1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_COMPACTIBLEFREELISTSPACE_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_COMPACTIBLEFREELISTSPACE_HPP
27
28 #include "gc_implementation/concurrentMarkSweep/adaptiveFreeList.hpp"
29 #include "gc_implementation/concurrentMarkSweep/promotionInfo.hpp"
30 #include "memory/binaryTreeDictionary.hpp"
31 #include "memory/blockOffsetTable.inline.hpp"
32 #include "memory/freeList.hpp"
33 #include "memory/space.hpp"
34
35 // Classes in support of keeping track of promotions into a non-Contiguous
36 // space, in this case a CompactibleFreeListSpace.
37
38 // Forward declarations
39 class CompactibleFreeListSpace;
40 class BlkClosure;
41 class BlkClosureCareful;
42 class FreeChunk;
43 class UpwardsObjectClosure;
44 class ObjectClosureCareful;
45 class Klass;
46
47 class LinearAllocBlock VALUE_OBJ_CLASS_SPEC {
48 public:
49 LinearAllocBlock() : _ptr(0), _word_size(0), _refillSize(0),
50 _allocation_size_limit(0) {}
51 void set(HeapWord* ptr, size_t word_size, size_t refill_size,
52 size_t allocation_size_limit) {
53 _ptr = ptr;
54 _word_size = word_size;
55 _refillSize = refill_size;
56 _allocation_size_limit = allocation_size_limit;
57 }
58 HeapWord* _ptr;
59 size_t _word_size;
60 size_t _refillSize;
61 size_t _allocation_size_limit; // Largest size that will be allocated
62
63 void print_on(outputStream* st) const;
64 };
65
66 // Concrete subclass of CompactibleSpace that implements
67 // a free list space, such as used in the concurrent mark sweep
68 // generation.
69
70 class CompactibleFreeListSpace: public CompactibleSpace {
71 friend class VMStructs;
72 friend class ConcurrentMarkSweepGeneration;
73 friend class CMSCollector;
74 // Local alloc buffer for promotion into this space.
75 friend class CFLS_LAB;
76
77 // "Size" of chunks of work (executed during parallel remark phases
78 // of CMS collection); this probably belongs in CMSCollector, although
79 // it's cached here because it's used in
80 // initialize_sequential_subtasks_for_rescan() which modifies
81 // par_seq_tasks which also lives in Space. XXX
82 const size_t _rescan_task_size;
83 const size_t _marking_task_size;
84
85 // Yet another sequential tasks done structure. This supports
86 // CMS GC, where we have threads dynamically
87 // claiming sub-tasks from a larger parallel task.
88 SequentialSubTasksDone _conc_par_seq_tasks;
89
90 BlockOffsetArrayNonContigSpace _bt;
91
92 CMSCollector* _collector;
93 ConcurrentMarkSweepGeneration* _gen;
94
95 // Data structures for free blocks (used during allocation/sweeping)
96
97 // Allocation is done linearly from two different blocks depending on
98 // whether the request is small or large, in an effort to reduce
99 // fragmentation. We assume that any locking for allocation is done
100 // by the containing generation. Thus, none of the methods in this
101 // space are re-entrant.
102 enum SomeConstants {
103 SmallForLinearAlloc = 16, // size < this then use _sLAB
104 SmallForDictionary = 257, // size < this then use _indexedFreeList
105 IndexSetSize = SmallForDictionary // keep this odd-sized
106 };
107 static size_t IndexSetStart;
108 static size_t IndexSetStride;
109
110 private:
111 enum FitStrategyOptions {
112 FreeBlockStrategyNone = 0,
113 FreeBlockBestFitFirst
114 };
115
116 PromotionInfo _promoInfo;
117
118 // Helps to impose a global total order on freelistLock ranks;
119 // assumes that CFLSpace's are allocated in global total order
120 static int _lockRank;
121
122 // A lock protecting the free lists and free blocks;
123 // mutable because of ubiquity of locking even for otherwise const methods
124 mutable Mutex _freelistLock;
125 // Locking verifier convenience function
126 void assert_locked() const PRODUCT_RETURN;
127 void assert_locked(const Mutex* lock) const PRODUCT_RETURN;
128
129 // Linear allocation blocks
130 LinearAllocBlock _smallLinearAllocBlock;
131
132 FreeBlockDictionary<FreeChunk>::DictionaryChoice _dictionaryChoice;
133 AFLBinaryTreeDictionary* _dictionary; // Pointer to dictionary for large size blocks
134
135 // Indexed array for small size blocks
136 AdaptiveFreeList<FreeChunk> _indexedFreeList[IndexSetSize];
137
138 // Allocation strategy
139 bool _fitStrategy; // Use best fit strategy
140 bool _adaptive_freelists; // Use adaptive freelists
141
142 // This is an address close to the largest free chunk in the heap.
