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
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 #include "precompiled.hpp"
26 #include "classfile/systemDictionary.hpp"
27 #include "gc_implementation/parallelScavenge/objectStartArray.hpp"
28 #include "gc_implementation/parallelScavenge/parallelScavengeHeap.hpp"
29 #include "gc_implementation/parallelScavenge/psMarkSweep.hpp"
30 #include "gc_implementation/parallelScavenge/psMarkSweepDecorator.hpp"
31 #include "gc_implementation/shared/liveRange.hpp"
32 #include "gc_implementation/shared/markSweep.inline.hpp"
33 #include "gc_implementation/shared/spaceDecorator.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "runtime/prefetch.inline.hpp"
36
37 PSMarkSweepDecorator* PSMarkSweepDecorator::_destination_decorator = NULL;
38
39
40 void PSMarkSweepDecorator::set_destination_decorator_tenured() {
41 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
42 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
43
44 _destination_decorator = heap->old_gen()->object_mark_sweep();
45 }
46
47 void PSMarkSweepDecorator::advance_destination_decorator() {
48 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
49 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
50
51 assert(_destination_decorator != NULL, "Sanity");
52
53 PSMarkSweepDecorator* first = heap->old_gen()->object_mark_sweep();
54 PSMarkSweepDecorator* second = heap->young_gen()->eden_mark_sweep();
55 PSMarkSweepDecorator* third = heap->young_gen()->from_mark_sweep();
56 PSMarkSweepDecorator* fourth = heap->young_gen()->to_mark_sweep();
57
58 if ( _destination_decorator == first ) {
59 _destination_decorator = second;
60 } else if ( _destination_decorator == second ) {
61 _destination_decorator = third;
62 } else if ( _destination_decorator == third ) {
63 _destination_decorator = fourth;
64 } else {
65 fatal("PSMarkSweep attempting to advance past last compaction area");
66 }
67 }
68
69 PSMarkSweepDecorator* PSMarkSweepDecorator::destination_decorator() {
70 assert(_destination_decorator != NULL, "Sanity");
71
72 return _destination_decorator;
73 }
74
75 // FIX ME FIX ME FIX ME FIX ME!!!!!!!!!
76 // The object forwarding code is duplicated. Factor this out!!!!!
77 //
78 // This method "precompacts" objects inside its space to dest. It places forwarding
79 // pointers into markOops for use by adjust_pointers. If "dest" should overflow, we
80 // finish by compacting into our own space.
81
82 void PSMarkSweepDecorator::precompact() {
83 // Reset our own compact top.
84 set_compaction_top(space()->bottom());
85
86 /* We allow some amount of garbage towards the bottom of the space, so
87 * we don't start compacting before there is a significant gain to be made.
88 * Occasionally, we want to ensure a full compaction, which is determined
89 * by the MarkSweepAlwaysCompactCount parameter. This is a significant
90 * performance improvement!
91 */
92 bool skip_dead = ((PSMarkSweep::total_invocations() % MarkSweepAlwaysCompactCount) != 0);
93
94 size_t allowed_deadspace = 0;
95 if (skip_dead) {
96 const size_t ratio = allowed_dead_ratio();
97 allowed_deadspace = space()->capacity_in_words() * ratio / 100;
98 }
99
100 // Fetch the current destination decorator
101 PSMarkSweepDecorator* dest = destination_decorator();
102 ObjectStartArray* start_array = dest->start_array();
103
104 HeapWord* compact_top = dest->compaction_top();
105 HeapWord* compact_end = dest->space()->end();
106
107 HeapWord* q = space()->bottom();
108 HeapWord* t = space()->top();
109
110 HeapWord* end_of_live= q; /* One byte beyond the last byte of the last
111 live object. */
112 HeapWord* first_dead = space()->end(); /* The first dead object. */
113 LiveRange* liveRange = NULL; /* The current live range, recorded in the
114 first header of preceding free area. */
115 _first_dead = first_dead;
116
117 const intx interval = PrefetchScanIntervalInBytes;
118
119 while (q < t) {
120 assert(oop(q)->mark()->is_marked() || oop(q)->mark()->is_unlocked() ||
121 oop(q)->mark()->has_bias_pattern(),
122 "these are the only valid states during a mark sweep");
123 if (oop(q)->is_gc_marked()) {
124 /* prefetch beyond q */
125 Prefetch::write(q, interval);
126 size_t size = oop(q)->size();
127
128 size_t compaction_max_size = pointer_delta(compact_end, compact_top);
129
130 // This should only happen if a space in the young gen overflows the
131 // old gen. If that should happen, we null out the start_array, because
132 // the young spaces are not covered by one.
