bs,
40 MemRegion mr, bool use_adaptive_freelists,
41 FreeBlockDictionary::DictionaryChoice dictionaryChoice) :
42 _dictionaryChoice(dictionaryChoice),
43 _adaptive_freelists(use_adaptive_freelists),
44 _bt(bs, mr),
45 // free list locks are in the range of values taken by _lockRank
46 // This range currently is [_leaf+2, _leaf+3]
47 // Note: this requires that CFLspace c'tors
48 // are called serially in the order in which the locks are
49 // are acquired in the program text. This is true today.
50 _freelistLock(_lockRank--, "CompactibleFreeListSpace._lock", true),
51 _parDictionaryAllocLock(Mutex::leaf - 1, // == rank(ExpandHeap_lock) - 1
52 "CompactibleFreeListSpace._dict_par_lock", true),
53 _rescan_task_size(CardTableModRefBS::card_size_in_words * BitsPerWord *
54 CMSRescanMultiple),
55 _marking_task_size(CardTableModRefBS::card_size_in_words * BitsPerWord *
56 CMSConcMarkMultiple),
57 _collector(NULL)
58 {
59 _bt.set_space(this);
60 initialize(mr, SpaceDecorator::Clear, SpaceDecorator::Mangle);
61 // We have all of "mr", all of which we place in the dictionary
62 // as one big chunk. We'll need to decide here which of several
63 // possible alternative dictionary implementations to use. For
64 // now the choice is easy, since we have only one working
65 // implementation, namely, the simple binary tree (splaying
66 // temporarily disabled).
67 switch (dictionaryChoice) {
68 case FreeBlockDictionary::dictionaryBinaryTree:
69 _dictionary = new BinaryTreeDictionary(mr);
70 break;
71 case FreeBlockDictionary::dictionarySplayTree:
72 case FreeBlockDictionary::dictionarySkipList:
73 default:
74 warning("dictionaryChoice: selected option not understood; using"
75 " default BinaryTreeDictionary implementation instead.");
76 _dictionary = new BinaryTreeDictionary(mr);
77 break;
78 }
79 splitBirth(mr.word_size());
80 assert(_dictionary != NULL, "CMS dictionary initialization");
81 // The indexed free lists are initially all empty and are lazily
82 // filled in on demand. Initialize the array elements to NULL.
83 initializeIndexedFreeListArray();
84
85 // Not using adaptive free lists assumes that allocation is first
86 // from the linAB's. Also a cms perm gen which can be compacted
87 // has to have the klass's klassKlass allocated at a lower
88 // address in the heap than the klass so that the klassKlass is
89 // moved to its new location before the klass is moved.
90 // Set the _refillSize for the linear allocation blocks
91 if (!use_adaptive_freelists) {
92 FreeChunk* fc = _dictionary->getChunk(mr.word_size());
93 // The small linAB initially has all the space and will allocate
94 // a chunk of any size.
95 HeapWord* addr = (HeapWord*) fc;
96 _smallLinearAllocBlock.set(addr, fc->size() ,
97 1024*SmallForLinearAlloc, fc->size());
98 // Note that _unallocated_block is not updated here.
99 // Allocations from the linear allocation block should
100 // update it.
101 } else {
102 _smallLinearAllocBlock.set(0, 0, 1024*SmallForLinearAlloc,
103 SmallForLinearAlloc);
104 }
105 // CMSIndexedFreeListReplenish should be at least 1
106 CMSIndexedFreeListReplenish = MAX2((uintx)1, CMSIndexedFreeListReplenish);
107 _promoInfo.setSpace(this);
108 if (UseCMSBestFit) {
109 _fitStrategy = FreeBlockBestFitFirst;
110 } else {
111 _fitStrategy = FreeBlockStrategyNone;
112 }
113 checkFreeListConsistency();
114
115 // Initialize locks for parallel case.
116 if (ParallelGCThreads > 0) {
117 for (size_t i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
118 _indexedFreeListParLocks[i] = new Mutex(Mutex::leaf - 1, // == ExpandHeap_lock - 1
119 "a freelist par lock",
120 true);
121 if (_indexedFreeListParLocks[i] == NULL)
122 vm_exit_during_initialization("Could not allocate a par lock");
123 DEBUG_ONLY(
124 _indexedFreeList[i].set_protecting_lock(_indexedFreeListParLocks[i]);
125 )
126 }
127 _dictionary->set_par_lock(&_parDictionaryAllocLock);
128 }
129 }
130
131 // Like CompactibleSpace forward() but always calls cross_threshold() to
132 // update the block offset table. Removed initialize_threshold call because
133 // CFLS does not use a block offset array for contiguous spaces.
134 HeapWord* CompactibleFreeListSpace::forward(oop q, size_t size,
135 CompactPoint* cp, HeapWord* compact_top) {
136 // q is alive
137 // First check if we should switch compaction space
138 assert(this == cp->space, "'this' should be current compaction space.");
139 size_t compaction_max_size = pointer_delta(end(), compact_top);
140 assert(adjustObjectSize(size) == cp->space->adjust_object_size_v(size),
141 "virtual adjustObjectSize_v() method is not correct");
142 size_t adjusted_size = adjustObjectSize(size);
143 assert(compaction_max_size >= MinChunkSize || compaction_max_size == 0,
144 "no small fragments allowed");
145 assert(minimum_free_block_size() == MinChunkSize,
146 "for de-virtualized reference below");
147 // Can't leave a nonzero size, residual fragment smaller than MinChunkSize
148 if (adjusted_size + MinChunkSize > compaction_max_size &&
149 adjusted_size != compaction_max_size) {
150 do {
151 // switch to next compaction space
152 cp->space->set_compaction_top(compact_top);
153 cp->space = cp->space->next_compaction_space();
154 if (cp->space == NULL) {
155 cp->gen = GenCollectedHeap::heap()->prev_gen(cp->gen);
156 assert(cp->gen != NULL, "compaction must succeed");
157 cp->space = cp->gen->first_compaction_space();
158 assert(cp->space != NULL, "generation must have a first compaction space");
159 }
160 compact_top = cp->space->bottom();
161 cp->space->set_compaction_top(compact_top);
162 // The correct adjusted_size may not be the same as that for this method
163 // (i.e., cp->space may no longer be "this" so adjust the size again.
164 // Use the virtual method which is not used above to save the virtual
165 // dispatch.
166 adjusted_size = cp->space->adjust_object_size_v(size);
167 compaction_max_size = pointer_delta(cp->space->end(), compact_top);
168 assert(cp->space->minimum_free_block_size() == 0, "just checking");
169 } while (adjusted_size > compaction_max_size);
170 }
171
172 // store the forwarding pointer into the mark word
173 if ((HeapWord*)q != compact_top) {
174 q->forward_to(oop(compact_top));
175 assert(q->is_gc_marked(), "encoding the pointer should preserve the mark");
176 } else {
177 // if the object isn't moving we can just set the mark to the default
178 // mark and handle it specially later on.
179 q->init_mark();
180 assert(q->forwardee() == NULL, "should be forwarded to NULL");
181 }
182
183 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::register_live_oop(q, adjusted_size));
184 compact_top += adjusted_size;
185
186 // we need to update the offset table so that the beginnings of objects can be
187 // found during scavenge. Note that we are updating the offset table based on
188 // where the object will be once the compaction phase finishes.
189
190 // Always call cross_threshold(). A contiguous space can only call it when
191 // the compaction_top exceeds the current threshold but not for an
192 // non-contiguous space.
193 cp->threshold =
194 cp->space->cross_threshold(compact_top - adjusted_size, compact_top);
195 return compact_top;
196 }
197
198 // A modified copy of OffsetTableContigSpace::cross_threshold() with _offsets -> _bt
199 // and use of single_block instead of alloc_block. The name here is not really
200 // appropriate - maybe a more general name could be invented for both the
201 // contiguous and noncontiguous spaces.
202
203 HeapWord* CompactibleFreeListSpace::cross_threshold(HeapWord* start, HeapWord* the_end) {
204 _bt.single_block(start, the_end);
205 return end();
206 }
207
208 // Initialize them to NULL.
209 void CompactibleFreeListSpace::initializeIndexedFreeListArray() {
210 for (size_t i = 0; i < IndexSetSize; i++) {
211 // Note that on platforms where objects are double word aligned,
212 // the odd array elements are not used. It is convenient, however,
213 // to map directly from the object size to the array element.
214 _indexedFreeList[i].reset(IndexSetSize);
215 _indexedFreeList[i].set_size(i);
216 assert(_indexedFreeList[i].count() == 0, "reset check failed");
217 assert(_indexedFreeList[i].head() == NULL, "reset check failed");
218 assert(_indexedFreeList[i].tail() == NULL, "reset check failed");
219 assert(_indexedFreeList[i].hint() == IndexSetSize, "reset check failed");
220 }
221 }
222
223 void CompactibleFreeListSpace::resetIndexedFreeListArray() {
224 for (int i = 1; i < IndexSetSize; i++) {
225 assert(_indexedFreeList[i].size() == (size_t) i,
226 "Indexed free list sizes are incorrect");
227 _indexedFreeList[i].reset(IndexSetSize);
228 assert(_indexedFreeList[i].count() == 0, "reset check failed");
229 assert(_indexedFreeList[i].head() == NULL, "reset check failed");
230 assert(_indexedFreeList[i].tail() == NULL, "reset check failed");
231 assert(_indexedFreeList[i].hint() == IndexSetSize, "reset check failed");
232 }
233 }
234
235 void CompactibleFreeListSpace::reset(MemRegion mr) {
236 resetIndexedFreeListArray();
237 dictionary()->reset();
238 if (BlockOffsetArrayUseUnallocatedBlock) {
239 assert(end() == mr.end(), "We are compacting to the bottom of CMS gen");
240 // Everything's allocated until proven otherwise.
241 _bt.set_unallocated_block(end());
242 }
243 if (!mr.is_empty()) {
244 assert(mr.word_size() >= MinChunkSize, "Chunk size is too small");
245 _bt.single_block(mr.start(), mr.word_size());
246 FreeChunk* fc = (FreeChunk*) mr.start();
247 fc->setSize(mr.word_size());
248 if (mr.word_size() >= IndexSetSize ) {
249 returnChunkToDictionary(fc);
250 } else {
251 _bt.verify_not_unallocated((HeapWord*)fc, fc->size());
252 _indexedFreeList[mr.word_size()].returnChunkAtHead(fc);
253 }
254 }
255 _promoInfo.reset();
256 _smallLinearAllocBlock._ptr = NULL;
257 _smallLinearAllocBlock._word_size = 0;
258 }
259
260 void CompactibleFreeListSpace::reset_after_compaction() {
261 // Reset the space to the new reality - one free chunk.
262 MemRegion mr(compaction_top(), end());
263 reset(mr);
264 // Now refill the linear allocation block(s) if possible.
265 if (_adaptive_freelists) {
266 refillLinearAllocBlocksIfNeeded();
267 } else {
268 // Place as much of mr in the linAB as we can get,
269 // provided it was big enough to go into the dictionary.
270 FreeChunk* fc = dictionary()->findLargestDict();
271 if (fc != NULL) {
272 assert(fc->size() == mr.word_size(),
273 "Why was the chunk broken up?");
274 removeChunkFromDictionary(fc);
275 HeapWord* addr = (HeapWord*) fc;
276 _smallLinearAllocBlock.set(addr, fc->size() ,
277 1024*SmallForLinearAlloc, fc->size());
278 // Note that _unallocated_block is not updated here.
279 }
280 }
281 }
282
283 // Walks the entire dictionary, returning a coterminal
284 // chunk, if it exists. Use with caution since it involves
285 // a potentially complete walk of a potentially large tree.
286 FreeChunk* CompactibleFreeListSpace::find_chunk_at_end() {
287
288 assert_lock_strong(&_freelistLock);
289
290 return dictionary()->find_chunk_ends_at(end());
291 }
292
293
294 #ifndef PRODUCT
295 void CompactibleFreeListSpace::initializeIndexedFreeListArrayReturnedBytes() {
296 for (size_t i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
297 _indexedFreeList[i].allocation_stats()->set_returnedBytes(0);
298 }
299 }
300
301 size_t CompactibleFreeListSpace::sumIndexedFreeListArrayReturnedBytes() {
302 size_t sum = 0;
303 for (size_t i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
304 sum += _indexedFreeList[i].allocation_stats()->returnedBytes();
305 }
306 return sum;
307 }
308
309 size_t CompactibleFreeListSpace::totalCountInIndexedFreeLists() const {
310 size_t count = 0;
311 for (int i = MinChunkSize; i < IndexSetSize; i++) {
312 debug_only(
313 ssize_t total_list_count = 0;
314 for (FreeChunk* fc = _indexedFreeList[i].head(); fc != NULL;
315 fc = fc->next()) {
316 total_list_count++;
317 }
318 assert(total_list_count == _indexedFreeList[i].count(),
319 "Count in list is incorrect");
320 )
321 count += _indexedFreeList[i].count();
322 }
323 return count;
324 }
325
326 size_t CompactibleFreeListSpace::totalCount() {
327 size_t num = totalCountInIndexedFreeLists();
328 num += dictionary()->totalCount();
329 if (_smallLinearAllocBlock._word_size != 0) {
330 num++;
331 }
332 return num;
333 }
334 #endif
335
336 bool CompactibleFreeListSpace::is_free_block(const HeapWord* p) const {
337 FreeChunk* fc = (FreeChunk*) p;
338 return fc->isFree();
339 }
340
341 size_t CompactibleFreeListSpace::used() const {
342 return capacity() - free();
343 }
344
345 size_t CompactibleFreeListSpace::free() const {
346 // "MT-safe, but not MT-precise"(TM), if you will: i.e.
347 // if you do this while the structures are in flux you
348 // may get an approximate answer only; for instance
349 // because there is concurrent allocation either
350 // directly by mutators or for promotion during a GC.
351 // It's "MT-safe", however, in the sense that you are guaranteed
352 // not to crash and burn, for instance, because of walking
353 // pointers that could disappear as you were walking them.
354 // The approximation is because the various components
355 // that are read below are not read atomically (and
356 // further the computation of totalSizeInIndexedFreeLists()
357 // is itself a non-atomic computation. The normal use of
358 // this is during a resize operation at the end of GC
359 // and at that time you are guaranteed to get the
360 // correct actual value. However, for instance, this is
361 // also read completely asynchronously by the "perf-sampler"
362 // that supports jvmstat, and you are apt to see the values
363 // flicker in such cases.
364 assert(_dictionary != NULL, "No _dictionary?");
365 return (_dictionary->totalChunkSize(DEBUG_ONLY(freelistLock())) +
366 totalSizeInIndexedFreeLists() +
367 _smallLinearAllocBlock._word_size) * HeapWordSize;
368 }
369
370 size_t CompactibleFreeListSpace::max_alloc_in_words() const {
371 assert(_dictionary != NULL, "No _dictionary?");
372 assert_locked();
373 size_t res = _dictionary->maxChunkSize();
374 res = MAX2(res, MIN2(_smallLinearAllocBlock._word_size,
375 (size_t) SmallForLinearAlloc - 1));
376 // XXX the following could potentially be pretty slow;
377 // should one, pesimally for the rare cases when res
378 // caclulated above is less than IndexSetSize,
379 // just return res calculated above? My reasoning was that
380 // those cases will be so rare that the extra time spent doesn't
381 // really matter....
382 // Note: do not change the loop test i >= res + IndexSetStride
383 // to i > res below, because i is unsigned and res may be zero.