143 // It is currently assumed to be at the end of the heap. Free
144 // chunks with addresses greater than nearLargestChunk are coalesced
145 // in an effort to maintain a large chunk at the end of the heap.
146 HeapWord* _nearLargestChunk;
147
148 // Used to keep track of limit of sweep for the space
149 HeapWord* _sweep_limit;
150
151 // Support for compacting cms
152 HeapWord* cross_threshold(HeapWord* start, HeapWord* end);
153 HeapWord* forward(oop q, size_t size, CompactPoint* cp, HeapWord* compact_top);
154
155 // Initialization helpers.
156 void initializeIndexedFreeListArray();
157
158 // Extra stuff to manage promotion parallelism.
159
160 // A lock protecting the dictionary during par promotion allocation.
161 mutable Mutex _parDictionaryAllocLock;
162 Mutex* parDictionaryAllocLock() const { return &_parDictionaryAllocLock; }
163
164 // Locks protecting the exact lists during par promotion allocation.
165 Mutex* _indexedFreeListParLocks[IndexSetSize];
166
167 // Attempt to obtain up to "n" blocks of the size "word_sz" (which is
168 // required to be smaller than "IndexSetSize".) If successful,
169 // adds them to "fl", which is required to be an empty free list.
170 // If the count of "fl" is negative, it's absolute value indicates a
171 // number of free chunks that had been previously "borrowed" from global
172 // list of size "word_sz", and must now be decremented.
173 void par_get_chunk_of_blocks(size_t word_sz, size_t n, AdaptiveFreeList<FreeChunk>* fl);
174
175 // Used by par_get_chunk_of_blocks() for the chunks from the
176 // indexed_free_lists.
177 bool par_get_chunk_of_blocks_IFL(size_t word_sz, size_t n, AdaptiveFreeList<FreeChunk>* fl);
178
179 // Used by par_get_chunk_of_blocks_dictionary() to get a chunk
180 // evenly splittable into "n" "word_sz" chunks. Returns that
181 // evenly splittable chunk. May split a larger chunk to get the
182 // evenly splittable chunk.
183 FreeChunk* get_n_way_chunk_to_split(size_t word_sz, size_t n);
184
185 // Used by par_get_chunk_of_blocks() for the chunks from the
186 // dictionary.
187 void par_get_chunk_of_blocks_dictionary(size_t word_sz, size_t n, AdaptiveFreeList<FreeChunk>* fl);
188
189 // Allocation helper functions
190 // Allocate using a strategy that takes from the indexed free lists
191 // first. This allocation strategy assumes a companion sweeping
192 // strategy that attempts to keep the needed number of chunks in each
193 // indexed free lists.
194 HeapWord* allocate_adaptive_freelists(size_t size);
195 // Allocate from the linear allocation buffers first. This allocation
196 // strategy assumes maximal coalescing can maintain chunks large enough
197 // to be used as linear allocation buffers.
198 HeapWord* allocate_non_adaptive_freelists(size_t size);
199
200 // Gets a chunk from the linear allocation block (LinAB). If there
201 // is not enough space in the LinAB, refills it.
202 HeapWord* getChunkFromLinearAllocBlock(LinearAllocBlock* blk, size_t size);
203 HeapWord* getChunkFromSmallLinearAllocBlock(size_t size);
204 // Get a chunk from the space remaining in the linear allocation block. Do
205 // not attempt to refill if the space is not available, return NULL. Do the
206 // repairs on the linear allocation block as appropriate.
207 HeapWord* getChunkFromLinearAllocBlockRemainder(LinearAllocBlock* blk, size_t size);
208 inline HeapWord* getChunkFromSmallLinearAllocBlockRemainder(size_t size);
209
210 // Helper function for getChunkFromIndexedFreeList.
