1 /*
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  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  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.
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  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).
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 24 
 25 #ifndef SHARE_GC_SHARED_CARDTABLE_HPP
 26 #define SHARE_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 public:
 36   typedef uint8_t CardValue;
 37 
 38   // All code generators assume that the size of a card table entry is one byte.
 39   // They need to be updated to reflect any change to this.
 40   // This code can typically be found by searching for the byte_map_base() method.
 41   STATIC_ASSERT(sizeof(CardValue) == 1);
 42 
 43 protected:
 44   // The declaration order of these const fields is important; see the
 45   // constructor before changing.
 46   const MemRegion _whole_heap;       // the region covered by the card table
 47   size_t          _guard_index;      // index of very last element in the card
 48                                      // table; it is set to a guard value
 49                                      // (last_card) and should never be modified
 50   size_t          _last_valid_index; // index of the last valid element
 51   const size_t    _page_size;        // page size used when mapping _byte_map
 52   size_t          _byte_map_size;    // in bytes
 53   CardValue*      _byte_map;         // the card marking array
 54   CardValue*      _byte_map_base;
 55 
 56   int _cur_covered_regions;
 57 
 58   // The covered regions should be in address order.
 59   MemRegion* _covered;
 60   // The committed regions correspond one-to-one to the covered regions.
 61   // They represent the card-table memory that has been committed to service
 62   // the corresponding covered region.  It may be that committed region for
 63   // one covered region corresponds to a larger region because of page-size
 64   // roundings.  Thus, a committed region for one covered region may
 65   // actually extend onto the card-table space for the next covered region.
 66   MemRegion* _committed;
 67 
 68   // The last card is a guard card, and we commit the page for it so
 69   // we can use the card for verification purposes. We make sure we never
 70   // uncommit the MemRegion for that page.
 71   MemRegion _guard_region;
 72 
 73   inline size_t compute_byte_map_size();
 74 
 75   // Finds and return the index of the region, if any, to which the given
 76   // region would be contiguous.  If none exists, assign a new region and
 77   // returns its index.  Requires that no more than the maximum number of
 78   // covered regions defined in the constructor are ever in use.
 79   int find_covering_region_by_base(HeapWord* base);
 80 
 81   // Same as above, but finds the region containing the given address
 82   // instead of starting at a given base address.
 83   int find_covering_region_containing(HeapWord* addr);
 84 
 85   // Returns the leftmost end of a committed region corresponding to a
 86   // covered region before covered region "ind", or else "NULL" if "ind" is
 87   // the first covered region.
 88   HeapWord* largest_prev_committed_end(int ind) const;
 89 
 90   // Returns the part of the region mr that doesn't intersect with
 91   // any committed region other than self.  Used to prevent uncommitting
 92   // regions that are also committed by other regions.  Also protects
 93   // against uncommitting the guard region.
 94   MemRegion committed_unique_to_self(int self, MemRegion mr) const;
 95 
 96   // Some barrier sets create tables whose elements correspond to parts of
 97   // the heap; the CardTableBarrierSet is an example.  Such barrier sets will
 98   // normally reserve space for such tables, and commit parts of the table
 99   // "covering" parts of the heap that are committed. At most one covered
100   // region per generation is needed.
101   static const int _max_covered_regions = 2;
102 
103   enum CardValues {
104     clean_card                  = (CardValue)-1,
105 
106     dirty_card                  =  0,
107     last_card                   =  1,
108     CT_MR_BS_last_reserved      =  2
109   };
110 
111   // a word's worth (row) of clean card values
112   static const intptr_t clean_card_row = (intptr_t)(-1);
113 
114 public:
115   CardTable(MemRegion whole_heap);
116   virtual ~CardTable();
117   virtual void initialize();
118 
119   // The kinds of precision a CardTable may offer.
120   enum PrecisionStyle {
121     Precise,
122     ObjHeadPreciseArray
123   };
124 
125   // Tells what style of precision this card table offers.
126   PrecisionStyle precision() {
127     return ObjHeadPreciseArray; // Only one supported for now.
128   }
129 
130   // *** Barrier set functions.
131 
132   // Initialization utilities; covered_words is the size of the covered region
133   // in, um, words.
134   inline size_t cards_required(size_t covered_words) {
135     // Add one for a guard card, used to detect errors.
136     const size_t words = align_up(covered_words, card_size_in_words);
137     return words / card_size_in_words + 1;
138   }
139 
140   // Dirty the bytes corresponding to "mr" (not all of which must be
141   // covered.)
142   void dirty_MemRegion(MemRegion mr);
143 
144   // Clear (to clean_card) the bytes entirely contained within "mr" (not
145   // all of which must be covered.)
146   void clear_MemRegion(MemRegion mr);
147 
148   // Return true if "p" is at the start of a card.
149   bool is_card_aligned(HeapWord* p) {
150     CardValue* pcard = byte_for(p);
151     return (addr_for(pcard) == p);
152   }
153 
154   // Mapping from address to card marking array entry
155   CardValue* byte_for(const void* p) const {
156     assert(_whole_heap.contains(p),
157            "Attempt to access p = " PTR_FORMAT " out of bounds of "
158            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
159            p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
160     CardValue* result = &_byte_map_base[uintptr_t(p) >> card_shift];
161     assert(result >= _byte_map && result < _byte_map + _byte_map_size,
162            "out of bounds accessor for card marking array");
163     return result;
164   }
165 
166   // The card table byte one after the card marking array
167   // entry for argument address. Typically used for higher bounds
168   // for loops iterating through the card table.
169   CardValue* byte_after(const void* p) const {
170     return byte_for(p) + 1;
171   }
172 
173   virtual void invalidate(MemRegion mr);
174   void clear(MemRegion mr);
175   void dirty(MemRegion mr);
176 
177   // Provide read-only access to the card table array.
178   const CardValue* byte_for_const(const void* p) const {
179     return byte_for(p);
180   }
181   const CardValue* byte_after_const(const void* p) const {
182     return byte_after(p);
183   }
184 
185   // Mapping from card marking array entry to address of first word
186   HeapWord* addr_for(const CardValue* p) const {
187     assert(p >= _byte_map && p < _byte_map + _byte_map_size,
188            "out of bounds access to card marking array. p: " PTR_FORMAT
189            " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,
190            p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));
191     size_t delta = pointer_delta(p, _byte_map_base, sizeof(CardValue));
192     HeapWord* result = (HeapWord*) (delta << card_shift);
193     assert(_whole_heap.contains(result),
194            "Returning result = " PTR_FORMAT " out of bounds of "
195            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
196            p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
197     return result;
198   }
199 
200   // Mapping from address to card marking array index.
201   size_t index_for(void* p) {
202     assert(_whole_heap.contains(p),
203            "Attempt to access p = " PTR_FORMAT " out of bounds of "
204            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
205            p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
206     return byte_for(p) - _byte_map;
207   }
208 
209   CardValue* byte_for_index(const size_t card_index) const {
210     return _byte_map + card_index;
211   }
212 
213   // Resize one of the regions covered by the remembered set.
214   virtual void resize_covered_region(MemRegion new_region);
215 
216   // *** Card-table-RemSet-specific things.
217 
218   static uintx ct_max_alignment_constraint();
219 
220   // Apply closure "cl" to the dirty cards containing some part of
221   // MemRegion "mr".
222   void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
223 
224   // Return the MemRegion corresponding to the first maximal run
225   // of dirty cards lying completely within MemRegion mr.
226   // If reset is "true", then sets those card table entries to the given
227   // value.
228   MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
229                                          int reset_val);
230 
231   // Constants
232   enum SomePublicConstants {
233     card_shift                  = 9,
234     card_size                   = 1 << card_shift,
235     card_size_in_words          = card_size / sizeof(HeapWord)
236   };
237 
238   static constexpr CardValue clean_card_val()          { return clean_card; }
239   static constexpr CardValue dirty_card_val()          { return dirty_card; }
240   static intptr_t clean_card_row_val()   { return clean_card_row; }
241 
242   // Card marking array base (adjusted for heap low boundary)
243   // This would be the 0th element of _byte_map, if the heap started at 0x0.
244   // But since the heap starts at some higher address, this points to somewhere
245   // before the beginning of the actual _byte_map.
246   CardValue* byte_map_base() const { return _byte_map_base; }
247 
248   virtual bool is_in_young(oop obj) const = 0;
249 
250   // Print a description of the memory for the card table
251   virtual void print_on(outputStream* st) const;
252 
253   void verify();
254   void verify_guard();
255 
256   // val_equals -> it will check that all cards covered by mr equal val
257   // !val_equals -> it will check that all cards covered by mr do not equal val
258   void verify_region(MemRegion mr, CardValue val, bool val_equals) PRODUCT_RETURN;
259   void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
260   void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
261 };
262 
263 #endif // SHARE_GC_SHARED_CARDTABLE_HPP