384 for (size_t i = IndexSetSize - 1; i >= res + IndexSetStride;
385 i -= IndexSetStride) {
386 if (_indexedFreeList[i].head() != NULL) {
387 assert(_indexedFreeList[i].count() != 0, "Inconsistent FreeList");
388 return i;
389 }
390 }
391 return res;
392 }
393
394 void CompactibleFreeListSpace::reportFreeListStatistics() const {
395 assert_lock_strong(&_freelistLock);
396 assert(PrintFLSStatistics != 0, "Reporting error");
397 _dictionary->reportStatistics();
398 if (PrintFLSStatistics > 1) {
399 reportIndexedFreeListStatistics();
400 size_t totalSize = totalSizeInIndexedFreeLists() +
401 _dictionary->totalChunkSize(DEBUG_ONLY(freelistLock()));
402 gclog_or_tty->print(" free=%ld frag=%1.4f\n", totalSize, flsFrag());
403 }
404 }
405
406 void CompactibleFreeListSpace::reportIndexedFreeListStatistics() const {
407 assert_lock_strong(&_freelistLock);
408 gclog_or_tty->print("Statistics for IndexedFreeLists:\n"
409 "--------------------------------\n");
410 size_t totalSize = totalSizeInIndexedFreeLists();
411 size_t freeBlocks = numFreeBlocksInIndexedFreeLists();
412 gclog_or_tty->print("Total Free Space: %d\n", totalSize);
413 gclog_or_tty->print("Max Chunk Size: %d\n", maxChunkSizeInIndexedFreeLists());
414 gclog_or_tty->print("Number of Blocks: %d\n", freeBlocks);
415 if (freeBlocks != 0) {
416 gclog_or_tty->print("Av. Block Size: %d\n", totalSize/freeBlocks);
417 }
418 }
419
420 size_t CompactibleFreeListSpace::numFreeBlocksInIndexedFreeLists() const {
421 size_t res = 0;
422 for (size_t i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
423 debug_only(
424 ssize_t recount = 0;
425 for (FreeChunk* fc = _indexedFreeList[i].head(); fc != NULL;
426 fc = fc->next()) {
427 recount += 1;
428 }
429 assert(recount == _indexedFreeList[i].count(),
430 "Incorrect count in list");
431 )
432 res += _indexedFreeList[i].count();
433 }
434 return res;
435 }
436
437 size_t CompactibleFreeListSpace::maxChunkSizeInIndexedFreeLists() const {
438 for (size_t i = IndexSetSize - 1; i != 0; i -= IndexSetStride) {
439 if (_indexedFreeList[i].head() != NULL) {
440 assert(_indexedFreeList[i].count() != 0, "Inconsistent FreeList");
441 return (size_t)i;
442 }
443 }
444 return 0;
445 }
446
447 void CompactibleFreeListSpace::set_end(HeapWord* value) {
448 HeapWord* prevEnd = end();
449 assert(prevEnd != value, "unnecessary set_end call");
450 assert(prevEnd == NULL || value >= unallocated_block(), "New end is below unallocated block");
451 _end = value;
452 if (prevEnd != NULL) {
453 // Resize the underlying block offset table.
454 _bt.resize(pointer_delta(value, bottom()));
455 if (value <= prevEnd) {
456 assert(value >= unallocated_block(), "New end is below unallocated block");
457 } else {
458 // Now, take this new chunk and add it to the free blocks.
459 // Note that the BOT has not yet been updated for this block.
460 size_t newFcSize = pointer_delta(value, prevEnd);
461 // XXX This is REALLY UGLY and should be fixed up. XXX
462 if (!_adaptive_freelists && _smallLinearAllocBlock._ptr == NULL) {
463 // Mark the boundary of the new block in BOT
464 _bt.mark_block(prevEnd, value);
465 // put it all in the linAB
466 if (ParallelGCThreads == 0) {
467 _smallLinearAllocBlock._ptr = prevEnd;
468 _smallLinearAllocBlock._word_size = newFcSize;
469 repairLinearAllocBlock(&_smallLinearAllocBlock);
470 } else { // ParallelGCThreads > 0
471 MutexLockerEx x(parDictionaryAllocLock(),
472 Mutex::_no_safepoint_check_flag);
473 _smallLinearAllocBlock._ptr = prevEnd;
474 _smallLinearAllocBlock._word_size = newFcSize;
475 repairLinearAllocBlock(&_smallLinearAllocBlock);
476 }
477 // Births of chunks put into a LinAB are not recorded. Births
478 // of chunks as they are allocated out of a LinAB are.
479 } else {
480 // Add the block to the free lists, if possible coalescing it
481 // with the last free block, and update the BOT and census data.
482 addChunkToFreeListsAtEndRecordingStats(prevEnd, newFcSize);
483 }
484 }
485 }
486 }
487
488 class FreeListSpace_DCTOC : public Filtering_DCTOC {
489 CompactibleFreeListSpace* _cfls;
490 CMSCollector* _collector;
491 protected:
492 // Override.
493 #define walk_mem_region_with_cl_DECL(ClosureType) \
494 virtual void walk_mem_region_with_cl(MemRegion mr, \
495 HeapWord* bottom, HeapWord* top, \
496 ClosureType* cl); \
497 void walk_mem_region_with_cl_par(MemRegion mr, \
498 HeapWord* bottom, HeapWord* top, \
499 ClosureType* cl); \
500 void walk_mem_region_with_cl_nopar(MemRegion mr, \
501 HeapWord* bottom, HeapWord* top, \
502 ClosureType* cl)
503 walk_mem_region_with_cl_DECL(OopClosure);
504 walk_mem_region_with_cl_DECL(FilteringClosure);
505
506 public:
507 FreeListSpace_DCTOC(CompactibleFreeListSpace* sp,
508 CMSCollector* collector,
509 OopClosure* cl,
510 CardTableModRefBS::PrecisionStyle precision,
511 HeapWord* boundary) :
512 Filtering_DCTOC(sp, cl, precision, boundary),
513 _cfls(sp), _collector(collector) {}
514 };
515
516 // We de-virtualize the block-related calls below, since we know that our
517 // space is a CompactibleFreeListSpace.
518 #define FreeListSpace_DCTOC__walk_mem_region_with_cl_DEFN(ClosureType) \
519 void FreeListSpace_DCTOC::walk_mem_region_with_cl(MemRegion mr, \
520 HeapWord* bottom, \
521 HeapWord* top, \
522 ClosureType* cl) { \
523 if (SharedHeap::heap()->n_par_threads() > 0) { \
524 walk_mem_region_with_cl_par(mr, bottom, top, cl); \
525 } else { \
526 walk_mem_region_with_cl_nopar(mr, bottom, top, cl); \
527 } \
528 } \
529 void FreeListSpace_DCTOC::walk_mem_region_with_cl_par(MemRegion mr, \
530 HeapWord* bottom, \
531 HeapWord* top, \
532 ClosureType* cl) { \
533 /* Skip parts that are before "mr", in case "block_start" sent us \
534 back too far. */ \
535 HeapWord* mr_start = mr.start(); \
536 size_t bot_size = _cfls->CompactibleFreeListSpace::block_size(bottom); \
537 HeapWord* next = bottom + bot_size; \
538 while (next < mr_start) { \
539 bottom = next; \
540 bot_size = _cfls->CompactibleFreeListSpace::block_size(bottom); \
541 next = bottom + bot_size; \
542 } \
543 \
544 while (bottom < top) { \
545 if (_cfls->CompactibleFreeListSpace::block_is_obj(bottom) && \
546 !_cfls->CompactibleFreeListSpace::obj_allocated_since_save_marks( \
547 oop(bottom)) && \
548 !_collector->CMSCollector::is_dead_obj(oop(bottom))) { \
549 size_t word_sz = oop(bottom)->oop_iterate(cl, mr); \
550 bottom += _cfls->adjustObjectSize(word_sz); \
551 } else { \
552 bottom += _cfls->CompactibleFreeListSpace::block_size(bottom); \
553 } \
554 } \
555 } \
556 void FreeListSpace_DCTOC::walk_mem_region_with_cl_nopar(MemRegion mr, \
557 HeapWord* bottom, \
558 HeapWord* top, \
559 ClosureType* cl) { \
560 /* Skip parts that are before "mr", in case "block_start" sent us \
561 back too far. */ \
562 HeapWord* mr_start = mr.start(); \
563 size_t bot_size = _cfls->CompactibleFreeListSpace::block_size_nopar(bottom); \
564 HeapWord* next = bottom + bot_size; \
565 while (next < mr_start) { \
566 bottom = next; \
567 bot_size = _cfls->CompactibleFreeListSpace::block_size_nopar(bottom); \
568 next = bottom + bot_size; \
569 } \
570 \
571 while (bottom < top) { \
572 if (_cfls->CompactibleFreeListSpace::block_is_obj_nopar(bottom) && \
573 !_cfls->CompactibleFreeListSpace::obj_allocated_since_save_marks( \
574 oop(bottom)) && \
575 !_collector->CMSCollector::is_dead_obj(oop(bottom))) { \
576 size_t word_sz = oop(bottom)->oop_iterate(cl, mr); \
577 bottom += _cfls->adjustObjectSize(word_sz); \
578 } else { \
579 bottom += _cfls->CompactibleFreeListSpace::block_size_nopar(bottom); \
580 } \
581 } \
582 }
583
584 // (There are only two of these, rather than N, because the split is due
585 // only to the introduction of the FilteringClosure, a local part of the
586 // impl of this abstraction.)
587 FreeListSpace_DCTOC__walk_mem_region_with_cl_DEFN(OopClosure)
588 FreeListSpace_DCTOC__walk_mem_region_with_cl_DEFN(FilteringClosure)
589
590 DirtyCardToOopClosure*
591 CompactibleFreeListSpace::new_dcto_cl(OopClosure* cl,
592 CardTableModRefBS::PrecisionStyle precision,
593 HeapWord* boundary) {
594 return new FreeListSpace_DCTOC(this, _collector, cl, precision, boundary);
595 }
596
597
598 // Note on locking for the space iteration functions:
599 // since the collector's iteration activities are concurrent with
600 // allocation activities by mutators, absent a suitable mutual exclusion
601 // mechanism the iterators may go awry. For instace a block being iterated
602 // may suddenly be allocated or divided up and part of it allocated and
603 // so on.
604
605 // Apply the given closure to each block in the space.
606 void CompactibleFreeListSpace::blk_iterate_careful(BlkClosureCareful* cl) {
607 assert_lock_strong(freelistLock());
608 HeapWord *cur, *limit;
609 for (cur = bottom(), limit = end(); cur < limit;
610 cur += cl->do_blk_careful(cur));
611 }
612
613 // Apply the given closure to each block in the space.
614 void CompactibleFreeListSpace::blk_iterate(BlkClosure* cl) {
615 assert_lock_strong(freelistLock());
616 HeapWord *cur, *limit;
617 for (cur = bottom(), limit = end(); cur < limit;
618 cur += cl->do_blk(cur));
619 }
620
621 // Apply the given closure to each oop in the space.
622 void CompactibleFreeListSpace::oop_iterate(OopClosure* cl) {
623 assert_lock_strong(freelistLock());
624 HeapWord *cur, *limit;
625 size_t curSize;
626 for (cur = bottom(), limit = end(); cur < limit;
627 cur += curSize) {
628 curSize = block_size(cur);
629 if (block_is_obj(cur)) {
630 oop(cur)->oop_iterate(cl);
631 }
632 }
633 }
634
635 // Apply the given closure to each oop in the space \intersect memory region.
636 void CompactibleFreeListSpace::oop_iterate(MemRegion mr, OopClosure* cl) {
637 assert_lock_strong(freelistLock());
638 if (is_empty()) {
639 return;
640 }
641 MemRegion cur = MemRegion(bottom(), end());
642 mr = mr.intersection(cur);
643 if (mr.is_empty()) {
644 return;
645 }
646 if (mr.equals(cur)) {
647 oop_iterate(cl);
648 return;
649 }
650 assert(mr.end() <= end(), "just took an intersection above");
651 HeapWord* obj_addr = block_start(mr.start());
652 HeapWord* t = mr.end();
653
654 SpaceMemRegionOopsIterClosure smr_blk(cl, mr);
655 if (block_is_obj(obj_addr)) {
656 // Handle first object specially.
657 oop obj = oop(obj_addr);
658 obj_addr += adjustObjectSize(obj->oop_iterate(&smr_blk));
659 } else {
660 FreeChunk* fc = (FreeChunk*)obj_addr;
661 obj_addr += fc->size();
662 }
663 while (obj_addr < t) {
664 HeapWord* obj = obj_addr;
665 obj_addr += block_size(obj_addr);
666 // If "obj_addr" is not greater than top, then the
667 // entire object "obj" is within the region.
668 if (obj_addr <= t) {
669 if (block_is_obj(obj)) {
670 oop(obj)->oop_iterate(cl);
671 }
672 } else {
673 // "obj" extends beyond end of region
674 if (block_is_obj(obj)) {
675 oop(obj)->oop_iterate(&smr_blk);
676 }
677 break;
678 }
679 }
680 }
681
682 // NOTE: In the following methods, in order to safely be able to
683 // apply the closure to an object, we need to be sure that the
684 // object has been initialized. We are guaranteed that an object
685 // is initialized if we are holding the Heap_lock with the
686 // world stopped.
687 void CompactibleFreeListSpace::verify_objects_initialized() const {
688 if (is_init_completed()) {
689 assert_locked_or_safepoint(Heap_lock);
690 if (Universe::is_fully_initialized()) {
691 guarantee(SafepointSynchronize::is_at_safepoint(),
692 "Required for objects to be initialized");
693 }
694 } // else make a concession at vm start-up
695 }
696
697 // Apply the given closure to each object in the space
698 void CompactibleFreeListSpace::object_iterate(ObjectClosure* blk) {
699 assert_lock_strong(freelistLock());
700 NOT_PRODUCT(verify_objects_initialized());
701 HeapWord *cur, *limit;
702 size_t curSize;
703 for (cur = bottom(), limit = end(); cur < limit;
704 cur += curSize) {
705 curSize = block_size(cur);
706 if (block_is_obj(cur)) {
707 blk->do_object(oop(cur));
708 }
709 }
710 }
711
712 void CompactibleFreeListSpace::object_iterate_mem(MemRegion mr,
713 UpwardsObjectClosure* cl) {
714 assert_locked();
715 NOT_PRODUCT(verify_objects_initialized());
716 Space::object_iterate_mem(mr, cl);
717 }
718
719 // Callers of this iterator beware: The closure application should
720 // be robust in the face of uninitialized objects and should (always)
721 // return a correct size so that the next addr + size below gives us a
722 // valid block boundary. [See for instance,
723 // ScanMarkedObjectsAgainCarefullyClosure::do_object_careful()
724 // in ConcurrentMarkSweepGeneration.cpp.]
725 HeapWord*
726 CompactibleFreeListSpace::object_iterate_careful(ObjectClosureCareful* cl) {
727 assert_lock_strong(freelistLock());
728 HeapWord *addr, *last;
729 size_t size;
730 for (addr = bottom(), last = end();
731 addr < last; addr += size) {
732 FreeChunk* fc = (FreeChunk*)addr;
733 if (fc->isFree()) {
734 // Since we hold the free list lock, which protects direct
735 // allocation in this generation by mutators, a free object
736 // will remain free throughout this iteration code.
737 size = fc->size();
738 } else {
739 // Note that the object need not necessarily be initialized,
740 // because (for instance) the free list lock does NOT protect
741 // object initialization. The closure application below must
742 // therefore be correct in the face of uninitialized objects.
743 size = cl->do_object_careful(oop(addr));
744 if (size == 0) {
745 // An unparsable object found. Signal early termination.
746 return addr;
747 }
748 }
749 }
750 return NULL;
751 }
752
753 // Callers of this iterator beware: The closure application should
754 // be robust in the face of uninitialized objects and should (always)
755 // return a correct size so that the next addr + size below gives us a
756 // valid block boundary. [See for instance,
757 // ScanMarkedObjectsAgainCarefullyClosure::do_object_careful()
758 // in ConcurrentMarkSweepGeneration.cpp.]
759 HeapWord*
760 CompactibleFreeListSpace::object_iterate_careful_m(MemRegion mr,
761 ObjectClosureCareful* cl) {
762 assert_lock_strong(freelistLock());
763 // Can't use used_region() below because it may not necessarily
764 // be the same as [bottom(),end()); although we could
765 // use [used_region().start(),round_to(used_region().end(),CardSize)),
766 // that appears too cumbersome, so we just do the simpler check
767 // in the assertion below.
768 assert(!mr.is_empty() && MemRegion(bottom(),end()).contains(mr),
769 "mr should be non-empty and within used space");
770 HeapWord *addr, *end;
771 size_t size;
772 for (addr = block_start_careful(mr.start()), end = mr.end();
773 addr < end; addr += size) {
774 FreeChunk* fc = (FreeChunk*)addr;
775 if (fc->isFree()) {
776 // Since we hold the free list lock, which protects direct
777 // allocation in this generation by mutators, a free object
778 // will remain free throughout this iteration code.
779 size = fc->size();
780 } else {
781 // Note that the object need not necessarily be initialized,
782 // because (for instance) the free list lock does NOT protect
783 // object initialization. The closure application below must
784 // therefore be correct in the face of uninitialized objects.
785 size = cl->do_object_careful_m(oop(addr), mr);
786 if (size == 0) {
787 // An unparsable object found. Signal early termination.
788 return addr;
789 }
790 }
791 }
792 return NULL;
793 }
794
795
796 HeapWord* CompactibleFreeListSpace::block_start_const(const void* p) const {
797 NOT_PRODUCT(verify_objects_initialized());
798 return _bt.block_start(p);
799 }
800
801 HeapWord* CompactibleFreeListSpace::block_start_careful(const void* p) const {
802 return _bt.block_start_careful(p);
803 }
804
805 size_t CompactibleFreeListSpace::block_size(const HeapWord* p) const {
806 NOT_PRODUCT(verify_objects_initialized());
807 assert(MemRegion(bottom(), end()).contains(p), "p not in space");
808 // This must be volatile, or else there is a danger that the compiler
809 // will compile the code below into a sometimes-infinite loop, by keeping
810 // the value read the first time in a register.
811 while (true) {
812 // We must do this until we get a consistent view of the object.
813 if (FreeChunk::indicatesFreeChunk(p)) {
814 volatile FreeChunk* fc = (volatile FreeChunk*)p;
815 size_t res = fc->size();
816 // If the object is still a free chunk, return the size, else it
817 // has been allocated so try again.
818 if (FreeChunk::indicatesFreeChunk(p)) {
819 assert(res != 0, "Block size should not be 0");
820 return res;
821 }
822 } else {
823 // must read from what 'p' points to in each loop.
824 klassOop k = ((volatile oopDesc*)p)->klass_or_null();
825 if (k != NULL) {
826 assert(k->is_oop(true /* ignore mark word */), "Should really be klass oop.");
827 oop o = (oop)p;
828 assert(o->is_parsable(), "Should be parsable");
829 assert(o->is_oop(true /* ignore mark word */), "Should be an oop.");
830 size_t res = o->size_given_klass(k->klass_part());
831 res = adjustObjectSize(res);
832 assert(res != 0, "Block size should not be 0");
833 return res;
834 }
835 }
836 }
837 }
838
839 // A variant of the above that uses the Printezis bits for
840 // unparsable but allocated objects. This avoids any possible
841 // stalls waiting for mutators to initialize objects, and is
842 // thus potentially faster than the variant above. However,
843 // this variant may return a zero size for a block that is
844 // under mutation and for which a consistent size cannot be
845 // inferred without stalling; see CMSCollector::block_size_if_printezis_bits().
846 size_t CompactibleFreeListSpace::block_size_no_stall(HeapWord* p,
847 const CMSCollector* c)
848 const {
849 assert(MemRegion(bottom(), end()).contains(p), "p not in space");
850 // This must be volatile, or else there is a danger that the compiler
851 // will compile the code below into a sometimes-infinite loop, by keeping
852 // the value read the first time in a register.
853 DEBUG_ONLY(uint loops = 0;)
854 while (true) {
855 // We must do this until we get a consistent view of the object.
856 if (FreeChunk::indicatesFreeChunk(p)) {
857 volatile FreeChunk* fc = (volatile FreeChunk*)p;
858 size_t res = fc->size();
859 if (FreeChunk::indicatesFreeChunk(p)) {
860 assert(res != 0, "Block size should not be 0");
861 assert(loops == 0, "Should be 0");
862 return res;
863 }
864 } else {
865 // must read from what 'p' points to in each loop.
866 klassOop k = ((volatile oopDesc*)p)->klass_or_null();
867 if (k != NULL && ((oopDesc*)p)->is_parsable()) {
868 assert(k->is_oop(), "Should really be klass oop.");
869 oop o = (oop)p;
870 assert(o->is_oop(), "Should be an oop");
871 size_t res = o->size_given_klass(k->klass_part());
872 res = adjustObjectSize(res);
873 assert(res != 0, "Block size should not be 0");
874 return res;
875 } else {
876 return c->block_size_if_printezis_bits(p);
877 }
878 }
879 assert(loops == 0, "Can loop at most once");
880 DEBUG_ONLY(loops++;)
881 }
882 }
883
884 size_t CompactibleFreeListSpace::block_size_nopar(const HeapWord* p) const {
885 NOT_PRODUCT(verify_objects_initialized());
886 assert(MemRegion(bottom(), end()).contains(p), "p not in space");
887 FreeChunk* fc = (FreeChunk*)p;
888 if (fc->isFree()) {
889 return fc->size();
890 } else {
891 // Ignore mark word because this may be a recently promoted
892 // object whose mark word is used to chain together grey
893 // objects (the last one would have a null value).
894 assert(oop(p)->is_oop(true), "Should be an oop");
895 return adjustObjectSize(oop(p)->size());
896 }
897 }
898
899 // This implementation assumes that the property of "being an object" is
900 // stable. But being a free chunk may not be (because of parallel
901 // promotion.)
902 bool CompactibleFreeListSpace::block_is_obj(const HeapWord* p) const {
903 FreeChunk* fc = (FreeChunk*)p;
904 assert(is_in_reserved(p), "Should be in space");
905 // When doing a mark-sweep-compact of the CMS generation, this
906 // assertion may fail because prepare_for_compaction() uses
907 // space that is garbage to maintain information on ranges of
908 // live objects so that these live ranges can be moved as a whole.
909 // Comment out this assertion until that problem can be solved
910 // (i.e., that the block start calculation may look at objects
911 // at address below "p" in finding the object that contains "p"
912 // and those objects (if garbage) may have been modified to hold
913 // live range information.
914 // assert(ParallelGCThreads > 0 || _bt.block_start(p) == p, "Should be a block boundary");
915 if (FreeChunk::indicatesFreeChunk(p)) return false;
916 klassOop k = oop(p)->klass_or_null();
917 if (k != NULL) {
918 // Ignore mark word because it may have been used to
919 // chain together promoted objects (the last one
920 // would have a null value).
921 assert(oop(p)->is_oop(true), "Should be an oop");
922 return true;
923 } else {
924 return false; // Was not an object at the start of collection.
925 }
926 }
927
928 // Check if the object is alive. This fact is checked either by consulting
929 // the main marking bitmap in the sweeping phase or, if it's a permanent
930 // generation and we're not in the sweeping phase, by checking the
931 // perm_gen_verify_bit_map where we store the "deadness" information if
932 // we did not sweep the perm gen in the most recent previous GC cycle.
933 bool CompactibleFreeListSpace::obj_is_alive(const HeapWord* p) const {
934 assert (block_is_obj(p), "The address should point to an object");
935
936 // If we're sweeping, we use object liveness information from the main bit map
937 // for both perm gen and old gen.
938 // We don't need to lock the bitmap (live_map or dead_map below), because
939 // EITHER we are in the middle of the sweeping phase, and the
940 // main marking bit map (live_map below) is locked,
941 // OR we're in other phases and perm_gen_verify_bit_map (dead_map below)
942 // is stable, because it's mutated only in the sweeping phase.
943 if (_collector->abstract_state() == CMSCollector::Sweeping) {
944 CMSBitMap* live_map = _collector->markBitMap();
945 return live_map->isMarked((HeapWord*) p);
946 } else {
947 // If we're not currently sweeping and we haven't swept the perm gen in
948 // the previous concurrent cycle then we may have dead but unswept objects
949 // in the perm gen. In this case, we use the "deadness" information
950 // that we had saved in perm_gen_verify_bit_map at the last sweep.
951 if (!CMSClassUnloadingEnabled && _collector->_permGen->reserved().contains(p)) {
952 if (_collector->verifying()) {
953 CMSBitMap* dead_map = _collector->perm_gen_verify_bit_map();
954 // Object is marked in the dead_map bitmap at the previous sweep
955 // when we know that it's dead; if the bitmap is not allocated then
956 // the object is alive.
957 return (dead_map->sizeInBits() == 0) // bit_map has been allocated
958 || !dead_map->par_isMarked((HeapWord*) p);
959 } else {
960 return false; // We can't say for sure if it's live, so we say that it's dead.
961 }
962 }
963 }
964 return true;
965 }
966
967 bool CompactibleFreeListSpace::block_is_obj_nopar(const HeapWord* p) const {
968 FreeChunk* fc = (FreeChunk*)p;
969 assert(is_in_reserved(p), "Should be in space");
970 assert(_bt.block_start(p) == p, "Should be a block boundary");
971 if (!fc->isFree()) {
972 // Ignore mark word because it may have been used to
973 // chain together promoted objects (the last one
974 // would have a null value).
975 assert(oop(p)->is_oop(true), "Should be an oop");
976 return true;
977 }
978 return false;
979 }
980
981 // "MT-safe but not guaranteed MT-precise" (TM); you may get an
982 // approximate answer if you don't hold the freelistlock when you call this.
983 size_t CompactibleFreeListSpace::totalSizeInIndexedFreeLists() const {
984 size_t size = 0;
985 for (size_t i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
986 debug_only(
987 // We may be calling here without the lock in which case we
988 // won't do this modest sanity check.
989 if (freelistLock()->owned_by_self()) {
990 size_t total_list_size = 0;
991 for (FreeChunk* fc = _indexedFreeList[i].head(); fc != NULL;
992 fc = fc->next()) {
993 total_list_size += i;
994 }
995 assert(total_list_size == i * _indexedFreeList[i].count(),
996 "Count in list is incorrect");
997 }
998 )
999 size += i * _indexedFreeList[i].count();
1000 }
1001 return size;
1002 }
1003
1004 HeapWord* CompactibleFreeListSpace::par_allocate(size_t size) {
1005 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
1006 return allocate(size);
1007 }
1008
1009 HeapWord*
1010 CompactibleFreeListSpace::getChunkFromSmallLinearAllocBlockRemainder(size_t size) {
1011 return getChunkFromLinearAllocBlockRemainder(&_smallLinearAllocBlock, size);
1012 }
1013
1014 HeapWord* CompactibleFreeListSpace::allocate(size_t size) {
1015 assert_lock_strong(freelistLock());
1016 HeapWord* res = NULL;
1017 assert(size == adjustObjectSize(size),
1018 "use adjustObjectSize() before calling into allocate()");
1019
1020 if (_adaptive_freelists) {
1021 res = allocate_adaptive_freelists(size);
1022 } else { // non-adaptive free lists
1023 res = allocate_non_adaptive_freelists(size);
1024 }
1025
1026 if (res != NULL) {
1027 // check that res does lie in this space!
1028 assert(is_in_reserved(res), "Not in this space!");
1029 assert(is_aligned((void*)res), "alignment check");
1030
1031 FreeChunk* fc = (FreeChunk*)res;
1032 fc->markNotFree();
1033 assert(!fc->isFree(), "shouldn't be marked free");
1034 assert(oop(fc)->klass_or_null() == NULL, "should look uninitialized");
1035 // Verify that the block offset table shows this to
1036 // be a single block, but not one which is unallocated.
1037 _bt.verify_single_block(res, size);
1038 _bt.verify_not_unallocated(res, size);
1039 // mangle a just allocated object with a distinct pattern.
1040 debug_only(fc->mangleAllocated(size));
1041 }
1042
1043 return res;
1044 }
1045
1046 HeapWord* CompactibleFreeListSpace::allocate_non_adaptive_freelists(size_t size) {
1047 HeapWord* res = NULL;
1048 // try and use linear allocation for smaller blocks
1049 if (size < _smallLinearAllocBlock._allocation_size_limit) {
1050 // if successful, the following also adjusts block offset table
1051 res = getChunkFromSmallLinearAllocBlock(size);
1052 }
1053 // Else triage to indexed lists for smaller sizes
1054 if (res == NULL) {
1055 if (size < SmallForDictionary) {
1056 res = (HeapWord*) getChunkFromIndexedFreeList(size);
1057 } else {
1058 // else get it from the big dictionary; if even this doesn't
1059 // work we are out of luck.
1060 res = (HeapWord*)getChunkFromDictionaryExact(size);
1061 }
1062 }
1063
1064 return res;
1065 }
1066
1067 HeapWord* CompactibleFreeListSpace::allocate_adaptive_freelists(size_t size) {
1068 assert_lock_strong(freelistLock());
1069 HeapWord* res = NULL;
1070 assert(size == adjustObjectSize(size),
1071 "use adjustObjectSize() before calling into allocate()");
1072
1073 // Strategy
1074 // if small
1075 // exact size from small object indexed list if small
1076 // small or large linear allocation block (linAB) as appropriate
1077 // take from lists of greater sized chunks
1078 // else
1079 // dictionary
1080 // small or large linear allocation block if it has the space
1081 // Try allocating exact size from indexTable first
1082 if (size < IndexSetSize) {
1083 res = (HeapWord*) getChunkFromIndexedFreeList(size);
1084 if(res != NULL) {
1085 assert(res != (HeapWord*)_indexedFreeList[size].head(),
1086 "Not removed from free list");
1087 // no block offset table adjustment is necessary on blocks in
1088 // the indexed lists.
1089
1090 // Try allocating from the small LinAB
1091 } else if (size < _smallLinearAllocBlock._allocation_size_limit &&
1092 (res = getChunkFromSmallLinearAllocBlock(size)) != NULL) {
1093 // if successful, the above also adjusts block offset table
1094 // Note that this call will refill the LinAB to
1095 // satisfy the request. This is different that
1096 // evm.
1097 // Don't record chunk off a LinAB? smallSplitBirth(size);
1098
1099 } else {
1100 // Raid the exact free lists larger than size, even if they are not
1101 // overpopulated.
1102 res = (HeapWord*) getChunkFromGreater(size);
1103 }
1104 } else {
1105 // Big objects get allocated directly from the dictionary.
1106 res = (HeapWord*) getChunkFromDictionaryExact(size);
1107 if (res == NULL) {
1108 // Try hard not to fail since an allocation failure will likely
1109 // trigger a synchronous GC. Try to get the space from the
1110 // allocation blocks.