211 // Replenish the indexed free list for this "size". Do not take from an
212 // underpopulated size.
213 FreeChunk* getChunkFromIndexedFreeListHelper(size_t size, bool replenish = true);
214
215 // Get a chunk from the indexed free list. If the indexed free list
216 // does not have a free chunk, try to replenish the indexed free list
217 // then get the free chunk from the replenished indexed free list.
218 inline FreeChunk* getChunkFromIndexedFreeList(size_t size);
219
220 // The returned chunk may be larger than requested (or null).
221 FreeChunk* getChunkFromDictionary(size_t size);
222 // The returned chunk is the exact size requested (or null).
223 FreeChunk* getChunkFromDictionaryExact(size_t size);
224
225 // Find a chunk in the indexed free list that is the best
226 // fit for size "numWords".
227 FreeChunk* bestFitSmall(size_t numWords);
228 // For free list "fl" of chunks of size > numWords,
229 // remove a chunk, split off a chunk of size numWords
230 // and return it. The split off remainder is returned to
231 // the free lists. The old name for getFromListGreater
232 // was lookInListGreater.
233 FreeChunk* getFromListGreater(AdaptiveFreeList<FreeChunk>* fl, size_t numWords);
234 // Get a chunk in the indexed free list or dictionary,
235 // by considering a larger chunk and splitting it.
236 FreeChunk* getChunkFromGreater(size_t numWords);
237 // Verify that the given chunk is in the indexed free lists.
238 bool verifyChunkInIndexedFreeLists(FreeChunk* fc) const;
239 // Remove the specified chunk from the indexed free lists.
240 void removeChunkFromIndexedFreeList(FreeChunk* fc);
241 // Remove the specified chunk from the dictionary.
242 void removeChunkFromDictionary(FreeChunk* fc);
243 // Split a free chunk into a smaller free chunk of size "new_size".
244 // Return the smaller free chunk and return the remainder to the
245 // free lists.
246 FreeChunk* splitChunkAndReturnRemainder(FreeChunk* chunk, size_t new_size);
247 // Add a chunk to the free lists.
248 void addChunkToFreeLists(HeapWord* chunk, size_t size);
249 // Add a chunk to the free lists, preferring to suffix it
250 // to the last free chunk at end of space if possible, and
251 // updating the block census stats as well as block offset table.
252 // Take any locks as appropriate if we are multithreaded.
253 void addChunkToFreeListsAtEndRecordingStats(HeapWord* chunk, size_t size);
254 // Add a free chunk to the indexed free lists.
255 void returnChunkToFreeList(FreeChunk* chunk);
256 // Add a free chunk to the dictionary.
257 void returnChunkToDictionary(FreeChunk* chunk);
258
259 // Functions for maintaining the linear allocation buffers (LinAB).
260 // Repairing a linear allocation block refers to operations
261 // performed on the remainder of a LinAB after an allocation
262 // has been made from it.
263 void repairLinearAllocationBlocks();
264 void repairLinearAllocBlock(LinearAllocBlock* blk);
265 void refillLinearAllocBlock(LinearAllocBlock* blk);
266 void refillLinearAllocBlockIfNeeded(LinearAllocBlock* blk);
267 void refillLinearAllocBlocksIfNeeded();
268
269 void verify_objects_initialized() const;
270
271 // Statistics reporting helper functions
272 void reportFreeListStatistics() const;
273 void reportIndexedFreeListStatistics() const;
274 size_t maxChunkSizeInIndexedFreeLists() const;
275 size_t numFreeBlocksInIndexedFreeLists() const;
276 // Accessor
277 HeapWord* unallocated_block() const {
278 if (BlockOffsetArrayUseUnallocatedBlock) {
279 HeapWord* ub = _bt.unallocated_block();
280 assert(ub >= bottom() &&
281 ub <= end(), "space invariant");
282 return ub;
283 } else {
284 return end();
285 }
286 }
287 void freed(HeapWord* start, size_t size) {
288 _bt.freed(start, size);
289 }
290
291 protected:
292 // Reset the indexed free list to its initial empty condition.
293 void resetIndexedFreeListArray();
294 // Reset to an initial state with a single free block described
295 // by the MemRegion parameter.
296 void reset(MemRegion mr);
297 // Return the total number of words in the indexed free lists.
298 size_t totalSizeInIndexedFreeLists() const;
299
300 public:
301 // Constructor
302 CompactibleFreeListSpace(BlockOffsetSharedArray* bs, MemRegion mr,
303 bool use_adaptive_freelists,
304 FreeBlockDictionary<FreeChunk>::DictionaryChoice);
305 // Accessors
306 bool bestFitFirst() { return _fitStrategy == FreeBlockBestFitFirst; }
307 FreeBlockDictionary<FreeChunk>* dictionary() const { return _dictionary; }
308 HeapWord* nearLargestChunk() const { return _nearLargestChunk; }
309 void set_nearLargestChunk(HeapWord* v) { _nearLargestChunk = v; }
310
311 // Set CMS global values.
312 static void set_cms_values();
313
314 // Return the free chunk at the end of the space. If no such
315 // chunk exists, return NULL.
316 FreeChunk* find_chunk_at_end();
317
318 bool adaptive_freelists() const { return _adaptive_freelists; }
319
320 void set_collector(CMSCollector* collector) { _collector = collector; }
321
322 // Support for parallelization of rescan and marking.
323 const size_t rescan_task_size() const { return _rescan_task_size; }
324 const size_t marking_task_size() const { return _marking_task_size; }
325 SequentialSubTasksDone* conc_par_seq_tasks() {return &_conc_par_seq_tasks; }
326 void initialize_sequential_subtasks_for_rescan(int n_threads);
327 void initialize_sequential_subtasks_for_marking(int n_threads,
328 HeapWord* low = NULL);
329
330 // Space enquiries
331 size_t used() const;
332 size_t free() const;
333 size_t max_alloc_in_words() const;
334 // XXX: should have a less conservative used_region() than that of
335 // Space; we could consider keeping track of highest allocated
336 // address and correcting that at each sweep, as the sweeper
337 // goes through the entire allocated part of the generation. We
338 // could also use that information to keep the sweeper from
339 // sweeping more than is necessary. The allocator and sweeper will
340 // of course need to synchronize on this, since the sweeper will
341 // try to bump down the address and the allocator will try to bump it up.
342 // For now, however, we'll just use the default used_region()
343 // which overestimates the region by returning the entire
344 // committed region (this is safe, but inefficient).
345
346 // Returns a subregion of the space containing all the objects in
347 // the space.
348 MemRegion used_region() const {
349 return MemRegion(bottom(),
350 BlockOffsetArrayUseUnallocatedBlock ?
351 unallocated_block() : end());
352 }
353
354 virtual bool is_free_block(const HeapWord* p) const;
355
356 // Resizing support
357 void set_end(HeapWord* value); // override
358
359 // Mutual exclusion support
360 Mutex* freelistLock() const { return &_freelistLock; }
361
362 // Iteration support
363 void oop_iterate(ExtendedOopClosure* cl);
364
365 void object_iterate(ObjectClosure* blk);
366 // Apply the closure to each object in the space whose references
367 // point to objects in the heap. The usage of CompactibleFreeListSpace
368 // by the ConcurrentMarkSweepGeneration for concurrent GC's allows
369 // objects in the space with references to objects that are no longer
370 // valid. For example, an object may reference another object
371 // that has already been sweep up (collected). This method uses
372 // obj_is_alive() to determine whether it is safe to iterate of
373 // an object.
374 void safe_object_iterate(ObjectClosure* blk);
375
376 // Iterate over all objects that intersect with mr, calling "cl->do_object"
377 // on each. There is an exception to this: if this closure has already
378 // been invoked on an object, it may skip such objects in some cases. This is
379 // Most likely to happen in an "upwards" (ascending address) iteration of
380 // MemRegions.
381 void object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl);
382
383 // Requires that "mr" be entirely within the space.
384 // Apply "cl->do_object" to all objects that intersect with "mr".
385 // If the iteration encounters an unparseable portion of the region,
386 // terminate the iteration and return the address of the start of the
387 // subregion that isn't done. Return of "NULL" indicates that the
388 // iteration completed.
389 HeapWord* object_iterate_careful_m(MemRegion mr,
390 ObjectClosureCareful* cl);
391
392 // Override: provides a DCTO_CL specific to this kind of space.
