1 /*

     2  * Copyright (c) 2000, 2016, 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_CARDTABLEMODREFBS_HPP

    26 #define SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP

    27 

    28 #include "gc/shared/modRefBarrierSet.hpp"

    29 #include "oops/oop.hpp"

    30 #include "utilities/align.hpp"

    31 

    32 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and

    33 // enumerate ref fields that have been modified (since the last

    34 // enumeration.)

    35 

    36 // As it currently stands, this barrier is *imprecise*: when a ref field in

    37 // an object "o" is modified, the card table entry for the card containing

    38 // the head of "o" is dirtied, not necessarily the card containing the

    39 // modified field itself.  For object arrays, however, the barrier *is*

    40 // precise; only the card containing the modified element is dirtied.

    41 // Closures used to scan dirty cards should take these

    42 // considerations into account.

    43 

    44 class CardTableModRefBS: public ModRefBarrierSet {

    45   // Some classes get to look at some private stuff.

    46   friend class VMStructs;

    47  protected:

    48 

    49   enum CardValues {

    50     clean_card                  = -1,

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

    52     clean_card_mask             = clean_card - 31,

    53 

    54     dirty_card                  =  0,

    55     precleaned_card             =  1,

    56     claimed_card                =  2,

    57     deferred_card               =  4,

    58     last_card                   =  8,

    59     CT_MR_BS_last_reserved      = 16

    60   };

    61 

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

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

    64 

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

    66   // constructor before changing.

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

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

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

    70                                      // (last_card) and should never be modified

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

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

    73   size_t          _byte_map_size;    // in bytes

    74   jbyte*          _byte_map;         // the card marking array

    75 

    76   int _cur_covered_regions;

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

    78   MemRegion* _covered;

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

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

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

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

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

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

    85   MemRegion* _committed;

    86 

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

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

    89   // uncommit the MemRegion for that page.

    90   MemRegion _guard_region;

    91 

    92  protected:

    93   inline size_t compute_byte_map_size();

    94 

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

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

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

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

    99   int find_covering_region_by_base(HeapWord* base);

   100 

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

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

   103   int find_covering_region_containing(HeapWord* addr);

   104 

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

   106   virtual void resize_covered_region(MemRegion new_region);

   107 

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

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

   110   // the first covered region.

   111   HeapWord* largest_prev_committed_end(int ind) const;

   112 

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

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

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

   116   // against uncommitting the guard region.

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

   118 

   119   // Mapping from address to card marking array entry

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

   121     assert(_whole_heap.contains(p),

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

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

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

   125     jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];

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

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

   128     return result;

   129   }

   130 

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

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

   133   // for loops iterating through the card table.

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

   135     return byte_for(p) + 1;

   136   }

   137 

   138  protected:

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

   140   // covered.)

   141   void dirty_MemRegion(MemRegion mr);

   142 

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

   144   // all of which must be covered.)

   145   void clear_MemRegion(MemRegion mr);

   146 

   147 public:

   148   // Constants

   149   enum SomePublicConstants {

   150     card_shift                  = 9,

   151     card_size                   = 1 << card_shift,

   152     card_size_in_words          = card_size / sizeof(HeapWord)

   153   };

   154 

   155   static int clean_card_val()      { return clean_card; }

   156   static int clean_card_mask_val() { return clean_card_mask; }

   157   static int dirty_card_val()      { return dirty_card; }

   158   static int claimed_card_val()    { return claimed_card; }

   159   static int precleaned_card_val() { return precleaned_card; }

   160   static int deferred_card_val()   { return deferred_card; }

   161 

   162   virtual void initialize();

   163 

   164   // *** Barrier set functions.

   165 

   166   bool has_write_ref_pre_barrier() { return false; }

   167 

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

   169   // in, um, words.

   170   inline size_t cards_required(size_t covered_words) {

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

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

   173     return words / card_size_in_words + 1;

   174   }

   175 

   176 protected:

   177 

   178   CardTableModRefBS(MemRegion whole_heap, const BarrierSet::FakeRtti& fake_rtti);

   179   ~CardTableModRefBS();

   180 

   181   // Record a reference update. Note that these versions are precise!