1111 res = getChunkFromSmallLinearAllocBlockRemainder(size);
1112 }
1113 }
1114
1115 return res;
1116 }
1117
1118 // A worst-case estimate of the space required (in HeapWords) to expand the heap
1119 // when promoting obj.
1120 size_t CompactibleFreeListSpace::expansionSpaceRequired(size_t obj_size) const {
1121 // Depending on the object size, expansion may require refilling either a
1122 // bigLAB or a smallLAB plus refilling a PromotionInfo object. MinChunkSize
1123 // is added because the dictionary may over-allocate to avoid fragmentation.
1124 size_t space = obj_size;
1125 if (!_adaptive_freelists) {
1126 space = MAX2(space, _smallLinearAllocBlock._refillSize);
1127 }
1128 space += _promoInfo.refillSize() + 2 * MinChunkSize;
1129 return space;
1130 }
1131
1132 FreeChunk* CompactibleFreeListSpace::getChunkFromGreater(size_t numWords) {
1133 FreeChunk* ret;
1134
1135 assert(numWords >= MinChunkSize, "Size is less than minimum");
1136 assert(linearAllocationWouldFail() || bestFitFirst(),
1137 "Should not be here");
1138
1139 size_t i;
1140 size_t currSize = numWords + MinChunkSize;
1141 assert(currSize % MinObjAlignment == 0, "currSize should be aligned");
1142 for (i = currSize; i < IndexSetSize; i += IndexSetStride) {
1143 FreeList* fl = &_indexedFreeList[i];
1144 if (fl->head()) {
1145 ret = getFromListGreater(fl, numWords);
1146 assert(ret == NULL || ret->isFree(), "Should be returning a free chunk");
1147 return ret;
1148 }
1149 }
1150
1151 currSize = MAX2((size_t)SmallForDictionary,
1152 (size_t)(numWords + MinChunkSize));
1153
1154 /* Try to get a chunk that satisfies request, while avoiding
1155 fragmentation that can't be handled. */
1156 {
1157 ret = dictionary()->getChunk(currSize);
1158 if (ret != NULL) {
1159 assert(ret->size() - numWords >= MinChunkSize,
1160 "Chunk is too small");
1161 _bt.allocated((HeapWord*)ret, ret->size());
1162 /* Carve returned chunk. */
1163 (void) splitChunkAndReturnRemainder(ret, numWords);
1164 /* Label this as no longer a free chunk. */
1165 assert(ret->isFree(), "This chunk should be free");
1166 ret->linkPrev(NULL);
1167 }
1168 assert(ret == NULL || ret->isFree(), "Should be returning a free chunk");
1169 return ret;
1170 }
1171 ShouldNotReachHere();
1172 }
1173
1174 bool CompactibleFreeListSpace::verifyChunkInIndexedFreeLists(FreeChunk* fc)
1175 const {
1176 assert(fc->size() < IndexSetSize, "Size of chunk is too large");
1177 return _indexedFreeList[fc->size()].verifyChunkInFreeLists(fc);
1178 }
1179
1180 bool CompactibleFreeListSpace::verifyChunkInFreeLists(FreeChunk* fc) const {
1181 if (fc->size() >= IndexSetSize) {
1182 return dictionary()->verifyChunkInFreeLists(fc);
1183 } else {
1184 return verifyChunkInIndexedFreeLists(fc);
1185 }
1186 }
1187
1188 #ifndef PRODUCT
1189 void CompactibleFreeListSpace::assert_locked() const {
1190 CMSLockVerifier::assert_locked(freelistLock(), parDictionaryAllocLock());
1191 }
1192 #endif
1193
1194 FreeChunk* CompactibleFreeListSpace::allocateScratch(size_t size) {
1195 // In the parallel case, the main thread holds the free list lock
1196 // on behalf the parallel threads.
1197 assert_locked();
1198 FreeChunk* fc;
1199 {
1200 // If GC is parallel, this might be called by several threads.
1201 // This should be rare enough that the locking overhead won't affect
1202 // the sequential code.
1203 MutexLockerEx x(parDictionaryAllocLock(),
1204 Mutex::_no_safepoint_check_flag);
1205 fc = getChunkFromDictionary(size);
1206 }
1207 if (fc != NULL) {
1208 fc->dontCoalesce();
1209 assert(fc->isFree(), "Should be free, but not coalescable");
1210 // Verify that the block offset table shows this to
1211 // be a single block, but not one which is unallocated.
1212 _bt.verify_single_block((HeapWord*)fc, fc->size());
1213 _bt.verify_not_unallocated((HeapWord*)fc, fc->size());
1214 }
1215 return fc;
1216 }
1217
1218 oop CompactibleFreeListSpace::promote(oop obj, size_t obj_size) {
1219 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1220 assert_locked();
1221
1222 // if we are tracking promotions, then first ensure space for
1223 // promotion (including spooling space for saving header if necessary).
1224 // then allocate and copy, then track promoted info if needed.
1225 // When tracking (see PromotionInfo::track()), the mark word may
1226 // be displaced and in this case restoration of the mark word
1227 // occurs in the (oop_since_save_marks_)iterate phase.
1228 if (_promoInfo.tracking() && !_promoInfo.ensure_spooling_space()) {
1229 return NULL;
1230 }
1231 // Call the allocate(size_t, bool) form directly to avoid the
1232 // additional call through the allocate(size_t) form. Having
1233 // the compile inline the call is problematic because allocate(size_t)
1234 // is a virtual method.
1235 HeapWord* res = allocate(adjustObjectSize(obj_size));
1236 if (res != NULL) {
1237 Copy::aligned_disjoint_words((HeapWord*)obj, res, obj_size);
1238 // if we should be tracking promotions, do so.
1239 if (_promoInfo.tracking()) {
1240 _promoInfo.track((PromotedObject*)res);
1241 }
1242 }
1243 return oop(res);
1244 }
1245
1246 HeapWord*
1247 CompactibleFreeListSpace::getChunkFromSmallLinearAllocBlock(size_t size) {
1248 assert_locked();
1249 assert(size >= MinChunkSize, "minimum chunk size");
1250 assert(size < _smallLinearAllocBlock._allocation_size_limit,
1251 "maximum from smallLinearAllocBlock");
1252 return getChunkFromLinearAllocBlock(&_smallLinearAllocBlock, size);
1253 }
1254
1255 HeapWord*
1256 CompactibleFreeListSpace::getChunkFromLinearAllocBlock(LinearAllocBlock *blk,
1257 size_t size) {
1258 assert_locked();
1259 assert(size >= MinChunkSize, "too small");
1260 HeapWord* res = NULL;
1261 // Try to do linear allocation from blk, making sure that
1262 if (blk->_word_size == 0) {
1263 // We have probably been unable to fill this either in the prologue or
1264 // when it was exhausted at the last linear allocation. Bail out until
1265 // next time.
1266 assert(blk->_ptr == NULL, "consistency check");
1267 return NULL;
1268 }
1269 assert(blk->_word_size != 0 && blk->_ptr != NULL, "consistency check");
1270 res = getChunkFromLinearAllocBlockRemainder(blk, size);
1271 if (res != NULL) return res;
1272
1273 // about to exhaust this linear allocation block
1274 if (blk->_word_size == size) { // exactly satisfied
1275 res = blk->_ptr;
1276 _bt.allocated(res, blk->_word_size);
1277 } else if (size + MinChunkSize <= blk->_refillSize) {
1278 // Update _unallocated_block if the size is such that chunk would be
1279 // returned to the indexed free list. All other chunks in the indexed
1280 // free lists are allocated from the dictionary so that _unallocated_block
1281 // has already been adjusted for them. Do it here so that the cost
1282 // for all chunks added back to the indexed free lists.
1283 if (blk->_word_size < SmallForDictionary) {
1284 _bt.allocated(blk->_ptr, blk->_word_size);
1285 }
1286 // Return the chunk that isn't big enough, and then refill below.
1287 addChunkToFreeLists(blk->_ptr, blk->_word_size);
1288 _bt.verify_single_block(blk->_ptr, (blk->_ptr + blk->_word_size));
1289 // Don't keep statistics on adding back chunk from a LinAB.
1290 } else {
1291 // A refilled block would not satisfy the request.
1292 return NULL;
1293 }
1294
1295 blk->_ptr = NULL; blk->_word_size = 0;
1296 refillLinearAllocBlock(blk);
1297 assert(blk->_ptr == NULL || blk->_word_size >= size + MinChunkSize,
1298 "block was replenished");
1299 if (res != NULL) {
1300 splitBirth(size);
1301 repairLinearAllocBlock(blk);
1302 } else if (blk->_ptr != NULL) {
1303 res = blk->_ptr;
1304 size_t blk_size = blk->_word_size;
1305 blk->_word_size -= size;
1306 blk->_ptr += size;
1307 splitBirth(size);
1308 repairLinearAllocBlock(blk);
1309 // Update BOT last so that other (parallel) GC threads see a consistent
1310 // view of the BOT and free blocks.
1311 // Above must occur before BOT is updated below.
1312 _bt.split_block(res, blk_size, size); // adjust block offset table
1313 }
1314 return res;
1315 }
1316
1317 HeapWord* CompactibleFreeListSpace::getChunkFromLinearAllocBlockRemainder(
1318 LinearAllocBlock* blk,
1319 size_t size) {
1320 assert_locked();
1321 assert(size >= MinChunkSize, "too small");
1322
1323 HeapWord* res = NULL;
1324 // This is the common case. Keep it simple.
1325 if (blk->_word_size >= size + MinChunkSize) {
1326 assert(blk->_ptr != NULL, "consistency check");
1327 res = blk->_ptr;
1328 // Note that the BOT is up-to-date for the linAB before allocation. It
1329 // indicates the start of the linAB. The split_block() updates the
1330 // BOT for the linAB after the allocation (indicates the start of the
1331 // next chunk to be allocated).
1332 size_t blk_size = blk->_word_size;
1333 blk->_word_size -= size;
1334 blk->_ptr += size;
1335 splitBirth(size);
1336 repairLinearAllocBlock(blk);
1337 // Update BOT last so that other (parallel) GC threads see a consistent
1338 // view of the BOT and free blocks.
1339 // Above must occur before BOT is updated below.
1340 _bt.split_block(res, blk_size, size); // adjust block offset table
1341 _bt.allocated(res, size);
1342 }
1343 return res;
1344 }
1345
1346 FreeChunk*
1347 CompactibleFreeListSpace::getChunkFromIndexedFreeList(size_t size) {
1348 assert_locked();
1349 assert(size < SmallForDictionary, "just checking");
1350 FreeChunk* res;
1351 res = _indexedFreeList[size].getChunkAtHead();
1352 if (res == NULL) {
1353 res = getChunkFromIndexedFreeListHelper(size);
1354 }
1355 _bt.verify_not_unallocated((HeapWord*) res, size);
1356 return res;
1357 }
1358
1359 FreeChunk*
1360 CompactibleFreeListSpace::getChunkFromIndexedFreeListHelper(size_t size) {
1361 assert_locked();
1362 FreeChunk* fc = NULL;
1363 if (size < SmallForDictionary) {
1364 assert(_indexedFreeList[size].head() == NULL ||
1365 _indexedFreeList[size].surplus() <= 0,
1366 "List for this size should be empty or under populated");
1367 // Try best fit in exact lists before replenishing the list
1368 if (!bestFitFirst() || (fc = bestFitSmall(size)) == NULL) {
1369 // Replenish list.
1370 //
1371 // Things tried that failed.
1372 // Tried allocating out of the two LinAB's first before
1373 // replenishing lists.
1374 // Tried small linAB of size 256 (size in indexed list)
1375 // and replenishing indexed lists from the small linAB.
1376 //
1377 FreeChunk* newFc = NULL;
1378 size_t replenish_size = CMSIndexedFreeListReplenish * size;
1379 if (replenish_size < SmallForDictionary) {
1380 // Do not replenish from an underpopulated size.
1381 if (_indexedFreeList[replenish_size].surplus() > 0 &&
1382 _indexedFreeList[replenish_size].head() != NULL) {
1383 newFc =
1384 _indexedFreeList[replenish_size].getChunkAtHead();
1385 } else {
1386 newFc = bestFitSmall(replenish_size);
1387 }
1388 }
1389 if (newFc != NULL) {
1390 splitDeath(replenish_size);
1391 } else if (replenish_size > size) {
1392 assert(CMSIndexedFreeListReplenish > 1, "ctl pt invariant");
1393 newFc =
1394 getChunkFromIndexedFreeListHelper(replenish_size);
1395 }
1396 if (newFc != NULL) {
1397 assert(newFc->size() == replenish_size, "Got wrong size");
1398 size_t i;
1399 FreeChunk *curFc, *nextFc;
1400 // carve up and link blocks 0, ..., CMSIndexedFreeListReplenish - 2
1401 // The last chunk is not added to the lists but is returned as the
1402 // free chunk.
1403 for (curFc = newFc, nextFc = (FreeChunk*)((HeapWord*)curFc + size),
1404 i = 0;
1405 i < (CMSIndexedFreeListReplenish - 1);
1406 curFc = nextFc, nextFc = (FreeChunk*)((HeapWord*)nextFc + size),
1407 i++) {
1408 curFc->setSize(size);
1409 // Don't record this as a return in order to try and
1410 // determine the "returns" from a GC.
1411 _bt.verify_not_unallocated((HeapWord*) fc, size);
1412 _indexedFreeList[size].returnChunkAtTail(curFc, false);
1413 _bt.mark_block((HeapWord*)curFc, size);
1414 splitBirth(size);
1415 // Don't record the initial population of the indexed list
1416 // as a split birth.
1417 }
1418
1419 // check that the arithmetic was OK above
1420 assert((HeapWord*)nextFc == (HeapWord*)newFc + replenish_size,
1421 "inconsistency in carving newFc");
1422 curFc->setSize(size);
1423 _bt.mark_block((HeapWord*)curFc, size);
1424 splitBirth(size);
1425 return curFc;
1426 }
1427 }
1428 } else {
1429 // Get a free chunk from the free chunk dictionary to be returned to
1430 // replenish the indexed free list.
1431 fc = getChunkFromDictionaryExact(size);
1432 }
1433 assert(fc == NULL || fc->isFree(), "Should be returning a free chunk");
1434 return fc;
1435 }
1436
1437 FreeChunk*
1438 CompactibleFreeListSpace::getChunkFromDictionary(size_t size) {
1439 assert_locked();
1440 FreeChunk* fc = _dictionary->getChunk(size);
1441 if (fc == NULL) {
1442 return NULL;
1443 }
1444 _bt.allocated((HeapWord*)fc, fc->size());
1445 if (fc->size() >= size + MinChunkSize) {
1446 fc = splitChunkAndReturnRemainder(fc, size);
1447 }
1448 assert(fc->size() >= size, "chunk too small");
1449 assert(fc->size() < size + MinChunkSize, "chunk too big");
1450 _bt.verify_single_block((HeapWord*)fc, fc->size());
1451 return fc;
1452 }
1453
1454 FreeChunk*
1455 CompactibleFreeListSpace::getChunkFromDictionaryExact(size_t size) {
1456 assert_locked();
1457 FreeChunk* fc = _dictionary->getChunk(size);
1458 if (fc == NULL) {
1459 return fc;
1460 }
1461 _bt.allocated((HeapWord*)fc, fc->size());
1462 if (fc->size() == size) {
1463 _bt.verify_single_block((HeapWord*)fc, size);
1464 return fc;
1465 }
1466 assert(fc->size() > size, "getChunk() guarantee");
1467 if (fc->size() < size + MinChunkSize) {
1468 // Return the chunk to the dictionary and go get a bigger one.
1469 returnChunkToDictionary(fc);
1470 fc = _dictionary->getChunk(size + MinChunkSize);
1471 if (fc == NULL) {
1472 return NULL;
1473 }
1474 _bt.allocated((HeapWord*)fc, fc->size());
1475 }
1476 assert(fc->size() >= size + MinChunkSize, "tautology");
1477 fc = splitChunkAndReturnRemainder(fc, size);
1478 assert(fc->size() == size, "chunk is wrong size");
1479 _bt.verify_single_block((HeapWord*)fc, size);
1480 return fc;
1481 }
1482
1483 void
1484 CompactibleFreeListSpace::returnChunkToDictionary(FreeChunk* chunk) {
1485 assert_locked();
1486
1487 size_t size = chunk->size();
1488 _bt.verify_single_block((HeapWord*)chunk, size);
1489 // adjust _unallocated_block downward, as necessary
1490 _bt.freed((HeapWord*)chunk, size);
1491 _dictionary->returnChunk(chunk);
1492 }
1493
1494 void
1495 CompactibleFreeListSpace::returnChunkToFreeList(FreeChunk* fc) {
1496 assert_locked();
1497 size_t size = fc->size();
1498 _bt.verify_single_block((HeapWord*) fc, size);
1499 _bt.verify_not_unallocated((HeapWord*) fc, size);
1500 if (_adaptive_freelists) {
1501 _indexedFreeList[size].returnChunkAtTail(fc);
1502 } else {
1503 _indexedFreeList[size].returnChunkAtHead(fc);
1504 }
1505 }
1506
1507 // Add chunk to end of last block -- if it's the largest
1508 // block -- and update BOT and census data. We would
1509 // of course have preferred to coalesce it with the
1510 // last block, but it's currently less expensive to find the
1511 // largest block than it is to find the last.
1512 void
1513 CompactibleFreeListSpace::addChunkToFreeListsAtEndRecordingStats(
1514 HeapWord* chunk, size_t size) {
1515 // check that the chunk does lie in this space!
1516 assert(chunk != NULL && is_in_reserved(chunk), "Not in this space!");
1517 assert_locked();
1518 // One of the parallel gc task threads may be here
1519 // whilst others are allocating.
1520 Mutex* lock = NULL;
1521 if (ParallelGCThreads != 0) {
1522 lock = &_parDictionaryAllocLock;
1523 }
1524 FreeChunk* ec;
1525 {
1526 MutexLockerEx x(lock, Mutex::_no_safepoint_check_flag);
1527 ec = dictionary()->findLargestDict(); // get largest block
1528 if (ec != NULL && ec->end() == chunk) {
1529 // It's a coterminal block - we can coalesce.
1530 size_t old_size = ec->size();
1531 coalDeath(old_size);
1532 removeChunkFromDictionary(ec);
1533 size += old_size;
1534 } else {
1535 ec = (FreeChunk*)chunk;
1536 }
1537 }
1538 ec->setSize(size);
1539 debug_only(ec->mangleFreed(size));
1540 if (size < SmallForDictionary) {
1541 lock = _indexedFreeListParLocks[size];
1542 }
1543 MutexLockerEx x(lock, Mutex::_no_safepoint_check_flag);
1544 addChunkAndRepairOffsetTable((HeapWord*)ec, size, true);
1545 // record the birth under the lock since the recording involves
1546 // manipulation of the list on which the chunk lives and
1547 // if the chunk is allocated and is the last on the list,
1548 // the list can go away.
1549 coalBirth(size);
1550 }
1551
1552 void
1553 CompactibleFreeListSpace::addChunkToFreeLists(HeapWord* chunk,
1554 size_t size) {
1555 // check that the chunk does lie in this space!
1556 assert(chunk != NULL && is_in_reserved(chunk), "Not in this space!");
1557 assert_locked();
1558 _bt.verify_single_block(chunk, size);
1559
1560 FreeChunk* fc = (FreeChunk*) chunk;
1561 fc->setSize(size);
1562 debug_only(fc->mangleFreed(size));
1563 if (size < SmallForDictionary) {
1564 returnChunkToFreeList(fc);
1565 } else {
1566 returnChunkToDictionary(fc);
1567 }
1568 }
1569
1570 void
1571 CompactibleFreeListSpace::addChunkAndRepairOffsetTable(HeapWord* chunk,
1572 size_t size, bool coalesced) {
1573 assert_locked();
1574 assert(chunk != NULL, "null chunk");
1575 if (coalesced) {
1576 // repair BOT
1577 _bt.single_block(chunk, size);
1578 }
1579 addChunkToFreeLists(chunk, size);
1580 }
1581
1582 // We _must_ find the purported chunk on our free lists;
1583 // we assert if we don't.
1584 void
1585 CompactibleFreeListSpace::removeFreeChunkFromFreeLists(FreeChunk* fc) {
1586 size_t size = fc->size();
1587 assert_locked();
1588 debug_only(verifyFreeLists());
1589 if (size < SmallForDictionary) {
1590 removeChunkFromIndexedFreeList(fc);
1591 } else {
1592 removeChunkFromDictionary(fc);
1593 }
1594 _bt.verify_single_block((HeapWord*)fc, size);
1595 debug_only(verifyFreeLists());
1596 }
1597
1598 void
1599 CompactibleFreeListSpace::removeChunkFromDictionary(FreeChunk* fc) {
1600 size_t size = fc->size();
1601 assert_locked();
1602 assert(fc != NULL, "null chunk");
1603 _bt.verify_single_block((HeapWord*)fc, size);
1604 _dictionary->removeChunk(fc);
1605 // adjust _unallocated_block upward, as necessary
1606 _bt.allocated((HeapWord*)fc, size);
1607 }
1608
1609 void
1610 CompactibleFreeListSpace::removeChunkFromIndexedFreeList(FreeChunk* fc) {
1611 assert_locked();
1612 size_t size = fc->size();
1613 _bt.verify_single_block((HeapWord*)fc, size);
1614 NOT_PRODUCT(
1615 if (FLSVerifyIndexTable) {
1616 verifyIndexedFreeList(size);
1617 }
1618 )
1619 _indexedFreeList[size].removeChunk(fc);
1620 debug_only(fc->clearNext());
1621 debug_only(fc->clearPrev());
1622 NOT_PRODUCT(
1623 if (FLSVerifyIndexTable) {
1624 verifyIndexedFreeList(size);
1625 }
1626 )
1627 }
1628
1629 FreeChunk* CompactibleFreeListSpace::bestFitSmall(size_t numWords) {
1630 /* A hint is the next larger size that has a surplus.
1631 Start search at a size large enough to guarantee that
1632 the excess is >= MIN_CHUNK. */
1633 size_t start = align_object_size(numWords + MinChunkSize);
1634 if (start < IndexSetSize) {
1635 FreeList* it = _indexedFreeList;
1636 size_t hint = _indexedFreeList[start].hint();
1637 while (hint < IndexSetSize) {
1638 assert(hint % MinObjAlignment == 0, "hint should be aligned");
1639 FreeList *fl = &_indexedFreeList[hint];
1640 if (fl->surplus() > 0 && fl->head() != NULL) {
1641 // Found a list with surplus, reset original hint
1642 // and split out a free chunk which is returned.
1643 _indexedFreeList[start].set_hint(hint);
1644 FreeChunk* res = getFromListGreater(fl, numWords);
1645 assert(res == NULL || res->isFree(),
1646 "Should be returning a free chunk");
1647 return res;
1648 }
1649 hint = fl->hint(); /* keep looking */
1650 }
1651 /* None found. */
1652 it[start].set_hint(IndexSetSize);
1653 }
1654 return NULL;
1655 }
1656
1657 /* Requires fl->size >= numWords + MinChunkSize */
1658 FreeChunk* CompactibleFreeListSpace::getFromListGreater(FreeList* fl,
1659 size_t numWords) {
1660 FreeChunk *curr = fl->head();
1661 size_t oldNumWords = curr->size();
1662 assert(numWords >= MinChunkSize, "Word size is too small");
1663 assert(curr != NULL, "List is empty");
1664 assert(oldNumWords >= numWords + MinChunkSize,
1665 "Size of chunks in the list is too small");
1666
1667 fl->removeChunk(curr);
1668 // recorded indirectly by splitChunkAndReturnRemainder -
1669 // smallSplit(oldNumWords, numWords);
1670 FreeChunk* new_chunk = splitChunkAndReturnRemainder(curr, numWords);
1671 // Does anything have to be done for the remainder in terms of
1672 // fixing the card table?
1673 assert(new_chunk == NULL || new_chunk->isFree(),
1674 "Should be returning a free chunk");
1675 return new_chunk;
1676 }
1677
1678 FreeChunk*
1679 CompactibleFreeListSpace::splitChunkAndReturnRemainder(FreeChunk* chunk,
1680 size_t new_size) {
1681 assert_locked();
1682 size_t size = chunk->size();
1683 assert(size > new_size, "Split from a smaller block?");
1684 assert(is_aligned(chunk), "alignment problem");
1685 assert(size == adjustObjectSize(size), "alignment problem");
1686 size_t rem_size = size - new_size;
1687 assert(rem_size == adjustObjectSize(rem_size), "alignment problem");
1688 assert(rem_size >= MinChunkSize, "Free chunk smaller than minimum");
1689 FreeChunk* ffc = (FreeChunk*)((HeapWord*)chunk + new_size);
1690 assert(is_aligned(ffc), "alignment problem");
1691 ffc->setSize(rem_size);
1692 ffc->linkNext(NULL);
1693 ffc->linkPrev(NULL); // Mark as a free block for other (parallel) GC threads.
1694 // Above must occur before BOT is updated below.
1695 // adjust block offset table
1696 _bt.split_block((HeapWord*)chunk, chunk->size(), new_size);
1697 if (rem_size < SmallForDictionary) {
1698 bool is_par = (SharedHeap::heap()->n_par_threads() > 0);
1699 if (is_par) _indexedFreeListParLocks[rem_size]->lock();
1700 returnChunkToFreeList(ffc);
1701 split(size, rem_size);
1702 if (is_par) _indexedFreeListParLocks[rem_size]->unlock();
1703 } else {
1704 returnChunkToDictionary(ffc);
1705 split(size ,rem_size);
1706 }
1707 chunk->setSize(new_size);
1708 return chunk;
1709 }
1710
1711 void
1712 CompactibleFreeListSpace::sweep_completed() {
1713 // Now that space is probably plentiful, refill linear
1714 // allocation blocks as needed.
1715 refillLinearAllocBlocksIfNeeded();
1716 }
1717
1718 void
1719 CompactibleFreeListSpace::gc_prologue() {
1720 assert_locked();
1721 if (PrintFLSStatistics != 0) {
1722 gclog_or_tty->print("Before GC:\n");
1723 reportFreeListStatistics();
1724 }
1725 refillLinearAllocBlocksIfNeeded();
1726 }
1727
1728 void
1729 CompactibleFreeListSpace::gc_epilogue() {
1730 assert_locked();
1731 if (PrintGCDetails && Verbose && !_adaptive_freelists) {
1732 if (_smallLinearAllocBlock._word_size == 0)
1733 warning("CompactibleFreeListSpace(epilogue):: Linear allocation failure");
1734 }
1735 assert(_promoInfo.noPromotions(), "_promoInfo inconsistency");
1736 _promoInfo.stopTrackingPromotions();
1737 repairLinearAllocationBlocks();
1738 // Print Space's stats
1739 if (PrintFLSStatistics != 0) {
1740 gclog_or_tty->print("After GC:\n");
1741 reportFreeListStatistics();
1742 }
1743 }
1744
1745 // Iteration support, mostly delegated from a CMS generation
1746
1747 void CompactibleFreeListSpace::save_marks() {
1748 // mark the "end" of the used space at the time of this call;
1749 // note, however, that promoted objects from this point
1750 // on are tracked in the _promoInfo below.
1751 set_saved_mark_word(BlockOffsetArrayUseUnallocatedBlock ?
1752 unallocated_block() : end());
1753 // inform allocator that promotions should be tracked.
1754 assert(_promoInfo.noPromotions(), "_promoInfo inconsistency");
1755 _promoInfo.startTrackingPromotions();
1756 }
1757
1758 bool CompactibleFreeListSpace::no_allocs_since_save_marks() {
1759 assert(_promoInfo.tracking(), "No preceding save_marks?");
1760 guarantee(SharedHeap::heap()->n_par_threads() == 0,
1761 "Shouldn't be called (yet) during parallel part of gc.");
1762 return _promoInfo.noPromotions();
1763 }
1764
1765 #define CFLS_OOP_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
1766 \
1767 void CompactibleFreeListSpace:: \
1768 oop_since_save_marks_iterate##nv_suffix(OopClosureType* blk) { \
1769 assert(SharedHeap::heap()->n_par_threads() == 0, \
1770 "Shouldn't be called (yet) during parallel part of gc."); \
1771 _promoInfo.promoted_oops_iterate##nv_suffix(blk); \
1772 /* \
1773 * This also restores any displaced headers and removes the elements from \
1774 * the iteration set as they are processed, so that we have a clean slate \
1775 * at the end of the iteration. Note, thus, that if new objects are \
1776 * promoted as a result of the iteration they are iterated over as well. \
1777 */ \
1778 assert(_promoInfo.noPromotions(), "_promoInfo inconsistency"); \
1779 }
1780
1781 ALL_SINCE_SAVE_MARKS_CLOSURES(CFLS_OOP_SINCE_SAVE_MARKS_DEFN)
1782
1783 //////////////////////////////////////////////////////////////////////////////
1784 // We go over the list of promoted objects, removing each from the list,
1785 // and applying the closure (this may, in turn, add more elements to
1786 // the tail of the promoted list, and these newly added objects will
1787 // also be processed) until the list is empty.
1788 // To aid verification and debugging, in the non-product builds
1789 // we actually forward _promoHead each time we process a promoted oop.
1790 // Note that this is not necessary in general (i.e. when we don't need to
1791 // call PromotionInfo::verify()) because oop_iterate can only add to the
1792 // end of _promoTail, and never needs to look at _promoHead.
1793
1794 #define PROMOTED_OOPS_ITERATE_DEFN(OopClosureType, nv_suffix) \
1795 \
1796 void PromotionInfo::promoted_oops_iterate##nv_suffix(OopClosureType* cl) { \
1797 NOT_PRODUCT(verify()); \
1798 PromotedObject *curObj, *nextObj; \
1799 for (curObj = _promoHead; curObj != NULL; curObj = nextObj) { \
1800 if ((nextObj = curObj->next()) == NULL) { \
1801 /* protect ourselves against additions due to closure application \
1802 below by resetting the list. */ \
1803 assert(_promoTail == curObj, "Should have been the tail"); \
1804 _promoHead = _promoTail = NULL; \
1805 } \
1806 if (curObj->hasDisplacedMark()) { \
1807 /* restore displaced header */ \
1808 oop(curObj)->set_mark(nextDisplacedHeader()); \
1809 } else { \
1810 /* restore prototypical header */ \
1811 oop(curObj)->init_mark(); \
1812 } \
1813 /* The "promoted_mark" should now not be set */ \
1814 assert(!curObj->hasPromotedMark(), \
1815 "Should have been cleared by restoring displaced mark-word"); \
1816 NOT_PRODUCT(_promoHead = nextObj); \
1817 if (cl != NULL) oop(curObj)->oop_iterate(cl); \
1818 if (nextObj == NULL) { /* start at head of list reset above */ \
1819 nextObj = _promoHead; \
1820 } \
1821 } \
1822 assert(noPromotions(), "post-condition violation"); \
1823 assert(_promoHead == NULL && _promoTail == NULL, "emptied promoted list");\
1824 assert(_spoolHead == _spoolTail, "emptied spooling buffers"); \
1825 assert(_firstIndex == _nextIndex, "empty buffer"); \
1826 }
1827
1828 // This should have been ALL_SINCE_...() just like the others,
1829 // but, because the body of the method above is somehwat longer,
1830 // the MSVC compiler cannot cope; as a workaround, we split the
1831 // macro into its 3 constituent parts below (see original macro
1832 // definition in specializedOopClosures.hpp).