393 DirtyCardToOopClosure* new_dcto_cl(ExtendedOopClosure* cl,
394 CardTableModRefBS::PrecisionStyle precision,
395 HeapWord* boundary);
396
397 void blk_iterate(BlkClosure* cl);
398 void blk_iterate_careful(BlkClosureCareful* cl);
399 HeapWord* block_start_const(const void* p) const;
400 HeapWord* block_start_careful(const void* p) const;
401 size_t block_size(const HeapWord* p) const;
402 size_t block_size_no_stall(HeapWord* p, const CMSCollector* c) const;
403 bool block_is_obj(const HeapWord* p) const;
404 bool obj_is_alive(const HeapWord* p) const;
405 size_t block_size_nopar(const HeapWord* p) const;
406 bool block_is_obj_nopar(const HeapWord* p) const;
407
408 // Functions for scan_and_{forward,adjust_pointers,compact} support.
409 inline HeapWord* scan_limit() const {
410 return end();
411 }
412
413 inline bool scanned_block_is_obj(const HeapWord* addr) const {
414 return CompactibleFreeListSpace::block_is_obj(addr); // Avoid virtual call
415 }
416
417 inline size_t scanned_block_size(const HeapWord* addr) const {
418 return CompactibleFreeListSpace::block_size(addr); // Avoid virtual call
419 }
420
421 inline size_t adjust_obj_size(size_t size) const {
422 return adjustObjectSize(size);
423 }
424
425 inline size_t obj_size(const HeapWord* addr) const {
426 return adjustObjectSize(oop(addr)->size());
427 }
428
429 // Iteration support for promotion
430 void save_marks();
431 bool no_allocs_since_save_marks();
432
433 // Iteration support for sweeping
434 void save_sweep_limit() {
435 _sweep_limit = BlockOffsetArrayUseUnallocatedBlock ?
436 unallocated_block() : end();
437 if (CMSTraceSweeper) {
438 gclog_or_tty->print_cr(">>>>> Saving sweep limit " PTR_FORMAT
439 " for space [" PTR_FORMAT "," PTR_FORMAT ") <<<<<<",
440 p2i(_sweep_limit), p2i(bottom()), p2i(end()));
441 }
442 }
443 NOT_PRODUCT(
444 void clear_sweep_limit() { _sweep_limit = NULL; }
445 )
446 HeapWord* sweep_limit() { return _sweep_limit; }
447
448 // Apply "blk->do_oop" to the addresses of all reference fields in objects
449 // promoted into this generation since the most recent save_marks() call.
450 // Fields in objects allocated by applications of the closure
451 // *are* included in the iteration. Thus, when the iteration completes
452 // there should be no further such objects remaining.
453 #define CFLS_OOP_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
454 void oop_since_save_marks_iterate##nv_suffix(OopClosureType* blk);
455 ALL_SINCE_SAVE_MARKS_CLOSURES(CFLS_OOP_SINCE_SAVE_MARKS_DECL)
456 #undef CFLS_OOP_SINCE_SAVE_MARKS_DECL
457
458 // Allocation support
459 HeapWord* allocate(size_t size);
460 HeapWord* par_allocate(size_t size);
461
462 oop promote(oop obj, size_t obj_size);
463 void gc_prologue();
464 void gc_epilogue();
465
466 // This call is used by a containing CMS generation / collector
467 // to inform the CFLS space that a sweep has been completed
468 // and that the space can do any related house-keeping functions.
469 void sweep_completed();
470
471 // For an object in this space, the mark-word's two
472 // LSB's having the value [11] indicates that it has been
473 // promoted since the most recent call to save_marks() on
474 // this generation and has not subsequently been iterated
475 // over (using oop_since_save_marks_iterate() above).
476 // This property holds only for single-threaded collections,
477 // and is typically used for Cheney scans; for MT scavenges,
478 // the property holds for all objects promoted during that
479 // scavenge for the duration of the scavenge and is used
480 // by card-scanning to avoid scanning objects (being) promoted
481 // during that scavenge.
482 bool obj_allocated_since_save_marks(const oop obj) const {
483 assert(is_in_reserved(obj), "Wrong space?");
484 return ((PromotedObject*)obj)->hasPromotedMark();
485 }
486
487 // A worst-case estimate of the space required (in HeapWords) to expand the
488 // heap when promoting an obj of size obj_size.
489 size_t expansionSpaceRequired(size_t obj_size) const;
490
491 FreeChunk* allocateScratch(size_t size);
492
493 // Returns true if either the small or large linear allocation buffer is empty.
494 bool linearAllocationWouldFail() const;
495
496 // Adjust the chunk for the minimum size. This version is called in
497 // most cases in CompactibleFreeListSpace methods.
498 inline static size_t adjustObjectSize(size_t size) {
499 return (size_t) align_object_size(MAX2(size, (size_t)MinChunkSize));
500 }
501 // This is a virtual version of adjustObjectSize() that is called
502 // only occasionally when the compaction space changes and the type
503 // of the new compaction space is is only known to be CompactibleSpace.
504 size_t adjust_object_size_v(size_t size) const {
505 return adjustObjectSize(size);
506 }
507 // Minimum size of a free block.
508 virtual size_t minimum_free_block_size() const { return MinChunkSize; }
509 void removeFreeChunkFromFreeLists(FreeChunk* chunk);
510 void addChunkAndRepairOffsetTable(HeapWord* chunk, size_t size,
511 bool coalesced);
512
513 // Support for decisions regarding concurrent collection policy.
514 bool should_concurrent_collect() const;
515
516 // Support for compaction.
517 void prepare_for_compaction(CompactPoint* cp);
518 void adjust_pointers();
519 void compact();
520 // Reset the space to reflect the fact that a compaction of the
521 // space has been done.
522 virtual void reset_after_compaction();
523
524 // Debugging support.
525 void print() const;
526 void print_on(outputStream* st) const;
527 void prepare_for_verify();
528 void verify() const;
529 void verifyFreeLists() const PRODUCT_RETURN;
530 void verifyIndexedFreeLists() const;
531 void verifyIndexedFreeList(size_t size) const;
532 // Verify that the given chunk is in the free lists:
533 // i.e. either the binary tree dictionary, the indexed free lists
534 // or the linear allocation block.
535 bool verify_chunk_in_free_list(FreeChunk* fc) const;
536 // Verify that the given chunk is the linear allocation block.
537 bool verify_chunk_is_linear_alloc_block(FreeChunk* fc) const;
538 // Do some basic checks on the the free lists.
539 void check_free_list_consistency() const PRODUCT_RETURN;
540
541 // Printing support
542 void dump_at_safepoint_with_locks(CMSCollector* c, outputStream* st);
543 void print_indexed_free_lists(outputStream* st) const;
544 void print_dictionary_free_lists(outputStream* st) const;
545 void print_promo_info_blocks(outputStream* st) const;
546
547 NOT_PRODUCT (
548 void initializeIndexedFreeListArrayReturnedBytes();
549 size_t sumIndexedFreeListArrayReturnedBytes();
550 // Return the total number of chunks in the indexed free lists.
551 size_t totalCountInIndexedFreeLists() const;
552 // Return the total number of chunks in the space.
553 size_t totalCount();
554 )
555
556 // The census consists of counts of the quantities such as
557 // the current count of the free chunks, number of chunks
558 // created as a result of the split of a larger chunk or
559 // coalescing of smaller chucks, etc. The counts in the
560 // census is used to make decisions on splitting and
561 // coalescing of chunks during the sweep of garbage.
562
563 // Print the statistics for the free lists.
564 void printFLCensus(size_t sweep_count) const;
565
566 // Statistics functions
567 // Initialize census for lists before the sweep.
568 void beginSweepFLCensus(float inter_sweep_current,
569 float inter_sweep_estimate,
570 float intra_sweep_estimate);
571 // Set the surplus for each of the free lists.
572 void setFLSurplus();
573 // Set the hint for each of the free lists.
574 void setFLHints();
575 // Clear the census for each of the free lists.
576 void clearFLCensus();
577 // Perform functions for the census after the end of the sweep.
578 void endSweepFLCensus(size_t sweep_count);
579 // Return true if the count of free chunks is greater
580 // than the desired number of free chunks.
581 bool coalOverPopulated(size_t size);
582
583 // Record (for each size):
584 //
585 // split-births = #chunks added due to splits in (prev-sweep-end,
586 // this-sweep-start)
587 // split-deaths = #chunks removed for splits in (prev-sweep-end,
588 // this-sweep-start)
589 // num-curr = #chunks at start of this sweep
590 // num-prev = #chunks at end of previous sweep
591 //
592 // The above are quantities that are measured. Now define:
593 //
594 // num-desired := num-prev + split-births - split-deaths - num-curr
595 //
596 // Roughly, num-prev + split-births is the supply,
597 // split-deaths is demand due to other sizes
598 // and num-curr is what we have left.
599 //
600 // Thus, num-desired is roughly speaking the "legitimate demand"
601 // for blocks of this size and what we are striving to reach at the
602 // end of the current sweep.
603 //
604 // For a given list, let num-len be its current population.
605 // Define, for a free list of a given size:
606 //
607 // coal-overpopulated := num-len >= num-desired * coal-surplus
608 // (coal-surplus is set to 1.05, i.e. we allow a little slop when
609 // coalescing -- we do not coalesce unless we think that the current
610 // supply has exceeded the estimated demand by more than 5%).
611 //
612 // For the set of sizes in the binary tree, which is neither dense nor
613 // closed, it may be the case that for a particular size we have never
614 // had, or do not now have, or did not have at the previous sweep,
615 // chunks of that size. We need to extend the definition of
616 // coal-overpopulated to such sizes as well:
617 //
618 // For a chunk in/not in the binary tree, extend coal-overpopulated
619 // defined above to include all sizes as follows:
620 //
621 // . a size that is non-existent is coal-overpopulated
622 // . a size that has a num-desired <= 0 as defined above is
623 // coal-overpopulated.
624 //
625 // Also define, for a chunk heap-offset C and mountain heap-offset M:
626 //
627 // close-to-mountain := C >= 0.99 * M
628 //
629 // Now, the coalescing strategy is:
630 //
631 // Coalesce left-hand chunk with right-hand chunk if and
632 // only if:
633 //
634 // EITHER
635 // . left-hand chunk is of a size that is coal-overpopulated
636 // OR
637 // . right-hand chunk is close-to-mountain
638 void smallCoalBirth(size_t size);
639 void smallCoalDeath(size_t size);
640 void coalBirth(size_t size);
641 void coalDeath(size_t size);
642 void smallSplitBirth(size_t size);
643 void smallSplitDeath(size_t size);
644 void split_birth(size_t size);
645 void splitDeath(size_t size);
646 void split(size_t from, size_t to1);
647
648 double flsFrag() const;
649 };
650
651 // A parallel-GC-thread-local allocation buffer for allocation into a
652 // CompactibleFreeListSpace.
653 class CFLS_LAB : public CHeapObj<mtGC> {
654 // The space that this buffer allocates into.
655 CompactibleFreeListSpace* _cfls;
656
657 // Our local free lists.
658 AdaptiveFreeList<FreeChunk> _indexedFreeList[CompactibleFreeListSpace::IndexSetSize];
659
660 // Initialized from a command-line arg.
661
662 // Allocation statistics in support of dynamic adjustment of
663 // #blocks to claim per get_from_global_pool() call below.
664 static AdaptiveWeightedAverage
665 _blocks_to_claim [CompactibleFreeListSpace::IndexSetSize];
666 static size_t _global_num_blocks [CompactibleFreeListSpace::IndexSetSize];
667 static uint _global_num_workers[CompactibleFreeListSpace::IndexSetSize];
668 size_t _num_blocks [CompactibleFreeListSpace::IndexSetSize];
669
670 // Internal work method
671 void get_from_global_pool(size_t word_sz, AdaptiveFreeList<FreeChunk>* fl);
672
673 public:
674 CFLS_LAB(CompactibleFreeListSpace* cfls);
675
676 // Allocate and return a block of the given size, or else return NULL.
677 HeapWord* alloc(size_t word_sz);
678
679 // Return any unused portions of the buffer to the global pool.
680 void retire(int tid);
681
682 // Dynamic OldPLABSize sizing
683 static void compute_desired_plab_size();
684 // When the settings are modified from default static initialization
685 static void modify_initialization(size_t n, unsigned wt);
686 };
687
688 size_t PromotionInfo::refillSize() const {
689 const size_t CMSSpoolBlockSize = 256;
690 const size_t sz = heap_word_size(sizeof(SpoolBlock) + sizeof(markOop)
691 * CMSSpoolBlockSize);
692 return CompactibleFreeListSpace::adjustObjectSize(sz);
693 }
694
695 #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_COMPACTIBLEFREELISTSPACE_HPP