1 /*

     2  * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

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

     4  *

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

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

     7  * published by the Free Software Foundation.

     8  *

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

    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).

    14  *

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

    16  * 2 along with this work; if not, write to the Free Software Foundation,

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

    18  *

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

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    23  */

    24 

    25 #ifndef SHARE_VM_GC_SHARED_CARDTABLE_HPP

    26 #define SHARE_VM_GC_SHARED_CARDTABLE_HPP

    27 

    28 #include "memory/allocation.hpp"

    29 #include "memory/memRegion.hpp"

    30 #include "oops/oopsHierarchy.hpp"

    31 #include "utilities/align.hpp"

    32 

    33 class CardTable: public CHeapObj<mtGC> {

    34   friend class VMStructs;

    35 protected:

    36   // The declaration order of these const fields is important; see the

    37   // constructor before changing.

    38   const bool      _scanned_concurrently;

    39   const MemRegion _whole_heap;       // the region covered by the card table

    40   size_t          _guard_index;      // index of very last element in the card

    41                                      // table; it is set to a guard value

    42                                      // (last_card) and should never be modified

    43   size_t          _last_valid_index; // index of the last valid element

    44   const size_t    _page_size;        // page size used when mapping _byte_map

    45   size_t          _byte_map_size;    // in bytes

    46   jbyte*          _byte_map;         // the card marking array

    47   jbyte*          _byte_map_base;

    48 

    49   int _cur_covered_regions;

    50 

    51   // The covered regions should be in address order.

    52   MemRegion* _covered;

    53   // The committed regions correspond one-to-one to the covered regions.

    54   // They represent the card-table memory that has been committed to service

    55   // the corresponding covered region.  It may be that committed region for

    56   // one covered region corresponds to a larger region because of page-size

    57   // roundings.  Thus, a committed region for one covered region may

    58   // actually extend onto the card-table space for the next covered region.

    59   MemRegion* _committed;

    60 

    61   // The last card is a guard card, and we commit the page for it so

    62   // we can use the card for verification purposes. We make sure we never

    63   // uncommit the MemRegion for that page.

    64   MemRegion _guard_region;

    65 

    66   inline size_t compute_byte_map_size();

    67 

    68   // Finds and return the index of the region, if any, to which the given

    69   // region would be contiguous.  If none exists, assign a new region and

    70   // returns its index.  Requires that no more than the maximum number of

    71   // covered regions defined in the constructor are ever in use.

    72   int find_covering_region_by_base(HeapWord* base);

    73 

    74   // Same as above, but finds the region containing the given address

    75   // instead of starting at a given base address.

    76   int find_covering_region_containing(HeapWord* addr);

    77 

    78   // Returns the leftmost end of a committed region corresponding to a

    79   // covered region before covered region "ind", or else "NULL" if "ind" is

    80   // the first covered region.

    81   HeapWord* largest_prev_committed_end(int ind) const;

    82 

    83   // Returns the part of the region mr that doesn't intersect with

    84   // any committed region other than self.  Used to prevent uncommitting

    85   // regions that are also committed by other regions.  Also protects

    86   // against uncommitting the guard region.

    87   MemRegion committed_unique_to_self(int self, MemRegion mr) const;

    88 

    89   // Some barrier sets create tables whose elements correspond to parts of

    90   // the heap; the CardTableModRefBS is an example.  Such barrier sets will

    91   // normally reserve space for such tables, and commit parts of the table

    92   // "covering" parts of the heap that are committed. At most one covered

    93   // region per generation is needed.

    94   static const int _max_covered_regions = 2;

    95 

    96   enum CardValues {

    97     clean_card                  = -1,

    98     // The mask contains zeros in places for all other values.

    99     clean_card_mask             = clean_card - 31,

   100 

   101     dirty_card                  =  0,

   102     precleaned_card             =  1,

   103     claimed_card                =  2,

   104     deferred_card               =  4,

   105     last_card                   =  8,

   106     CT_MR_BS_last_reserved      = 16

   107   };

   108 

   109   // a word's worth (row) of clean card values

   110   static const intptr_t clean_card_row = (intptr_t)(-1);

   111 

   112 public:

   113   CardTable(MemRegion whole_heap, bool conc_scan);

   114   virtual ~CardTable();

   115   virtual void initialize();

   116 

   117   // The kinds of precision a CardTableModRefBS may offer.

   118   enum PrecisionStyle {

   119     Precise,

   120     ObjHeadPreciseArray

   121   };

   122 

   123   // Tells what style of precision this card table offers.

   124   PrecisionStyle precision() {

   125     return ObjHeadPreciseArray; // Only one supported for now.

   126   }

   127 

   128   // *** Barrier set functions.

   129 

   130   // Initialization utilities; covered_words is the size of the covered region

   131   // in, um, words.

   132   inline size_t cards_required(size_t covered_words) {

   133     // Add one for a guard card, used to detect errors.

   134     const size_t words = align_up(covered_words, card_size_in_words);

   135     return words / card_size_in_words + 1;

   136   }

   137 

   138   // Dirty the bytes corresponding to "mr" (not all of which must be

   139   // covered.)