   182   // The scanning code has to handle the fact that the write barrier may be

   183   // either precise or imprecise. We make non-virtual inline variants of

   184   // these functions here for performance.

   185 

   186   void write_ref_field_work(oop obj, size_t offset, oop newVal);

   187   virtual void write_ref_field_work(void* field, oop newVal, bool release);

   188 public:

   189 

   190   bool has_write_ref_array_opt() { return true; }

   191   bool has_write_region_opt() { return true; }

   192 

   193   inline void inline_write_region(MemRegion mr) {

   194     dirty_MemRegion(mr);

   195   }

   196 protected:

   197   void write_region_work(MemRegion mr) {

   198     inline_write_region(mr);

   199   }

   200 public:

   201 

   202   inline void inline_write_ref_array(MemRegion mr) {

   203     dirty_MemRegion(mr);

   204   }

   205 protected:

   206   void write_ref_array_work(MemRegion mr) {

   207     inline_write_ref_array(mr);

   208   }

   209 public:

   210 

   211   bool is_aligned(HeapWord* addr) {

   212     return is_card_aligned(addr);

   213   }

   214 

   215   // *** Card-table-barrier-specific things.

   216 

   217   template <class T> inline void inline_write_ref_field_pre(T* field, oop newVal) {}

   218 

   219   template <class T> inline void inline_write_ref_field(T* field, oop newVal, bool release);

   220 

   221   // These are used by G1, when it uses the card table as a temporary data

   222   // structure for card claiming.

   223   bool is_card_dirty(size_t card_index) {

   224     return _byte_map[card_index] == dirty_card_val();

   225   }

   226 

   227   void mark_card_dirty(size_t card_index) {

   228     _byte_map[card_index] = dirty_card_val();

   229   }

   230 

   231   bool is_card_clean(size_t card_index) {

   232     return _byte_map[card_index] == clean_card_val();

   233   }

   234 

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

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

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

   238   // before the beginning of the actual _byte_map.

   239   jbyte* byte_map_base;

   240 

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

   242   bool is_card_aligned(HeapWord* p) {

   243     jbyte* pcard = byte_for(p);

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

   245   }

   246 

   247   HeapWord* align_to_card_boundary(HeapWord* p) {

   248     jbyte* pcard = byte_for(p + card_size_in_words - 1);

   249     return addr_for(pcard);

   250   }

   251 

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

   253   enum PrecisionStyle {

   254     Precise,

   255     ObjHeadPreciseArray

   256   };

   257 

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

   259   PrecisionStyle precision() {

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

   261   }

   262 

   263   // ModRefBS functions.

   264   virtual void invalidate(MemRegion mr);

   265   void clear(MemRegion mr);

   266   void dirty(MemRegion mr);

   267 

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

   269 

   270   static uintx ct_max_alignment_constraint();

   271 

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

   273   // MemRegion "mr".

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

   275 

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

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

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

   279   // value.

   280   MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,

   281                                          int reset_val);

   282 

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

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

   285     return byte_for(p);

   286   }

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

   288     return byte_after(p);

   289   }

   290 

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

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

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

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

   295            " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,

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

   297     size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));

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

   299     assert(_whole_heap.contains(result),

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

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

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

   303     return result;

   304   }

   305 

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

   307   size_t index_for(void* p) {

   308     assert(_whole_heap.contains(p),

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

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

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

   312     return byte_for(p) - _byte_map;

   313   }

   314 

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

   316     return _byte_map + card_index;

   317   }

   318 

   319   // Print a description of the memory for the barrier set

   320   virtual void print_on(outputStream* st) const;

   321 

   322   void verify();

   323   void verify_guard();

   324 

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

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

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

   328   void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;

   329   void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;

   330 };

   331 

   332 template<>

   333 struct BarrierSet::GetName<CardTableModRefBS> {

   334   static const BarrierSet::Name value = BarrierSet::CardTableModRef;

   335 };

   336 

   337 

   338 #endif // SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP