1 /*
2 * Copyright (c) 2016, Red Hat, Inc. and/or its affiliates.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #include "precompiled.hpp"
25 #include "gc_implementation/shenandoah/shenandoahFreeSet.hpp"
26 #include "gc_implementation/shenandoah/shenandoahHeap.inline.hpp"
27
28 ShenandoahFreeSet::ShenandoahFreeSet(ShenandoahHeap* heap,size_t max_regions) :
29 _heap(heap),
30 _mutator_free_bitmap(max_regions, /* in_resource_area = */ false),
31 _collector_free_bitmap(max_regions, /* in_resource_area = */ false),
32 _max(max_regions)
33 {
34 clear_internal();
35 }
36
37 void ShenandoahFreeSet::increase_used(size_t num_bytes) {
38 assert_heaplock_owned_by_current_thread();
39 _used += num_bytes;
40
41 assert(_used <= _capacity, err_msg("must not use more than we have: used: "SIZE_FORMAT
42 ", capacity: "SIZE_FORMAT", num_bytes: "SIZE_FORMAT,
43 _used, _capacity, num_bytes));
44 }
45
46 bool ShenandoahFreeSet::is_mutator_free(size_t idx) const {
47 assert (idx < _max,
48 err_msg("index is sane: " SIZE_FORMAT " < " SIZE_FORMAT " (left: " SIZE_FORMAT ", right: " SIZE_FORMAT ")",
49 idx, _max, _mutator_leftmost, _mutator_rightmost));
50 return _mutator_free_bitmap.at(idx);
51 }
52
53 bool ShenandoahFreeSet::is_collector_free(size_t idx) const {
54 assert (idx < _max,
55 err_msg("index is sane: " SIZE_FORMAT " < " SIZE_FORMAT " (left: " SIZE_FORMAT ", right: " SIZE_FORMAT ")",
56 idx, _max, _collector_leftmost, _collector_rightmost));
57 return _collector_free_bitmap.at(idx);
58 }
59
60 HeapWord* ShenandoahFreeSet::allocate_single(ShenandoahHeap::ShenandoahAllocationRequest& req, bool& in_new_region) {
61 // Scan the bitmap looking for a first fit.
62 //
63 // Leftmost and rightmost bounds provide enough caching to walk bitmap efficiently. Normally,
64 // we would find the region to allocate at right away.
65 //
66 // Allocations are biased: new application allocs go to beginning of the heap, and GC allocs
67 // go to the end. This makes application allocation faster, because we would clear lots
68 // of regions from the beginning most of the time.
69 //
70 // Free set maintains mutator and collector views, and normally they allocate in their views only,
71 // unless we special cases for stealing and mixed allocations.
72
73 switch (req.type()) {
74 case ShenandoahHeap::_alloc_tlab:
75 case ShenandoahHeap::_alloc_shared: {
76
77 // Try to allocate in the mutator view
78 for (size_t idx = _mutator_leftmost; idx <= _mutator_rightmost; idx++) {
79 if (is_mutator_free(idx)) {
80 HeapWord* result = try_allocate_in(_heap->get_region(idx), req, in_new_region);
81 if (result != NULL) {
82 return result;
83 }
84 }
85 }
86
87 // There is no recovery. Mutator does not touch collector view at all.
88 break;
89 }
90 case ShenandoahHeap::_alloc_gclab:
91 case ShenandoahHeap::_alloc_shared_gc: {
92 // size_t is unsigned, need to dodge underflow when _leftmost = 0
93
94 // Fast-path: try to allocate in the collector view first
95 for (size_t c = _collector_rightmost + 1; c > _collector_leftmost; c--) {
96 size_t idx = c - 1;
97 if (is_collector_free(idx)) {
98 HeapWord* result = try_allocate_in(_heap->get_region(idx), req, in_new_region);
99 if (result != NULL) {
100 return result;
101 }
102 }
103 }
104
105 // No dice. Can we borrow space from mutator view?
