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.
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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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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
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23 */
24
25 #ifndef SHARE_VM_GC_SHARED_SPACE_INLINE_HPP
26 #define SHARE_VM_GC_SHARED_SPACE_INLINE_HPP
27
28 #include "gc/serial/markSweep.inline.hpp"
29 #include "gc/shared/collectedHeap.hpp"
30 #include "gc/shared/generation.hpp"
31 #include "gc/shared/space.hpp"
32 #include "gc/shared/spaceDecorator.hpp"
33 #include "memory/universe.hpp"
34 #include "oops/oopsHierarchy.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/prefetch.inline.hpp"
37 #include "runtime/safepoint.hpp"
38
39 inline HeapWord* Space::block_start(const void* p) {
40 return block_start_const(p);
41 }
42
43 inline HeapWord* OffsetTableContigSpace::allocate(size_t size) {
44 HeapWord* res = ContiguousSpace::allocate(size);
45 if (res != NULL) {
46 _offsets.alloc_block(res, size);
47 }
48 return res;
49 }
50
51 // Because of the requirement of keeping "_offsets" up to date with the
52 // allocations, we sequentialize these with a lock. Therefore, best if
53 // this is used for larger LAB allocations only.
54 inline HeapWord* OffsetTableContigSpace::par_allocate(size_t size) {
55 MutexLocker x(&_par_alloc_lock);
56 // This ought to be just "allocate", because of the lock above, but that
57 // ContiguousSpace::allocate asserts that either the allocating thread
58 // holds the heap lock or it is the VM thread and we're at a safepoint.
59 // The best I (dld) could figure was to put a field in ContiguousSpace
60 // meaning "locking at safepoint taken care of", and set/reset that
61 // here. But this will do for now, especially in light of the comment
62 // above. Perhaps in the future some lock-free manner of keeping the
63 // coordination.
64 HeapWord* res = ContiguousSpace::par_allocate(size);
65 if (res != NULL) {
66 _offsets.alloc_block(res, size);
67 }
68 return res;
69 }
70
71 inline HeapWord*
72 OffsetTableContigSpace::block_start_const(const void* p) const {
73 return _offsets.block_start(p);
74 }
75
76 size_t CompactibleSpace::obj_size(const HeapWord* addr) const {
77 return oop(addr)->size();
78 }
79
80 class DeadSpacer : StackObj {
81 size_t _allowed_deadspace_words;
82 bool _active;
83 CompactibleSpace* _space;
84
85 public:
86 DeadSpacer(CompactibleSpace* space) : _space(space), _allowed_deadspace_words(0) {
87 size_t ratio = _space->allowed_dead_ratio();
88 _active = ratio > 0;
89
90 if (_active) {
91 assert(!UseG1GC, "G1 should not be using dead space");
92
93 // We allow some amount of garbage towards the bottom of the space, so
94 // we don't start compacting before there is a significant gain to be made.
95 // Occasionally, we want to ensure a full compaction, which is determined
96 // by the MarkSweepAlwaysCompactCount parameter.
97 if ((MarkSweep::total_invocations() % MarkSweepAlwaysCompactCount) != 0) {
98 _allowed_deadspace_words = (space->capacity() * ratio / 100) / HeapWordSize;
99 } else {
100 _active = false;
101 }
102 }
103 }
104
105
106 bool insert_deadspace(HeapWord* dead_start, HeapWord* dead_end) {
107 if (!_active) {
108 return false;
109 }
110
111 size_t dead_length = pointer_delta(dead_end, dead_start);
112 if (_allowed_deadspace_words >= dead_length) {
113 _allowed_deadspace_words -= dead_length;
114 CollectedHeap::fill_with_object(dead_start, dead_length);
115 oop obj = oop(dead_start);
116 obj->set_mark_raw(obj->mark_raw()->set_marked());
117
118 assert(dead_length == (size_t)obj->size(), "bad filler object size");
119 log_develop_trace(gc, compaction)("Inserting object to dead space: " PTR_FORMAT ", " PTR_FORMAT ", " SIZE_FORMAT "b",
120 p2i(dead_start), p2i(dead_end), dead_length * HeapWordSize);
121
122 return true;
123 } else {
124 _active = false;
125 return false;
126 }
127 }
128
129 };
130
131 template <class SpaceType>
132 inline void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* cp) {
133 // Compute the new addresses for the live objects and store it in the mark
134 // Used by universe::mark_sweep_phase2()
135
136 // We're sure to be here before any objects are compacted into this
137 // space, so this is a good time to initialize this:
138 space->set_compaction_top(space->bottom());
139
140 if (cp->space == NULL) {
141 assert(cp->gen != NULL, "need a generation");
142 assert(cp->threshold == NULL, "just checking");
143 assert(cp->gen->first_compaction_space() == space, "just checking");
144 cp->space = cp->gen->first_compaction_space();
145 cp->threshold = cp->space->initialize_threshold();
146 cp->space->set_compaction_top(cp->space->bottom());
147 }
148
149 HeapWord* compact_top = cp->space->compaction_top(); // This is where we are currently compacting to.
150
151 DeadSpacer dead_spacer(space);
152
153 HeapWord* end_of_live = space->bottom(); // One byte beyond the last byte of the last live object.
154 HeapWord* first_dead = NULL; // The first dead object.
155
156 const intx interval = PrefetchScanIntervalInBytes;
157
158 HeapWord* cur_obj = space->bottom();
159 HeapWord* scan_limit = space->scan_limit();
160
161 while (cur_obj < scan_limit) {
162 assert(!space->scanned_block_is_obj(cur_obj) ||
163 oop(cur_obj)->mark_raw()->is_marked() || oop(cur_obj)->mark_raw()->is_unlocked() ||
164 oop(cur_obj)->mark_raw()->has_bias_pattern(),
165 "these are the only valid states during a mark sweep");
166 if (space->scanned_block_is_obj(cur_obj) && oop(cur_obj)->is_gc_marked()) {
167 // prefetch beyond cur_obj
168 Prefetch::write(cur_obj, interval);
169 size_t size = space->scanned_block_size(cur_obj);
170 compact_top = cp->space->forward(oop(cur_obj), size, cp, compact_top);
171 cur_obj += size;
172 end_of_live = cur_obj;
173 } else {
174 // run over all the contiguous dead objects
175 HeapWord* end = cur_obj;
176 do {
177 // prefetch beyond end
178 Prefetch::write(end, interval);
179 end += space->scanned_block_size(end);
180 } while (end < scan_limit && (!space->scanned_block_is_obj(end) || !oop(end)->is_gc_marked()));
181
182 // see if we might want to pretend this object is alive so that
183 // we don't have to compact quite as often.
184 if (cur_obj == compact_top && dead_spacer.insert_deadspace(cur_obj, end)) {
185 oop obj = oop(cur_obj);
186 compact_top = cp->space->forward(obj, obj->size(), cp, compact_top);
187 end_of_live = end;
188 } else {
189 // otherwise, it really is a free region.
190
191 // cur_obj is a pointer to a dead object. Use this dead memory to store a pointer to the next live object.
192 *(HeapWord**)cur_obj = end;
193
194 // see if this is the first dead region.
195 if (first_dead == NULL) {
196 first_dead = cur_obj;
197 }
198 }
199
200 // move on to the next object
201 cur_obj = end;
202 }
203 }
204
205 assert(cur_obj == scan_limit, "just checking");
206 space->_end_of_live = end_of_live;
207 if (first_dead != NULL) {
208 space->_first_dead = first_dead;
209 } else {
210 space->_first_dead = end_of_live;
211 }
212
213 // save the compaction_top of the compaction space.
214 cp->space->set_compaction_top(compact_top);
215 }
216
217 template <class SpaceType>
218 inline void CompactibleSpace::scan_and_adjust_pointers(SpaceType* space) {
219 // adjust all the interior pointers to point at the new locations of objects
220 // Used by MarkSweep::mark_sweep_phase3()
221
222 HeapWord* cur_obj = space->bottom();
223 HeapWord* const end_of_live = space->_end_of_live; // Established by "scan_and_forward".
224 HeapWord* const first_dead = space->_first_dead; // Established by "scan_and_forward".
225
226 assert(first_dead <= end_of_live, "Stands to reason, no?");
227
228 const intx interval = PrefetchScanIntervalInBytes;
229
230 debug_only(HeapWord* prev_obj = NULL);
231 while (cur_obj < end_of_live) {
232 Prefetch::write(cur_obj, interval);
233 if (cur_obj < first_dead || oop(cur_obj)->is_gc_marked()) {
234 // cur_obj is alive
235 // point all the oops to the new location
236 size_t size = MarkSweep::adjust_pointers(oop(cur_obj));
237 size = space->adjust_obj_size(size);
238 debug_only(prev_obj = cur_obj);
239 cur_obj += size;
240 } else {
241 debug_only(prev_obj = cur_obj);
242 // cur_obj is not a live object, instead it points at the next live object
243 cur_obj = *(HeapWord**)cur_obj;
244 assert(cur_obj > prev_obj, "we should be moving forward through memory, cur_obj: " PTR_FORMAT ", prev_obj: " PTR_FORMAT, p2i(cur_obj), p2i(prev_obj));
245 }
246 }
247
248 assert(cur_obj == end_of_live, "just checking");
249 }
250
251 #ifdef ASSERT
252 template <class SpaceType>
253 inline void CompactibleSpace::verify_up_to_first_dead(SpaceType* space) {
254 HeapWord* cur_obj = space->bottom();
255
256 if (cur_obj < space->_end_of_live && space->_first_dead > cur_obj && !oop(cur_obj)->is_gc_marked()) {
257 // we have a chunk of the space which hasn't moved and we've reinitialized
258 // the mark word during the previous pass, so we can't use is_gc_marked for
259 // the traversal.
