1 /*

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

     4  *

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

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

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

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

    13  * accompanied this code).

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    24 

    25 #ifndef SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP

    26 #define SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP

    27 

    28 #include "gc/g1/g1RegionToSpaceMapper.hpp"

    29 #include "memory/memRegion.hpp"

    30 #include "memory/virtualspace.hpp"

    31 #include "utilities/globalDefinitions.hpp"

    32 

    33 // The CollectedHeap type requires subtypes to implement a method

    34 // "block_start".  For some subtypes, notably generational

    35 // systems using card-table-based write barriers, the efficiency of this

    36 // operation may be important.  Implementations of the "BlockOffsetArray"

    37 // class may be useful in providing such efficient implementations.

    38 //

    39 // While generally mirroring the structure of the BOT for GenCollectedHeap,

    40 // the following types are tailored more towards G1's uses; these should,

    41 // however, be merged back into a common BOT to avoid code duplication

    42 // and reduce maintenance overhead.

    43 //

    44 //    G1BlockOffsetTable (abstract)

    45 //    -- G1BlockOffsetArray                (uses G1BlockOffsetSharedArray)

    46 //       -- G1BlockOffsetArrayContigSpace

    47 //

    48 // A main impediment to the consolidation of this code might be the

    49 // effect of making some of the block_start*() calls non-const as

    50 // below. Whether that might adversely affect performance optimizations

    51 // that compilers might normally perform in the case of non-G1

    52 // collectors needs to be carefully investigated prior to any such

    53 // consolidation.

    54 

    55 // Forward declarations

    56 class G1BlockOffsetSharedArray;

    57 class G1OffsetTableContigSpace;

    58 

    59 class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC {

    60   friend class VMStructs;

    61 protected:

    62   // These members describe the region covered by the table.

    63 

    64   // The space this table is covering.

    65   HeapWord* _bottom;    // == reserved.start

    66   HeapWord* _end;       // End of currently allocated region.

    67 

    68 public:

    69   // Initialize the table to cover the given space.

    70   // The contents of the initial table are undefined.

    71   G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) :

    72     _bottom(bottom), _end(end)

    73     {

    74       assert(_bottom <= _end, "arguments out of order");

    75     }

    76 

    77   // Note that the committed size of the covered space may have changed,

    78   // so the table size might also wish to change.

    79   virtual void resize(size_t new_word_size) = 0;

    80 

    81   virtual void set_bottom(HeapWord* new_bottom) {

    82     assert(new_bottom <= _end,

    83            err_msg("new_bottom (" PTR_FORMAT ") > _end (" PTR_FORMAT ")",

    84                    p2i(new_bottom), p2i(_end)));

    85     _bottom = new_bottom;

    86     resize(pointer_delta(_end, _bottom));

    87   }

    88 

    89   // Requires "addr" to be contained by a block, and returns the address of

    90   // the start of that block.  (May have side effects, namely updating of

    91   // shared array entries that "point" too far backwards.  This can occur,

    92   // for example, when LAB allocation is used in a space covered by the

    93   // table.)

    94   virtual HeapWord* block_start_unsafe(const void* addr) = 0;

    95   // Same as above, but does not have any of the possible side effects

    96   // discussed above.

    97   virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0;

    98 

    99   // Returns the address of the start of the block containing "addr", or

   100   // else "null" if it is covered by no block.  (May have side effects,

   101   // namely updating of shared array entries that "point" too far

   102   // backwards.  This can occur, for example, when lab allocation is used

   103   // in a space covered by the table.)

   104   inline HeapWord* block_start(const void* addr);

   105   // Same as above, but does not have any of the possible side effects

   106   // discussed above.

   107   inline HeapWord* block_start_const(const void* addr) const;

   108 };

   109 

   110 class G1BlockOffsetSharedArrayMappingChangedListener : public G1MappingChangedListener {

   111  public:

   112   virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled) {

   113     // Nothing to do. The BOT is hard-wired to be part of the HeapRegion, and we cannot

   114     // retrieve it here since this would cause firing of several asserts. The code

   115     // executed after commit of a region already needs to do some re-initialization of

   116     // the HeapRegion, so we combine that.

   117   }

   118 };

   119 

   120 // This implementation of "G1BlockOffsetTable" divides the covered region

   121 // into "N"-word subregions (where "N" = 2^"LogN".  An array with an entry

   122 // for each such subregion indicates how far back one must go to find the

   123 // start of the chunk that includes the first word of the subregion.

   124 //

   125 // Each BlockOffsetArray is owned by a Space.  However, the actual array

   126 // may be shared by several BlockOffsetArrays; this is useful

   127 // when a single resizable area (such as a generation) is divided up into

   128 // several spaces in which contiguous allocation takes place,

   129 // such as, for example, in G1 or in the train generation.)

   130 

   131 // Here is the shared array type.