106 if (!ShenandoahEvacReserveOverflow) {
107 return NULL;
108 }
109
110 // Try to steal the empty region from the mutator view
111 for (size_t c = _mutator_rightmost + 1; c > _mutator_leftmost; c--) {
112 size_t idx = c - 1;
113 if (is_mutator_free(idx)) {
114 ShenandoahHeapRegion* r = _heap->get_region(idx);
115 if (is_empty_or_trash(r)) {
116 flip_to_gc(r);
117 HeapWord *result = try_allocate_in(r, req, in_new_region);
118 if (result != NULL) {
119 return result;
120 }
121 }
122 }
123 }
124
125 // Try to mix the allocation into the mutator view:
126 if (ShenandoahAllowMixedAllocs) {
127 for (size_t c = _mutator_rightmost + 1; c > _mutator_leftmost; c--) {
128 size_t idx = c - 1;
129 if (is_mutator_free(idx)) {
130 HeapWord* result = try_allocate_in(_heap->get_region(idx), req, in_new_region);
131 if (result != NULL) {
132 return result;
133 }
134 }
135 }
136 }
137 break;
138 }
139 default:
140 ShouldNotReachHere();
141 }
142
143 return NULL;
144 }
145
146 HeapWord* ShenandoahFreeSet::try_allocate_in(ShenandoahHeapRegion* r, ShenandoahHeap::ShenandoahAllocationRequest& req, bool& in_new_region) {
147 assert (!has_no_alloc_capacity(r), err_msg("Performance: should avoid full regions on this path: " SIZE_FORMAT, r->region_number()));
148
149 try_recycle_trashed(r);
150
151 in_new_region = r->is_empty();
152
153 HeapWord* result = NULL;
154 size_t size = req.size();
155
156 if (ShenandoahElasticTLAB && req.is_lab_alloc()) {
157 size_t free = align_size_down(r->free() >> LogHeapWordSize, MinObjAlignment);
158 if (size > free) {
159 size = free;
160 }
161 if (size >= req.min_size()) {
162 result = r->allocate(size, req.type());
163 assert (result != NULL, err_msg("Allocation must succeed: free " SIZE_FORMAT ", actual " SIZE_FORMAT, free, size));
164 }
165 } else {
166 result = r->allocate(size, req.type());
167 }
168
169 if (result != NULL) {
170 // Allocation successful, bump stats:
171 if (req.is_mutator_alloc()) {
172 increase_used(size * HeapWordSize);
173 }
174
175 // Record actual allocation size
176 req.set_actual_size(size);
177 }
178
179 if (result == NULL || has_no_alloc_capacity(r)) {
180 // Region cannot afford this or future allocations. Retire it.
181 //
182 // While this seems a bit harsh, especially in the case when this large allocation does not
183 // fit, but the next small one would, we are risking to inflate scan times when lots of
184 // almost-full regions precede the fully-empty region where we want allocate the entire TLAB.
185 // TODO: Record first fully-empty region, and use that for large allocations
186
187 // Record the remainder as allocation waste
188 if (req.is_mutator_alloc()) {
189 size_t waste = r->free();
190 if (waste > 0) {
191 increase_used(waste);
192 _heap->notify_mutator_alloc_words(waste >> LogHeapWordSize, true);
193 }
194 }
195
196 size_t num = r->region_number();
197 _collector_free_bitmap.clear_bit(num);
198 _mutator_free_bitmap.clear_bit(num);
199 // Touched the bounds? Need to update:
200 if (touches_bounds(num)) {
201 adjust_bounds();
202 }
203 assert_bounds();
204 }
205 return result;
206 }
207
208 bool ShenandoahFreeSet::touches_bounds(size_t num) const {
209 return num == _collector_leftmost || num == _collector_rightmost || num == _mutator_leftmost || num == _mutator_rightmost;
210 }
211
212 void ShenandoahFreeSet::recompute_bounds() {
213 // Reset to the most pessimistic case:
214 _mutator_rightmost = _max - 1;
215 _mutator_leftmost = 0;
216 _collector_rightmost = _max - 1;
217 _collector_leftmost = 0;
218
219 // ...and adjust from there
220 adjust_bounds();
221 }
222
223 void ShenandoahFreeSet::adjust_bounds() {
224 // Rewind both mutator bounds until the next bit.
