1 /*
2 * Copyright (c) 2016, 2021, Red Hat, Inc. All rights reserved.
3 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "precompiled.hpp"
27 #include "gc/shared/tlab_globals.hpp"
28 #include "gc/shenandoah/shenandoahAffiliation.hpp"
29 #include "gc/shenandoah/shenandoahBarrierSet.hpp"
30 #include "gc/shenandoah/shenandoahFreeSet.hpp"
31 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
32 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
33 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
34 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
35 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
36 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
37 #include "logging/logStream.hpp"
38 #include "memory/resourceArea.hpp"
39 #include "runtime/orderAccess.hpp"
40
41 ShenandoahSetsOfFree::ShenandoahSetsOfFree(size_t max_regions, ShenandoahFreeSet* free_set) :
42 _max(max_regions),
43 _free_set(free_set),
44 _region_size_bytes(ShenandoahHeapRegion::region_size_bytes())
45 {
46 _membership = NEW_C_HEAP_ARRAY(ShenandoahFreeMemoryType, max_regions, mtGC);
47 clear_internal();
48 }
49
50 ShenandoahSetsOfFree::~ShenandoahSetsOfFree() {
51 FREE_C_HEAP_ARRAY(ShenandoahFreeMemoryType, _membership);
52 }
53
54
55 void ShenandoahSetsOfFree::clear_internal() {
56 for (size_t idx = 0; idx < _max; idx++) {
57 _membership[idx] = NotFree;
58 }
59
60 for (size_t idx = 0; idx < NumFreeSets; idx++) {
61 _leftmosts[idx] = _max;
62 _rightmosts[idx] = 0;
63 _leftmosts_empty[idx] = _max;
64 _rightmosts_empty[idx] = 0;
65 _capacity_of[idx] = 0;
66 _used_by[idx] = 0;
67 }
68
69 _left_to_right_bias[Mutator] = true;
70 _left_to_right_bias[Collector] = false;
71 _left_to_right_bias[OldCollector] = false;
72
73 _region_counts[Mutator] = 0;
74 _region_counts[Collector] = 0;
75 _region_counts[OldCollector] = 0;
76 _region_counts[NotFree] = _max;
77 }
78
79 void ShenandoahSetsOfFree::clear_all() {
80 clear_internal();
81 }
82
83 void ShenandoahSetsOfFree::increase_used(ShenandoahFreeMemoryType which_set, size_t bytes) {
84 assert (which_set > NotFree && which_set < NumFreeSets, "Set must correspond to a valid freeset");
85 _used_by[which_set] += bytes;
86 assert (_used_by[which_set] <= _capacity_of[which_set],
87 "Must not use (" SIZE_FORMAT ") more than capacity (" SIZE_FORMAT ") after increase by " SIZE_FORMAT,
88 _used_by[which_set], _capacity_of[which_set], bytes);
89 }
90
91 inline void ShenandoahSetsOfFree::shrink_bounds_if_touched(ShenandoahFreeMemoryType set, size_t idx) {
92 if (idx == _leftmosts[set]) {
93 while ((_leftmosts[set] < _max) && !in_free_set(_leftmosts[set], set)) {
94 _leftmosts[set]++;
95 }
96 if (_leftmosts_empty[set] < _leftmosts[set]) {
97 // This gets us closer to where we need to be; we'll scan further when leftmosts_empty is requested.
98 _leftmosts_empty[set] = _leftmosts[set];
99 }
100 }
101 if (idx == _rightmosts[set]) {
102 while (_rightmosts[set] > 0 && !in_free_set(_rightmosts[set], set)) {
103 _rightmosts[set]--;
104 }
105 if (_rightmosts_empty[set] > _rightmosts[set]) {
106 // This gets us closer to where we need to be; we'll scan further when rightmosts_empty is requested.
107 _rightmosts_empty[set] = _rightmosts[set];
108 }
109 }
110 }
111
112 inline void ShenandoahSetsOfFree::expand_bounds_maybe(ShenandoahFreeMemoryType set, size_t idx, size_t region_capacity) {
113 if (region_capacity == _region_size_bytes) {
114 if (_leftmosts_empty[set] > idx) {
115 _leftmosts_empty[set] = idx;
116 }
117 if (_rightmosts_empty[set] < idx) {
118 _rightmosts_empty[set] = idx;
119 }
120 }
121 if (_leftmosts[set] > idx) {
122 _leftmosts[set] = idx;
123 }
124 if (_rightmosts[set] < idx) {
125 _rightmosts[set] = idx;
126 }
127 }
128
129 void ShenandoahSetsOfFree::remove_from_free_sets(size_t idx) {
130 assert (idx < _max, "index is sane: " SIZE_FORMAT " < " SIZE_FORMAT, idx, _max);
131 ShenandoahFreeMemoryType orig_set = membership(idx);
132 assert (orig_set > NotFree && orig_set < NumFreeSets, "Cannot remove from free sets if not already free");
133 _membership[idx] = NotFree;
134 shrink_bounds_if_touched(orig_set, idx);
135
136 _region_counts[orig_set]--;
137 _region_counts[NotFree]++;
138 }
139
140
141 void ShenandoahSetsOfFree::make_free(size_t idx, ShenandoahFreeMemoryType which_set, size_t region_capacity) {
142 assert (idx < _max, "index is sane: " SIZE_FORMAT " < " SIZE_FORMAT, idx, _max);
143 assert (_membership[idx] == NotFree, "Cannot make free if already free");
144 assert (which_set > NotFree && which_set < NumFreeSets, "selected free set must be valid");
145 _membership[idx] = which_set;
146 _capacity_of[which_set] += region_capacity;
147 expand_bounds_maybe(which_set, idx, region_capacity);
148
149 _region_counts[NotFree]--;
150 _region_counts[which_set]++;
151 }
152
153 void ShenandoahSetsOfFree::move_to_set(size_t idx, ShenandoahFreeMemoryType new_set, size_t region_capacity) {
154 assert (idx < _max, "index is sane: " SIZE_FORMAT " < " SIZE_FORMAT, idx, _max);
155 assert ((new_set > NotFree) && (new_set < NumFreeSets), "New set must be valid");
156 ShenandoahFreeMemoryType orig_set = _membership[idx];
157 assert ((orig_set > NotFree) && (orig_set < NumFreeSets), "Cannot move free unless already free");
158 // Expected transitions:
159 // During rebuild: Mutator => Collector
160 // Mutator empty => Collector
161 // During flip_to_gc:
162 // Mutator empty => Collector
163 // Mutator empty => Old Collector
164 // At start of update refs:
165 // Collector => Mutator
166 // OldCollector Empty => Mutator
167 assert (((region_capacity <= _region_size_bytes) &&
168 ((orig_set == Mutator) && (new_set == Collector)) ||
169 ((orig_set == Collector) && (new_set == Mutator))) ||
170 ((region_capacity == _region_size_bytes) &&
171 ((orig_set == Mutator) && (new_set == Collector)) ||
172 ((orig_set == OldCollector) && (new_set == Mutator)) ||
173 (new_set == OldCollector)), "Unexpected movement between sets");
174
175 _membership[idx] = new_set;
176 _capacity_of[orig_set] -= region_capacity;
177 shrink_bounds_if_touched(orig_set, idx);
178
179 _capacity_of[new_set] += region_capacity;
180 expand_bounds_maybe(new_set, idx, region_capacity);
181
182 _region_counts[orig_set]--;
183 _region_counts[new_set]++;
184 }
185
186 inline ShenandoahFreeMemoryType ShenandoahSetsOfFree::membership(size_t idx) const {
187 assert (idx < _max, "index is sane: " SIZE_FORMAT " < " SIZE_FORMAT, idx, _max);
188 return _membership[idx];
189 }
190
191 // Returns true iff region idx is in the test_set free_set. Before returning true, asserts that the free
192 // set is not empty. Requires that test_set != NotFree or NumFreeSets.
193 inline bool ShenandoahSetsOfFree::in_free_set(size_t idx, ShenandoahFreeMemoryType test_set) const {
194 assert (idx < _max, "index is sane: " SIZE_FORMAT " < " SIZE_FORMAT, idx, _max);
195 if (_membership[idx] == test_set) {
196 assert (test_set == NotFree || _free_set->alloc_capacity(idx) > 0, "Free regions must have alloc capacity");
197 return true;
198 } else {
199 return false;
200 }
201 }
202
203 inline size_t ShenandoahSetsOfFree::leftmost(ShenandoahFreeMemoryType which_set) const {
204 assert (which_set > NotFree && which_set < NumFreeSets, "selected free set must be valid");
205 size_t idx = _leftmosts[which_set];
206 if (idx >= _max) {
207 return _max;
208 } else {
209 assert (in_free_set(idx, which_set), "left-most region must be free");
210 return idx;
211 }
212 }
213
214 inline size_t ShenandoahSetsOfFree::rightmost(ShenandoahFreeMemoryType which_set) const {
215 assert (which_set > NotFree && which_set < NumFreeSets, "selected free set must be valid");
216 size_t idx = _rightmosts[which_set];
217 assert ((_leftmosts[which_set] == _max) || in_free_set(idx, which_set), "right-most region must be free");
218 return idx;
219 }
220
221 size_t ShenandoahSetsOfFree::leftmost_empty(ShenandoahFreeMemoryType which_set) {
222 assert (which_set > NotFree && which_set < NumFreeSets, "selected free set must be valid");
223 for (size_t idx = _leftmosts_empty[which_set]; idx < _max; idx++) {
224 if ((membership(idx) == which_set) && (_free_set->alloc_capacity(idx) == _region_size_bytes)) {
225 _leftmosts_empty[which_set] = idx;
226 return idx;
227 }
228 }
229 _leftmosts_empty[which_set] = _max;
230 _rightmosts_empty[which_set] = 0;
231 return _max;
232 }
233
234 inline size_t ShenandoahSetsOfFree::rightmost_empty(ShenandoahFreeMemoryType which_set) {
235 assert (which_set > NotFree && which_set < NumFreeSets, "selected free set must be valid");
236 for (intptr_t idx = _rightmosts_empty[which_set]; idx >= 0; idx--) {
237 if ((membership(idx) == which_set) && (_free_set->alloc_capacity(idx) == _region_size_bytes)) {
238 _rightmosts_empty[which_set] = idx;
239 return idx;
240 }
241 }
242 _leftmosts_empty[which_set] = _max;
243 _rightmosts_empty[which_set] = 0;
244 return 0;
245 }
246
247 inline bool ShenandoahSetsOfFree::alloc_from_left_bias(ShenandoahFreeMemoryType which_set) {
248 assert (which_set > NotFree && which_set < NumFreeSets, "selected free set must be valid");
249 return _left_to_right_bias[which_set];
250 }
251
252 void ShenandoahSetsOfFree::establish_alloc_bias(ShenandoahFreeMemoryType which_set) {
253 ShenandoahHeap* heap = ShenandoahHeap::heap();
254 shenandoah_assert_heaplocked();
255 assert (which_set > NotFree && which_set < NumFreeSets, "selected free set must be valid");
256
257 size_t middle = (_leftmosts[which_set] + _rightmosts[which_set]) / 2;
258 size_t available_in_first_half = 0;
259 size_t available_in_second_half = 0;
260
261 for (size_t index = _leftmosts[which_set]; index < middle; index++) {
262 if (in_free_set(index, which_set)) {
263 ShenandoahHeapRegion* r = heap->get_region(index);
264 available_in_first_half += r->free();
265 }
266 }
267 for (size_t index = middle; index <= _rightmosts[which_set]; index++) {
268 if (in_free_set(index, which_set)) {
269 ShenandoahHeapRegion* r = heap->get_region(index);
270 available_in_second_half += r->free();
271 }
272 }
273
274 // We desire to first consume the sparsely distributed regions in order that the remaining regions are densely packed.
275 // Densely packing regions reduces the effort to search for a region that has sufficient memory to satisfy a new allocation
276 // request. Regions become sparsely distributed following a Full GC, which tends to slide all regions to the front of the
277 // heap rather than allowing survivor regions to remain at the high end of the heap where we intend for them to congregate.
278
279 // TODO: In the future, we may modify Full GC so that it slides old objects to the end of the heap and young objects to the
280 // front of the heap. If this is done, we can always search survivor Collector and OldCollector regions right to left.
281 _left_to_right_bias[which_set] = (available_in_second_half > available_in_first_half);
282 }
283
284 #ifdef ASSERT
285 void ShenandoahSetsOfFree::assert_bounds() {
286
287 size_t leftmosts[NumFreeSets];
288 size_t rightmosts[NumFreeSets];
289 size_t empty_leftmosts[NumFreeSets];
290 size_t empty_rightmosts[NumFreeSets];
291
292 for (int i = 0; i < NumFreeSets; i++) {
293 leftmosts[i] = _max;
294 empty_leftmosts[i] = _max;
295 rightmosts[i] = 0;
296 empty_rightmosts[i] = 0;
297 }
298
299 for (size_t i = 0; i < _max; i++) {
300 ShenandoahFreeMemoryType set = membership(i);
301 switch (set) {
302 case NotFree:
303 break;
304
305 case Mutator:
306 case Collector:
307 case OldCollector:
308 {
309 size_t capacity = _free_set->alloc_capacity(i);
310 bool is_empty = (capacity == _region_size_bytes);
311 assert(capacity > 0, "free regions must have allocation capacity");
312 if (i < leftmosts[set]) {
313 leftmosts[set] = i;
314 }
315 if (is_empty && (i < empty_leftmosts[set])) {
316 empty_leftmosts[set] = i;
317 }
318 if (i > rightmosts[set]) {
319 rightmosts[set] = i;
320 }
321 if (is_empty && (i > empty_rightmosts[set])) {
322 empty_rightmosts[set] = i;
323 }
324 break;
325 }
326
327 case NumFreeSets:
328 default:
329 ShouldNotReachHere();
330 }
331 }
332
333 // Performance invariants. Failing these would not break the free set, but performance would suffer.
334 assert (leftmost(Mutator) <= _max, "leftmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, leftmost(Mutator), _max);
335 assert (rightmost(Mutator) < _max, "rightmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, rightmost(Mutator), _max);
336
337 assert (leftmost(Mutator) == _max || in_free_set(leftmost(Mutator), Mutator),
338 "leftmost region should be free: " SIZE_FORMAT, leftmost(Mutator));
339 assert (leftmost(Mutator) == _max || in_free_set(rightmost(Mutator), Mutator),
340 "rightmost region should be free: " SIZE_FORMAT, rightmost(Mutator));
341
342 // If Mutator set is empty, leftmosts will both equal max, rightmosts will both equal zero. Likewise for empty region sets.
343 size_t beg_off = leftmosts[Mutator];
344 size_t end_off = rightmosts[Mutator];
345 assert (beg_off >= leftmost(Mutator),
346 "free regions before the leftmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, beg_off, leftmost(Mutator));
347 assert (end_off <= rightmost(Mutator),
348 "free regions past the rightmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, end_off, rightmost(Mutator));
349
350 beg_off = empty_leftmosts[Mutator];
351 end_off = empty_rightmosts[Mutator];
352 assert (beg_off >= leftmost_empty(Mutator),
353 "free empty regions before the leftmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, beg_off, leftmost_empty(Mutator));
354 assert (end_off <= rightmost_empty(Mutator),
355 "free empty regions past the rightmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, end_off, rightmost_empty(Mutator));
356
357 // Performance invariants. Failing these would not break the free set, but performance would suffer.
358 assert (leftmost(Collector) <= _max, "leftmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, leftmost(Collector), _max);
359 assert (rightmost(Collector) < _max, "rightmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, rightmost(Collector), _max);
360
361 assert (leftmost(Collector) == _max || in_free_set(leftmost(Collector), Collector),
362 "leftmost region should be free: " SIZE_FORMAT, leftmost(Collector));
363 assert (leftmost(Collector) == _max || in_free_set(rightmost(Collector), Collector),
364 "rightmost region should be free: " SIZE_FORMAT, rightmost(Collector));
365
366 // If Collector set is empty, leftmosts will both equal max, rightmosts will both equal zero. Likewise for empty region sets.
367 beg_off = leftmosts[Collector];
368 end_off = rightmosts[Collector];
369 assert (beg_off >= leftmost(Collector),
370 "free regions before the leftmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, beg_off, leftmost(Collector));
371 assert (end_off <= rightmost(Collector),
372 "free regions past the rightmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, end_off, rightmost(Collector));
373
374 beg_off = empty_leftmosts[Collector];
375 end_off = empty_rightmosts[Collector];
376 assert (beg_off >= leftmost_empty(Collector),
377 "free empty regions before the leftmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, beg_off, leftmost_empty(Collector));
378 assert (end_off <= rightmost_empty(Collector),
379 "free empty regions past the rightmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, end_off, rightmost_empty(Collector));
380
381 // Performance invariants. Failing these would not break the free set, but performance would suffer.
382 assert (leftmost(OldCollector) <= _max, "leftmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, leftmost(OldCollector), _max);
383 assert (rightmost(OldCollector) < _max, "rightmost in bounds: " SIZE_FORMAT " < " SIZE_FORMAT, rightmost(OldCollector), _max);
384
385 assert (leftmost(OldCollector) == _max || in_free_set(leftmost(OldCollector), OldCollector),
386 "leftmost region should be free: " SIZE_FORMAT, leftmost(OldCollector));
387 assert (leftmost(OldCollector) == _max || in_free_set(rightmost(OldCollector), OldCollector),
388 "rightmost region should be free: " SIZE_FORMAT, rightmost(OldCollector));
389
390 // If OldCollector set is empty, leftmosts will both equal max, rightmosts will both equal zero. Likewise for empty region sets.
391 beg_off = leftmosts[OldCollector];
392 end_off = rightmosts[OldCollector];
393 assert (beg_off >= leftmost(OldCollector),
394 "free regions before the leftmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, beg_off, leftmost(OldCollector));
395 assert (end_off <= rightmost(OldCollector),
396 "free regions past the rightmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, end_off, rightmost(OldCollector));
397
398 beg_off = empty_leftmosts[OldCollector];
399 end_off = empty_rightmosts[OldCollector];
400 assert (beg_off >= leftmost_empty(OldCollector),
401 "free empty regions before the leftmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, beg_off, leftmost_empty(OldCollector));
402 assert (end_off <= rightmost_empty(OldCollector),
403 "free empty regions past the rightmost: " SIZE_FORMAT ", bound " SIZE_FORMAT, end_off, rightmost_empty(OldCollector));
404 }
405 #endif
406
407 ShenandoahFreeSet::ShenandoahFreeSet(ShenandoahHeap* heap, size_t max_regions) :
408 _heap(heap),
409 _free_sets(max_regions, this)
410 {
411 clear_internal();
412 }
413
414 // This allocates from a region within the old_collector_set. If affiliation equals OLD, the allocation must be taken
415 // from a region that is_old(). Otherwise, affiliation should be FREE, in which case this will put a previously unaffiliated
416 // region into service.