   132 

   133 class G1BlockOffsetSharedArray: public CHeapObj<mtGC> {

   134   friend class G1BlockOffsetArray;

   135   friend class G1BlockOffsetArrayContigSpace;

   136   friend class VMStructs;

   137 

   138 private:

   139   G1BlockOffsetSharedArrayMappingChangedListener _listener;

   140   // The reserved region covered by the shared array.

   141   MemRegion _reserved;

   142 

   143   // End of the current committed region.

   144   HeapWord* _end;

   145 

   146   // Array for keeping offsets for retrieving object start fast given an

   147   // address.

   148   u_char* _offset_array;          // byte array keeping backwards offsets

   149 

   150   void check_offset(size_t offset, const char* msg) const {

   151     assert(offset <= N_words,

   152            err_msg("%s - "

   153                    "offset: " SIZE_FORMAT", N_words: %u",

   154                    msg, offset, (uint)N_words));

   155   }

   156 

   157   // Bounds checking accessors:

   158   // For performance these have to devolve to array accesses in product builds.

   159   inline u_char offset_array(size_t index) const;

   160 

   161   void set_offset_array_raw(size_t index, u_char offset) {

   162     _offset_array[index] = offset;

   163   }

   164 

   165   inline void set_offset_array(size_t index, u_char offset);

   166 

   167   inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);

   168 

   169   inline void set_offset_array(size_t left, size_t right, u_char offset);

   170 

   171   bool is_card_boundary(HeapWord* p) const;

   172 

   173   void check_index(size_t index, const char* msg) const NOT_DEBUG_RETURN;

   174 

   175 public:

   176 

   177   // Return the number of slots needed for an offset array

   178   // that covers mem_region_words words.

   179   static size_t compute_size(size_t mem_region_words) {

   180     size_t number_of_slots = (mem_region_words / N_words);

   181     return ReservedSpace::allocation_align_size_up(number_of_slots);

   182   }

   183 

   184   // Returns how many bytes of the heap a single byte of the BOT corresponds to.

   185   static size_t heap_map_factor() {

   186     return N_bytes;

   187   }

   188 

   189   enum SomePublicConstants {

   190     LogN = 9,

   191     LogN_words = LogN - LogHeapWordSize,

   192     N_bytes = 1 << LogN,

   193     N_words = 1 << LogN_words

   194   };

   195 

   196   // Initialize the table to cover from "base" to (at least)

   197   // "base + init_word_size".  In the future, the table may be expanded

   198   // (see "resize" below) up to the size of "_reserved" (which must be at

   199   // least "init_word_size".) The contents of the initial table are

   200   // undefined; it is the responsibility of the constituent

   201   // G1BlockOffsetTable(s) to initialize cards.

   202   G1BlockOffsetSharedArray(MemRegion heap, G1RegionToSpaceMapper* storage);

   203 

   204   // Return the appropriate index into "_offset_array" for "p".

   205   inline size_t index_for(const void* p) const;

   206   inline size_t index_for_raw(const void* p) const;

   207 

   208   // Return the address indicating the start of the region corresponding to

   209   // "index" in "_offset_array".

   210   inline HeapWord* address_for_index(size_t index) const;

   211   // Variant of address_for_index that does not check the index for validity.

   212   inline HeapWord* address_for_index_raw(size_t index) const {

   213     return _reserved.start() + (index << LogN_words);

   214   }

   215 };

   216 

   217 // And here is the G1BlockOffsetTable subtype that uses the array.

   218 

   219 class G1BlockOffsetArray: public G1BlockOffsetTable {

   220   friend class G1BlockOffsetSharedArray;

   221   friend class G1BlockOffsetArrayContigSpace;

   222   friend class VMStructs;

   223 private:

   224   enum SomePrivateConstants {

   225     N_words = G1BlockOffsetSharedArray::N_words,

   226     LogN    = G1BlockOffsetSharedArray::LogN

   227   };

   228 

   229   // This is the array, which can be shared by several BlockOffsetArray's

   230   // servicing different

   231   G1BlockOffsetSharedArray* _array;

   232 

   233   // The space that owns this subregion.

   234   G1OffsetTableContigSpace* _gsp;

   235 

   236   // The portion [_unallocated_block, _sp.end()) of the space that

   237   // is a single block known not to contain any objects.

   238   // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.

   239   HeapWord* _unallocated_block;

   240 

   241   // Sets the entries

   242   // corresponding to the cards starting at "start" and ending at "end"

   243   // to point back to the card before "start": the interval [start, end)

   244   // is right-open.

   245   void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);

   246   // Same as above, except that the args here are a card _index_ interval

   247   // that is closed: [start_index, end_index]

   248   void set_remainder_to_point_to_start_incl(size_t start, size_t end);

   249 

   250 protected:

   251 

   252   G1OffsetTableContigSpace* gsp() const { return _gsp; }

   253 

   254   inline size_t block_size(const HeapWord* p) const;

   255 

   256   // Returns the address of a block whose start is at most "addr".

   257   // If "has_max_index" is true, "assumes "max_index" is the last valid one

   258   // in the array.