225 while (_mutator_leftmost < _max && !is_mutator_free(_mutator_leftmost)) {
226 _mutator_leftmost++;
227 }
228 while (_mutator_rightmost > 0 && !is_mutator_free(_mutator_rightmost)) {
229 _mutator_rightmost--;
230 }
231 // Rewind both collector bounds until the next bit.
232 while (_collector_leftmost < _max && !is_collector_free(_collector_leftmost)) {
233 _collector_leftmost++;
234 }
235 while (_collector_rightmost > 0 && !is_collector_free(_collector_rightmost)) {
236 _collector_rightmost--;
237 }
238 }
239
240 HeapWord* ShenandoahFreeSet::allocate_contiguous(ShenandoahHeap::ShenandoahAllocationRequest& req) {
241 assert_heaplock_owned_by_current_thread();
242
243 size_t words_size = req.size();
244 size_t num = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
245
246 // No regions left to satisfy allocation, bye.
247 if (num > mutator_count()) {
248 return NULL;
249 }
250
251 // Find the continuous interval of $num regions, starting from $beg and ending in $end,
252 // inclusive. Contiguous allocations are biased to the beginning.
253
254 size_t beg = _mutator_leftmost;
255 size_t end = beg;
256
257 while (true) {
258 if (end >= _max) {
259 // Hit the end, goodbye
260 return NULL;
261 }
262
263 // If regions are not adjacent, then current [beg; end] is useless, and we may fast-forward.
264 // If region is not completely free, the current [beg; end] is useless, and we may fast-forward.
265 if (!is_mutator_free(end) || !is_empty_or_trash(_heap->get_region(end))) {
266 end++;
267 beg = end;
268 continue;
269 }
270
271 if ((end - beg + 1) == num) {
272 // found the match
273 break;
274 }
275
276 end++;
277 };
278
279 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
280
281 // Initialize regions:
282 for (size_t i = beg; i <= end; i++) {
283 ShenandoahHeapRegion* r = _heap->get_region(i);
284 try_recycle_trashed(r);
285
286 assert(i == beg || _heap->get_region(i-1)->region_number() + 1 == r->region_number(), "Should be contiguous");
287 assert(r->is_empty(), "Should be empty");
288
289 if (i == beg) {
290 r->make_humongous_start();
291 } else {
292 r->make_humongous_cont();
293 }
294
295 // Trailing region may be non-full, record the remainder there
296 size_t used_words;
297 if ((i == end) && (remainder != 0)) {
298 used_words = remainder;
299 } else {
300 used_words = ShenandoahHeapRegion::region_size_words();
301 }
302
303 r->set_top(r->bottom() + used_words);
304 r->reset_alloc_metadata_to_shared();
305
306 _mutator_free_bitmap.clear_bit(r->region_number());
307 }
308
309 // While individual regions report their true use, all humongous regions are
310 // marked used in the free set.
311 increase_used(ShenandoahHeapRegion::region_size_bytes() * num);
312
313 if (remainder != 0) {
314 // Record this remainder as allocation waste
315 _heap->notify_mutator_alloc_words(ShenandoahHeapRegion::region_size_words() - remainder, true);
316 }
317
318 // Allocated at left/rightmost? Move the bounds appropriately.
319 if (beg == _mutator_leftmost || end == _mutator_rightmost) {
320 adjust_bounds();
321 }
322 assert_bounds();
323
324 req.set_actual_size(words_size);
325 return _heap->get_region(beg)->bottom();
326 }
327
328 bool ShenandoahFreeSet::is_empty_or_trash(ShenandoahHeapRegion *r) {
329 return r->is_empty() || r->is_trash();
330 }
331
332 size_t ShenandoahFreeSet::alloc_capacity(ShenandoahHeapRegion *r) {
333 if (r->is_trash()) {
334 // This would be recycled on allocation path
335 return ShenandoahHeapRegion::region_size_bytes();
336 } else {
337 return r->free();
338 }
339 }
340
341 bool ShenandoahFreeSet::has_no_alloc_capacity(ShenandoahHeapRegion *r) {
342 return alloc_capacity(r) == 0;
343 }
344
345 void ShenandoahFreeSet::try_recycle_trashed(ShenandoahHeapRegion *r) {
346 if (r->is_trash()) {
347 _heap->decrease_used(r->used());
348 r->recycle();
349 }
350 }
351
352 void ShenandoahFreeSet::recycle_trash() {
353 // lock is not reentrable, check we don't have it
354 assert_heaplock_not_owned_by_current_thread();
355
356 for (size_t i = 0; i < _heap->num_regions(); i++) {
357 ShenandoahHeapRegion* r = _heap->get_region(i);
358 if (r->is_trash()) {
359 ShenandoahHeapLocker locker(_heap->lock());
360 try_recycle_trashed(r);
361 }
362 SpinPause(); // allow allocators to take the lock
363 }
364 }
365
366 void ShenandoahFreeSet::flip_to_gc(ShenandoahHeapRegion* r) {
367 size_t idx = r->region_number();
368
369 assert(_mutator_free_bitmap.at(idx), "Should be in mutator view");
370 assert(is_empty_or_trash(r), "Should not be allocated");
371
372 _mutator_free_bitmap.clear_bit(idx);
373 _collector_free_bitmap.set_bit(idx);
374 _collector_leftmost = MIN2(idx, _collector_leftmost);
375 _collector_rightmost = MAX2(idx, _collector_rightmost);
376
377 _capacity -= alloc_capacity(r);
378
379 if (touches_bounds(idx)) {
380 adjust_bounds();
381 }
382 assert_bounds();
383 }
384
385 void ShenandoahFreeSet::clear() {
386 assert_heaplock_owned_by_current_thread();
387 clear_internal();
388 }
389
390 void ShenandoahFreeSet::clear_internal() {
391 _mutator_free_bitmap.clear();
392 _collector_free_bitmap.clear();
393 _mutator_leftmost = _max;
394 _mutator_rightmost = 0;
395 _collector_leftmost = _max;
396 _collector_rightmost = 0;
397 _capacity = 0;
398 _used = 0;
399 }
400
401 void ShenandoahFreeSet::rebuild() {
402 assert_heaplock_owned_by_current_thread();
403 clear();
404
405 for (size_t idx = 0; idx < _heap->num_regions(); idx++) {
406 ShenandoahHeapRegion* region = _heap->get_region(idx);
407 if (region->is_alloc_allowed() || region->is_trash()) {
408 assert(!region->in_collection_set(), "Shouldn't be adding those to the free set");
409
410 // Do not add regions that would surely fail allocation
411 if (has_no_alloc_capacity(region)) continue;
412
413 _capacity += alloc_capacity(region);
414 assert(_used <= _capacity, "must not use more than we have");
415
416 assert(!is_mutator_free(idx), "We are about to add it, it shouldn't be there already");
417 _mutator_free_bitmap.set_bit(idx);
418 }
419 }
420
421 // Evac reserve: reserve trailing space for evacuations
422 size_t to_reserve = ShenandoahEvacReserve * _heap->capacity() / 100;
423 size_t reserved = 0;
424
425 for (size_t idx = _heap->num_regions() - 1; idx > 0; idx--) {
426 if (reserved >= to_reserve) break;
427
428 ShenandoahHeapRegion* region = _heap->get_region(idx);
429 if (_mutator_free_bitmap.at(idx) && is_empty_or_trash(region)) {
