1 /*
2 * Copyright (c) 2001, 2009, 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 "incls/_precompiled.incl"
26 # include "incls/_psMarkSweepDecorator.cpp.incl"
27
28 PSMarkSweepDecorator* PSMarkSweepDecorator::_destination_decorator = NULL;
29
30
31 void PSMarkSweepDecorator::set_destination_decorator_tenured() {
32 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
33 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
34
35 _destination_decorator = heap->old_gen()->object_mark_sweep();
36 }
37
38 void PSMarkSweepDecorator::set_destination_decorator_perm_gen() {
39 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
40 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
41
42 _destination_decorator = heap->perm_gen()->object_mark_sweep();
43 }
44
45 void PSMarkSweepDecorator::advance_destination_decorator() {
46 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
47 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
48
49 assert(_destination_decorator != NULL, "Sanity");
50 guarantee(_destination_decorator != heap->perm_gen()->object_mark_sweep(), "Cannot advance perm gen decorator");
51
52 PSMarkSweepDecorator* first = heap->old_gen()->object_mark_sweep();
53 PSMarkSweepDecorator* second = heap->young_gen()->eden_mark_sweep();
54 PSMarkSweepDecorator* third = heap->young_gen()->from_mark_sweep();
55 PSMarkSweepDecorator* fourth = heap->young_gen()->to_mark_sweep();
56
57 if ( _destination_decorator == first ) {
58 _destination_decorator = second;
59 } else if ( _destination_decorator == second ) {
60 _destination_decorator = third;
61 } else if ( _destination_decorator == third ) {
62 _destination_decorator = fourth;
63 } else {
64 fatal("PSMarkSweep attempting to advance past last compaction area");
65 }
66 }
67
68 PSMarkSweepDecorator* PSMarkSweepDecorator::destination_decorator() {
69 assert(_destination_decorator != NULL, "Sanity");
70
71 return _destination_decorator;
72 }
73
74 // FIX ME FIX ME FIX ME FIX ME!!!!!!!!!
75 // The object forwarding code is duplicated. Factor this out!!!!!
76 //
77 // This method "precompacts" objects inside its space to dest. It places forwarding
78 // pointers into markOops for use by adjust_pointers. If "dest" should overflow, we
79 // finish by compacting into our own space.
80
81 void PSMarkSweepDecorator::precompact() {
82 // Reset our own compact top.
83 set_compaction_top(space()->bottom());
84
85 /* We allow some amount of garbage towards the bottom of the space, so
86 * we don't start compacting before there is a significant gain to be made.
87 * Occasionally, we want to ensure a full compaction, which is determined
88 * by the MarkSweepAlwaysCompactCount parameter. This is a significant
89 * performance improvement!
90 */
91 bool skip_dead = ((PSMarkSweep::total_invocations() % MarkSweepAlwaysCompactCount) != 0);
92
93 size_t allowed_deadspace = 0;
94 if (skip_dead) {
95 const size_t ratio = allowed_dead_ratio();
96 allowed_deadspace = space()->capacity_in_words() * ratio / 100;
97 }
98
99 // Fetch the current destination decorator
100 PSMarkSweepDecorator* dest = destination_decorator();
101 ObjectStartArray* start_array = dest->start_array();
102
103 HeapWord* compact_top = dest->compaction_top();
104 HeapWord* compact_end = dest->space()->end();
105
106 HeapWord* q = space()->bottom();
107 HeapWord* t = space()->top();
108
109 HeapWord* end_of_live= q; /* One byte beyond the last byte of the last
110 live object. */
111 HeapWord* first_dead = space()->end(); /* The first dead object. */
112 LiveRange* liveRange = NULL; /* The current live range, recorded in the
113 first header of preceding free area. */
114 _first_dead = first_dead;
115
116 const intx interval = PrefetchScanIntervalInBytes;
117
118 while (q < t) {
119 assert(oop(q)->mark()->is_marked() || oop(q)->mark()->is_unlocked() ||
120 oop(q)->mark()->has_bias_pattern(),
121 "these are the only valid states during a mark sweep");
122 if (oop(q)->is_gc_marked()) {
123 /* prefetch beyond q */
124 Prefetch::write(q, interval);
125 size_t size = oop(q)->size();
126
127 size_t compaction_max_size = pointer_delta(compact_end, compact_top);
128
129 // This should only happen if a space in the young gen overflows the
130 // old gen. If that should happen, we null out the start_array, because
131 // the young spaces are not covered by one.