133 while(size > compaction_max_size) {
134 // First record the last compact_top
135 dest->set_compaction_top(compact_top);
136
137 // Advance to the next compaction decorator
138 advance_destination_decorator();
139 dest = destination_decorator();
140
141 // Update compaction info
142 start_array = dest->start_array();
143 compact_top = dest->compaction_top();
144 compact_end = dest->space()->end();
145 assert(compact_top == dest->space()->bottom(), "Advanced to space already in use");
146 assert(compact_end > compact_top, "Must always be space remaining");
147 compaction_max_size =
148 pointer_delta(compact_end, compact_top);
149 }
150
151 // store the forwarding pointer into the mark word
152 if (q != compact_top) {
153 oop(q)->forward_to(oop(compact_top));
154 assert(oop(q)->is_gc_marked(), "encoding the pointer should preserve the mark");
155 } else {
156 // if the object isn't moving we can just set the mark to the default
157 // mark and handle it specially later on.
158 oop(q)->init_mark();
159 assert(oop(q)->forwardee() == NULL, "should be forwarded to NULL");
160 }
161
162 // Update object start array
163 if (start_array) {
164 start_array->allocate_block(compact_top);
165 }
166
167 compact_top += size;
168 assert(compact_top <= dest->space()->end(),
169 "Exceeding space in destination");
170
171 q += size;
172 end_of_live = q;
173 } else {
174 /* run over all the contiguous dead objects */
175 HeapWord* end = q;
176 do {
177 /* prefetch beyond end */
178 Prefetch::write(end, interval);
179 end += oop(end)->size();
180 } while (end < t && (!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 */
185 if (allowed_deadspace > 0 && q == compact_top) {
186 size_t sz = pointer_delta(end, q);
187 if (insert_deadspace(allowed_deadspace, q, sz)) {
188 size_t compaction_max_size = pointer_delta(compact_end, compact_top);
189
190 // This should only happen if a space in the young gen overflows the
191 // old gen. If that should happen, we null out the start_array, because
192 // the young spaces are not covered by one.
193 while (sz > compaction_max_size) {
194 // First record the last compact_top
195 dest->set_compaction_top(compact_top);
196
197 // Advance to the next compaction decorator
198 advance_destination_decorator();
199 dest = destination_decorator();
200
201 // Update compaction info
202 start_array = dest->start_array();
203 compact_top = dest->compaction_top();
204 compact_end = dest->space()->end();
205 assert(compact_top == dest->space()->bottom(), "Advanced to space already in use");
206 assert(compact_end > compact_top, "Must always be space remaining");
207 compaction_max_size =
208 pointer_delta(compact_end, compact_top);
209 }
210
211 // store the forwarding pointer into the mark word
212 if (q != compact_top) {
213 oop(q)->forward_to(oop(compact_top));
214 assert(oop(q)->is_gc_marked(), "encoding the pointer should preserve the mark");
215 } else {
216 // if the object isn't moving we can just set the mark to the default
217 // mark and handle it specially later on.
218 oop(q)->init_mark();
219 assert(oop(q)->forwardee() == NULL, "should be forwarded to NULL");
220 }
221
222 // Update object start array
223 if (start_array) {
224 start_array->allocate_block(compact_top);
225 }
226
227 compact_top += sz;
228 assert(compact_top <= dest->space()->end(),
229 "Exceeding space in destination");
230
231 q = end;
232 end_of_live = end;
233 continue;
234 }
235 }
236
237 /* for the previous LiveRange, record the end of the live objects. */
238 if (liveRange) {
239 liveRange->set_end(q);
240 }
241
242 /* record the current LiveRange object.
243 * liveRange->start() is overlaid on the mark word.
244 */
245 liveRange = (LiveRange*)q;
246 liveRange->set_start(end);
247 liveRange->set_end(end);
248
249 /* see if this is the first dead region. */
250 if (q < first_dead) {
251 first_dead = q;
252 }
253
254 /* move on to the next object */
255 q = end;
256 }
257 }
258
259 assert(q == t, "just checking");
260 if (liveRange != NULL) {
261 liveRange->set_end(q);
262 }
263 _end_of_live = end_of_live;
264 if (end_of_live < first_dead) {
265 first_dead = end_of_live;
266 }
267 _first_dead = first_dead;
268
269 // Update compaction top
270 dest->set_compaction_top(compact_top);
271 }
272
273 bool PSMarkSweepDecorator::insert_deadspace(size_t& allowed_deadspace_words,
274 HeapWord* q, size_t deadlength) {
275 if (allowed_deadspace_words >= deadlength) {
276 allowed_deadspace_words -= deadlength;
277 CollectedHeap::fill_with_object(q, deadlength);
278 oop(q)->set_mark(oop(q)->mark()->set_marked());
279 assert((int) deadlength == oop(q)->size(), "bad filler object size");
280 // Recall that we required "q == compaction_top".