   140   void dirty_MemRegion(MemRegion mr);

   141 

   142   // Clear (to clean_card) the bytes entirely contained within "mr" (not

   143   // all of which must be covered.)

   144   void clear_MemRegion(MemRegion mr);

   145 

   146   // Return true if "p" is at the start of a card.

   147   bool is_card_aligned(HeapWord* p) {

   148     jbyte* pcard = byte_for(p);

   149     return (addr_for(pcard) == p);

   150   }

   151 

   152   // Mapping from address to card marking array entry

   153   jbyte* byte_for(const void* p) const {

   154     assert(_whole_heap.contains(p),

   155            "Attempt to access p = " PTR_FORMAT " out of bounds of "

   156            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",

   157            p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));

   158     jbyte* result = &_byte_map_base[uintptr_t(p) >> card_shift];

   159     assert(result >= _byte_map && result < _byte_map + _byte_map_size,

   160            "out of bounds accessor for card marking array");

   161     return result;

   162   }

   163 

   164   // The card table byte one after the card marking array

   165   // entry for argument address. Typically used for higher bounds

   166   // for loops iterating through the card table.

   167   jbyte* byte_after(const void* p) const {

   168     return byte_for(p) + 1;

   169   }

   170 

   171   virtual void invalidate(MemRegion mr);

   172   void clear(MemRegion mr);

   173   void dirty(MemRegion mr);

   174 

   175   // Provide read-only access to the card table array.

   176   const jbyte* byte_for_const(const void* p) const {

   177     return byte_for(p);

   178   }

   179   const jbyte* byte_after_const(const void* p) const {

   180     return byte_after(p);

   181   }

   182 

   183   // Mapping from card marking array entry to address of first word

   184   HeapWord* addr_for(const jbyte* p) const {

   185     assert(p >= _byte_map && p < _byte_map + _byte_map_size,

   186            "out of bounds access to card marking array. p: " PTR_FORMAT

   187            " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,

   188            p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));

   189     size_t delta = pointer_delta(p, _byte_map_base, sizeof(jbyte));

   190     HeapWord* result = (HeapWord*) (delta << card_shift);

   191     assert(_whole_heap.contains(result),

   192            "Returning result = " PTR_FORMAT " out of bounds of "

   193            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",

   194            p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));

   195     return result;

   196   }

   197 

   198   // Mapping from address to card marking array index.

   199   size_t index_for(void* p) {

   200     assert(_whole_heap.contains(p),

   201            "Attempt to access p = " PTR_FORMAT " out of bounds of "

   202            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",

   203            p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));

   204     return byte_for(p) - _byte_map;

   205   }

   206 

   207   const jbyte* byte_for_index(const size_t card_index) const {

   208     return _byte_map + card_index;

   209   }

   210 

   211   // Resize one of the regions covered by the remembered set.

   212   virtual void resize_covered_region(MemRegion new_region);

   213 

   214   // *** Card-table-RemSet-specific things.

   215 

   216   static uintx ct_max_alignment_constraint();

   217 

   218   // Apply closure "cl" to the dirty cards containing some part of

   219   // MemRegion "mr".

   220   void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);

   221 

   222   // Return the MemRegion corresponding to the first maximal run

   223   // of dirty cards lying completely within MemRegion mr.

   224   // If reset is "true", then sets those card table entries to the given

   225   // value.

   226   MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,

   227                                          int reset_val);

   228 

   229   // Constants

   230   enum SomePublicConstants {

   231     card_shift                  = 9,

   232     card_size                   = 1 << card_shift,

   233     card_size_in_words          = card_size / sizeof(HeapWord)

   234   };

   235 

   236   static jbyte clean_card_val()          { return clean_card; }

   237   static jbyte clean_card_mask_val()     { return clean_card_mask; }

   238   static jbyte dirty_card_val()          { return dirty_card; }

   239   static jbyte claimed_card_val()        { return claimed_card; }

   240   static jbyte precleaned_card_val()     { return precleaned_card; }

   241   static jbyte deferred_card_val()       { return deferred_card; }

   242   static intptr_t clean_card_row_val()   { return clean_card_row; }

   243 

   244   // Card marking array base (adjusted for heap low boundary)

   245   // This would be the 0th element of _byte_map, if the heap started at 0x0.

   246   // But since the heap starts at some higher address, this points to somewhere

   247   // before the beginning of the actual _byte_map.

   248   jbyte* byte_map_base() const { return _byte_map_base; }

   249   bool scanned_concurrently() const { return _scanned_concurrently; }

   250 

   251   virtual bool is_in_young(oop obj) const = 0;

   252 

   253   // Print a description of the memory for the card table

   254   virtual void print_on(outputStream* st) const;

   255 

   256   void verify();

   257   void verify_guard();

   258 

   259   // val_equals -> it will check that all cards covered by mr equal val

   260   // !val_equals -> it will check that all cards covered by mr do not equal val

   261   void verify_region(MemRegion mr, jbyte val, bool val_equals) PRODUCT_RETURN;

   262   void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;

   263   void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;

   264 };

   265 

   266 #endif // SHARE_VM_GC_SHARED_CARDTABLE_HPP