132 while(size > compaction_max_size) {
133 // First record the last compact_top
134 dest->set_compaction_top(compact_top);
135
136 // Advance to the next compaction decorator
137 advance_destination_decorator();
138 dest = destination_decorator();
139
140 // Update compaction info
141 start_array = dest->start_array();
142 compact_top = dest->compaction_top();
143 compact_end = dest->space()->end();
144 assert(compact_top == dest->space()->bottom(), "Advanced to space already in use");
145 assert(compact_end > compact_top, "Must always be space remaining");
146 compaction_max_size =
147 pointer_delta(compact_end, compact_top);
148 }
149
150 // store the forwarding pointer into the mark word
151 if (q != compact_top) {
152 oop(q)->forward_to(oop(compact_top));
153 assert(oop(q)->is_gc_marked(), "encoding the pointer should preserve the mark");
154 } else {
155 // if the object isn't moving we can just set the mark to the default
156 // mark and handle it specially later on.
157 oop(q)->init_mark();
158 assert(oop(q)->forwardee() == NULL, "should be forwarded to NULL");
159 }
160
161 // Update object start array
162 if (start_array) {
163 start_array->allocate_block(compact_top);
164 }
165
166 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::register_live_oop(oop(q), size));
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 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::register_live_oop(oop(q), sz));
228 compact_top += sz;
229 assert(compact_top <= dest->space()->end(),
230 "Exceeding space in destination");
231
232 q = end;
233 end_of_live = end;
234 continue;
235 }
236 }
237
238 /* for the previous LiveRange, record the end of the live objects. */
239 if (liveRange) {
240 liveRange->set_end(q);
241 }
242
243 /* record the current LiveRange object.
244 * liveRange->start() is overlaid on the mark word.
245 */
246 liveRange = (LiveRange*)q;
247 liveRange->set_start(end);
248 liveRange->set_end(end);
249
250 /* see if this is the first dead region. */
251 if (q < first_dead) {
252 first_dead = q;
253 }
254
255 /* move on to the next object */
256 q = end;
257 }
258 }
259
260 assert(q == t, "just checking");
261 if (liveRange != NULL) {
262 liveRange->set_end(q);
263 }
264 _end_of_live = end_of_live;
265 if (end_of_live < first_dead) {
266 first_dead = end_of_live;
267 }
268 _first_dead = first_dead;
269
270 // Update compaction top
271 dest->set_compaction_top(compact_top);
272 }
273
274 bool PSMarkSweepDecorator::insert_deadspace(size_t& allowed_deadspace_words,
275 HeapWord* q, size_t deadlength) {
276 if (allowed_deadspace_words >= deadlength) {
277 allowed_deadspace_words -= deadlength;
278 CollectedHeap::fill_with_object(q, deadlength);
279 oop(q)->set_mark(oop(q)->mark()->set_marked());
280 assert((int) deadlength == oop(q)->size(), "bad filler object size");
281 // Recall that we required "q == compaction_top".
282 return true;
283 } else {
284 allowed_deadspace_words = 0;
285 return false;
286 }
287 }
288
289 void PSMarkSweepDecorator::adjust_pointers() {
290 // adjust all the interior pointers to point at the new locations of objects
291 // Used by MarkSweep::mark_sweep_phase3()
292
293 HeapWord* q = space()->bottom();
294 HeapWord* t = _end_of_live; // Established by "prepare_for_compaction".
295
296 assert(_first_dead <= _end_of_live, "Stands to reason, no?");
297
298 if (q < t && _first_dead > q &&
299 !oop(q)->is_gc_marked()) {
300 // we have a chunk of the space which hasn't moved and we've
301 // reinitialized the mark word during the previous pass, so we can't
302 // use is_gc_marked for the traversal.
