1 /*
2 * Copyright (c) 2001, 2015, 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
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7 * published by the Free Software Foundation.
8 *
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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,
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23 */
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 // Forward declarations
34 class G1BlockOffsetTable;
35 class G1ContiguousSpace;
36
37 // This implementation of "G1BlockOffsetTable" divides the covered region
38 // into "N"-word subregions (where "N" = 2^"LogN". An array with an entry
39 // for each such subregion indicates how far back one must go to find the
40 // start of the chunk that includes the first word of the subregion.
41 //
42 // Each G1BlockOffsetTablePart is owned by a G1ContiguousSpace.
43
44 class G1BlockOffsetTable: public CHeapObj<mtGC> {
45 friend class G1BlockOffsetTablePart;
46 friend class VMStructs;
47
48 private:
49 // The reserved region covered by the table.
50 MemRegion _reserved;
51
52 // Array for keeping offsets for retrieving object start fast given an
53 // address.
54 u_char* _offset_array; // byte array keeping backwards offsets
55
56 void check_offset(size_t offset, const char* msg) const {
57 assert(offset <= N_words,
58 "%s - offset: " SIZE_FORMAT ", N_words: %u",
59 msg, offset, (uint)N_words);
60 }
61
62 // Bounds checking accessors:
63 // For performance these have to devolve to array accesses in product builds.
64 inline u_char offset_array(size_t index) const;
65
66 void set_offset_array_raw(size_t index, u_char offset) {
67 _offset_array[index] = offset;
68 }
69
70 inline void set_offset_array(size_t index, u_char offset);
71
72 inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);
73
74 inline void set_offset_array(size_t left, size_t right, u_char offset);
75
76 bool is_card_boundary(HeapWord* p) const;
77
78 void check_index(size_t index, const char* msg) const NOT_DEBUG_RETURN;
79
80 public:
81
82 // Return the number of slots needed for an offset array
83 // that covers mem_region_words words.
84 static size_t compute_size(size_t mem_region_words) {
85 size_t number_of_slots = (mem_region_words / N_words);
86 return ReservedSpace::allocation_align_size_up(number_of_slots);
87 }
88
89 // Returns how many bytes of the heap a single byte of the BOT corresponds to.
90 static size_t heap_map_factor() {
91 return N_bytes;
92 }
93
94 enum SomePublicConstants {
95 LogN = 9,
96 LogN_words = LogN - LogHeapWordSize,
97 N_bytes = 1 << LogN,
98 N_words = 1 << LogN_words
99 };
100
101 // Initialize the Block Offset Table to cover the memory region passed
102 // in the heap parameter.
103 G1BlockOffsetTable(MemRegion heap, G1RegionToSpaceMapper* storage);
104
105 // Return the appropriate index into "_offset_array" for "p".
106 inline size_t index_for(const void* p) const;
107 inline size_t index_for_raw(const void* p) const;
108
109 // Return the address indicating the start of the region corresponding to
110 // "index" in "_offset_array".
111 inline HeapWord* address_for_index(size_t index) const;
112 // Variant of address_for_index that does not check the index for validity.
113 inline HeapWord* address_for_index_raw(size_t index) const {
114 return _reserved.start() + (index << LogN_words);
115 }
116 };
117
118 class G1BlockOffsetTablePart VALUE_OBJ_CLASS_SPEC {
119 friend class G1BlockOffsetTable;
120 friend class VMStructs;
121 private:
122 enum SomePrivateConstants {
123 N_words = G1BlockOffsetTable::N_words,
124 LogN = G1BlockOffsetTable::LogN
125 };
126
127 // allocation boundary at which offset array must be updated
128 HeapWord* _next_offset_threshold;
129 size_t _next_offset_index; // index corresponding to that boundary
130
131 // This is the global BlockOffsetTable.
132 G1BlockOffsetTable* _bot;
133
134 // The space that owns this subregion.
135 G1ContiguousSpace* _space;
136
137 // Sets the entries
138 // corresponding to the cards starting at "start" and ending at "end"
139 // to point back to the card before "start": the interval [start, end)
140 // is right-open.