260 HeapWord* prev_obj = NULL;
261
262 while (cur_obj < space->_first_dead) {
263 size_t size = space->obj_size(cur_obj);
264 assert(!oop(cur_obj)->is_gc_marked(), "should be unmarked (special dense prefix handling)");
265 prev_obj = cur_obj;
266 cur_obj += size;
267 }
268 }
269 }
270 #endif
271
272 template <class SpaceType>
273 inline void CompactibleSpace::clear_empty_region(SpaceType* space) {
274 // Let's remember if we were empty before we did the compaction.
275 bool was_empty = space->used_region().is_empty();
276 // Reset space after compaction is complete
277 space->reset_after_compaction();
278 // We do this clear, below, since it has overloaded meanings for some
279 // space subtypes. For example, OffsetTableContigSpace's that were
280 // compacted into will have had their offset table thresholds updated
281 // continuously, but those that weren't need to have their thresholds
282 // re-initialized. Also mangles unused area for debugging.
283 if (space->used_region().is_empty()) {
284 if (!was_empty) space->clear(SpaceDecorator::Mangle);
285 } else {
286 if (ZapUnusedHeapArea) space->mangle_unused_area();
287 }
288 }
289
290 template <class SpaceType>
291 inline void CompactibleSpace::scan_and_compact(SpaceType* space) {
292 // Copy all live objects to their new location
293 // Used by MarkSweep::mark_sweep_phase4()
294
295 verify_up_to_first_dead(space);
296
297 HeapWord* const bottom = space->bottom();
298 HeapWord* const end_of_live = space->_end_of_live;
299
300 assert(space->_first_dead <= end_of_live, "Invariant. _first_dead: " PTR_FORMAT " <= end_of_live: " PTR_FORMAT, p2i(space->_first_dead), p2i(end_of_live));
301 if (space->_first_dead == end_of_live && (bottom == end_of_live || !oop(bottom)->is_gc_marked())) {
302 // Nothing to compact. The space is either empty or all live object should be left in place.
303 clear_empty_region(space);
304 return;
305 }
306
307 const intx scan_interval = PrefetchScanIntervalInBytes;
308 const intx copy_interval = PrefetchCopyIntervalInBytes;
309
310 assert(bottom < end_of_live, "bottom: " PTR_FORMAT " should be < end_of_live: " PTR_FORMAT, p2i(bottom), p2i(end_of_live));
311 HeapWord* cur_obj = bottom;
312 if (space->_first_dead > cur_obj && !oop(cur_obj)->is_gc_marked()) {
313 // All object before _first_dead can be skipped. They should not be moved.
314 // A pointer to the first live object is stored at the memory location for _first_dead.
315 cur_obj = *(HeapWord**)(space->_first_dead);
316 }
317
318 debug_only(HeapWord* prev_obj = NULL);
319 while (cur_obj < end_of_live) {
320 if (!oop(cur_obj)->is_gc_marked()) {
321 debug_only(prev_obj = cur_obj);
322 // The first word of the dead object contains a pointer to the next live object or end of space.
323 cur_obj = *(HeapWord**)cur_obj;
324 assert(cur_obj > prev_obj, "we should be moving forward through memory");
325 } else {
326 // prefetch beyond q
327 Prefetch::read(cur_obj, scan_interval);
328
329 // size and destination
330 size_t size = space->obj_size(cur_obj);
331 HeapWord* compaction_top = (HeapWord*)oop(cur_obj)->forwardee();
332
333 // prefetch beyond compaction_top
334 Prefetch::write(compaction_top, copy_interval);
335
336 // copy object and reinit its mark
337 assert(cur_obj != compaction_top, "everything in this pass should be moving");
338 Copy::aligned_conjoint_words(cur_obj, compaction_top, size);
339 oop(compaction_top)->init_mark_raw();
340 assert(oop(compaction_top)->klass() != NULL, "should have a class");
341
342 debug_only(prev_obj = cur_obj);
343 cur_obj += size;
344 }
345 }
346
347 clear_empty_region(space);
348 }
349
350 size_t ContiguousSpace::scanned_block_size(const HeapWord* addr) const {
351 return oop(addr)->size();
352 }
353
354 #endif // SHARE_VM_GC_SHARED_SPACE_INLINE_HPP