303 HeapWord* end = _first_dead;
304
305 while (q < end) {
306 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::track_interior_pointers(oop(q)));
307 // point all the oops to the new location
308 size_t size = oop(q)->adjust_pointers();
309 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::check_interior_pointers());
310 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::validate_live_oop(oop(q), size));
311 q += size;
312 }
313
314 if (_first_dead == t) {
315 q = t;
316 } else {
317 // $$$ This is funky. Using this to read the previously written
318 // LiveRange. See also use below.
319 q = (HeapWord*)oop(_first_dead)->mark()->decode_pointer();
320 }
321 }
322 const intx interval = PrefetchScanIntervalInBytes;
323
324 debug_only(HeapWord* prev_q = NULL);
325 while (q < t) {
326 // prefetch beyond q
327 Prefetch::write(q, interval);
328 if (oop(q)->is_gc_marked()) {
329 // q is alive
330 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::track_interior_pointers(oop(q)));
331 // point all the oops to the new location
332 size_t size = oop(q)->adjust_pointers();
333 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::check_interior_pointers());
334 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::validate_live_oop(oop(q), size));
335 debug_only(prev_q = q);
336 q += size;
337 } else {
338 // q is not a live object, so its mark should point at the next
339 // live object
340 debug_only(prev_q = q);
341 q = (HeapWord*) oop(q)->mark()->decode_pointer();
342 assert(q > prev_q, "we should be moving forward through memory");
343 }
344 }
345
346 assert(q == t, "just checking");
347 }
348
349 void PSMarkSweepDecorator::compact(bool mangle_free_space ) {
350 // Copy all live objects to their new location
351 // Used by MarkSweep::mark_sweep_phase4()
352
353 HeapWord* q = space()->bottom();
354 HeapWord* const t = _end_of_live;
355 debug_only(HeapWord* prev_q = NULL);
356
357 if (q < t && _first_dead > q &&
358 !oop(q)->is_gc_marked()) {
359 #ifdef ASSERT
360 // we have a chunk of the space which hasn't moved and we've reinitialized the
361 // mark word during the previous pass, so we can't use is_gc_marked for the
362 // traversal.
363 HeapWord* const end = _first_dead;
364
365 while (q < end) {
366 size_t size = oop(q)->size();
367 assert(!oop(q)->is_gc_marked(), "should be unmarked (special dense prefix handling)");
368 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::live_oop_moved_to(q, size, q));
369 debug_only(prev_q = q);
370 q += size;
371 }
372 #endif
373
374 if (_first_dead == t) {
375 q = t;
376 } else {
377 // $$$ Funky
378 q = (HeapWord*) oop(_first_dead)->mark()->decode_pointer();
379 }
380 }
381
382 const intx scan_interval = PrefetchScanIntervalInBytes;
383 const intx copy_interval = PrefetchCopyIntervalInBytes;
384
385 while (q < t) {
386 if (!oop(q)->is_gc_marked()) {
387 // mark is pointer to next marked oop
388 debug_only(prev_q = q);
389 q = (HeapWord*) oop(q)->mark()->decode_pointer();
390 assert(q > prev_q, "we should be moving forward through memory");
391 } else {
392 // prefetch beyond q
393 Prefetch::read(q, scan_interval);
394
395 // size and destination
396 size_t size = oop(q)->size();
397 HeapWord* compaction_top = (HeapWord*)oop(q)->forwardee();
398
399 // prefetch beyond compaction_top
400 Prefetch::write(compaction_top, copy_interval);
401
402 // copy object and reinit its mark
403 VALIDATE_MARK_SWEEP_ONLY(MarkSweep::live_oop_moved_to(q, size, compaction_top));
404 assert(q != compaction_top, "everything in this pass should be moving");
405 Copy::aligned_conjoint_words(q, compaction_top, size);
406 oop(compaction_top)->init_mark();
407 assert(oop(compaction_top)->klass() != NULL, "should have a class");
408
409 debug_only(prev_q = q);
410 q += size;
411 }
412 }
413
414 assert(compaction_top() >= space()->bottom() && compaction_top() <= space()->end(),
415 "should point inside space");
416 space()->set_top(compaction_top());
417
418 if (mangle_free_space) {
419 space()->mangle_unused_area();
420 }
421 }