430 _mutator_free_bitmap.clear_bit(idx);
431 _collector_free_bitmap.set_bit(idx);
432 size_t ac = alloc_capacity(region);
433 _capacity -= ac;
434 reserved += ac;
435 }
436 }
437
438 recompute_bounds();
439 assert_bounds();
440 }
441
442 void ShenandoahFreeSet::log_status() {
443 assert_heaplock_owned_by_current_thread();
444
445 if (ShenandoahLogInfo || PrintGCDetails) {
446 ResourceMark rm;
447 outputStream* ls = gclog_or_tty;
448
449 {
450 size_t last_idx = 0;
451 size_t max = 0;
452 size_t max_contig = 0;
453 size_t empty_contig = 0;
454
455 size_t total_used = 0;
456 size_t total_free = 0;
457
458 for (size_t idx = _mutator_leftmost; idx <= _mutator_rightmost; idx++) {
459 if (is_mutator_free(idx)) {
460 ShenandoahHeapRegion *r = _heap->get_region(idx);
461 size_t free = alloc_capacity(r);
462
463 max = MAX2(max, free);
464
465 if (r->is_empty() && (last_idx + 1 == idx)) {
466 empty_contig++;
467 } else {
468 empty_contig = 0;
469 }
470
471 total_used += r->used();
472 total_free += free;
473
474 max_contig = MAX2(max_contig, empty_contig);
475 last_idx = idx;
476 }
477 }
478
479 size_t max_humongous = max_contig * ShenandoahHeapRegion::region_size_bytes();
480 size_t free = capacity() - used();
481
482 ls->print("Free: " SIZE_FORMAT "M (" SIZE_FORMAT " regions), Max regular: " SIZE_FORMAT "K, Max humongous: " SIZE_FORMAT "K, ",
483 total_free / M, mutator_count(), max / K, max_humongous / K);
484
485 size_t frag_ext;
486 if (free > 0) {
487 frag_ext = 100 - (100 * max_humongous / free);
488 } else {
489 frag_ext = 0;
490 }
491 ls->print("External frag: " SIZE_FORMAT "%%, ", frag_ext);
492
493 size_t frag_int;
494 if (mutator_count() > 0) {
495 frag_int = (100 * (total_used / mutator_count()) / ShenandoahHeapRegion::region_size_bytes());
496 } else {
497 frag_int = 0;
498 }
499 ls->print("Internal frag: " SIZE_FORMAT "%%", frag_int);
500 ls->cr();
501 }
502
503 {
504 size_t max = 0;
505 size_t total_free = 0;
506
507 for (size_t idx = _collector_leftmost; idx <= _collector_rightmost; idx++) {
508 if (is_collector_free(idx)) {
509 ShenandoahHeapRegion *r = _heap->get_region(idx);
510 size_t free = alloc_capacity(r);
511 max = MAX2(max, free);
512 total_free += free;
513 }
514 }
515
516 ls->print_cr("Evacuation Reserve: " SIZE_FORMAT "M (" SIZE_FORMAT " regions), Max regular: " SIZE_FORMAT "K",
517 total_free / M, collector_count(), max / K);
518 }
519 }
520 }
521
522 HeapWord* ShenandoahFreeSet::allocate(ShenandoahHeap::ShenandoahAllocationRequest& req, bool& in_new_region) {
523 assert_heaplock_owned_by_current_thread();
524 assert_bounds();
525
526 if (req.size() > ShenandoahHeapRegion::humongous_threshold_words()) {
527 switch (req.type()) {
528 case ShenandoahHeap::_alloc_shared:
529 case ShenandoahHeap::_alloc_shared_gc:
530 in_new_region = true;
531 return allocate_contiguous(req);
532 case ShenandoahHeap::_alloc_gclab:
533 case ShenandoahHeap::_alloc_tlab:
534 in_new_region = false;
535 assert(false, err_msg("Trying to allocate TLAB larger than the humongous threshold: " SIZE_FORMAT " > " SIZE_FORMAT,
536 req.size(), ShenandoahHeapRegion::humongous_threshold_words()));
537 return NULL;
538 default:
539 ShouldNotReachHere();
540 return NULL;
541 }
542 } else {
543 return allocate_single(req, in_new_region);
544 }
545 }
546
547 size_t ShenandoahFreeSet::unsafe_peek_free() const {
548 // Deliberately not locked, this method is unsafe when free set is modified.
549
550 for (size_t index = _mutator_leftmost; index <= _mutator_rightmost; index++) {
551 if (index < _max && is_mutator_free(index)) {
552 ShenandoahHeapRegion* r = _heap->get_region(index);
553 if (r->free() >= MinTLABSize) {
554 return r->free();
555 }
556 }
557 }
558
559 // It appears that no regions left
560 return 0;
561 }
562
563 void ShenandoahFreeSet::print_on(outputStream* out) const {
564 out->print_cr("Mutator Free Set: " SIZE_FORMAT "", mutator_count());
565 for (size_t index = _mutator_leftmost; index <= _mutator_rightmost; index++) {
566 if (is_mutator_free(index)) {
567 _heap->get_region(index)->print_on(out);
568 }
569 }
570 out->print_cr("Collector Free Set: " SIZE_FORMAT "", collector_count());
571 for (size_t index = _collector_leftmost; index <= _collector_rightmost; index++) {
572 if (is_collector_free(index)) {
573 _heap->get_region(index)->print_on(out);
574 }
575 }
576 }
577
578 #ifdef ASSERT
579 void ShenandoahFreeSet::assert_heaplock_owned_by_current_thread() const {
580 _heap->assert_heaplock_owned_by_current_thread();
581 }
582
583
584
585 void ShenandoahFreeSet::assert_heaplock_not_owned_by_current_thread() const {
586 _heap->assert_heaplock_not_owned_by_current_thread();
587 }
588
589 void ShenandoahFreeSet::assert_bounds() const {
590 // Performance invariants. Failing these would not break the free set, but performance
591 // would suffer.
592 assert (_mutator_leftmost <= _max, err_msg("leftmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, _mutator_leftmost, _max));
593 assert (_mutator_rightmost < _max, err_msg("rightmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, _mutator_rightmost, _max));
594
595 assert (_mutator_leftmost == _max || is_mutator_free(_mutator_leftmost), err_msg("leftmost region should be free: " SIZE_FORMAT, _mutator_leftmost));
596 assert (_mutator_rightmost == 0 || is_mutator_free(_mutator_rightmost), err_msg("rightmost region should be free: " SIZE_FORMAT, _mutator_rightmost));
597
598 size_t beg_off = _mutator_free_bitmap.get_next_one_offset(0);
599 size_t end_off = _mutator_free_bitmap.get_next_one_offset(_mutator_rightmost + 1);
600 assert (beg_off >= _mutator_leftmost, err_msg("free regions before the leftmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, beg_off, _mutator_leftmost));
601 assert (end_off == _max, err_msg("free regions past the rightmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, end_off, _mutator_rightmost));
602
603 assert (_collector_leftmost <= _max, err_msg("leftmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, _collector_leftmost, _max));
604 assert (_collector_rightmost < _max, err_msg("rightmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, _collector_rightmost, _max));
605
606 assert (_collector_leftmost == _max || is_collector_free(_collector_leftmost), err_msg("leftmost region should be free: " SIZE_FORMAT, _collector_leftmost));
607 assert (_collector_rightmost == 0 || is_collector_free(_collector_rightmost), err_msg("rightmost region should be free: " SIZE_FORMAT, _collector_rightmost));
608
609 beg_off = _collector_free_bitmap.get_next_one_offset(0);
610 end_off = _collector_free_bitmap.get_next_one_offset(_collector_rightmost + 1);
611 assert (beg_off >= _collector_leftmost, err_msg("free regions before the leftmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, beg_off, _collector_leftmost));
612 assert (end_off == _max, err_msg("free regions past the rightmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, end_off, _collector_rightmost));
613 }
614 #endif