417 HeapWord* ShenandoahFreeSet::allocate_old_with_affiliation(ShenandoahAffiliation affiliation,
418 ShenandoahAllocRequest& req, bool& in_new_region) {
419 shenandoah_assert_heaplocked();
420
421 size_t rightmost =
422 (affiliation == ShenandoahAffiliation::FREE)? _free_sets.rightmost_empty(OldCollector): _free_sets.rightmost(OldCollector);
423 size_t leftmost =
424 (affiliation == ShenandoahAffiliation::FREE)? _free_sets.leftmost_empty(OldCollector): _free_sets.leftmost(OldCollector);
425 if (_free_sets.alloc_from_left_bias(OldCollector)) {
426 // This mode picks up stragglers left by a full GC
427 for (size_t idx = leftmost; idx <= rightmost; idx++) {
428 if (_free_sets.in_free_set(idx, OldCollector)) {
429 ShenandoahHeapRegion* r = _heap->get_region(idx);
430 assert(r->is_trash() || !r->is_affiliated() || r->is_old(), "old_collector_set region has bad affiliation");
431 if (r->affiliation() == affiliation) {
432 HeapWord* result = try_allocate_in(r, req, in_new_region);
433 if (result != nullptr) {
434 return result;
435 }
436 }
437 }
438 }
439 } else {
440 // This mode picks up stragglers left by a previous concurrent GC
441 for (size_t count = rightmost + 1; count > leftmost; count--) {
442 // size_t is unsigned, need to dodge underflow when _leftmost = 0
443 size_t idx = count - 1;
444 if (_free_sets.in_free_set(idx, OldCollector)) {
445 ShenandoahHeapRegion* r = _heap->get_region(idx);
446 assert(r->is_trash() || !r->is_affiliated() || r->is_old(), "old_collector_set region has bad affiliation");
447 if (r->affiliation() == affiliation) {
448 HeapWord* result = try_allocate_in(r, req, in_new_region);
449 if (result != nullptr) {
450 return result;
451 }
452 }
453 }
454 }
455 }
456 return nullptr;
457 }
458
459 void ShenandoahFreeSet::add_old_collector_free_region(ShenandoahHeapRegion* region) {
460 shenandoah_assert_heaplocked();
461 size_t idx = region->index();
462 size_t capacity = alloc_capacity(region);
463 assert(_free_sets.membership(idx) == NotFree, "Regions promoted in place should not be in any free set");
464 if (capacity >= PLAB::min_size() * HeapWordSize) {
465 _free_sets.make_free(idx, OldCollector, capacity);
466 _heap->augment_promo_reserve(capacity);
467 }
468 }
469
470 HeapWord* ShenandoahFreeSet::allocate_with_affiliation(ShenandoahAffiliation affiliation,
471 ShenandoahAllocRequest& req, bool& in_new_region) {
472 shenandoah_assert_heaplocked();
473 size_t rightmost =
474 (affiliation == ShenandoahAffiliation::FREE)? _free_sets.rightmost_empty(Collector): _free_sets.rightmost(Collector);
475 size_t leftmost =
476 (affiliation == ShenandoahAffiliation::FREE)? _free_sets.leftmost_empty(Collector): _free_sets.leftmost(Collector);
477 for (size_t c = rightmost + 1; c > leftmost; c--) {
478 // size_t is unsigned, need to dodge underflow when _leftmost = 0
479 size_t idx = c - 1;
480 if (_free_sets.in_free_set(idx, Collector)) {
481 ShenandoahHeapRegion* r = _heap->get_region(idx);
482 if (r->affiliation() == affiliation) {
483 HeapWord* result = try_allocate_in(r, req, in_new_region);
484 if (result != nullptr) {
485 return result;
486 }
487 }
488 }
489 }
490 log_debug(gc, free)("Could not allocate collector region with affiliation: %s for request " PTR_FORMAT,
491 shenandoah_affiliation_name(affiliation), p2i(&req));
492 return nullptr;
493 }
494
495 HeapWord* ShenandoahFreeSet::allocate_single(ShenandoahAllocRequest& req, bool& in_new_region) {
496 shenandoah_assert_heaplocked();
497
498 // Scan the bitmap looking for a first fit.
499 //
500 // Leftmost and rightmost bounds provide enough caching to walk bitmap efficiently. Normally,
501 // we would find the region to allocate at right away.
502 //
503 // Allocations are biased: new application allocs go to beginning of the heap, and GC allocs
504 // go to the end. This makes application allocation faster, because we would clear lots
505 // of regions from the beginning most of the time.
506 //
507 // Free set maintains mutator and collector views, and normally they allocate in their views only,
508 // unless we special cases for stealing and mixed allocations.
509
510 // Overwrite with non-zero (non-NULL) values only if necessary for allocation bookkeeping.
511
512 bool allow_new_region = true;
513 if (_heap->mode()->is_generational()) {
514 switch (req.affiliation()) {
515 case ShenandoahAffiliation::OLD_GENERATION:
516 // Note: unsigned result from free_unaffiliated_regions() will never be less than zero, but it may equal zero.
517 if (_heap->old_generation()->free_unaffiliated_regions() <= 0) {
518 allow_new_region = false;
519 }
520 break;
521
522 case ShenandoahAffiliation::YOUNG_GENERATION:
523 // Note: unsigned result from free_unaffiliated_regions() will never be less than zero, but it may equal zero.
524 if (_heap->young_generation()->free_unaffiliated_regions() <= 0) {
525 allow_new_region = false;
526 }
527 break;
528
529 case ShenandoahAffiliation::FREE:
530 fatal("Should request affiliation");
531
532 default:
533 ShouldNotReachHere();
534 break;
535 }
536 }
537 switch (req.type()) {
538 case ShenandoahAllocRequest::_alloc_tlab:
539 case ShenandoahAllocRequest::_alloc_shared: {
540 // Try to allocate in the mutator view
541 for (size_t idx = _free_sets.leftmost(Mutator); idx <= _free_sets.rightmost(Mutator); idx++) {
542 ShenandoahHeapRegion* r = _heap->get_region(idx);
543 if (_free_sets.in_free_set(idx, Mutator) && (allow_new_region || r->is_affiliated())) {
544 // try_allocate_in() increases used if the allocation is successful.
545 HeapWord* result;
546 size_t min_size = (req.type() == ShenandoahAllocRequest::_alloc_tlab)? req.min_size(): req.size();
547 if ((alloc_capacity(r) >= min_size) && ((result = try_allocate_in(r, req, in_new_region)) != nullptr)) {
548 return result;
549 }
550 }
551 }
552 // There is no recovery. Mutator does not touch collector view at all.
553 break;
554 }
555 case ShenandoahAllocRequest::_alloc_gclab:
556 // GCLABs are for evacuation so we must be in evacuation phase. If this allocation is successful, increment
557 // the relevant evac_expended rather than used value.
558
559 case ShenandoahAllocRequest::_alloc_plab:
560 // PLABs always reside in old-gen and are only allocated during evacuation phase.
561
562 case ShenandoahAllocRequest::_alloc_shared_gc: {
563 if (!_heap->mode()->is_generational()) {
564 // size_t is unsigned, need to dodge underflow when _leftmost = 0
565 // Fast-path: try to allocate in the collector view first
566 for (size_t c = _free_sets.rightmost(Collector) + 1; c > _free_sets.leftmost(Collector); c--) {
567 size_t idx = c - 1;
568 if (_free_sets.in_free_set(idx, Collector)) {
569 HeapWord* result = try_allocate_in(_heap->get_region(idx), req, in_new_region);
570 if (result != nullptr) {
571 return result;
572 }
573 }
574 }
575 } else {
576 // First try to fit into a region that is already in use in the same generation.
577 HeapWord* result;
578 if (req.is_old()) {
579 result = allocate_old_with_affiliation(req.affiliation(), req, in_new_region);
580 } else {
581 result = allocate_with_affiliation(req.affiliation(), req, in_new_region);
582 }
583 if (result != nullptr) {
584 return result;
585 }
586 if (allow_new_region) {
587 // Then try a free region that is dedicated to GC allocations.
588 if (req.is_old()) {
589 result = allocate_old_with_affiliation(FREE, req, in_new_region);
590 } else {
591 result = allocate_with_affiliation(FREE, req, in_new_region);
592 }
593 if (result != nullptr) {
594 return result;
595 }
596 }
597 }
598 // No dice. Can we borrow space from mutator view?
599 if (!ShenandoahEvacReserveOverflow) {
600 return nullptr;
601 }
602
603 if (!allow_new_region && req.is_old() && (_heap->young_generation()->free_unaffiliated_regions() > 0)) {
604 // This allows us to flip a mutator region to old_collector
605 allow_new_region = true;
606 }
607
608 // We should expand old-gen if this can prevent an old-gen evacuation failure. We don't care so much about
609 // promotion failures since they can be mitigated in a subsequent GC pass. Would be nice to know if this
610 // allocation request is for evacuation or promotion. Individual threads limit their use of PLAB memory for
611 // promotions, so we already have an assurance that any additional memory set aside for old-gen will be used
612 // only for old-gen evacuations.
613
614 // Also TODO:
615 // if (GC is idle (out of cycle) and mutator allocation fails and there is memory reserved in Collector
616 // or OldCollector sets, transfer a region of memory so that we can satisfy the allocation request, and
617 // immediately trigger the start of GC. Is better to satisfy the allocation than to trigger out-of-cycle
618 // allocation failure (even if this means we have a little less memory to handle evacuations during the
619 // subsequent GC pass).
620
621 if (allow_new_region) {
622 // Try to steal an empty region from the mutator view.
623 for (size_t c = _free_sets.rightmost_empty(Mutator) + 1; c > _free_sets.leftmost_empty(Mutator); c--) {
624 size_t idx = c - 1;
625 if (_free_sets.in_free_set(idx, Mutator)) {
626 ShenandoahHeapRegion* r = _heap->get_region(idx);
627 if (can_allocate_from(r)) {
628 if (req.is_old()) {
629 flip_to_old_gc(r);
630 } else {
631 flip_to_gc(r);
632 }
633 HeapWord *result = try_allocate_in(r, req, in_new_region);
634 if (result != nullptr) {
635 log_debug(gc, free)("Flipped region " SIZE_FORMAT " to gc for request: " PTR_FORMAT, idx, p2i(&req));
636 return result;
637 }
638 }
639 }
640 }
641 }
642
643 // No dice. Do not try to mix mutator and GC allocations, because
644 // URWM moves due to GC allocations would expose unparsable mutator
645 // allocations.
646 break;
647 }
648 default:
649 ShouldNotReachHere();
650 }
651 return nullptr;
652 }
653
654 // This work method takes an argument corresponding to the number of bytes
655 // free in a region, and returns the largest amount in heapwords that can be allocated
656 // such that both of the following conditions are satisfied:
657 //
658 // 1. it is a multiple of card size
659 // 2. any remaining shard may be filled with a filler object
660 //
661 // The idea is that the allocation starts and ends at card boundaries. Because
662 // a region ('s end) is card-aligned, the remainder shard that must be filled is
663 // at the start of the free space.
664 //
665 // This is merely a helper method to use for the purpose of such a calculation.
666 size_t get_usable_free_words(size_t free_bytes) {
667 // e.g. card_size is 512, card_shift is 9, min_fill_size() is 8
668 // free is 514
669 // usable_free is 512, which is decreased to 0
670 size_t usable_free = (free_bytes / CardTable::card_size()) << CardTable::card_shift();
671 assert(usable_free <= free_bytes, "Sanity check");
672 if ((free_bytes != usable_free) && (free_bytes - usable_free < ShenandoahHeap::min_fill_size() * HeapWordSize)) {
673 // After aligning to card multiples, the remainder would be smaller than
674 // the minimum filler object, so we'll need to take away another card's
675 // worth to construct a filler object.
676 if (usable_free >= CardTable::card_size()) {
677 usable_free -= CardTable::card_size();
678 } else {
679 assert(usable_free == 0, "usable_free is a multiple of card_size and card_size > min_fill_size");
680 }
681 }
682
683 return usable_free / HeapWordSize;
684 }
685
686 // Given a size argument, which is a multiple of card size, a request struct
687 // for a PLAB, and an old region, return a pointer to the allocated space for
688 // a PLAB which is card-aligned and where any remaining shard in the region
689 // has been suitably filled by a filler object.
690 // It is assumed (and assertion-checked) that such an allocation is always possible.
691 HeapWord* ShenandoahFreeSet::allocate_aligned_plab(size_t size, ShenandoahAllocRequest& req, ShenandoahHeapRegion* r) {
692 assert(_heap->mode()->is_generational(), "PLABs are only for generational mode");
693 assert(r->is_old(), "All PLABs reside in old-gen");
694 assert(!req.is_mutator_alloc(), "PLABs should not be allocated by mutators.");
695 assert(size % CardTable::card_size_in_words() == 0, "size must be multiple of card table size, was " SIZE_FORMAT, size);
696
697 HeapWord* result = r->allocate_aligned(size, req, CardTable::card_size());
698 assert(result != nullptr, "Allocation cannot fail");
699 assert(r->top() <= r->end(), "Allocation cannot span end of region");
700 assert(req.actual_size() == size, "Should not have needed to adjust size for PLAB.");
701 assert(((uintptr_t) result) % CardTable::card_size_in_words() == 0, "PLAB start must align with card boundary");
702
703 return result;
704 }
705
706 HeapWord* ShenandoahFreeSet::try_allocate_in(ShenandoahHeapRegion* r, ShenandoahAllocRequest& req, bool& in_new_region) {
707 assert (has_alloc_capacity(r), "Performance: should avoid full regions on this path: " SIZE_FORMAT, r->index());
708 if (_heap->is_concurrent_weak_root_in_progress() && r->is_trash()) {
709 return nullptr;
710 }
711
712 try_recycle_trashed(r);
713 if (!r->is_affiliated()) {
714 ShenandoahMarkingContext* const ctx = _heap->complete_marking_context();
715 r->set_affiliation(req.affiliation());
716 if (r->is_old()) {
717 // Any OLD region allocated during concurrent coalesce-and-fill does not need to be coalesced and filled because
718 // all objects allocated within this region are above TAMS (and thus are implicitly marked). In case this is an
719 // OLD region and concurrent preparation for mixed evacuations visits this region before the start of the next
720 // old-gen concurrent mark (i.e. this region is allocated following the start of old-gen concurrent mark but before
721 // concurrent preparations for mixed evacuations are completed), we mark this region as not requiring any
722 // coalesce-and-fill processing.
723 r->end_preemptible_coalesce_and_fill();
724 _heap->clear_cards_for(r);
725 _heap->old_generation()->increment_affiliated_region_count();
726 } else {
727 _heap->young_generation()->increment_affiliated_region_count();
728 }
729
730 assert(ctx->top_at_mark_start(r) == r->bottom(), "Newly established allocation region starts with TAMS equal to bottom");
731 assert(ctx->is_bitmap_clear_range(ctx->top_bitmap(r), r->end()), "Bitmap above top_bitmap() must be clear");
732 } else if (r->affiliation() != req.affiliation()) {
733 assert(_heap->mode()->is_generational(), "Request for %s from %s region should only happen in generational mode.",
734 req.affiliation_name(), r->affiliation_name());
735 return nullptr;
736 }
737
738 in_new_region = r->is_empty();
739 HeapWord* result = nullptr;
740
741 if (in_new_region) {
742 log_debug(gc, free)("Using new region (" SIZE_FORMAT ") for %s (" PTR_FORMAT ").",
743 r->index(), ShenandoahAllocRequest::alloc_type_to_string(req.type()), p2i(&req));
744 }
745
746 // req.size() is in words, r->free() is in bytes.
747 if (ShenandoahElasticTLAB && req.is_lab_alloc()) {
748 if (req.type() == ShenandoahAllocRequest::_alloc_plab) {
749 assert(_heap->mode()->is_generational(), "PLABs are only for generational mode");
750 assert(_free_sets.in_free_set(r->index(), OldCollector), "PLABS must be allocated in old_collector_free regions");
751 // Need to assure that plabs are aligned on multiple of card region.
752 // Since we have Elastic TLABs, align sizes up. They may be decreased to fit in the usable
753 // memory remaining in the region (which will also be aligned to cards).
754 size_t adjusted_size = align_up(req.size(), CardTable::card_size_in_words());
755 size_t adjusted_min_size = align_up(req.min_size(), CardTable::card_size_in_words());
756 size_t usable_free = get_usable_free_words(r->free());
757
758 if (adjusted_size > usable_free) {
759 adjusted_size = usable_free;
760 }
761
762 if (adjusted_size >= adjusted_min_size) {
763 result = allocate_aligned_plab(adjusted_size, req, r);
764 }
765 // Otherwise, leave result == nullptr because the adjusted size is smaller than min size.
766 } else {
767 // This is a GCLAB or a TLAB allocation
768 size_t adjusted_size = req.size();
769 size_t free = align_down(r->free() >> LogHeapWordSize, MinObjAlignment);
770 if (adjusted_size > free) {
771 adjusted_size = free;
772 }
773 if (adjusted_size >= req.min_size()) {
774 result = r->allocate(adjusted_size, req);
775 assert (result != nullptr, "Allocation must succeed: free " SIZE_FORMAT ", actual " SIZE_FORMAT, free, adjusted_size);
776 req.set_actual_size(adjusted_size);
777 } else {
778 log_trace(gc, free)("Failed to shrink TLAB or GCLAB request (" SIZE_FORMAT ") in region " SIZE_FORMAT " to " SIZE_FORMAT
779 " because min_size() is " SIZE_FORMAT, req.size(), r->index(), adjusted_size, req.min_size());
780 }
781 }
782 } else if (req.is_lab_alloc() && req.type() == ShenandoahAllocRequest::_alloc_plab) {
783
784 // inelastic PLAB
785 size_t size = req.size();
786 size_t usable_free = get_usable_free_words(r->free());
787 if (size <= usable_free) {
788 result = allocate_aligned_plab(size, req, r);
789 }
790 } else {
791 size_t size = req.size();
792 result = r->allocate(size, req);
793 if (result != nullptr) {
794 // Record actual allocation size
795 req.set_actual_size(size);
796 }
797 }
798
799 ShenandoahGeneration* generation = _heap->generation_for(req.affiliation());
800 if (result != nullptr) {
801 // Allocation successful, bump stats:
802 if (req.is_mutator_alloc()) {
803 assert(req.is_young(), "Mutator allocations always come from young generation.");
804 _free_sets.increase_used(Mutator, req.actual_size() * HeapWordSize);
805 } else {
806 assert(req.is_gc_alloc(), "Should be gc_alloc since req wasn't mutator alloc");
807
808 // For GC allocations, we advance update_watermark because the objects relocated into this memory during
809 // evacuation are not updated during evacuation. For both young and old regions r, it is essential that all
810 // PLABs be made parsable at the end of evacuation. This is enabled by retiring all plabs at end of evacuation.
811 // TODO: Making a PLAB parsable involves placing a filler object in its remnant memory but does not require
812 // that the PLAB be disabled for all future purposes. We may want to introduce a new service to make the
813 // PLABs parsable while still allowing the PLAB to serve future allocation requests that arise during the
814 // next evacuation pass.
815 r->set_update_watermark(r->top());
816 if (r->is_old()) {
817 assert(req.type() != ShenandoahAllocRequest::_alloc_gclab, "old-gen allocations use PLAB or shared allocation");
818 // for plabs, we'll sort the difference between evac and promotion usage when we retire the plab
819 }
820 }
821 }
822
823 if (result == nullptr || alloc_capacity(r) < PLAB::min_size() * HeapWordSize) {
824 // Region cannot afford this and is likely to not afford future allocations. Retire it.
825 //
826 // While this seems a bit harsh, especially in the case when this large allocation does not
827 // fit but the next small one would, we are risking to inflate scan times when lots of
828 // almost-full regions precede the fully-empty region where we want to allocate the entire TLAB.
829
830 // Record the remainder as allocation waste
831 size_t idx = r->index();
832 if (req.is_mutator_alloc()) {
833 size_t waste = r->free();
834 if (waste > 0) {
835 _free_sets.increase_used(Mutator, waste);
836 // This one request could cause several regions to be "retired", so we must accumulate the waste
837 req.set_waste((waste >> LogHeapWordSize) + req.waste());
838 }
839 assert(_free_sets.membership(idx) == Mutator, "Must be mutator free: " SIZE_FORMAT, idx);
840 } else {
841 assert(_free_sets.membership(idx) == Collector || _free_sets.membership(idx) == OldCollector,
842 "Must be collector or old-collector free: " SIZE_FORMAT, idx);
843 }
844 // This region is no longer considered free (in any set)
845 _free_sets.remove_from_free_sets(idx);
846 _free_sets.assert_bounds();
847 }
848 return result;
849 }
850
851 HeapWord* ShenandoahFreeSet::allocate_contiguous(ShenandoahAllocRequest& req) {
852 shenandoah_assert_heaplocked();
853
854 size_t words_size = req.size();
855 size_t num = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
856
857 assert(req.is_young(), "Humongous regions always allocated in YOUNG");
858 ShenandoahGeneration* generation = _heap->generation_for(req.affiliation());
859
860 // Check if there are enough regions left to satisfy allocation.
861 if (_heap->mode()->is_generational()) {
862 size_t avail_young_regions = generation->free_unaffiliated_regions();
863 if (num > _free_sets.count(Mutator) || (num > avail_young_regions)) {
864 return nullptr;
865 }
866 } else {
867 if (num > _free_sets.count(Mutator)) {
868 return nullptr;
869 }
870 }
871
872 // Find the continuous interval of $num regions, starting from $beg and ending in $end,
873 // inclusive. Contiguous allocations are biased to the beginning.
874
875 size_t beg = _free_sets.leftmost(Mutator);
876 size_t end = beg;
877
878 while (true) {
879 if (end >= _free_sets.max()) {
880 // Hit the end, goodbye
881 return nullptr;
882 }
883
884 // If regions are not adjacent, then current [beg; end] is useless, and we may fast-forward.
885 // If region is not completely free, the current [beg; end] is useless, and we may fast-forward.
886 if (!_free_sets.in_free_set(end, Mutator) || !can_allocate_from(_heap->get_region(end))) {
887 end++;
888 beg = end;
889 continue;
890 }
891
892 if ((end - beg + 1) == num) {
893 // found the match
894 break;
895 }
896
897 end++;
898 };
899
900 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
901 ShenandoahMarkingContext* const ctx = _heap->complete_marking_context();
902
903 // Initialize regions:
904 for (size_t i = beg; i <= end; i++) {
905 ShenandoahHeapRegion* r = _heap->get_region(i);
906 try_recycle_trashed(r);
907
908 assert(i == beg || _heap->get_region(i - 1)->index() + 1 == r->index(), "Should be contiguous");
909 assert(r->is_empty(), "Should be empty");
910
911 if (i == beg) {
912 r->make_humongous_start();
913 } else {
914 r->make_humongous_cont();
915 }
916
917 // Trailing region may be non-full, record the remainder there
918 size_t used_words;
919 if ((i == end) && (remainder != 0)) {
920 used_words = remainder;
921 } else {
922 used_words = ShenandoahHeapRegion::region_size_words();
923 }
924
925 r->set_affiliation(req.affiliation());
926 r->set_update_watermark(r->bottom());
927 r->set_top(r->bottom() + used_words);
928
929 // While individual regions report their true use, all humongous regions are marked used in the free set.
930 _free_sets.remove_from_free_sets(r->index());
931 }
932 _heap->young_generation()->increase_affiliated_region_count(num);
933
934 size_t total_humongous_size = ShenandoahHeapRegion::region_size_bytes() * num;
935 _free_sets.increase_used(Mutator, total_humongous_size);
936 _free_sets.assert_bounds();
937 req.set_actual_size(words_size);
938 if (remainder != 0) {
939 req.set_waste(ShenandoahHeapRegion::region_size_words() - remainder);
940 }
941 return _heap->get_region(beg)->bottom();
942 }
943
944 // Returns true iff this region is entirely available, either because it is empty() or because it has been found to represent
945 // immediate trash and we'll be able to immediately recycle it. Note that we cannot recycle immediate trash if
946 // concurrent weak root processing is in progress.
947 bool ShenandoahFreeSet::can_allocate_from(ShenandoahHeapRegion *r) const {
948 return r->is_empty() || (r->is_trash() && !_heap->is_concurrent_weak_root_in_progress());
949 }
950
951 bool ShenandoahFreeSet::can_allocate_from(size_t idx) const {
952 ShenandoahHeapRegion* r = _heap->get_region(idx);
953 return can_allocate_from(r);
954 }
955
956 size_t ShenandoahFreeSet::alloc_capacity(size_t idx) const {
957 ShenandoahHeapRegion* r = _heap->get_region(idx);
958 return alloc_capacity(r);
959 }
960
961 size_t ShenandoahFreeSet::alloc_capacity(ShenandoahHeapRegion *r) const {
962 if (r->is_trash()) {
963 // This would be recycled on allocation path
964 return ShenandoahHeapRegion::region_size_bytes();
965 } else {
966 return r->free();
967 }
968 }
969
970 bool ShenandoahFreeSet::has_alloc_capacity(ShenandoahHeapRegion *r) const {
971 return alloc_capacity(r) > 0;
972 }
973
974 bool ShenandoahFreeSet::has_alloc_capacity(size_t idx) const {
975 ShenandoahHeapRegion* r = _heap->get_region(idx);
976 return alloc_capacity(r) > 0;
977 }
978
979 bool ShenandoahFreeSet::has_no_alloc_capacity(ShenandoahHeapRegion *r) const {
980 return alloc_capacity(r) == 0;
981 }
982
983 void ShenandoahFreeSet::try_recycle_trashed(ShenandoahHeapRegion *r) {
984 if (r->is_trash()) {
985 r->recycle();
986 }
987 }
988
989 void ShenandoahFreeSet::recycle_trash() {
990 // lock is not reentrable, check we don't have it
991 shenandoah_assert_not_heaplocked();
992
993 for (size_t i = 0; i < _heap->num_regions(); i++) {
994 ShenandoahHeapRegion* r = _heap->get_region(i);
995 if (r->is_trash()) {
996 ShenandoahHeapLocker locker(_heap->lock());
997 try_recycle_trashed(r);
998 }
999 SpinPause(); // allow allocators to take the lock
1000 }
1001 }
1002
1003 void ShenandoahFreeSet::flip_to_old_gc(ShenandoahHeapRegion* r) {
1004 size_t idx = r->index();
1005
1006 assert(_free_sets.in_free_set(idx, Mutator), "Should be in mutator view");
1007 // Note: can_allocate_from(r) means r is entirely empty
1008 assert(can_allocate_from(r), "Should not be allocated");
1009
1010 size_t region_capacity = alloc_capacity(r);
1011 _free_sets.move_to_set(idx, OldCollector, region_capacity);
1012 _free_sets.assert_bounds();
1013 _heap->generation_sizer()->force_transfer_to_old(1);
1014 _heap->augment_old_evac_reserve(region_capacity);
1015 // We do not ensure that the region is no longer trash, relying on try_allocate_in(), which always comes next,
1016 // to recycle trash before attempting to allocate anything in the region.
1017 }
1018
1019 void ShenandoahFreeSet::flip_to_gc(ShenandoahHeapRegion* r) {
1020 size_t idx = r->index();
1021
1022 assert(_free_sets.in_free_set(idx, Mutator), "Should be in mutator view");
1023 assert(can_allocate_from(r), "Should not be allocated");
1024
1025 size_t region_capacity = alloc_capacity(r);
1026 _free_sets.move_to_set(idx, Collector, region_capacity);
1027 _free_sets.assert_bounds();
1028
1029 // We do not ensure that the region is no longer trash, relying on try_allocate_in(), which always comes next,
1030 // to recycle trash before attempting to allocate anything in the region.
1031 }
1032
1033 void ShenandoahFreeSet::clear() {
1034 shenandoah_assert_heaplocked();
1035 clear_internal();
1036 }
1037
1038 void ShenandoahFreeSet::clear_internal() {
1039 _free_sets.clear_all();
1040 }
1041
1042 // This function places all is_old() regions that have allocation capacity into the old_collector set. It places
1043 // all other regions (not is_old()) that have allocation capacity into the mutator_set. Subsequently, we will
1044 // move some of the mutator regions into the collector set or old_collector set with the intent of packing
1045 // old_collector memory into the highest (rightmost) addresses of the heap and the collector memory into the
1046 // next highest addresses of the heap, with mutator memory consuming the lowest addresses of the heap.
1047 void ShenandoahFreeSet::find_regions_with_alloc_capacity(size_t &young_cset_regions, size_t &old_cset_regions) {
1048
1049 old_cset_regions = 0;
1050 young_cset_regions = 0;
1051 for (size_t idx = 0; idx < _heap->num_regions(); idx++) {
1052 ShenandoahHeapRegion* region = _heap->get_region(idx);
1053 if (region->is_trash()) {
1054 // Trashed regions represent regions that had been in the collection set but have not yet been "cleaned up".
1055 if (region->is_old()) {
1056 old_cset_regions++;
1057 } else {
1058 assert(region->is_young(), "Trashed region should be old or young");
1059 young_cset_regions++;
1060 }
1061 }
1062 if (region->is_alloc_allowed() || region->is_trash()) {
1063 assert(!region->is_cset(), "Shouldn't be adding cset regions to the free set");
1064 assert(_free_sets.in_free_set(idx, NotFree), "We are about to make region free; it should not be free already");
1065
1066 // Do not add regions that would almost surely fail allocation
1067 if (alloc_capacity(region) < PLAB::min_size() * HeapWordSize) continue;
1068
1069 if (region->is_old()) {
1070 _free_sets.make_free(idx, OldCollector, alloc_capacity(region));
1071 log_debug(gc, free)(
1072 " Adding Region " SIZE_FORMAT " (Free: " SIZE_FORMAT "%s, Used: " SIZE_FORMAT "%s) to old collector set",
1073 idx, byte_size_in_proper_unit(region->free()), proper_unit_for_byte_size(region->free()),
1074 byte_size_in_proper_unit(region->used()), proper_unit_for_byte_size(region->used()));
1075 } else {
1076 _free_sets.make_free(idx, Mutator, alloc_capacity(region));
1077 log_debug(gc, free)(
1078 " Adding Region " SIZE_FORMAT " (Free: " SIZE_FORMAT "%s, Used: " SIZE_FORMAT "%s) to mutator set",
1079 idx, byte_size_in_proper_unit(region->free()), proper_unit_for_byte_size(region->free()),
1080 byte_size_in_proper_unit(region->used()), proper_unit_for_byte_size(region->used()));
1081 }
1082 }
1083 }
1084 }
1085
1086 // Move no more than cset_regions from the existing Collector and OldCollector free sets to the Mutator free set.
1087 // This is called from outside the heap lock.
1088 void ShenandoahFreeSet::move_collector_sets_to_mutator(size_t max_xfer_regions) {
1089 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
1090 size_t collector_empty_xfer = 0;
1091 size_t collector_not_empty_xfer = 0;
1092 size_t old_collector_empty_xfer = 0;
1093
1094 // Process empty regions within the Collector free set
1095 if ((max_xfer_regions > 0) && (_free_sets.leftmost_empty(Collector) <= _free_sets.rightmost_empty(Collector))) {
1096 ShenandoahHeapLocker locker(_heap->lock());
1097 for (size_t idx = _free_sets.leftmost_empty(Collector);
1098 (max_xfer_regions > 0) && (idx <= _free_sets.rightmost_empty(Collector)); idx++) {
1099 if (_free_sets.in_free_set(idx, Collector) && can_allocate_from(idx)) {
1100 _free_sets.move_to_set(idx, Mutator, region_size_bytes);
1101 max_xfer_regions--;
1102 collector_empty_xfer += region_size_bytes;
1103 }
1104 }
1105 }
1106
1107 // Process empty regions within the OldCollector free set
1108 size_t old_collector_regions = 0;
1109 if ((max_xfer_regions > 0) && (_free_sets.leftmost_empty(OldCollector) <= _free_sets.rightmost_empty(OldCollector))) {
1110 ShenandoahHeapLocker locker(_heap->lock());
1111 for (size_t idx = _free_sets.leftmost_empty(OldCollector);
1112 (max_xfer_regions > 0) && (idx <= _free_sets.rightmost_empty(OldCollector)); idx++) {
1113 if (_free_sets.in_free_set(idx, OldCollector) && can_allocate_from(idx)) {
1114 _free_sets.move_to_set(idx, Mutator, region_size_bytes);
1115 max_xfer_regions--;
1116 old_collector_empty_xfer += region_size_bytes;
1117 old_collector_regions++;
1118 }
1119 }
1120 if (old_collector_regions > 0) {
1121 _heap->generation_sizer()->transfer_to_young(old_collector_regions);
1122 }
1123 }
1124
1125 // If there are any non-empty regions within Collector set, we can also move them to the Mutator free set
1126 if ((max_xfer_regions > 0) && (_free_sets.leftmost(Collector) <= _free_sets.rightmost(Collector))) {
1127 ShenandoahHeapLocker locker(_heap->lock());
1128 for (size_t idx = _free_sets.leftmost(Collector); (max_xfer_regions > 0) && (idx <= _free_sets.rightmost(Collector)); idx++) {
1129 size_t alloc_capacity = this->alloc_capacity(idx);
1130 if (_free_sets.in_free_set(idx, Collector) && (alloc_capacity > 0)) {
1131 _free_sets.move_to_set(idx, Mutator, alloc_capacity);
1132 max_xfer_regions--;
1133 collector_not_empty_xfer += alloc_capacity;
1134 }
1135 }
1136 }
1137
1138 size_t collector_xfer = collector_empty_xfer + collector_not_empty_xfer;
1139 size_t total_xfer = collector_xfer + old_collector_empty_xfer;
1140 log_info(gc, free)("At start of update refs, moving " SIZE_FORMAT "%s to Mutator free set from Collector Reserve ("
1141 SIZE_FORMAT "%s) and from Old Collector Reserve (" SIZE_FORMAT "%s)",
1142 byte_size_in_proper_unit(total_xfer), proper_unit_for_byte_size(total_xfer),
1143 byte_size_in_proper_unit(collector_xfer), proper_unit_for_byte_size(collector_xfer),
1144 byte_size_in_proper_unit(old_collector_empty_xfer), proper_unit_for_byte_size(old_collector_empty_xfer));
1145 }
1146
1147
1148 // Overwrite arguments to represent the amount of memory in each generation that is about to be recycled
1149 void ShenandoahFreeSet::prepare_to_rebuild(size_t &young_cset_regions, size_t &old_cset_regions) {
1150 shenandoah_assert_heaplocked();
1151 // This resets all state information, removing all regions from all sets.
1152 clear();
1153 log_debug(gc, free)("Rebuilding FreeSet");
1154
1155 // This places regions that have alloc_capacity into the old_collector set if they identify as is_old() or the
1156 // mutator set otherwise.
1157 find_regions_with_alloc_capacity(young_cset_regions, old_cset_regions);
1158 }
1159
1160 void ShenandoahFreeSet::rebuild(size_t young_cset_regions, size_t old_cset_regions) {
1161 shenandoah_assert_heaplocked();
1162 size_t young_reserve, old_reserve;
1163 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
1164
1165 size_t old_capacity = _heap->old_generation()->max_capacity();
1166 size_t old_available = _heap->old_generation()->available();
1167 size_t old_unaffiliated_regions = _heap->old_generation()->free_unaffiliated_regions();
1168 size_t young_capacity = _heap->young_generation()->max_capacity();
1169 size_t young_available = _heap->young_generation()->available();
1170 size_t young_unaffiliated_regions = _heap->young_generation()->free_unaffiliated_regions();
1171
1172 old_unaffiliated_regions += old_cset_regions;
1173 old_available += old_cset_regions * region_size_bytes;
1174 young_unaffiliated_regions += young_cset_regions;
1175 young_available += young_cset_regions * region_size_bytes;
1176
1177 // Consult old-region surplus and deficit to make adjustments to current generation capacities and availability.
1178 // The generation region transfers take place after we rebuild.
1179 size_t old_region_surplus = _heap->get_old_region_surplus();
1180 size_t old_region_deficit = _heap->get_old_region_deficit();
1181
1182 if (old_region_surplus > 0) {
1183 size_t xfer_bytes = old_region_surplus * region_size_bytes;
1184 assert(old_region_surplus <= old_unaffiliated_regions, "Cannot transfer regions that are affiliated");
1185 old_capacity -= xfer_bytes;
1186 old_available -= xfer_bytes;
1187 old_unaffiliated_regions -= old_region_surplus;
1188 young_capacity += xfer_bytes;
1189 young_available += xfer_bytes;
1190 young_unaffiliated_regions += old_region_surplus;
1191 } else if (old_region_deficit > 0) {
1192 size_t xfer_bytes = old_region_deficit * region_size_bytes;
1193 assert(old_region_deficit <= young_unaffiliated_regions, "Cannot transfer regions that are affiliated");
1194 old_capacity += xfer_bytes;
1195 old_available += xfer_bytes;
1196 old_unaffiliated_regions += old_region_deficit;
1197 young_capacity -= xfer_bytes;;
1198 young_available -= xfer_bytes;
1199 young_unaffiliated_regions -= old_region_deficit;
1200 }
1201
1202 // Evac reserve: reserve trailing space for evacuations, with regions reserved for old evacuations placed to the right
1203 // of regions reserved of young evacuations.
1204 if (!_heap->mode()->is_generational()) {
1205 young_reserve = (_heap->max_capacity() / 100) * ShenandoahEvacReserve;
1206 old_reserve = 0;
1207 } else {
1208 // All allocations taken from the old collector set are performed by GC, generally using PLABs for both
1209 // promotions and evacuations. The partition between which old memory is reserved for evacuation and
1210 // which is reserved for promotion is enforced using thread-local variables that prescribe intentons for
1211 // each PLAB's available memory.
1212 if (_heap->has_evacuation_reserve_quantities()) {
1213 // We are rebuilding at the end of final mark, having already established evacuation budgets for this GC pass.
1214 young_reserve = _heap->get_young_evac_reserve();
1215 old_reserve = _heap->get_promoted_reserve() + _heap->get_old_evac_reserve();
1216 assert(old_reserve <= old_available,
1217 "Cannot reserve (" SIZE_FORMAT " + " SIZE_FORMAT") more OLD than is available: " SIZE_FORMAT,
1218 _heap->get_promoted_reserve(), _heap->get_old_evac_reserve(), old_available);
1219 } else {
1220 // We are rebuilding at end of GC, so we set aside budgets specified on command line (or defaults)
1221 young_reserve = (young_capacity * ShenandoahEvacReserve) / 100;
1222 // The auto-sizer has already made old-gen large enough to hold all anticipated evacuations and promotions.
1223 // Affiliated old-gen regions are already in the OldCollector free set. Add in the relevant number of
1224 // unaffiliated regions.
1225 old_reserve = old_available;
1226 }
1227 }
1228 if (old_reserve > _free_sets.capacity_of(OldCollector)) {
1229 // Old available regions that have less than PLAB::min_size() of available memory are not placed into the OldCollector
1230 // free set. Because of this, old_available may not have enough memory to represent the intended reserve. Adjust
1231 // the reserve downward to account for this possibility. This loss is part of the reason why the original budget
1232 // was adjusted with ShenandoahOldEvacWaste and ShenandoahOldPromoWaste multipliers.
1233 if (old_reserve > _free_sets.capacity_of(OldCollector) + old_unaffiliated_regions * region_size_bytes) {
1234 old_reserve = _free_sets.capacity_of(OldCollector) + old_unaffiliated_regions * region_size_bytes;
1235 }
1236 }
1237 if (young_reserve > young_unaffiliated_regions * region_size_bytes) {
1238 young_reserve = young_unaffiliated_regions * region_size_bytes;
1239 }
1240
1241 reserve_regions(young_reserve, old_reserve);
1242 _free_sets.establish_alloc_bias(OldCollector);
1243 _free_sets.assert_bounds();
1244 log_status();
1245 }
1246
1247 // Having placed all regions that have allocation capacity into the mutator set if they identify as is_young()
1248 // or into the old collector set if they identify as is_old(), move some of these regions from the mutator set
1249 // into the collector set or old collector set in order to assure that the memory available for allocations within
1250 // the collector set is at least to_reserve, and the memory available for allocations within the old collector set
1251 // is at least to_reserve_old.
1252 void ShenandoahFreeSet::reserve_regions(size_t to_reserve, size_t to_reserve_old) {
1253 for (size_t i = _heap->num_regions(); i > 0; i--) {
1254 size_t idx = i - 1;
1255 ShenandoahHeapRegion* r = _heap->get_region(idx);
1256 if (_free_sets.in_free_set(idx, Mutator)) {
1257 assert (!r->is_old(), "mutator_is_free regions should not be affiliated OLD");
1258 size_t ac = alloc_capacity(r);
1259 assert (ac > 0, "Membership in free set implies has capacity");
1260
1261 // OLD regions that have available memory are already in the old_collector free set
1262 if ((_free_sets.capacity_of(OldCollector) < to_reserve_old) && (r->is_trash() || !r->is_affiliated())) {
1263 _free_sets.move_to_set(idx, OldCollector, alloc_capacity(r));
1264 log_debug(gc, free)(" Shifting region " SIZE_FORMAT " from mutator_free to old_collector_free", idx);
1265 } else if (_free_sets.capacity_of(Collector) < to_reserve) {
1266 // Note: In a previous implementation, regions were only placed into the survivor space (collector_is_free) if
1267 // they were entirely empty. I'm not sure I understand the rational for that. That alternative behavior would
1268 // tend to mix survivor objects with ephemeral objects, making it more difficult to reclaim the memory for the
1269 // ephemeral objects. It also delays aging of regions, causing promotion in place to be delayed.
1270 _free_sets.move_to_set(idx, Collector, ac);
1271 log_debug(gc)(" Shifting region " SIZE_FORMAT " from mutator_free to collector_free", idx);
1272 } else {
1273 // We've satisfied both to_reserve and to_reserved_old
1274 break;
1275 }
1276 }
1277 }
1278 }
1279
1280 void ShenandoahFreeSet::log_status() {
1281 shenandoah_assert_heaplocked();
1282
1283 #ifdef ASSERT
1284 // Dump of the FreeSet details is only enabled if assertions are enabled
1285 {
1286 #define BUFFER_SIZE 80
1287 size_t retired_old = 0;
1288 size_t retired_old_humongous = 0;
1289 size_t retired_young = 0;
1290 size_t retired_young_humongous = 0;
1291 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
1292 size_t retired_young_waste = 0;
1293 size_t retired_old_waste = 0;
1294 size_t consumed_collector = 0;
1295 size_t consumed_old_collector = 0;
1296 size_t consumed_mutator = 0;
1297 size_t available_old = 0;
1298 size_t available_young = 0;
1299 size_t available_mutator = 0;
1300 size_t available_collector = 0;
1301 size_t available_old_collector = 0;
1302
1303 char buffer[BUFFER_SIZE];
1304 for (uint i = 0; i < BUFFER_SIZE; i++) {
1305 buffer[i] = '\0';
1306 }
1307 log_info(gc, free)("FreeSet map legend:"
1308 " M:mutator_free C:collector_free O:old_collector_free"
1309 " H:humongous ~:retired old _:retired young");
1310 log_info(gc, free)(" mutator free range [" SIZE_FORMAT ".." SIZE_FORMAT "], "
1311 " collector free range [" SIZE_FORMAT ".." SIZE_FORMAT "], "
1312 "old collector free range [" SIZE_FORMAT ".." SIZE_FORMAT "] allocates from %s",
1313 _free_sets.leftmost(Mutator), _free_sets.rightmost(Mutator),
1314 _free_sets.leftmost(Collector), _free_sets.rightmost(Collector),
1315 _free_sets.leftmost(OldCollector), _free_sets.rightmost(OldCollector),
1316 _free_sets.alloc_from_left_bias(OldCollector)? "left to right": "right to left");
1317
1318 for (uint i = 0; i < _heap->num_regions(); i++) {
1319 ShenandoahHeapRegion *r = _heap->get_region(i);
1320 uint idx = i % 64;
1321 if ((i != 0) && (idx == 0)) {
1322 log_info(gc, free)(" %6u: %s", i-64, buffer);
1323 }
1324 if (_free_sets.in_free_set(i, Mutator)) {
1325 assert(!r->is_old(), "Old regions should not be in mutator_free set");
1326 size_t capacity = alloc_capacity(r);
1327 available_mutator += capacity;
1328 consumed_mutator += region_size_bytes - capacity;
1329 buffer[idx] = (capacity == region_size_bytes)? 'M': 'm';
1330 } else if (_free_sets.in_free_set(i, Collector)) {
1331 assert(!r->is_old(), "Old regions should not be in collector_free set");
1332 size_t capacity = alloc_capacity(r);
1333 available_collector += capacity;
1334 consumed_collector += region_size_bytes - capacity;
1335 buffer[idx] = (capacity == region_size_bytes)? 'C': 'c';
1336 } else if (_free_sets.in_free_set(i, OldCollector)) {
1337 size_t capacity = alloc_capacity(r);
1338 available_old_collector += capacity;
1339 consumed_old_collector += region_size_bytes - capacity;
1340 buffer[idx] = (capacity == region_size_bytes)? 'O': 'o';
1341 } else if (r->is_humongous()) {
1342 if (r->is_old()) {
1343 buffer[idx] = 'H';
1344 retired_old_humongous += region_size_bytes;
1345 } else {
1346 buffer[idx] = 'h';
1347 retired_young_humongous += region_size_bytes;
1348 }
1349 } else {
1350 if (r->is_old()) {
1351 buffer[idx] = '~';
1352 retired_old_waste += alloc_capacity(r);
1353 retired_old += region_size_bytes;
1354 } else {
1355 buffer[idx] = '_';
1356 retired_young_waste += alloc_capacity(r);
1357 retired_young += region_size_bytes;
1358 }
1359 }
1360 }
1361 uint remnant = _heap->num_regions() % 64;
1362 if (remnant > 0) {
1363 buffer[remnant] = '\0';
1364 } else {
1365 remnant = 64;
1366 }
1367 log_info(gc, free)(" %6u: %s", (uint) (_heap->num_regions() - remnant), buffer);
1368 size_t total_young = retired_young + retired_young_humongous;
1369 size_t total_old = retired_old + retired_old_humongous;
1370 }
1371 #endif
1372
1373 LogTarget(Info, gc, free) lt;
1374 if (lt.is_enabled()) {
1375 ResourceMark rm;
1376 LogStream ls(lt);
1377
1378 {
1379 size_t last_idx = 0;
1380 size_t max = 0;
1381 size_t max_contig = 0;
1382 size_t empty_contig = 0;
1383
1384 size_t total_used = 0;
1385 size_t total_free = 0;
1386 size_t total_free_ext = 0;
1387
1388 for (size_t idx = _free_sets.leftmost(Mutator); idx <= _free_sets.rightmost(Mutator); idx++) {
1389 if (_free_sets.in_free_set(idx, Mutator)) {
1390 ShenandoahHeapRegion *r = _heap->get_region(idx);
1391 size_t free = alloc_capacity(r);
1392 max = MAX2(max, free);
1393 if (r->is_empty()) {
1394 total_free_ext += free;
1395 if (last_idx + 1 == idx) {
1396 empty_contig++;
1397 } else {
1398 empty_contig = 1;
1399 }
1400 } else {
1401 empty_contig = 0;
1402 }
1403 total_used += r->used();
1404 total_free += free;
1405 max_contig = MAX2(max_contig, empty_contig);
1406 last_idx = idx;
1407 }
1408 }
1409
1410 size_t max_humongous = max_contig * ShenandoahHeapRegion::region_size_bytes();
1411 size_t free = capacity() - used();
1412
1413 assert(free == total_free, "Sum of free within mutator regions (" SIZE_FORMAT
1414 ") should match mutator capacity (" SIZE_FORMAT ") minus mutator used (" SIZE_FORMAT ")",
1415 total_free, capacity(), used());
1416
1417 ls.print("Free: " SIZE_FORMAT "%s, Max: " SIZE_FORMAT "%s regular, " SIZE_FORMAT "%s humongous, ",
1418 byte_size_in_proper_unit(total_free), proper_unit_for_byte_size(total_free),
1419 byte_size_in_proper_unit(max), proper_unit_for_byte_size(max),
1420 byte_size_in_proper_unit(max_humongous), proper_unit_for_byte_size(max_humongous)
1421 );
1422
1423 ls.print("Frag: ");
1424 size_t frag_ext;
1425 if (total_free_ext > 0) {
1426 frag_ext = 100 - (100 * max_humongous / total_free_ext);
1427 } else {
1428 frag_ext = 0;
1429 }
1430 ls.print(SIZE_FORMAT "%% external, ", frag_ext);
1431
1432 size_t frag_int;
1433 if (_free_sets.count(Mutator) > 0) {
1434 frag_int = (100 * (total_used / _free_sets.count(Mutator)) / ShenandoahHeapRegion::region_size_bytes());
1435 } else {
1436 frag_int = 0;
1437 }
1438 ls.print(SIZE_FORMAT "%% internal; ", frag_int);
1439 ls.print("Used: " SIZE_FORMAT "%s, Mutator Free: " SIZE_FORMAT,
1440 byte_size_in_proper_unit(total_used), proper_unit_for_byte_size(total_used), _free_sets.count(Mutator));
1441 }
1442
1443 {
1444 size_t max = 0;
1445 size_t total_free = 0;
1446 size_t total_used = 0;
1447
1448 for (size_t idx = _free_sets.leftmost(Collector); idx <= _free_sets.rightmost(Collector); idx++) {
1449 if (_free_sets.in_free_set(idx, Collector)) {
1450 ShenandoahHeapRegion *r = _heap->get_region(idx);
1451 size_t free = alloc_capacity(r);
1452 max = MAX2(max, free);
1453 total_free += free;
1454 total_used += r->used();
1455 }
1456 }
1457 ls.print(" Collector Reserve: " SIZE_FORMAT "%s, Max: " SIZE_FORMAT "%s; Used: " SIZE_FORMAT "%s",
1458 byte_size_in_proper_unit(total_free), proper_unit_for_byte_size(total_free),
1459 byte_size_in_proper_unit(max), proper_unit_for_byte_size(max),
1460 byte_size_in_proper_unit(total_used), proper_unit_for_byte_size(total_used));
1461 }
1462
1463 if (_heap->mode()->is_generational()) {
1464 size_t max = 0;
1465 size_t total_free = 0;
1466 size_t total_used = 0;
1467
1468 for (size_t idx = _free_sets.leftmost(OldCollector); idx <= _free_sets.rightmost(OldCollector); idx++) {
1469 if (_free_sets.in_free_set(idx, OldCollector)) {
1470 ShenandoahHeapRegion *r = _heap->get_region(idx);
1471 size_t free = alloc_capacity(r);
1472 max = MAX2(max, free);
1473 total_free += free;
1474 total_used += r->used();
1475 }
1476 }
1477 ls.print_cr(" Old Collector Reserve: " SIZE_FORMAT "%s, Max: " SIZE_FORMAT "%s; Used: " SIZE_FORMAT "%s",
1478 byte_size_in_proper_unit(total_free), proper_unit_for_byte_size(total_free),
1479 byte_size_in_proper_unit(max), proper_unit_for_byte_size(max),
1480 byte_size_in_proper_unit(total_used), proper_unit_for_byte_size(total_used));
1481 }
1482 }
1483 }
1484
1485 HeapWord* ShenandoahFreeSet::allocate(ShenandoahAllocRequest& req, bool& in_new_region) {
1486 shenandoah_assert_heaplocked();
1487 _free_sets.assert_bounds();
1488
1489 // Allocation request is known to satisfy all memory budgeting constraints.
1490 if (req.size() > ShenandoahHeapRegion::humongous_threshold_words()) {
1491 switch (req.type()) {
1492 case ShenandoahAllocRequest::_alloc_shared:
1493 case ShenandoahAllocRequest::_alloc_shared_gc:
1494 in_new_region = true;
1495 return allocate_contiguous(req);
1496 case ShenandoahAllocRequest::_alloc_plab:
1497 case ShenandoahAllocRequest::_alloc_gclab:
1498 case ShenandoahAllocRequest::_alloc_tlab:
1499 in_new_region = false;
1500 assert(false, "Trying to allocate TLAB larger than the humongous threshold: " SIZE_FORMAT " > " SIZE_FORMAT,
1501 req.size(), ShenandoahHeapRegion::humongous_threshold_words());
1502 return nullptr;
1503 default:
1504 ShouldNotReachHere();
1505 return nullptr;
1506 }
1507 } else {
1508 return allocate_single(req, in_new_region);
1509 }
1510 }
1511
1512 size_t ShenandoahFreeSet::unsafe_peek_free() const {
1513 // Deliberately not locked, this method is unsafe when free set is modified.
1514
1515 for (size_t index = _free_sets.leftmost(Mutator); index <= _free_sets.rightmost(Mutator); index++) {
1516 if (index < _free_sets.max() && _free_sets.in_free_set(index, Mutator)) {
1517 ShenandoahHeapRegion* r = _heap->get_region(index);
1518 if (r->free() >= MinTLABSize) {
1519 return r->free();
1520 }
1521 }
1522 }
1523
1524 // It appears that no regions left
1525 return 0;
1526 }
1527
1528 void ShenandoahFreeSet::print_on(outputStream* out) const {
1529 out->print_cr("Mutator Free Set: " SIZE_FORMAT "", _free_sets.count(Mutator));
1530 for (size_t index = _free_sets.leftmost(Mutator); index <= _free_sets.rightmost(Mutator); index++) {
1531 if (_free_sets.in_free_set(index, Mutator)) {
1532 _heap->get_region(index)->print_on(out);
1533 }
1534 }
1535 out->print_cr("Collector Free Set: " SIZE_FORMAT "", _free_sets.count(Collector));
1536 for (size_t index = _free_sets.leftmost(Collector); index <= _free_sets.rightmost(Collector); index++) {
1537 if (_free_sets.in_free_set(index, Collector)) {
1538 _heap->get_region(index)->print_on(out);
1539 }
1540 }
1541 if (_heap->mode()->is_generational()) {
1542 out->print_cr("Old Collector Free Set: " SIZE_FORMAT "", _free_sets.count(OldCollector));
1543 for (size_t index = _free_sets.leftmost(OldCollector); index <= _free_sets.rightmost(OldCollector); index++) {
1544 if (_free_sets.in_free_set(index, OldCollector)) {
1545 _heap->get_region(index)->print_on(out);
1546 }
1547 }
1548 }
1549 }
1550
1551 /*
1552 * Internal fragmentation metric: describes how fragmented the heap regions are.
1553 *
1554 * It is derived as:
1555 *
1556 * sum(used[i]^2, i=0..k)
1557 * IF = 1 - ------------------------------
1558 * C * sum(used[i], i=0..k)
1559 *
1560 * ...where k is the number of regions in computation, C is the region capacity, and
1561 * used[i] is the used space in the region.
1562 *
1563 * The non-linearity causes IF to be lower for the cases where the same total heap
1564 * used is densely packed. For example:
1565 * a) Heap is completely full => IF = 0
1566 * b) Heap is half full, first 50% regions are completely full => IF = 0
1567 * c) Heap is half full, each region is 50% full => IF = 1/2
1568 * d) Heap is quarter full, first 50% regions are completely full => IF = 0
1569 * e) Heap is quarter full, each region is 25% full => IF = 3/4
1570 * f) Heap has one small object per each region => IF =~ 1
1571 */
1572 double ShenandoahFreeSet::internal_fragmentation() {
1573 double squared = 0;
1574 double linear = 0;
1575 int count = 0;
1576
1577 for (size_t index = _free_sets.leftmost(Mutator); index <= _free_sets.rightmost(Mutator); index++) {
1578 if (_free_sets.in_free_set(index, Mutator)) {
1579 ShenandoahHeapRegion* r = _heap->get_region(index);
1580 size_t used = r->used();
1581 squared += used * used;
1582 linear += used;
1583 count++;
1584 }
1585 }
1586
1587 if (count > 0) {
1588 double s = squared / (ShenandoahHeapRegion::region_size_bytes() * linear);
1589 return 1 - s;
1590 } else {
1591 return 0;
1592 }
1593 }
1594
1595 /*
1596 * External fragmentation metric: describes how fragmented the heap is.
1597 *
1598 * It is derived as:
1599 *
1600 * EF = 1 - largest_contiguous_free / total_free
1601 *
1602 * For example:
1603 * a) Heap is completely empty => EF = 0
1604 * b) Heap is completely full => EF = 0
1605 * c) Heap is first-half full => EF = 1/2
1606 * d) Heap is half full, full and empty regions interleave => EF =~ 1
1607 */
1608 double ShenandoahFreeSet::external_fragmentation() {
1609 size_t last_idx = 0;
1610 size_t max_contig = 0;
1611 size_t empty_contig = 0;
1612
1613 size_t free = 0;
1614
1615 for (size_t index = _free_sets.leftmost(Mutator); index <= _free_sets.rightmost(Mutator); index++) {
1616 if (_free_sets.in_free_set(index, Mutator)) {
1617 ShenandoahHeapRegion* r = _heap->get_region(index);
1618 if (r->is_empty()) {
1619 free += ShenandoahHeapRegion::region_size_bytes();
1620 if (last_idx + 1 == index) {
1621 empty_contig++;
1622 } else {
1623 empty_contig = 1;
1624 }
1625 } else {
1626 empty_contig = 0;
1627 }
1628
1629 max_contig = MAX2(max_contig, empty_contig);
1630 last_idx = index;
1631 }
1632 }
1633
1634 if (free > 0) {
1635 return 1 - (1.0 * max_contig * ShenandoahHeapRegion::region_size_bytes() / free);
1636 } else {
1637 return 0;
1638 }
1639 }
1640