141 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
142 // Same as above, except that the args here are a card _index_ interval
143 // that is closed: [start_index, end_index]
144 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
145
146 // Zero out the entry for _bottom (offset will be zero). Does not check for availability of the
147 // memory first.
148 void zero_bottom_entry_raw();
149 // Variant of initialize_threshold that does not check for availability of the
150 // memory first.
151 HeapWord* initialize_threshold_raw();
152
153 inline size_t block_size(const HeapWord* p) const;
154
155 // Returns the address of a block whose start is at most "addr".
156 // If "has_max_index" is true, "assumes "max_index" is the last valid one
157 // in the array.
158 inline HeapWord* block_at_or_preceding(const void* addr,
159 bool has_max_index,
160 size_t max_index) const;
161
162 // "q" is a block boundary that is <= "addr"; "n" is the address of the
163 // next block (or the end of the space.) Return the address of the
164 // beginning of the block that contains "addr". Does so without side
165 // effects (see, e.g., spec of block_start.)
166 inline HeapWord* forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
167 const void* addr) const;
168
169 // "q" is a block boundary that is <= "addr"; return the address of the
170 // beginning of the block that contains "addr". May have side effects
171 // on "this", by updating imprecise entries.
172 inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
173 const void* addr);
174
175 // "q" is a block boundary that is <= "addr"; "n" is the address of the
176 // next block (or the end of the space.) Return the address of the
177 // beginning of the block that contains "addr". May have side effects
178 // on "this", by updating imprecise entries.
179 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
180 HeapWord* n,
181 const void* addr);
182
183 // Requires that "*threshold_" be the first array entry boundary at or
184 // above "blk_start", and that "*index_" be the corresponding array
185 // index. If the block starts at or crosses "*threshold_", records
186 // "blk_start" as the appropriate block start for the array index
187 // starting at "*threshold_", and for any other indices crossed by the
188 // block. Updates "*threshold_" and "*index_" to correspond to the first
189 // index after the block end.
190 void alloc_block_work(HeapWord** threshold_, size_t* index_,
191 HeapWord* blk_start, HeapWord* blk_end);
192
193 void check_all_cards(size_t left_card, size_t right_card) const;
194
195 public:
196 // The elements of the array are initialized to zero.
197 G1BlockOffsetTablePart(G1BlockOffsetTable* array, G1ContiguousSpace* gsp);
198
199 void verify() const;
200
201 // Returns the address of the start of the block containing "addr", or
202 // else "null" if it is covered by no block. (May have side effects,
203 // namely updating of shared array entries that "point" too far
204 // backwards. This can occur, for example, when lab allocation is used
205 // in a space covered by the table.)
206 inline HeapWord* block_start(const void* addr);
207 // Same as above, but does not have any of the possible side effects
208 // discussed above.
209 inline HeapWord* block_start_const(const void* addr) const;
210
211 // Initialize the threshold to reflect the first boundary after the
212 // bottom of the covered region.
213 HeapWord* initialize_threshold();
214
215 void reset_bot() {
216 zero_bottom_entry_raw();
217 initialize_threshold_raw();
218 }
219
220 // Return the next threshold, the point at which the table should be
221 // updated.
222 HeapWord* threshold() const { return _next_offset_threshold; }
223
224 // These must be guaranteed to work properly (i.e., do nothing)
225 // when "blk_start" ("blk" for second version) is "NULL". In this
226 // implementation, that's true because NULL is represented as 0, and thus
227 // never exceeds the "_next_offset_threshold".
228 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
229 if (blk_end > _next_offset_threshold) {
230 alloc_block_work(&_next_offset_threshold, &_next_offset_index, blk_start, blk_end);
231 }
232 }
233 void alloc_block(HeapWord* blk, size_t size) {
234 alloc_block(blk, blk+size);
235 }
236
237 void set_for_starts_humongous(HeapWord* obj_top, size_t fill_size);
238
239 void print_on(outputStream* out) PRODUCT_RETURN;
240 };
241
242 #endif // SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP