Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 2001, 2009, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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  */

 // Classes in support of keeping track of promotions into a non-Contiguous

 // space, in this case a CompactibleFreeListSpace.

 // Forward declarations

 class CompactibleFreeListSpace;

 class BlkClosure;

 class BlkClosureCareful;

 class UpwardsObjectClosure;

 class ObjectClosureCareful;

 class Klass;

 class LinearAllocBlock VALUE_OBJ_CLASS_SPEC {

  public:

   LinearAllocBlock() : _ptr(0), _word_size(0), _refillSize(0),

     _allocation_size_limit(0) {}

   void set(HeapWord* ptr, size_t word_size, size_t refill_size,

     size_t allocation_size_limit) {

     _ptr = ptr;

     _word_size = word_size;

     _refillSize = refill_size;

     _allocation_size_limit = allocation_size_limit;

   }

   HeapWord* _ptr;

   size_t    _word_size;

   size_t    _refillSize;

   size_t    _allocation_size_limit;  // largest size that will be allocated

 };

 // Concrete subclass of CompactibleSpace that implements

 // a free list space, such as used in the concurrent mark sweep

 // generation.

 class CompactibleFreeListSpace: public CompactibleSpace {

   friend class VMStructs;

   friend class ConcurrentMarkSweepGeneration;

   friend class ASConcurrentMarkSweepGeneration;

   friend class CMSCollector;

   friend class CMSPermGenGen;

   // Local alloc buffer for promotion into this space.

   friend class CFLS_LAB;

   // "Size" of chunks of work (executed during parallel remark phases

   // of CMS collection); this probably belongs in CMSCollector, although

   // it's cached here because it's used in

   // initialize_sequential_subtasks_for_rescan() which modifies

   // par_seq_tasks which also lives in Space. XXX

   const size_t _rescan_task_size;

   const size_t _marking_task_size;

   // Yet another sequential tasks done structure. This supports

   // CMS GC, where we have threads dynamically

   // claiming sub-tasks from a larger parallel task.

   SequentialSubTasksDone _conc_par_seq_tasks;

   BlockOffsetArrayNonContigSpace _bt;

   CMSCollector* _collector;

   ConcurrentMarkSweepGeneration* _gen;

   // Data structures for free blocks (used during allocation/sweeping)

   // Allocation is done linearly from two different blocks depending on

   // whether the request is small or large, in an effort to reduce

   // fragmentation. We assume that any locking for allocation is done

   // by the containing generation. Thus, none of the methods in this

   // space are re-entrant.

   enum SomeConstants {

     SmallForLinearAlloc = 16,        // size < this then use _sLAB

     SmallForDictionary  = 257,       // size < this then use _indexedFreeList

     IndexSetSize        = SmallForDictionary  // keep this odd-sized

   };

   static int IndexSetStart;

   static int IndexSetStride;

  private:

   enum FitStrategyOptions {

     FreeBlockStrategyNone = 0,

     FreeBlockBestFitFirst

   };

   PromotionInfo _promoInfo;

   // helps to impose a global total order on freelistLock ranks;

   // assumes that CFLSpace's are allocated in global total order

   static int   _lockRank;

   // a lock protecting the free lists and free blocks;

   // mutable because of ubiquity of locking even for otherwise const methods

   mutable Mutex _freelistLock;

   // locking verifier convenience function

   void assert_locked() const PRODUCT_RETURN;

   void assert_locked(const Mutex* lock) const PRODUCT_RETURN;

   // Linear allocation blocks

   LinearAllocBlock _smallLinearAllocBlock;

   FreeBlockDictionary::DictionaryChoice _dictionaryChoice;

   FreeBlockDictionary* _dictionary;    // ptr to dictionary for large size blocks

   FreeList _indexedFreeList[IndexSetSize];

                                        // indexed array for small size blocks

   // allocation stategy

   bool       _fitStrategy;      // Use best fit strategy.

   bool       _adaptive_freelists; // Use adaptive freelists

   // This is an address close to the largest free chunk in the heap.

   // It is currently assumed to be at the end of the heap.  Free

   // chunks with addresses greater than nearLargestChunk are coalesced

   // in an effort to maintain a large chunk at the end of the heap.

   HeapWord*  _nearLargestChunk;

   // Used to keep track of limit of sweep for the space

   HeapWord* _sweep_limit;

   // Support for compacting cms

   HeapWord* cross_threshold(HeapWord* start, HeapWord* end);

   HeapWord* forward(oop q, size_t size, CompactPoint* cp, HeapWord* compact_top);

   // Initialization helpers.

   void initializeIndexedFreeListArray();

   // Extra stuff to manage promotion parallelism.

   // a lock protecting the dictionary during par promotion allocation.

   mutable Mutex _parDictionaryAllocLock;

   Mutex* parDictionaryAllocLock() const { return &_parDictionaryAllocLock; }

   // Locks protecting the exact lists during par promotion allocation.

   Mutex* _indexedFreeListParLocks[IndexSetSize];

   // Attempt to obtain up to "n" blocks of the size "word_sz" (which is

   // required to be smaller than "IndexSetSize".)  If successful,

   // adds them to "fl", which is required to be an empty free list.

   // If the count of "fl" is negative, it's absolute value indicates a

   // number of free chunks that had been previously "borrowed" from global

   // list of size "word_sz", and must now be decremented.

   void par_get_chunk_of_blocks(size_t word_sz, size_t n, FreeList* fl);

   // Allocation helper functions

   // Allocate using a strategy that takes from the indexed free lists

   // first.  This allocation strategy assumes a companion sweeping

   // strategy that attempts to keep the needed number of chunks in each

   // indexed free lists.

   HeapWord* allocate_adaptive_freelists(size_t size);

   // Allocate from the linear allocation buffers first.  This allocation

   // strategy assumes maximal coalescing can maintain chunks large enough

   // to be used as linear allocation buffers.

   HeapWord* allocate_non_adaptive_freelists(size_t size);

   // Gets a chunk from the linear allocation block (LinAB).  If there

   // is not enough space in the LinAB, refills it.

   HeapWord*  getChunkFromLinearAllocBlock(LinearAllocBlock* blk, size_t size);

   HeapWord*  getChunkFromSmallLinearAllocBlock(size_t size);

   // Get a chunk from the space remaining in the linear allocation block.  Do

   // not attempt to refill if the space is not available, return NULL.  Do the

   // repairs on the linear allocation block as appropriate.

   HeapWord*  getChunkFromLinearAllocBlockRemainder(LinearAllocBlock* blk, size_t size);

   inline HeapWord*  getChunkFromSmallLinearAllocBlockRemainder(size_t size);

   // Helper function for getChunkFromIndexedFreeList.

   // Replenish the indexed free list for this "size".  Do not take from an

   // underpopulated size.

   FreeChunk*  getChunkFromIndexedFreeListHelper(size_t size, bool replenish = true);

   // Get a chunk from the indexed free list.  If the indexed free list

   // does not have a free chunk, try to replenish the indexed free list

   // then get the free chunk from the replenished indexed free list.

   inline FreeChunk* getChunkFromIndexedFreeList(size_t size);

   // The returned chunk may be larger than requested (or null).

   FreeChunk* getChunkFromDictionary(size_t size);

   // The returned chunk is the exact size requested (or null).

   FreeChunk* getChunkFromDictionaryExact(size_t size);

   // Find a chunk in the indexed free list that is the best

   // fit for size "numWords".

   FreeChunk* bestFitSmall(size_t numWords);

   // For free list "fl" of chunks of size > numWords,

   // remove a chunk, split off a chunk of size numWords

   // and return it.  The split off remainder is returned to

   // the free lists.  The old name for getFromListGreater

   // was lookInListGreater.

   FreeChunk* getFromListGreater(FreeList* fl, size_t numWords);

   // Get a chunk in the indexed free list or dictionary,

   // by considering a larger chunk and splitting it.

   FreeChunk* getChunkFromGreater(size_t numWords);

   //  Verify that the given chunk is in the indexed free lists.

   bool verifyChunkInIndexedFreeLists(FreeChunk* fc) const;

   // Remove the specified chunk from the indexed free lists.

   void       removeChunkFromIndexedFreeList(FreeChunk* fc);

   // Remove the specified chunk from the dictionary.

   void       removeChunkFromDictionary(FreeChunk* fc);

   // Split a free chunk into a smaller free chunk of size "new_size".

   // Return the smaller free chunk and return the remainder to the

   // free lists.

   FreeChunk* splitChunkAndReturnRemainder(FreeChunk* chunk, size_t new_size);

   // Add a chunk to the free lists.

   void       addChunkToFreeLists(HeapWord* chunk, size_t size);

   // Add a chunk to the free lists, preferring to suffix it

   // to the last free chunk at end of space if possible, and

   // updating the block census stats as well as block offset table.

   // Take any locks as appropriate if we are multithreaded.

   void       addChunkToFreeListsAtEndRecordingStats(HeapWord* chunk, size_t size);

   // Add a free chunk to the indexed free lists.

   void       returnChunkToFreeList(FreeChunk* chunk);

   // Add a free chunk to the dictionary.

   void       returnChunkToDictionary(FreeChunk* chunk);

   // Functions for maintaining the linear allocation buffers (LinAB).

   // Repairing a linear allocation block refers to operations

   // performed on the remainder of a LinAB after an allocation

   // has been made from it.

   void       repairLinearAllocationBlocks();

   void       repairLinearAllocBlock(LinearAllocBlock* blk);

   void       refillLinearAllocBlock(LinearAllocBlock* blk);

   void       refillLinearAllocBlockIfNeeded(LinearAllocBlock* blk);

   void       refillLinearAllocBlocksIfNeeded();

   void       verify_objects_initialized() const;

   // Statistics reporting helper functions

   void       reportFreeListStatistics() const;

   void       reportIndexedFreeListStatistics() const;

   size_t     maxChunkSizeInIndexedFreeLists() const;

   size_t     numFreeBlocksInIndexedFreeLists() const;

   // Accessor

   HeapWord* unallocated_block() const {

     HeapWord* ub = _bt.unallocated_block();

     assert(ub >= bottom() &&

            ub <= end(), "space invariant");

     return ub;

   }

   void freed(HeapWord* start, size_t size) {

     _bt.freed(start, size);

   }

  protected:

   // reset the indexed free list to its initial empty condition.

   void resetIndexedFreeListArray();

   // reset to an initial state with a single free block described

   // by the MemRegion parameter.

   void reset(MemRegion mr);

   // Return the total number of words in the indexed free lists.

   size_t     totalSizeInIndexedFreeLists() const;

  public:

   // Constructor...

   CompactibleFreeListSpace(BlockOffsetSharedArray* bs, MemRegion mr,

                            bool use_adaptive_freelists,

                            FreeBlockDictionary::DictionaryChoice);

   // accessors

   bool bestFitFirst() { return _fitStrategy == FreeBlockBestFitFirst; }

   FreeBlockDictionary* dictionary() const { return _dictionary; }

   HeapWord* nearLargestChunk() const { return _nearLargestChunk; }

   void set_nearLargestChunk(HeapWord* v) { _nearLargestChunk = v; }

   // Set CMS global values

   static void set_cms_values();

   // Return the free chunk at the end of the space.  If no such

   // chunk exists, return NULL.

   FreeChunk* find_chunk_at_end();

   bool adaptive_freelists() const { return _adaptive_freelists; }

   void set_collector(CMSCollector* collector) { _collector = collector; }

   // Support for parallelization of rescan and marking

   const size_t rescan_task_size()  const { return _rescan_task_size;  }

   const size_t marking_task_size() const { return _marking_task_size; }

   SequentialSubTasksDone* conc_par_seq_tasks() {return &_conc_par_seq_tasks; }

   void initialize_sequential_subtasks_for_rescan(int n_threads);

   void initialize_sequential_subtasks_for_marking(int n_threads,

          HeapWord* low = NULL);

   // Space enquiries

   size_t used() const;

   size_t free() const;

   size_t max_alloc_in_words() const;

   // XXX: should have a less conservative used_region() than that of

   // Space; we could consider keeping track of highest allocated

   // address and correcting that at each sweep, as the sweeper

   // goes through the entire allocated part of the generation. We

   // could also use that information to keep the sweeper from

   // sweeping more than is necessary. The allocator and sweeper will

   // of course need to synchronize on this, since the sweeper will

   // try to bump down the address and the allocator will try to bump it up.

   // For now, however, we'll just use the default used_region()

   // which overestimates the region by returning the entire

   // committed region (this is safe, but inefficient).

   // Returns a subregion of the space containing all the objects in

   // the space.

   MemRegion used_region() const {

     return MemRegion(bottom(),

                      BlockOffsetArrayUseUnallocatedBlock ?

                      unallocated_block() : end());

   }

   // This is needed because the default implementation uses block_start()

   // which can;t be used at certain times (for example phase 3 of mark-sweep).

   // A better fix is to change the assertions in phase 3 of mark-sweep to

   // use is_in_reserved(), but that is deferred since the is_in() assertions

   // are buried through several layers of callers and are used elsewhere

   // as well.

   bool is_in(const void* p) const {

     return used_region().contains(p);

   }

   virtual bool is_free_block(const HeapWord* p) const;

   // Resizing support

   void set_end(HeapWord* value);  // override

   // mutual exclusion support

   Mutex* freelistLock() const { return &_freelistLock; }

   // Iteration support

   void oop_iterate(MemRegion mr, OopClosure* cl);

   void oop_iterate(OopClosure* cl);

   void object_iterate(ObjectClosure* blk);

   // Apply the closure to each object in the space whose references

   // point to objects in the heap.  The usage of CompactibleFreeListSpace

   // by the ConcurrentMarkSweepGeneration for concurrent GC's allows

   // objects in the space with references to objects that are no longer

   // valid.  For example, an object may reference another object

   // that has already been sweep up (collected).  This method uses

   // obj_is_alive() to determine whether it is safe to iterate of

   // an object.

   void safe_object_iterate(ObjectClosure* blk);

   void object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl);

   // Requires that "mr" be entirely within the space.

   // Apply "cl->do_object" to all objects that intersect with "mr".

   // If the iteration encounters an unparseable portion of the region,

   // terminate the iteration and return the address of the start of the

   // subregion that isn't done.  Return of "NULL" indicates that the

   // interation completed.

   virtual HeapWord*

        object_iterate_careful_m(MemRegion mr,

                                 ObjectClosureCareful* cl);

   virtual HeapWord*

        object_iterate_careful(ObjectClosureCareful* cl);

   // Override: provides a DCTO_CL specific to this kind of space.

   DirtyCardToOopClosure* new_dcto_cl(OopClosure* cl,

                                      CardTableModRefBS::PrecisionStyle precision,

                                      HeapWord* boundary);

   void blk_iterate(BlkClosure* cl);

   void blk_iterate_careful(BlkClosureCareful* cl);

   HeapWord* block_start_const(const void* p) const;

   HeapWord* block_start_careful(const void* p) const;

   size_t block_size(const HeapWord* p) const;

   size_t block_size_no_stall(HeapWord* p, const CMSCollector* c) const;

   bool block_is_obj(const HeapWord* p) const;

   bool obj_is_alive(const HeapWord* p) const;

   size_t block_size_nopar(const HeapWord* p) const;

   bool block_is_obj_nopar(const HeapWord* p) const;

   // iteration support for promotion

   void save_marks();

   bool no_allocs_since_save_marks();

   void object_iterate_since_last_GC(ObjectClosure* cl);

   // iteration support for sweeping

   void save_sweep_limit() {

     _sweep_limit = BlockOffsetArrayUseUnallocatedBlock ?

                    unallocated_block() : end();

   }

   NOT_PRODUCT(

     void clear_sweep_limit() { _sweep_limit = NULL; }

   )

   HeapWord* sweep_limit() { return _sweep_limit; }

   // Apply "blk->do_oop" to the addresses of all reference fields in objects

   // promoted into this generation since the most recent save_marks() call.

   // Fields in objects allocated by applications of the closure

   // *are* included in the iteration. Thus, when the iteration completes

   // there should be no further such objects remaining.

   #define CFLS_OOP_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)  \

     void oop_since_save_marks_iterate##nv_suffix(OopClosureType* blk);

   ALL_SINCE_SAVE_MARKS_CLOSURES(CFLS_OOP_SINCE_SAVE_MARKS_DECL)

   #undef CFLS_OOP_SINCE_SAVE_MARKS_DECL

   // Allocation support

   HeapWord* allocate(size_t size);

   HeapWord* par_allocate(size_t size);

   oop       promote(oop obj, size_t obj_size);

   void      gc_prologue();

   void      gc_epilogue();

   // This call is used by a containing CMS generation / collector

   // to inform the CFLS space that a sweep has been completed

   // and that the space can do any related house-keeping functions.

   void      sweep_completed();

   // For an object in this space, the mark-word's two

   // LSB's having the value [11] indicates that it has been

   // promoted since the most recent call to save_marks() on

   // this generation and has not subsequently been iterated

   // over (using oop_since_save_marks_iterate() above).

   // This property holds only for single-threaded collections,

   // and is typically used for Cheney scans; for MT scavenges,

   // the property holds for all objects promoted during that

   // scavenge for the duration of the scavenge and is used

   // by card-scanning to avoid scanning objects (being) promoted

   // during that scavenge.

   bool obj_allocated_since_save_marks(const oop obj) const {

     assert(is_in_reserved(obj), "Wrong space?");

     return ((PromotedObject*)obj)->hasPromotedMark();

   }

   // A worst-case estimate of the space required (in HeapWords) to expand the

   // heap when promoting an obj of size obj_size.

   size_t expansionSpaceRequired(size_t obj_size) const;

   FreeChunk* allocateScratch(size_t size);

   // returns true if either the small or large linear allocation buffer is empty.

   bool       linearAllocationWouldFail() const;

   // Adjust the chunk for the minimum size.  This version is called in

   // most cases in CompactibleFreeListSpace methods.

   inline static size_t adjustObjectSize(size_t size) {

     return (size_t) align_object_size(MAX2(size, (size_t)MinChunkSize));

   }

   // This is a virtual version of adjustObjectSize() that is called

   // only occasionally when the compaction space changes and the type

   // of the new compaction space is is only known to be CompactibleSpace.

   size_t adjust_object_size_v(size_t size) const {

     return adjustObjectSize(size);

   }

   // Minimum size of a free block.

   virtual size_t minimum_free_block_size() const { return MinChunkSize; }

   void      removeFreeChunkFromFreeLists(FreeChunk* chunk);

   void      addChunkAndRepairOffsetTable(HeapWord* chunk, size_t size,

               bool coalesced);

   // Support for decisions regarding concurrent collection policy

   bool should_concurrent_collect() const;

   // Support for compaction

   void prepare_for_compaction(CompactPoint* cp);

   void adjust_pointers();

   void compact();

   // reset the space to reflect the fact that a compaction of the

   // space has been done.

   virtual void reset_after_compaction();

   // Debugging support

   void print()                            const;

   void prepare_for_verify();

   void verify(bool allow_dirty)           const;

   void verifyFreeLists()                  const PRODUCT_RETURN;

   void verifyIndexedFreeLists()           const;

   void verifyIndexedFreeList(size_t size) const;

   // verify that the given chunk is in the free lists.

   bool verifyChunkInFreeLists(FreeChunk* fc) const;

   // Do some basic checks on the the free lists.

   void checkFreeListConsistency()         const PRODUCT_RETURN;

   // Printing support

   void dump_at_safepoint_with_locks(CMSCollector* c, outputStream* st);

   void print_indexed_free_lists(outputStream* st) const;

   void print_dictionary_free_lists(outputStream* st) const;

   void print_promo_info_blocks(outputStream* st) const;

   NOT_PRODUCT (

     void initializeIndexedFreeListArrayReturnedBytes();

     size_t sumIndexedFreeListArrayReturnedBytes();

     // Return the total number of chunks in the indexed free lists.

     size_t totalCountInIndexedFreeLists() const;

     // Return the total numberof chunks in the space.

     size_t totalCount();

   )

   // The census consists of counts of the quantities such as

   // the current count of the free chunks, number of chunks

   // created as a result of the split of a larger chunk or

   // coalescing of smaller chucks, etc.  The counts in the

   // census is used to make decisions on splitting and

   // coalescing of chunks during the sweep of garbage.

   // Print the statistics for the free lists.

   void printFLCensus(size_t sweep_count) const;

   // Statistics functions

   // Initialize census for lists before the sweep.

   void beginSweepFLCensus(float inter_sweep_current,

                           float inter_sweep_estimate,

                           float intra_sweep_estimate);

   // Set the surplus for each of the free lists.

   void setFLSurplus();

   // Set the hint for each of the free lists.

   void setFLHints();

   // Clear the census for each of the free lists.

   void clearFLCensus();

   // Perform functions for the census after the end of the sweep.

   void endSweepFLCensus(size_t sweep_count);

   // Return true if the count of free chunks is greater

   // than the desired number of free chunks.

   bool coalOverPopulated(size_t size);

 // Record (for each size):

 //

 //   split-births = #chunks added due to splits in (prev-sweep-end,

 //      this-sweep-start)

 //   split-deaths = #chunks removed for splits in (prev-sweep-end,

 //      this-sweep-start)

 //   num-curr     = #chunks at start of this sweep

 //   num-prev     = #chunks at end of previous sweep

 //

 // The above are quantities that are measured. Now define:

 //

 //   num-desired := num-prev + split-births - split-deaths - num-curr

 //

 // Roughly, num-prev + split-births is the supply,

 // split-deaths is demand due to other sizes

 // and num-curr is what we have left.

 //

 // Thus, num-desired is roughly speaking the "legitimate demand"

 // for blocks of this size and what we are striving to reach at the

 // end of the current sweep.

 //

 // For a given list, let num-len be its current population.

 // Define, for a free list of a given size:

 //

 //   coal-overpopulated := num-len >= num-desired * coal-surplus

 // (coal-surplus is set to 1.05, i.e. we allow a little slop when

 // coalescing -- we do not coalesce unless we think that the current

 // supply has exceeded the estimated demand by more than 5%).

 //

 // For the set of sizes in the binary tree, which is neither dense nor

 // closed, it may be the case that for a particular size we have never

 // had, or do not now have, or did not have at the previous sweep,

 // chunks of that size. We need to extend the definition of

 // coal-overpopulated to such sizes as well:

 //

 //   For a chunk in/not in the binary tree, extend coal-overpopulated

 //   defined above to include all sizes as follows:

 //

 //   . a size that is non-existent is coal-overpopulated

 //   . a size that has a num-desired <= 0 as defined above is

 //     coal-overpopulated.

 //

 // Also define, for a chunk heap-offset C and mountain heap-offset M:

 //

 //   close-to-mountain := C >= 0.99 * M

 //

 // Now, the coalescing strategy is:

 //

 //    Coalesce left-hand chunk with right-hand chunk if and

 //    only if:

 //

 //      EITHER

 //        . left-hand chunk is of a size that is coal-overpopulated

 //      OR

 //        . right-hand chunk is close-to-mountain

   void smallCoalBirth(size_t size);

   void smallCoalDeath(size_t size);

   void coalBirth(size_t size);

   void coalDeath(size_t size);

   void smallSplitBirth(size_t size);

   void smallSplitDeath(size_t size);

   void splitBirth(size_t size);

   void splitDeath(size_t size);

   void split(size_t from, size_t to1);

   double flsFrag() const;

 };

 // A parallel-GC-thread-local allocation buffer for allocation into a

 // CompactibleFreeListSpace.

 class CFLS_LAB : public CHeapObj {

   // The space that this buffer allocates into.

   CompactibleFreeListSpace* _cfls;

   // Our local free lists.

   FreeList _indexedFreeList[CompactibleFreeListSpace::IndexSetSize];

   // Initialized from a command-line arg.

   // Allocation statistics in support of dynamic adjustment of

   // #blocks to claim per get_from_global_pool() call below.

   static AdaptiveWeightedAverage

                  _blocks_to_claim  [CompactibleFreeListSpace::IndexSetSize];

   static size_t _global_num_blocks [CompactibleFreeListSpace::IndexSetSize];

   static int    _global_num_workers[CompactibleFreeListSpace::IndexSetSize];

   size_t        _num_blocks        [CompactibleFreeListSpace::IndexSetSize];

   // Internal work method

   void get_from_global_pool(size_t word_sz, FreeList* fl);

 public:

   CFLS_LAB(CompactibleFreeListSpace* cfls);

   // Allocate and return a block of the given size, or else return NULL.

   HeapWord* alloc(size_t word_sz);

   // Return any unused portions of the buffer to the global pool.

   void retire(int tid);

   // Dynamic OldPLABSize sizing

   static void compute_desired_plab_size();

   // When the settings are modified from default static initialization

   static void modify_initialization(size_t n, unsigned wt);

 };

 size_t PromotionInfo::refillSize() const {

   const size_t CMSSpoolBlockSize = 256;

   const size_t sz = heap_word_size(sizeof(SpoolBlock) + sizeof(markOop)

                                    * CMSSpoolBlockSize);

   return CompactibleFreeListSpace::adjustObjectSize(sz);

 }