1833 SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES_YOUNG(PROMOTED_OOPS_ITERATE_DEFN)
1834 PROMOTED_OOPS_ITERATE_DEFN(OopsInGenClosure,_v)
1835
1836
1837 void CompactibleFreeListSpace::object_iterate_since_last_GC(ObjectClosure* cl) {
1838 // ugghh... how would one do this efficiently for a non-contiguous space?
1839 guarantee(false, "NYI");
1840 }
1841
1842 bool CompactibleFreeListSpace::linearAllocationWouldFail() const {
1843 return _smallLinearAllocBlock._word_size == 0;
1844 }
1845
1846 void CompactibleFreeListSpace::repairLinearAllocationBlocks() {
1847 // Fix up linear allocation blocks to look like free blocks
1848 repairLinearAllocBlock(&_smallLinearAllocBlock);
1849 }
1850
1851 void CompactibleFreeListSpace::repairLinearAllocBlock(LinearAllocBlock* blk) {
1852 assert_locked();
1853 if (blk->_ptr != NULL) {
1854 assert(blk->_word_size != 0 && blk->_word_size >= MinChunkSize,
1855 "Minimum block size requirement");
1856 FreeChunk* fc = (FreeChunk*)(blk->_ptr);
1857 fc->setSize(blk->_word_size);
1858 fc->linkPrev(NULL); // mark as free
1859 fc->dontCoalesce();
1860 assert(fc->isFree(), "just marked it free");
1861 assert(fc->cantCoalesce(), "just marked it uncoalescable");
1862 }
1863 }
1864
1865 void CompactibleFreeListSpace::refillLinearAllocBlocksIfNeeded() {
1866 assert_locked();
1867 if (_smallLinearAllocBlock._ptr == NULL) {
1868 assert(_smallLinearAllocBlock._word_size == 0,
1869 "Size of linAB should be zero if the ptr is NULL");
1870 // Reset the linAB refill and allocation size limit.
1871 _smallLinearAllocBlock.set(0, 0, 1024*SmallForLinearAlloc, SmallForLinearAlloc);
1872 }
1873 refillLinearAllocBlockIfNeeded(&_smallLinearAllocBlock);
1874 }
1875
1876 void
1877 CompactibleFreeListSpace::refillLinearAllocBlockIfNeeded(LinearAllocBlock* blk) {
1878 assert_locked();
1879 assert((blk->_ptr == NULL && blk->_word_size == 0) ||
1880 (blk->_ptr != NULL && blk->_word_size >= MinChunkSize),
1881 "blk invariant");
1882 if (blk->_ptr == NULL) {
1883 refillLinearAllocBlock(blk);
1884 }
1885 if (PrintMiscellaneous && Verbose) {
1886 if (blk->_word_size == 0) {
1887 warning("CompactibleFreeListSpace(prologue):: Linear allocation failure");
1888 }
1889 }
1890 }
1891
1892 void
1893 CompactibleFreeListSpace::refillLinearAllocBlock(LinearAllocBlock* blk) {
1894 assert_locked();
1895 assert(blk->_word_size == 0 && blk->_ptr == NULL,
1896 "linear allocation block should be empty");
1897 FreeChunk* fc;
1898 if (blk->_refillSize < SmallForDictionary &&
1899 (fc = getChunkFromIndexedFreeList(blk->_refillSize)) != NULL) {
1900 // A linAB's strategy might be to use small sizes to reduce
1901 // fragmentation but still get the benefits of allocation from a
1902 // linAB.
1903 } else {
1904 fc = getChunkFromDictionary(blk->_refillSize);
1905 }
1906 if (fc != NULL) {
1907 blk->_ptr = (HeapWord*)fc;
1908 blk->_word_size = fc->size();
1909 fc->dontCoalesce(); // to prevent sweeper from sweeping us up
1910 }
1911 }
1912
1913 // Support for concurrent collection policy decisions.
1914 bool CompactibleFreeListSpace::should_concurrent_collect() const {
1915 // In the future we might want to add in frgamentation stats --
1916 // including erosion of the "mountain" into this decision as well.
1917 return !adaptive_freelists() && linearAllocationWouldFail();
1918 }
1919
1920 // Support for compaction
1921
1922 void CompactibleFreeListSpace::prepare_for_compaction(CompactPoint* cp) {
1923 SCAN_AND_FORWARD(cp,end,block_is_obj,block_size);
1924 // prepare_for_compaction() uses the space between live objects
1925 // so that later phase can skip dead space quickly. So verification
1926 // of the free lists doesn't work after.
1927 }
1928
1929 #define obj_size(q) adjustObjectSize(oop(q)->size())
1930 #define adjust_obj_size(s) adjustObjectSize(s)
1931
1932 void CompactibleFreeListSpace::adjust_pointers() {
1933 // In other versions of adjust_pointers(), a bail out
1934 // based on the amount of live data in the generation
1935 // (i.e., if 0, bail out) may be used.
1936 // Cannot test used() == 0 here because the free lists have already
1937 // been mangled by the compaction.
1938
1939 SCAN_AND_ADJUST_POINTERS(adjust_obj_size);
1940 // See note about verification in prepare_for_compaction().
1941 }
1942
1943 void CompactibleFreeListSpace::compact() {
1944 SCAN_AND_COMPACT(obj_size);
1945 }
1946
1947 // fragmentation_metric = 1 - [sum of (fbs**2) / (sum of fbs)**2]
1948 // where fbs is free block sizes
1949 double CompactibleFreeListSpace::flsFrag() const {
1950 size_t itabFree = totalSizeInIndexedFreeLists();
1951 double frag = 0.0;
1952 size_t i;
1953
1954 for (i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
1955 double sz = i;
1956 frag += _indexedFreeList[i].count() * (sz * sz);
1957 }
1958
1959 double totFree = itabFree +
1960 _dictionary->totalChunkSize(DEBUG_ONLY(freelistLock()));
1961 if (totFree > 0) {
1962 frag = ((frag + _dictionary->sum_of_squared_block_sizes()) /
1963 (totFree * totFree));
1964 frag = (double)1.0 - frag;
1965 } else {
1966 assert(frag == 0.0, "Follows from totFree == 0");
1967 }
1968 return frag;
1969 }
1970
1971 #define CoalSurplusPercent 1.05
1972 #define SplitSurplusPercent 1.10
1973
1974 void CompactibleFreeListSpace::beginSweepFLCensus(
1975 float inter_sweep_current,
1976 float inter_sweep_estimate) {
1977 assert_locked();
1978 size_t i;
1979 for (i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
1980 FreeList* fl = &_indexedFreeList[i];
1981 fl->compute_desired(inter_sweep_current, inter_sweep_estimate);
1982 fl->set_coalDesired((ssize_t)((double)fl->desired() * CoalSurplusPercent));
1983 fl->set_beforeSweep(fl->count());
1984 fl->set_bfrSurp(fl->surplus());
1985 }
1986 _dictionary->beginSweepDictCensus(CoalSurplusPercent,
1987 inter_sweep_current,
1988 inter_sweep_estimate);
1989 }
1990
1991 void CompactibleFreeListSpace::setFLSurplus() {
1992 assert_locked();
1993 size_t i;
1994 for (i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
1995 FreeList *fl = &_indexedFreeList[i];
1996 fl->set_surplus(fl->count() -
1997 (ssize_t)((double)fl->desired() * SplitSurplusPercent));
1998 }
1999 }
2000
2001 void CompactibleFreeListSpace::setFLHints() {
2002 assert_locked();
2003 size_t i;
2004 size_t h = IndexSetSize;
2005 for (i = IndexSetSize - 1; i != 0; i -= IndexSetStride) {
2006 FreeList *fl = &_indexedFreeList[i];
2007 fl->set_hint(h);
2008 if (fl->surplus() > 0) {
2009 h = i;
2010 }
2011 }
2012 }
2013
2014 void CompactibleFreeListSpace::clearFLCensus() {
2015 assert_locked();
2016 int i;
2017 for (i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
2018 FreeList *fl = &_indexedFreeList[i];
2019 fl->set_prevSweep(fl->count());
2020 fl->set_coalBirths(0);
2021 fl->set_coalDeaths(0);
2022 fl->set_splitBirths(0);
2023 fl->set_splitDeaths(0);
2024 }
2025 }
2026
2027 void CompactibleFreeListSpace::endSweepFLCensus(size_t sweep_count) {
2028 setFLSurplus();
2029 setFLHints();
2030 if (PrintGC && PrintFLSCensus > 0) {
2031 printFLCensus(sweep_count);
2032 }
2033 clearFLCensus();
2034 assert_locked();
2035 _dictionary->endSweepDictCensus(SplitSurplusPercent);
2036 }
2037
2038 bool CompactibleFreeListSpace::coalOverPopulated(size_t size) {
2039 if (size < SmallForDictionary) {
2040 FreeList *fl = &_indexedFreeList[size];
2041 return (fl->coalDesired() < 0) ||
2042 ((int)fl->count() > fl->coalDesired());
2043 } else {
2044 return dictionary()->coalDictOverPopulated(size);
2045 }
2046 }
2047
2048 void CompactibleFreeListSpace::smallCoalBirth(size_t size) {
2049 assert(size < SmallForDictionary, "Size too large for indexed list");
2050 FreeList *fl = &_indexedFreeList[size];
2051 fl->increment_coalBirths();
2052 fl->increment_surplus();
2053 }
2054
2055 void CompactibleFreeListSpace::smallCoalDeath(size_t size) {
2056 assert(size < SmallForDictionary, "Size too large for indexed list");
2057 FreeList *fl = &_indexedFreeList[size];
2058 fl->increment_coalDeaths();
2059 fl->decrement_surplus();
2060 }
2061
2062 void CompactibleFreeListSpace::coalBirth(size_t size) {
2063 if (size < SmallForDictionary) {
2064 smallCoalBirth(size);
2065 } else {
2066 dictionary()->dictCensusUpdate(size,
2067 false /* split */,
2068 true /* birth */);
2069 }
2070 }
2071
2072 void CompactibleFreeListSpace::coalDeath(size_t size) {
2073 if(size < SmallForDictionary) {
2074 smallCoalDeath(size);
2075 } else {
2076 dictionary()->dictCensusUpdate(size,
2077 false /* split */,
2078 false /* birth */);
2079 }
2080 }
2081
2082 void CompactibleFreeListSpace::smallSplitBirth(size_t size) {
2083 assert(size < SmallForDictionary, "Size too large for indexed list");
2084 FreeList *fl = &_indexedFreeList[size];
2085 fl->increment_splitBirths();
2086 fl->increment_surplus();
2087 }
2088
2089 void CompactibleFreeListSpace::smallSplitDeath(size_t size) {
2090 assert(size < SmallForDictionary, "Size too large for indexed list");
2091 FreeList *fl = &_indexedFreeList[size];
2092 fl->increment_splitDeaths();
2093 fl->decrement_surplus();
2094 }
2095
2096 void CompactibleFreeListSpace::splitBirth(size_t size) {
2097 if (size < SmallForDictionary) {
2098 smallSplitBirth(size);
2099 } else {
2100 dictionary()->dictCensusUpdate(size,
2101 true /* split */,
2102 true /* birth */);
2103 }
2104 }
2105
2106 void CompactibleFreeListSpace::splitDeath(size_t size) {
2107 if (size < SmallForDictionary) {
2108 smallSplitDeath(size);
2109 } else {
2110 dictionary()->dictCensusUpdate(size,
2111 true /* split */,
2112 false /* birth */);
2113 }
2114 }
2115
2116 void CompactibleFreeListSpace::split(size_t from, size_t to1) {
2117 size_t to2 = from - to1;
2118 splitDeath(from);
2119 splitBirth(to1);
2120 splitBirth(to2);
2121 }
2122
2123 void CompactibleFreeListSpace::print() const {
2124 tty->print(" CompactibleFreeListSpace");
2125 Space::print();
2126 }
2127
2128 void CompactibleFreeListSpace::prepare_for_verify() {
2129 assert_locked();
2130 repairLinearAllocationBlocks();
2131 // Verify that the SpoolBlocks look like free blocks of
2132 // appropriate sizes... To be done ...
2133 }
2134
2135 class VerifyAllBlksClosure: public BlkClosure {
2136 private:
2137 const CompactibleFreeListSpace* _sp;
2138 const MemRegion _span;
2139
2140 public:
2141 VerifyAllBlksClosure(const CompactibleFreeListSpace* sp,
2142 MemRegion span) : _sp(sp), _span(span) { }
2143
2144 virtual size_t do_blk(HeapWord* addr) {
2145 size_t res;
2146 if (_sp->block_is_obj(addr)) {
2147 oop p = oop(addr);
2148 guarantee(p->is_oop(), "Should be an oop");
2149 res = _sp->adjustObjectSize(p->size());
2150 if (_sp->obj_is_alive(addr)) {
2151 p->verify();
2152 }
2153 } else {
2154 FreeChunk* fc = (FreeChunk*)addr;
2155 res = fc->size();
2156 if (FLSVerifyLists && !fc->cantCoalesce()) {
2157 guarantee(_sp->verifyChunkInFreeLists(fc),
2158 "Chunk should be on a free list");
2159 }
2160 }
2161 guarantee(res != 0, "Livelock: no rank reduction!");
2162 return res;
2163 }
2164 };
2165
2166 class VerifyAllOopsClosure: public OopClosure {
2167 private:
2168 const CMSCollector* _collector;
2169 const CompactibleFreeListSpace* _sp;
2170 const MemRegion _span;
2171 const bool _past_remark;
2172 const CMSBitMap* _bit_map;
2173
2174 protected:
2175 void do_oop(void* p, oop obj) {
2176 if (_span.contains(obj)) { // the interior oop points into CMS heap
2177 if (!_span.contains(p)) { // reference from outside CMS heap
2178 // Should be a valid object; the first disjunct below allows
2179 // us to sidestep an assertion in block_is_obj() that insists
2180 // that p be in _sp. Note that several generations (and spaces)
2181 // are spanned by _span (CMS heap) above.
2182 guarantee(!_sp->is_in_reserved(obj) ||
2183 _sp->block_is_obj((HeapWord*)obj),
2184 "Should be an object");
2185 guarantee(obj->is_oop(), "Should be an oop");
2186 obj->verify();
2187 if (_past_remark) {
2188 // Remark has been completed, the object should be marked
2189 _bit_map->isMarked((HeapWord*)obj);
2190 }
2191 } else { // reference within CMS heap
2192 if (_past_remark) {
2193 // Remark has been completed -- so the referent should have
2194 // been marked, if referring object is.
2195 if (_bit_map->isMarked(_collector->block_start(p))) {
2196 guarantee(_bit_map->isMarked((HeapWord*)obj), "Marking error?");
2197 }
2198 }
2199 }
2200 } else if (_sp->is_in_reserved(p)) {
2201 // the reference is from FLS, and points out of FLS
2202 guarantee(obj->is_oop(), "Should be an oop");
2203 obj->verify();
2204 }
2205 }
2206
2207 template <class T> void do_oop_work(T* p) {
2208 T heap_oop = oopDesc::load_heap_oop(p);
2209 if (!oopDesc::is_null(heap_oop)) {
2210 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
2211 do_oop(p, obj);
2212 }
2213 }
2214
2215 public:
2216 VerifyAllOopsClosure(const CMSCollector* collector,
2217 const CompactibleFreeListSpace* sp, MemRegion span,
2218 bool past_remark, CMSBitMap* bit_map) :
2219 OopClosure(), _collector(collector), _sp(sp), _span(span),
2220 _past_remark(past_remark), _bit_map(bit_map) { }
2221
2222 virtual void do_oop(oop* p) { VerifyAllOopsClosure::do_oop_work(p); }
2223 virtual void do_oop(narrowOop* p) { VerifyAllOopsClosure::do_oop_work(p); }
2224 };
2225
2226 void CompactibleFreeListSpace::verify(bool ignored) const {
2227 assert_lock_strong(&_freelistLock);
2228 verify_objects_initialized();
2229 MemRegion span = _collector->_span;
2230 bool past_remark = (_collector->abstract_state() ==
2231 CMSCollector::Sweeping);
2232
2233 ResourceMark rm;
2234 HandleMark hm;
2235
2236 // Check integrity of CFL data structures
2237 _promoInfo.verify();
2238 _dictionary->verify();
2239 if (FLSVerifyIndexTable) {
2240 verifyIndexedFreeLists();
2241 }
2242 // Check integrity of all objects and free blocks in space
2243 {
2244 VerifyAllBlksClosure cl(this, span);
2245 ((CompactibleFreeListSpace*)this)->blk_iterate(&cl); // cast off const
2246 }
2247 // Check that all references in the heap to FLS
2248 // are to valid objects in FLS or that references in
2249 // FLS are to valid objects elsewhere in the heap
2250 if (FLSVerifyAllHeapReferences)
2251 {
2252 VerifyAllOopsClosure cl(_collector, this, span, past_remark,
2253 _collector->markBitMap());
2254 CollectedHeap* ch = Universe::heap();
2255 ch->oop_iterate(&cl); // all oops in generations
2256 ch->permanent_oop_iterate(&cl); // all oops in perm gen
2257 }
2258
2259 if (VerifyObjectStartArray) {
2260 // Verify the block offset table
2261 _bt.verify();
2262 }
2263 }
2264
2265 #ifndef PRODUCT
2266 void CompactibleFreeListSpace::verifyFreeLists() const {
2267 if (FLSVerifyLists) {
2268 _dictionary->verify();
2269 verifyIndexedFreeLists();
2270 } else {
2271 if (FLSVerifyDictionary) {
2272 _dictionary->verify();
2273 }
2274 if (FLSVerifyIndexTable) {
2275 verifyIndexedFreeLists();
2276 }
2277 }
2278 }
2279 #endif
2280
2281 void CompactibleFreeListSpace::verifyIndexedFreeLists() const {
2282 size_t i = 0;
2283 for (; i < MinChunkSize; i++) {
2284 guarantee(_indexedFreeList[i].head() == NULL, "should be NULL");
2285 }
2286 for (; i < IndexSetSize; i++) {
2287 verifyIndexedFreeList(i);
2288 }
2289 }
2290
2291 void CompactibleFreeListSpace::verifyIndexedFreeList(size_t size) const {
2292 FreeChunk* fc = _indexedFreeList[size].head();
2293 guarantee((size % 2 == 0) || fc == NULL, "Odd slots should be empty");
2294 for (; fc != NULL; fc = fc->next()) {
2295 guarantee(fc->size() == size, "Size inconsistency");
2296 guarantee(fc->isFree(), "!free?");
2297 guarantee(fc->next() == NULL || fc->next()->prev() == fc, "Broken list");
2298 }
2299 }
2300
2301 #ifndef PRODUCT
2302 void CompactibleFreeListSpace::checkFreeListConsistency() const {
2303 assert(_dictionary->minSize() <= IndexSetSize,
2304 "Some sizes can't be allocated without recourse to"
2305 " linear allocation buffers");
2306 assert(MIN_TREE_CHUNK_SIZE*HeapWordSize == sizeof(TreeChunk),
2307 "else MIN_TREE_CHUNK_SIZE is wrong");
2308 assert((IndexSetStride == 2 && IndexSetStart == 2) ||
2309 (IndexSetStride == 1 && IndexSetStart == 1), "just checking");
2310 assert((IndexSetStride != 2) || (MinChunkSize % 2 == 0),
2311 "Some for-loops may be incorrectly initialized");
2312 assert((IndexSetStride != 2) || (IndexSetSize % 2 == 1),
2313 "For-loops that iterate over IndexSet with stride 2 may be wrong");
2314 }
2315 #endif
2316
2317 void CompactibleFreeListSpace::printFLCensus(size_t sweep_count) const {
2318 assert_lock_strong(&_freelistLock);
2319 FreeList total;
2320 gclog_or_tty->print("end sweep# " SIZE_FORMAT "\n", sweep_count);
2321 FreeList::print_labels_on(gclog_or_tty, "size");
2322 size_t totalFree = 0;
2323 for (size_t i = IndexSetStart; i < IndexSetSize; i += IndexSetStride) {
2324 const FreeList *fl = &_indexedFreeList[i];
2325 totalFree += fl->count() * fl->size();
2326 if (i % (40*IndexSetStride) == 0) {
2327 FreeList::print_labels_on(gclog_or_tty, "size");
2328 }
2329 fl->print_on(gclog_or_tty);
2330 total.set_bfrSurp( total.bfrSurp() + fl->bfrSurp() );
2331 total.set_surplus( total.surplus() + fl->surplus() );
2332 total.set_desired( total.desired() + fl->desired() );
2333 total.set_prevSweep( total.prevSweep() + fl->prevSweep() );
2334 total.set_beforeSweep(total.beforeSweep() + fl->beforeSweep());
2335 total.set_count( total.count() + fl->count() );
2336 total.set_coalBirths( total.coalBirths() + fl->coalBirths() );
2337 total.set_coalDeaths( total.coalDeaths() + fl->coalDeaths() );
2338 total.set_splitBirths(total.splitBirths() + fl->splitBirths());
2339 total.set_splitDeaths(total.splitDeaths() + fl->splitDeaths());
2340 }
2341 total.print_on(gclog_or_tty, "TOTAL");
2342 gclog_or_tty->print_cr("Total free in indexed lists "
2343 SIZE_FORMAT " words", totalFree);
2344 gclog_or_tty->print("growth: %8.5f deficit: %8.5f\n",
2345 (double)(total.splitBirths()+total.coalBirths()-total.splitDeaths()-total.coalDeaths())/
2346 (total.prevSweep() != 0 ? (double)total.prevSweep() : 1.0),
2347 (double)(total.desired() - total.count())/(total.desired() != 0 ? (double)total.desired() : 1.0));
2348 _dictionary->printDictCensus();
2349 }
2350
2351 // Return the next displaced header, incrementing the pointer and
2352 // recycling spool area as necessary.
2353 markOop PromotionInfo::nextDisplacedHeader() {
2354 assert(_spoolHead != NULL, "promotionInfo inconsistency");
2355 assert(_spoolHead != _spoolTail || _firstIndex < _nextIndex,
2356 "Empty spool space: no displaced header can be fetched");
2357 assert(_spoolHead->bufferSize > _firstIndex, "Off by one error at head?");
2358 markOop hdr = _spoolHead->displacedHdr[_firstIndex];
2359 // Spool forward
2360 if (++_firstIndex == _spoolHead->bufferSize) { // last location in this block
2361 // forward to next block, recycling this block into spare spool buffer
2362 SpoolBlock* tmp = _spoolHead->nextSpoolBlock;
2363 assert(_spoolHead != _spoolTail, "Spooling storage mix-up");
2364 _spoolHead->nextSpoolBlock = _spareSpool;
2365 _spareSpool = _spoolHead;
2366 _spoolHead = tmp;
2367 _firstIndex = 1;
2368 NOT_PRODUCT(
2369 if (_spoolHead == NULL) { // all buffers fully consumed
2370 assert(_spoolTail == NULL && _nextIndex == 1,
2371 "spool buffers processing inconsistency");
2372 }
2373 )
2374 }
2375 return hdr;
2376 }
2377
2378 void PromotionInfo::track(PromotedObject* trackOop) {
2379 track(trackOop, oop(trackOop)->klass());
2380 }
2381
2382 void PromotionInfo::track(PromotedObject* trackOop, klassOop klassOfOop) {
2383 // make a copy of header as it may need to be spooled
2384 markOop mark = oop(trackOop)->mark();
2385 trackOop->clearNext();
2386 if (mark->must_be_preserved_for_cms_scavenge(klassOfOop)) {
2387 // save non-prototypical header, and mark oop
2388 saveDisplacedHeader(mark);
2389 trackOop->setDisplacedMark();
2390 } else {
2391 // we'd like to assert something like the following:
2392 // assert(mark == markOopDesc::prototype(), "consistency check");
2393 // ... but the above won't work because the age bits have not (yet) been
2394 // cleared. The remainder of the check would be identical to the
2395 // condition checked in must_be_preserved() above, so we don't really
2396 // have anything useful to check here!
2397 }
2398 if (_promoTail != NULL) {
2399 assert(_promoHead != NULL, "List consistency");
2400 _promoTail->setNext(trackOop);
2401 _promoTail = trackOop;
2402 } else {
2403 assert(_promoHead == NULL, "List consistency");
2404 _promoHead = _promoTail = trackOop;
2405 }
2406 // Mask as newly promoted, so we can skip over such objects
2407 // when scanning dirty cards
2408 assert(!trackOop->hasPromotedMark(), "Should not have been marked");
2409 trackOop->setPromotedMark();
2410 }
2411
2412 // Save the given displaced header, incrementing the pointer and
2413 // obtaining more spool area as necessary.
2414 void PromotionInfo::saveDisplacedHeader(markOop hdr) {
2415 assert(_spoolHead != NULL && _spoolTail != NULL,
2416 "promotionInfo inconsistency");
2417 assert(_spoolTail->bufferSize > _nextIndex, "Off by one error at tail?");
2418 _spoolTail->displacedHdr[_nextIndex] = hdr;
2419 // Spool forward
2420 if (++_nextIndex == _spoolTail->bufferSize) { // last location in this block
2421 // get a new spooling block
2422 assert(_spoolTail->nextSpoolBlock == NULL, "tail should terminate spool list");
2423 _splice_point = _spoolTail; // save for splicing
2424 _spoolTail->nextSpoolBlock = getSpoolBlock(); // might fail
2425 _spoolTail = _spoolTail->nextSpoolBlock; // might become NULL ...
2426 // ... but will attempt filling before next promotion attempt
2427 _nextIndex = 1;
2428 }
2429 }
2430
2431 // Ensure that spooling space exists. Return false if spooling space
2432 // could not be obtained.
2433 bool PromotionInfo::ensure_spooling_space_work() {
2434 assert(!has_spooling_space(), "Only call when there is no spooling space");
2435 // Try and obtain more spooling space
2436 SpoolBlock* newSpool = getSpoolBlock();
2437 assert(newSpool == NULL ||
2438 (newSpool->bufferSize != 0 && newSpool->nextSpoolBlock == NULL),
2439 "getSpoolBlock() sanity check");
2440 if (newSpool == NULL) {
2441 return false;
2442 }
2443 _nextIndex = 1;
2444 if (_spoolTail == NULL) {
2445 _spoolTail = newSpool;
2446 if (_spoolHead == NULL) {
2447 _spoolHead = newSpool;
2448 _firstIndex = 1;
2449 } else {
2450 assert(_splice_point != NULL && _splice_point->nextSpoolBlock == NULL,
2451 "Splice point invariant");
2452 // Extra check that _splice_point is connected to list
2453 #ifdef ASSERT
2454 {
2455 SpoolBlock* blk = _spoolHead;
2456 for (; blk->nextSpoolBlock != NULL;
2457 blk = blk->nextSpoolBlock);
2458 assert(blk != NULL && blk == _splice_point,
2459 "Splice point incorrect");
2460 }
2461 #endif // ASSERT
2462 _splice_point->nextSpoolBlock = newSpool;
2463 }
2464 } else {
2465 assert(_spoolHead != NULL, "spool list consistency");
2466 _spoolTail->nextSpoolBlock = newSpool;
2467 _spoolTail = newSpool;
2468 }
2469 return true;
2470 }
2471
2472 // Get a free spool buffer from the free pool, getting a new block
2473 // from the heap if necessary.
2474 SpoolBlock* PromotionInfo::getSpoolBlock() {
2475 SpoolBlock* res;
2476 if ((res = _spareSpool) != NULL) {
2477 _spareSpool = _spareSpool->nextSpoolBlock;
2478 res->nextSpoolBlock = NULL;
2479 } else { // spare spool exhausted, get some from heap
2480 res = (SpoolBlock*)(space()->allocateScratch(refillSize()));
2481 if (res != NULL) {
2482 res->init();
2483 }
2484 }
2485 assert(res == NULL || res->nextSpoolBlock == NULL, "postcondition");
2486 return res;
2487 }
2488
2489 void PromotionInfo::startTrackingPromotions() {
2490 assert(_spoolHead == _spoolTail && _firstIndex == _nextIndex,
2491 "spooling inconsistency?");
2492 _firstIndex = _nextIndex = 1;
2493 _tracking = true;
2494 }
2495
2496 void PromotionInfo::stopTrackingPromotions() {
2497 assert(_spoolHead == _spoolTail && _firstIndex == _nextIndex,
2498 "spooling inconsistency?");
2499 _firstIndex = _nextIndex = 1;
2500 _tracking = false;
2501 }
2502
2503 // When _spoolTail is not NULL, then the slot <_spoolTail, _nextIndex>
2504 // points to the next slot available for filling.
2505 // The set of slots holding displaced headers are then all those in the
2506 // right-open interval denoted by:
2507 //
2508 // [ <_spoolHead, _firstIndex>, <_spoolTail, _nextIndex> )
2509 //
2510 // When _spoolTail is NULL, then the set of slots with displaced headers
2511 // is all those starting at the slot <_spoolHead, _firstIndex> and
2512 // going up to the last slot of last block in the linked list.
2513 // In this lartter case, _splice_point points to the tail block of
2514 // this linked list of blocks holding displaced headers.
2515 void PromotionInfo::verify() const {
2516 // Verify the following:
2517 // 1. the number of displaced headers matches the number of promoted
2518 // objects that have displaced headers
2519 // 2. each promoted object lies in this space
2520 debug_only(
2521 PromotedObject* junk = NULL;
2522 assert(junk->next_addr() == (void*)(oop(junk)->mark_addr()),
2523 "Offset of PromotedObject::_next is expected to align with "
2524 " the OopDesc::_mark within OopDesc");
2525 )
2526 // FIXME: guarantee????
2527 guarantee(_spoolHead == NULL || _spoolTail != NULL ||
2528 _splice_point != NULL, "list consistency");
2529 guarantee(_promoHead == NULL || _promoTail != NULL, "list consistency");
2530 // count the number of objects with displaced headers
2531 size_t numObjsWithDisplacedHdrs = 0;
2532 for (PromotedObject* curObj = _promoHead; curObj != NULL; curObj = curObj->next()) {
2533 guarantee(space()->is_in_reserved((HeapWord*)curObj), "Containment");
2534 // the last promoted object may fail the mark() != NULL test of is_oop().
2535 guarantee(curObj->next() == NULL || oop(curObj)->is_oop(), "must be an oop");
2536 if (curObj->hasDisplacedMark()) {
2537 numObjsWithDisplacedHdrs++;
2538 }
2539 }
2540 // Count the number of displaced headers
2541 size_t numDisplacedHdrs = 0;
2542 for (SpoolBlock* curSpool = _spoolHead;
2543 curSpool != _spoolTail && curSpool != NULL;
2544 curSpool = curSpool->nextSpoolBlock) {
2545 // the first entry is just a self-pointer; indices 1 through
2546 // bufferSize - 1 are occupied (thus, bufferSize - 1 slots).
2547 guarantee((void*)curSpool->displacedHdr == (void*)&curSpool->displacedHdr,
2548 "first entry of displacedHdr should be self-referential");
2549 numDisplacedHdrs += curSpool->bufferSize - 1;
2550 }
2551 guarantee((_spoolHead == _spoolTail) == (numDisplacedHdrs == 0),
2552 "internal consistency");
2553 guarantee(_spoolTail != NULL || _nextIndex == 1,
2554 "Inconsistency between _spoolTail and _nextIndex");
2555 // We overcounted (_firstIndex-1) worth of slots in block
2556 // _spoolHead and we undercounted (_nextIndex-1) worth of
2557 // slots in block _spoolTail. We make an appropriate
2558 // adjustment by subtracting the first and adding the
2559 // second: - (_firstIndex - 1) + (_nextIndex - 1)
2560 numDisplacedHdrs += (_nextIndex - _firstIndex);
2561 guarantee(numDisplacedHdrs == numObjsWithDisplacedHdrs, "Displaced hdr count");
2562 }
2563
2564
2565 CFLS_LAB::CFLS_LAB(CompactibleFreeListSpace* cfls) :
2566 _cfls(cfls)
2567 {
2568 _blocks_to_claim = CMSParPromoteBlocksToClaim;
2569 for (size_t i = CompactibleFreeListSpace::IndexSetStart;
2570 i < CompactibleFreeListSpace::IndexSetSize;
2571 i += CompactibleFreeListSpace::IndexSetStride) {
2572 _indexedFreeList[i].set_size(i);
2573 }
2574 }
2575
2576 HeapWord* CFLS_LAB::alloc(size_t word_sz) {
2577 FreeChunk* res;
2578 word_sz = _cfls->adjustObjectSize(word_sz);
2579 if (word_sz >= CompactibleFreeListSpace::IndexSetSize) {
2580 // This locking manages sync with other large object allocations.
2581 MutexLockerEx x(_cfls->parDictionaryAllocLock(),
2582 Mutex::_no_safepoint_check_flag);
2583 res = _cfls->getChunkFromDictionaryExact(word_sz);
2584 if (res == NULL) return NULL;
2585 } else {
2586 FreeList* fl = &_indexedFreeList[word_sz];
2587 bool filled = false; //TRAP
2588 if (fl->count() == 0) {
2589 bool filled = true; //TRAP
2590 // Attempt to refill this local free list.
2591 _cfls->par_get_chunk_of_blocks(word_sz, _blocks_to_claim, fl);
2592 // If it didn't work, give up.
2593 if (fl->count() == 0) return NULL;
2594 }
2595 res = fl->getChunkAtHead();
2596 assert(res != NULL, "Why was count non-zero?");
2597 }
2598 res->markNotFree();
2599 assert(!res->isFree(), "shouldn't be marked free");
2600 assert(oop(res)->klass_or_null() == NULL, "should look uninitialized");
2601 // mangle a just allocated object with a distinct pattern.
2602 debug_only(res->mangleAllocated(word_sz));
2603 return (HeapWord*)res;
2604 }
2605
2606 void CFLS_LAB::retire() {
2607 for (size_t i = CompactibleFreeListSpace::IndexSetStart;
2608 i < CompactibleFreeListSpace::IndexSetSize;
2609 i += CompactibleFreeListSpace::IndexSetStride) {
2610 if (_indexedFreeList[i].count() > 0) {
2611 MutexLockerEx x(_cfls->_indexedFreeListParLocks[i],
2612 Mutex::_no_safepoint_check_flag);
2613 _cfls->_indexedFreeList[i].prepend(&_indexedFreeList[i]);
2614 // Reset this list.
2615 _indexedFreeList[i] = FreeList();
2616 _indexedFreeList[i].set_size(i);
2617 }
2618 }
2619 }
2620
2621 void
2622 CompactibleFreeListSpace::
2623 par_get_chunk_of_blocks(size_t word_sz, size_t n, FreeList* fl) {
2624 assert(fl->count() == 0, "Precondition.");
2625 assert(word_sz < CompactibleFreeListSpace::IndexSetSize,
2626 "Precondition");
2627
2628 // We'll try all multiples of word_sz in the indexed set (starting with
2629 // word_sz itself), then try getting a big chunk and splitting it.
2630 int k = 1;
2631 size_t cur_sz = k * word_sz;
2632 bool found = false;
2633 while (cur_sz < CompactibleFreeListSpace::IndexSetSize && k == 1) {
2634 FreeList* gfl = &_indexedFreeList[cur_sz];
2635 FreeList fl_for_cur_sz; // Empty.
2636 fl_for_cur_sz.set_size(cur_sz);
2637 {
2638 MutexLockerEx x(_indexedFreeListParLocks[cur_sz],
2639 Mutex::_no_safepoint_check_flag);
2640 if (gfl->count() != 0) {
2641 size_t nn = MAX2(n/k, (size_t)1);
2642 gfl->getFirstNChunksFromList(nn, &fl_for_cur_sz);
2643 found = true;
2644 }
2645 }
2646 // Now transfer fl_for_cur_sz to fl. Common case, we hope, is k = 1.
2647 if (found) {
2648 if (k == 1) {
2649 fl->prepend(&fl_for_cur_sz);
2650 } else {
2651 // Divide each block on fl_for_cur_sz up k ways.
2652 FreeChunk* fc;
2653 while ((fc = fl_for_cur_sz.getChunkAtHead()) != NULL) {
2654 // Must do this in reverse order, so that anybody attempting to
2655 // access the main chunk sees it as a single free block until we
2656 // change it.
2657 size_t fc_size = fc->size();
2658 for (int i = k-1; i >= 0; i--) {
2659 FreeChunk* ffc = (FreeChunk*)((HeapWord*)fc + i * word_sz);
2660 ffc->setSize(word_sz);
2661 ffc->linkNext(NULL);
2662 ffc->linkPrev(NULL); // Mark as a free block for other (parallel) GC threads.
2663 // Above must occur before BOT is updated below.
2664 // splitting from the right, fc_size == (k - i + 1) * wordsize
2665 _bt.mark_block((HeapWord*)ffc, word_sz);
2666 fc_size -= word_sz;
2667 _bt.verify_not_unallocated((HeapWord*)ffc, ffc->size());
2668 _bt.verify_single_block((HeapWord*)fc, fc_size);
2669 _bt.verify_single_block((HeapWord*)ffc, ffc->size());
2670 // Push this on "fl".
2671 fl->returnChunkAtHead(ffc);
2672 }
2673 // TRAP
2674 assert(fl->tail()->next() == NULL, "List invariant.");
2675 }
2676 }
2677 return;
2678 }
2679 k++; cur_sz = k * word_sz;
2680 }
2681 // Otherwise, we'll split a block from the dictionary.
2682 FreeChunk* fc = NULL;
2683 FreeChunk* rem_fc = NULL;
2684 size_t rem;
2685 {
2686 MutexLockerEx x(parDictionaryAllocLock(),
2687 Mutex::_no_safepoint_check_flag);
2688 while (n > 0) {
2689 fc = dictionary()->getChunk(MAX2(n * word_sz,
2690 _dictionary->minSize()),
2691 FreeBlockDictionary::atLeast);
2692 if (fc != NULL) {
2693 _bt.allocated((HeapWord*)fc, fc->size()); // update _unallocated_blk
2694 dictionary()->dictCensusUpdate(fc->size(),
2695 true /*split*/,
2696 false /*birth*/);
2697 break;
2698 } else {
2699 n--;
2700 }
2701 }
2702 if (fc == NULL) return;
2703 // Otherwise, split up that block.
2704 size_t nn = fc->size() / word_sz;
2705 n = MIN2(nn, n);
2706 rem = fc->size() - n * word_sz;
2707 // If there is a remainder, and it's too small, allocate one fewer.
2708 if (rem > 0 && rem < MinChunkSize) {
2709 n--; rem += word_sz;
2710 }
2711 // First return the remainder, if any.
2712 // Note that we hold the lock until we decide if we're going to give
2713 // back the remainder to the dictionary, since a contending allocator
2714 // may otherwise see the heap as empty. (We're willing to take that
2715 // hit if the block is a small block.)
2716 if (rem > 0) {
2717 size_t prefix_size = n * word_sz;
2718 rem_fc = (FreeChunk*)((HeapWord*)fc + prefix_size);
2719 rem_fc->setSize(rem);
2720 rem_fc->linkNext(NULL);
2721 rem_fc->linkPrev(NULL); // Mark as a free block for other (parallel) GC threads.
2722 // Above must occur before BOT is updated below.
2723 _bt.split_block((HeapWord*)fc, fc->size(), prefix_size);
2724 if (rem >= IndexSetSize) {
2725 returnChunkToDictionary(rem_fc);
2726 dictionary()->dictCensusUpdate(fc->size(),
2727 true /*split*/,
2728 true /*birth*/);
2729 rem_fc = NULL;
2730 }
2731 // Otherwise, return it to the small list below.
2732 }
2733 }
2734 //
2735 if (rem_fc != NULL) {
2736 MutexLockerEx x(_indexedFreeListParLocks[rem],
2737 Mutex::_no_safepoint_check_flag);
2738 _bt.verify_not_unallocated((HeapWord*)rem_fc, rem_fc->size());
2739 _indexedFreeList[rem].returnChunkAtHead(rem_fc);
2740 smallSplitBirth(rem);
2741 }
2742
2743 // Now do the splitting up.
2744 // Must do this in reverse order, so that anybody attempting to
2745 // access the main chunk sees it as a single free block until we
2746 // change it.
2747 size_t fc_size = n * word_sz;
2748 // All but first chunk in this loop
2749 for (ssize_t i = n-1; i > 0; i--) {
2750 FreeChunk* ffc = (FreeChunk*)((HeapWord*)fc + i * word_sz);
2751 ffc->setSize(word_sz);
2752 ffc->linkNext(NULL);
2753 ffc->linkPrev(NULL); // Mark as a free block for other (parallel) GC threads.
2754 // Above must occur before BOT is updated below.
2755 // splitting from the right, fc_size == (n - i + 1) * wordsize
2756 _bt.mark_block((HeapWord*)ffc, word_sz);
2757 fc_size -= word_sz;
2758 _bt.verify_not_unallocated((HeapWord*)ffc, ffc->size());
2759 _bt.verify_single_block((HeapWord*)ffc, ffc->size());
2760 _bt.verify_single_block((HeapWord*)fc, fc_size);
2761 // Push this on "fl".
2762 fl->returnChunkAtHead(ffc);
2763 }
2764 // First chunk
2765 fc->setSize(word_sz);
2766 fc->linkNext(NULL);
2767 fc->linkPrev(NULL);
2768 _bt.verify_not_unallocated((HeapWord*)fc, fc->size());
2769 _bt.verify_single_block((HeapWord*)fc, fc->size());
2770 fl->returnChunkAtHead(fc);
2771
2772 {
2773 MutexLockerEx x(_indexedFreeListParLocks[word_sz],
2774 Mutex::_no_safepoint_check_flag);
2775 ssize_t new_births = _indexedFreeList[word_sz].splitBirths() + n;
2776 _indexedFreeList[word_sz].set_splitBirths(new_births);
2777 ssize_t new_surplus = _indexedFreeList[word_sz].surplus() + n;
2778 _indexedFreeList[word_sz].set_surplus(new_surplus);
2779 }
2780
2781 // TRAP
2782 assert(fl->tail()->next() == NULL, "List invariant.");
2783 }
2784
2785 // Set up the space's par_seq_tasks structure for work claiming
2786 // for parallel rescan. See CMSParRemarkTask where this is currently used.
2787 // XXX Need to suitably abstract and generalize this and the next
2788 // method into one.
2789 void
2790 CompactibleFreeListSpace::
2791 initialize_sequential_subtasks_for_rescan(int n_threads) {
2792 // The "size" of each task is fixed according to rescan_task_size.
2793 assert(n_threads > 0, "Unexpected n_threads argument");
2794 const size_t task_size = rescan_task_size();
2795 size_t n_tasks = (used_region().word_size() + task_size - 1)/task_size;
2796 assert((n_tasks == 0) == used_region().is_empty(), "n_tasks incorrect");
2797 assert(n_tasks == 0 ||
2798 ((used_region().start() + (n_tasks - 1)*task_size < used_region().end()) &&
2799 (used_region().start() + n_tasks*task_size >= used_region().end())),
2800 "n_tasks calculation incorrect");
2801 SequentialSubTasksDone* pst = conc_par_seq_tasks();
2802 assert(!pst->valid(), "Clobbering existing data?");
2803 pst->set_par_threads(n_threads);
2804 pst->set_n_tasks((int)n_tasks);
2805 }
2806
2807 // Set up the space's par_seq_tasks structure for work claiming
2808 // for parallel concurrent marking. See CMSConcMarkTask where this is currently used.
2809 void
2810 CompactibleFreeListSpace::
2811 initialize_sequential_subtasks_for_marking(int n_threads,
2812 HeapWord* low) {
2813 // The "size" of each task is fixed according to rescan_task_size.
2814 assert(n_threads > 0, "Unexpected n_threads argument");
2815 const size_t task_size = marking_task_size();
2816 assert(task_size > CardTableModRefBS::card_size_in_words &&
2817 (task_size % CardTableModRefBS::card_size_in_words == 0),
2818 "Otherwise arithmetic below would be incorrect");
2819 MemRegion span = _gen->reserved();
2820 if (low != NULL) {
2821 if (span.contains(low)) {
2822 // Align low down to a card boundary so that
2823 // we can use block_offset_careful() on span boundaries.
2824 HeapWord* aligned_low = (HeapWord*)align_size_down((uintptr_t)low,
2825 CardTableModRefBS::card_size);
2826 // Clip span prefix at aligned_low
2827 span = span.intersection(MemRegion(aligned_low, span.end()));
2828 } else if (low > span.end()) {
2829 span = MemRegion(low, low); // Null region
2830 } // else use entire span
2831 }
2832 assert(span.is_empty() ||
2833 ((uintptr_t)span.start() % CardTableModRefBS::card_size == 0),
2834 "span should start at a card boundary");
2835 size_t n_tasks = (span.word_size() + task_size - 1)/task_size;
2836 assert((n_tasks == 0) == span.is_empty(), "Inconsistency");
2837 assert(n_tasks == 0 ||
2838 ((span.start() + (n_tasks - 1)*task_size < span.end()) &&
2839 (span.start() + n_tasks*task_size >= span.end())),
2840 "n_tasks calculation incorrect");
2841 SequentialSubTasksDone* pst = conc_par_seq_tasks();
2842 assert(!pst->valid(), "Clobbering existing data?");
2843 pst->set_par_threads(n_threads);
2844 pst->set_n_tasks((int)n_tasks);
2845 }
2846