281 return true;
282 } else {
283 allowed_deadspace_words = 0;
284 return false;
285 }
286 }
287
288 void PSMarkSweepDecorator::adjust_pointers() {
289 // adjust all the interior pointers to point at the new locations of objects
290 // Used by MarkSweep::mark_sweep_phase3()
291
292 HeapWord* q = space()->bottom();
293 HeapWord* t = _end_of_live; // Established by "prepare_for_compaction".
294
295 assert(_first_dead <= _end_of_live, "Stands to reason, no?");
296
297 if (q < t && _first_dead > q &&
298 !oop(q)->is_gc_marked()) {
299 // we have a chunk of the space which hasn't moved and we've
300 // reinitialized the mark word during the previous pass, so we can't
301 // use is_gc_marked for the traversal.
302 HeapWord* end = _first_dead;
303
304 while (q < end) {
305 // point all the oops to the new location
306 size_t size = MarkSweep::adjust_pointers(oop(q));
307 q += size;
308 }
309
310 if (_first_dead == t) {
311 q = t;
312 } else {
313 // $$$ This is funky. Using this to read the previously written
314 // LiveRange. See also use below.
315 q = (HeapWord*)oop(_first_dead)->mark()->decode_pointer();
316 }
317 }
318 const intx interval = PrefetchScanIntervalInBytes;
319
320 debug_only(HeapWord* prev_q = NULL);
321 while (q < t) {
322 // prefetch beyond q
323 Prefetch::write(q, interval);
324 if (oop(q)->is_gc_marked()) {
325 // q is alive
326 // point all the oops to the new location
327 size_t size = MarkSweep::adjust_pointers(oop(q));
328 debug_only(prev_q = q);
329 q += size;
330 } else {
331 // q is not a live object, so its mark should point at the next
332 // live object
333 debug_only(prev_q = q);
334 q = (HeapWord*) oop(q)->mark()->decode_pointer();
335 assert(q > prev_q, "we should be moving forward through memory");
336 }
337 }
338
339 assert(q == t, "just checking");
340 }
341
342 void PSMarkSweepDecorator::compact(bool mangle_free_space ) {
343 // Copy all live objects to their new location
344 // Used by MarkSweep::mark_sweep_phase4()
345
346 HeapWord* q = space()->bottom();
347 HeapWord* const t = _end_of_live;
348 debug_only(HeapWord* prev_q = NULL);
349
350 if (q < t && _first_dead > q &&
351 !oop(q)->is_gc_marked()) {
352 #ifdef ASSERT
353 // we have a chunk of the space which hasn't moved and we've reinitialized the
354 // mark word during the previous pass, so we can't use is_gc_marked for the
355 // traversal.
356 HeapWord* const end = _first_dead;
357
358 while (q < end) {
359 size_t size = oop(q)->size();
360 assert(!oop(q)->is_gc_marked(), "should be unmarked (special dense prefix handling)");
361 debug_only(prev_q = q);
362 q += size;
363 }
364 #endif
365
366 if (_first_dead == t) {
367 q = t;
368 } else {
369 // $$$ Funky
370 q = (HeapWord*) oop(_first_dead)->mark()->decode_pointer();
371 }
372 }
373
374 const intx scan_interval = PrefetchScanIntervalInBytes;
375 const intx copy_interval = PrefetchCopyIntervalInBytes;
376
377 while (q < t) {
378 if (!oop(q)->is_gc_marked()) {
379 // mark is pointer to next marked oop
380 debug_only(prev_q = q);
381 q = (HeapWord*) oop(q)->mark()->decode_pointer();
382 assert(q > prev_q, "we should be moving forward through memory");
383 } else {
384 // prefetch beyond q
385 Prefetch::read(q, scan_interval);
386
387 // size and destination
388 size_t size = oop(q)->size();
389 HeapWord* compaction_top = (HeapWord*)oop(q)->forwardee();
390
391 // prefetch beyond compaction_top
392 Prefetch::write(compaction_top, copy_interval);
393
394 // copy object and reinit its mark
395 assert(q != compaction_top, "everything in this pass should be moving");
396 Copy::aligned_conjoint_words(q, compaction_top, size);
397 oop(compaction_top)->init_mark();
398 assert(oop(compaction_top)->klass() != NULL, "should have a class");
399
400 debug_only(prev_q = q);
401 q += size;
402 }
403 }
404
405 assert(compaction_top() >= space()->bottom() && compaction_top() <= space()->end(),
406 "should point inside space");
407 space()->set_top(compaction_top());
408
409 if (mangle_free_space) {
410 space()->mangle_unused_area();
411 }
412 }