   259   inline HeapWord* block_at_or_preceding(const void* addr,

   260                                          bool has_max_index,

   261                                          size_t max_index) const;

   262 

   263   // "q" is a block boundary that is <= "addr"; "n" is the address of the

   264   // next block (or the end of the space.)  Return the address of the

   265   // beginning of the block that contains "addr".  Does so without side

   266   // effects (see, e.g., spec of  block_start.)

   267   inline HeapWord*

   268   forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,

   269                                          const void* addr) const;

   270 

   271   // "q" is a block boundary that is <= "addr"; return the address of the

   272   // beginning of the block that contains "addr".  May have side effects

   273   // on "this", by updating imprecise entries.

   274   inline HeapWord* forward_to_block_containing_addr(HeapWord* q,

   275                                                     const void* addr);

   276 

   277   // "q" is a block boundary that is <= "addr"; "n" is the address of the

   278   // next block (or the end of the space.)  Return the address of the

   279   // beginning of the block that contains "addr".  May have side effects

   280   // on "this", by updating imprecise entries.

   281   HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,

   282                                                   HeapWord* n,

   283                                                   const void* addr);

   284 

   285   // Requires that "*threshold_" be the first array entry boundary at or

   286   // above "blk_start", and that "*index_" be the corresponding array

   287   // index.  If the block starts at or crosses "*threshold_", records

   288   // "blk_start" as the appropriate block start for the array index

   289   // starting at "*threshold_", and for any other indices crossed by the

   290   // block.  Updates "*threshold_" and "*index_" to correspond to the first

   291   // index after the block end.

   292   void alloc_block_work2(HeapWord** threshold_, size_t* index_,

   293                          HeapWord* blk_start, HeapWord* blk_end);

   294 

   295 public:

   296   // The space may not have it's bottom and top set yet, which is why the

   297   // region is passed as a parameter. The elements of the array are

   298   // initialized to zero.

   299   G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr);

   300 

   301   // Note: this ought to be part of the constructor, but that would require

   302   // "this" to be passed as a parameter to a member constructor for

   303   // the containing concrete subtype of Space.

   304   // This would be legal C++, but MS VC++ doesn't allow it.

   305   void set_space(G1OffsetTableContigSpace* sp);

   306 

   307   // Resets the covered region to one with the same _bottom as before but

   308   // the "new_word_size".

   309   void resize(size_t new_word_size);

   310 

   311   virtual HeapWord* block_start_unsafe(const void* addr);

   312   virtual HeapWord* block_start_unsafe_const(const void* addr) const;

   313 

   314   void check_all_cards(size_t left_card, size_t right_card) const;

   315 

   316   void verify() const;

   317 

   318   virtual void print_on(outputStream* out) PRODUCT_RETURN;

   319 };

   320 

   321 // A subtype of BlockOffsetArray that takes advantage of the fact

   322 // that its underlying space is a ContiguousSpace, so that its "active"

   323 // region can be more efficiently tracked (than for a non-contiguous space).

   324 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {

   325   friend class VMStructs;

   326 

   327   // allocation boundary at which offset array must be updated

   328   HeapWord* _next_offset_threshold;

   329   size_t    _next_offset_index;      // index corresponding to that boundary

   330 

   331   // Work function to be called when allocation start crosses the next

   332   // threshold in the contig space.

   333   void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {

   334     alloc_block_work2(&_next_offset_threshold, &_next_offset_index,

   335                       blk_start, blk_end);

   336   }

   337 

   338   // Zero out the entry for _bottom (offset will be zero). Does not check for availability of the

   339   // memory first.

   340   void zero_bottom_entry_raw();

   341   // Variant of initialize_threshold that does not check for availability of the

   342   // memory first.

   343   HeapWord* initialize_threshold_raw();

   344  public:

   345   G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);

   346 

   347   // Initialize the threshold to reflect the first boundary after the

   348   // bottom of the covered region.

   349   HeapWord* initialize_threshold();

   350 

   351   void reset_bot() {

   352     zero_bottom_entry_raw();

   353     initialize_threshold_raw();

   354   }

   355 

   356   // Return the next threshold, the point at which the table should be

   357   // updated.

   358   HeapWord* threshold() const { return _next_offset_threshold; }

   359 

   360   // These must be guaranteed to work properly (i.e., do nothing)

   361   // when "blk_start" ("blk" for second version) is "NULL".  In this

   362   // implementation, that's true because NULL is represented as 0, and thus

   363   // never exceeds the "_next_offset_threshold".

   364   void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {

   365     if (blk_end > _next_offset_threshold)

   366       alloc_block_work1(blk_start, blk_end);

   367   }

   368   void alloc_block(HeapWord* blk, size_t size) {

   369      alloc_block(blk, blk+size);

   370   }

   371 

   372   HeapWord* block_start_unsafe(const void* addr);

   373   HeapWord* block_start_unsafe_const(const void* addr) const;

   374 

   375   void set_for_starts_humongous(HeapWord* new_top);

   376 

   377   virtual void print_on(outputStream* out) PRODUCT_RETURN;

   378 };

   379 

   380 #endif // SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP