1 /*
2 * Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23
24 #include "precompiled.hpp"
25 #include "gc/shared/suspendibleThreadSet.hpp"
26 #include "gc/z/zAddress.inline.hpp"
27 #include "gc/z/zCollectedHeap.hpp"
28 #include "gc/z/zFuture.inline.hpp"
29 #include "gc/z/zGlobals.hpp"
30 #include "gc/z/zLock.inline.hpp"
31 #include "gc/z/zPage.inline.hpp"
32 #include "gc/z/zPageAllocator.hpp"
33 #include "gc/z/zPageCache.inline.hpp"
34 #include "gc/z/zSafeDelete.inline.hpp"
35 #include "gc/z/zStat.hpp"
36 #include "gc/z/zTracer.inline.hpp"
37 #include "runtime/globals.hpp"
38 #include "runtime/init.hpp"
39 #include "runtime/java.hpp"
40 #include "utilities/debug.hpp"
41
42 static const ZStatCounter ZCounterAllocationRate("Memory", "Allocation Rate", ZStatUnitBytesPerSecond);
43 static const ZStatCounter ZCounterPageCacheFlush("Memory", "Page Cache Flush", ZStatUnitBytesPerSecond);
44 static const ZStatCounter ZCounterUncommit("Memory", "Uncommit", ZStatUnitBytesPerSecond);
45 static const ZStatCriticalPhase ZCriticalPhaseAllocationStall("Allocation Stall");
46
47 class ZPageAllocRequest : public StackObj {
48 friend class ZList<ZPageAllocRequest>;
49
50 private:
51 const uint8_t _type;
52 const size_t _size;
53 const ZAllocationFlags _flags;
54 const unsigned int _total_collections;
55 ZListNode<ZPageAllocRequest> _node;
56 ZFuture<ZPage*> _result;
57
58 public:
59 ZPageAllocRequest(uint8_t type, size_t size, ZAllocationFlags flags, unsigned int total_collections) :
60 _type(type),
61 _size(size),
62 _flags(flags),
63 _total_collections(total_collections) {}
64
65 uint8_t type() const {
66 return _type;
67 }
68
69 size_t size() const {
70 return _size;
71 }
72
73 ZAllocationFlags flags() const {
74 return _flags;
75 }
76
77 unsigned int total_collections() const {
78 return _total_collections;
79 }
80
81 ZPage* wait() {
82 return _result.get();
83 }
84
85 void satisfy(ZPage* page) {
86 _result.set(page);
87 }
88 };
89
90 ZPage* const ZPageAllocator::gc_marker = (ZPage*)-1;
91
92 ZPageAllocator::ZPageAllocator(size_t min_capacity,
93 size_t initial_capacity,
94 size_t max_capacity,
95 size_t max_reserve) :
96 _lock(),
97 _virtual(),
98 _physical(),
99 _cache(),
100 _min_capacity(min_capacity),
101 _max_capacity(max_capacity),
102 _max_reserve(max_reserve),
103 _current_max_capacity(max_capacity),
104 _capacity(0),
105 _used_high(0),
106 _used_low(0),
107 _used(0),
108 _allocated(0),
109 _reclaimed(0),
110 _queue(),
111 _safe_delete(),
112 _uncommit(false),
113 _initialized(false) {
114
115 if (!_virtual.is_initialized() || !_physical.is_initialized()) {
116 return;
117 }
118
119 log_info(gc, init)("Min Capacity: " SIZE_FORMAT "M", min_capacity / M);
120 log_info(gc, init)("Initial Capacity: " SIZE_FORMAT "M", initial_capacity / M);
121 log_info(gc, init)("Max Capacity: " SIZE_FORMAT "M", max_capacity / M);
122 log_info(gc, init)("Max Reserve: " SIZE_FORMAT "M", max_reserve / M);
123 log_info(gc, init)("Pre-touch: %s", AlwaysPreTouch ? "Enabled" : "Disabled");
124
125 // Warn if system limits could stop us from reaching max capacity
126 _physical.warn_commit_limits(max_capacity);
127
128 // Commit initial capacity
129 _capacity = _physical.commit(initial_capacity);
130 if (_capacity != initial_capacity) {
131 log_error(gc)("Failed to allocate initial Java heap (" SIZE_FORMAT "M)", initial_capacity / M);
132 return;
133 }
134
135 // If uncommit is not explicitly disabled, max capacity is greater than
136 // min capacity, and uncommit is supported by the platform, then we will
137 // try to uncommit unused memory.
138 _uncommit = ZUncommit && (max_capacity > min_capacity) && _physical.supports_uncommit();
139 if (_uncommit) {
140 log_info(gc, init)("Uncommit: Enabled, Delay: " UINTX_FORMAT "s", ZUncommitDelay);
141 } else {
142 log_info(gc, init)("Uncommit: Disabled");
143 }
144
145 // Pre-map initial capacity
146 prime_cache(initial_capacity);
147
148 // Successfully initialized
149 _initialized = true;
150 }
151
152 void ZPageAllocator::prime_cache(size_t size) {
153 // Allocate physical memory
154 const ZPhysicalMemory pmem = _physical.alloc(size);
155 guarantee(!pmem.is_null(), "Invalid size");
156
157 // Allocate virtual memory
158 const ZVirtualMemory vmem = _virtual.alloc(size, true /* alloc_from_front */);
159 guarantee(!vmem.is_null(), "Invalid size");
160
161 // Allocate page
162 ZPage* const page = new ZPage(vmem, pmem);
163
164 // Map page
165 map_page(page);
166 page->set_pre_mapped();
167
168 // Add page to cache
169 page->set_last_used();
170 _cache.free_page(page);
171 }
172
173 bool ZPageAllocator::is_initialized() const {
174 return _initialized;
175 }
176
177 size_t ZPageAllocator::min_capacity() const {
178 return _min_capacity;
179 }
180
181 size_t ZPageAllocator::max_capacity() const {
182 return _max_capacity;
183 }
184
185 size_t ZPageAllocator::soft_max_capacity() const {
186 // Note that SoftMaxHeapSize is a manageable flag
187 return MIN2(SoftMaxHeapSize, _current_max_capacity);
188 }
189
190 size_t ZPageAllocator::capacity() const {
191 return _capacity;
192 }
193
194 size_t ZPageAllocator::max_reserve() const {
195 return _max_reserve;
196 }
197
198 size_t ZPageAllocator::used_high() const {
199 return _used_high;
200 }
201
202 size_t ZPageAllocator::used_low() const {
203 return _used_low;
204 }
205
206 size_t ZPageAllocator::used() const {
207 return _used;
208 }
209
210 size_t ZPageAllocator::unused() const {
211 const ssize_t unused = (ssize_t)_capacity - (ssize_t)_used - (ssize_t)_max_reserve;
212 return unused > 0 ? (size_t)unused : 0;
213 }
214
215 size_t ZPageAllocator::allocated() const {
216 return _allocated;
217 }
218
219 size_t ZPageAllocator::reclaimed() const {
220 return _reclaimed > 0 ? (size_t)_reclaimed : 0;
221 }
222
223 void ZPageAllocator::reset_statistics() {
224 assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
225 _allocated = 0;
226 _reclaimed = 0;
227 _used_high = _used_low = _used;
228 }
229
230 void ZPageAllocator::increase_used(size_t size, bool relocation) {
231 if (relocation) {
232 // Allocating a page for the purpose of relocation has a
233 // negative contribution to the number of reclaimed bytes.
234 _reclaimed -= size;
235 }
236 _allocated += size;
237 _used += size;
238 if (_used > _used_high) {
239 _used_high = _used;
240 }
241 }
242
243 void ZPageAllocator::decrease_used(size_t size, bool reclaimed) {
244 if (reclaimed) {
245 // Only pages explicitly released with the reclaimed flag set
246 // counts as reclaimed bytes. This flag is typically true when
247 // a worker releases a page after relocation, and is typically
248 // false when we release a page to undo an allocation.
249 _reclaimed += size;
250 }
251 _used -= size;
252 if (_used < _used_low) {
253 _used_low = _used;
254 }
255 }
256
257 ZPage* ZPageAllocator::create_page(uint8_t type, size_t size) {
258 // Allocate virtual memory
259 const ZVirtualMemory vmem = _virtual.alloc(size);
260 if (vmem.is_null()) {
261 // Out of address space
262 return NULL;
263 }
264
265 // Allocate physical memory
266 const ZPhysicalMemory pmem = _physical.alloc(size);
267 assert(!pmem.is_null(), "Invalid size");
268
269 // Allocate page
270 return new ZPage(type, vmem, pmem);
271 }
272
273 void ZPageAllocator::destroy_page(ZPage* page) {
274 const ZVirtualMemory& vmem = page->virtual_memory();
275 const ZPhysicalMemory& pmem = page->physical_memory();
276
277 // Unmap memory
278 _physical.unmap(pmem, vmem.start());
279
280 // Free physical memory
281 _physical.free(pmem);
282
283 // Free virtual memory
284 _virtual.free(vmem);
285
286 // Delete page safely
287 _safe_delete(page);
288 }
289
290 void ZPageAllocator::map_page(const ZPage* page) const {
291 // Map physical memory
292 if (!page->is_mapped()) {
293 _physical.map(page->physical_memory(), page->start());
294 } else if (ZVerifyViews) {
295 _physical.debug_map(page->physical_memory(), page->start());
296 }
297 }
298
299 size_t ZPageAllocator::max_available(bool no_reserve) const {
300 size_t available = _current_max_capacity - _used;
301
302 if (no_reserve) {
303 // The reserve should not be considered available
304 available -= MIN2(available, _max_reserve);
305 }
306
307 return available;
308 }
309
310 bool ZPageAllocator::ensure_available(size_t size, bool no_reserve) {
311 if (max_available(no_reserve) < size) {
312 // Not enough free memory
313 return false;
314 }
315
316 // We add the max_reserve to the requested size to avoid losing
317 // the reserve because of failure to increase capacity before
318 // reaching max capacity.
319 size += _max_reserve;
320
321 // Don't try to increase capacity if enough unused capacity
322 // is available or if current max capacity has been reached.
323 const size_t available = _capacity - _used;
324 if (available < size && _capacity < _current_max_capacity) {
325 // Try to increase capacity
326 const size_t commit = MIN2(size - available, _current_max_capacity - _capacity);
327 const size_t committed = _physical.commit(commit);
328 _capacity += committed;
329
330 log_trace(gc, heap)("Make Available: Size: " SIZE_FORMAT "M, NoReserve: %s, "
331 "Available: " SIZE_FORMAT "M, Commit: " SIZE_FORMAT "M, "
332 "Committed: " SIZE_FORMAT "M, Capacity: " SIZE_FORMAT "M",
333 size / M, no_reserve ? "True" : "False", available / M,
334 commit / M, committed / M, _capacity / M);
335
336 if (committed != commit) {
337 // Failed, or partly failed, to increase capacity. Adjust current
338 // max capacity to avoid further attempts to increase capacity.
339 log_error(gc)("Forced to lower max Java heap size from "
340 SIZE_FORMAT "M(%.0f%%) to " SIZE_FORMAT "M(%.0f%%)",
341 _current_max_capacity / M, percent_of(_current_max_capacity, _max_capacity),
342 _capacity / M, percent_of(_capacity, _max_capacity));
343
344 _current_max_capacity = _capacity;
345 }
346 }
347
348 if (!no_reserve) {
349 size -= _max_reserve;
350 }
351
352 const size_t new_available = _capacity - _used;
353 return new_available >= size;
354 }
355
356 void ZPageAllocator::ensure_uncached_available(size_t size) {
357 assert(_capacity - _used >= size, "Invalid size");
358 const size_t uncached_available = _capacity - _used - _cache.available();
359 if (size > uncached_available) {
360 flush_cache_for_allocation(size - uncached_available);
361 }
362 }
363
364 ZPage* ZPageAllocator::alloc_page_common_inner(uint8_t type, size_t size, bool no_reserve) {
365 if (!ensure_available(size, no_reserve)) {
366 // Not enough free memory
367 return NULL;
368 }
369
370 // Try allocate page from the cache
371 ZPage* const page = _cache.alloc_page(type, size);
372 if (page != NULL) {
373 return page;
374 }
375
376 // Try flush pages from the cache
377 ensure_uncached_available(size);
378
379 // Create new page
380 return create_page(type, size);
381 }
382
383 ZPage* ZPageAllocator::alloc_page_common(uint8_t type, size_t size, ZAllocationFlags flags) {
384 ZPage* const page = alloc_page_common_inner(type, size, flags.no_reserve());
385 if (page == NULL) {
386 // Out of memory
387 return NULL;
388 }
389
390 // Update used statistics
391 increase_used(size, flags.relocation());
392
393 // Send trace event
394 ZTracer::tracer()->report_page_alloc(size, _used, max_available(flags.no_reserve()), _cache.available(), flags);
395
396 return page;
397 }
398
399 void ZPageAllocator::check_out_of_memory_during_initialization() {
400 if (!is_init_completed()) {
401 vm_exit_during_initialization("java.lang.OutOfMemoryError", "Java heap too small");
402 }
403 }
404
405 ZPage* ZPageAllocator::alloc_page_blocking(uint8_t type, size_t size, ZAllocationFlags flags) {
406 // Prepare to block
407 ZPageAllocRequest request(type, size, flags, ZCollectedHeap::heap()->total_collections());
408
409 _lock.lock();
410
411 // Try non-blocking allocation
412 ZPage* page = alloc_page_common(type, size, flags);
413 if (page == NULL) {
414 // Allocation failed, enqueue request
415 _queue.insert_last(&request);
416 }
417
418 _lock.unlock();
419
420 if (page == NULL) {
421 // Allocation failed
422 ZStatTimer timer(ZCriticalPhaseAllocationStall);
423
424 // We can only block if VM is fully initialized
425 check_out_of_memory_during_initialization();
426
427 do {
428 // Start asynchronous GC
429 ZCollectedHeap::heap()->collect(GCCause::_z_allocation_stall);
430
431 // Wait for allocation to complete or fail
432 page = request.wait();
433 } while (page == gc_marker);
434
435 {
436 // Guard deletion of underlying semaphore. This is a workaround for a
437 // bug in sem_post() in glibc < 2.21, where it's not safe to destroy
438 // the semaphore immediately after returning from sem_wait(). The
439 // reason is that sem_post() can touch the semaphore after a waiting
440 // thread have returned from sem_wait(). To avoid this race we are
441 // forcing the waiting thread to acquire/release the lock held by the
442 // posting thread. https://sourceware.org/bugzilla/show_bug.cgi?id=12674
443 ZLocker<ZLock> locker(&_lock);
444 }
445 }
446
447 return page;
448 }
449
450 ZPage* ZPageAllocator::alloc_page_nonblocking(uint8_t type, size_t size, ZAllocationFlags flags) {
451 ZLocker<ZLock> locker(&_lock);
452 return alloc_page_common(type, size, flags);
453 }
454
455 ZPage* ZPageAllocator::alloc_page(uint8_t type, size_t size, ZAllocationFlags flags) {
456 ZPage* const page = flags.non_blocking()
457 ? alloc_page_nonblocking(type, size, flags)
458 : alloc_page_blocking(type, size, flags);
459 if (page == NULL) {
460 // Out of memory
461 return NULL;
462 }
463
464 // Map page if needed
465 map_page(page);
466
467 // Reset page. This updates the page's sequence number and must
468 // be done after page allocation, which potentially blocked in
469 // a safepoint where the global sequence number was updated.
470 page->reset();
471
472 // Update allocation statistics. Exclude worker threads to avoid
473 // artificial inflation of the allocation rate due to relocation.
474 if (!flags.worker_thread()) {
475 // Note that there are two allocation rate counters, which have
476 // different purposes and are sampled at different frequencies.
477 const size_t bytes = page->size();
478 ZStatInc(ZCounterAllocationRate, bytes);
479 ZStatInc(ZStatAllocRate::counter(), bytes);
480 }
481
482 return page;
483 }
484
485 void ZPageAllocator::satisfy_alloc_queue() {
486 for (;;) {
487 ZPageAllocRequest* const request = _queue.first();
488 if (request == NULL) {
489 // Allocation queue is empty
490 return;
491 }
492
493 ZPage* const page = alloc_page_common(request->type(), request->size(), request->flags());
494 if (page == NULL) {
495 // Allocation could not be satisfied, give up
496 return;
497 }
498
499 // Allocation succeeded, dequeue and satisfy request. Note that
500 // the dequeue operation must happen first, since the request
501 // will immediately be deallocated once it has been satisfied.
502 _queue.remove(request);
503 request->satisfy(page);
504 }
505 }
506
507 void ZPageAllocator::free_page(ZPage* page, bool reclaimed) {
508 ZLocker<ZLock> locker(&_lock);
509
510 // Update used statistics
511 decrease_used(page->size(), reclaimed);
512
513 // Set time when last used
514 page->set_last_used();
515
516 // Cache page
517 _cache.free_page(page);
518
519 // Try satisfy blocked allocations
520 satisfy_alloc_queue();
521 }
522
523 size_t ZPageAllocator::flush_cache(ZPageCacheFlushClosure* cl) {
524 ZList<ZPage> list;
525
526 // Flush pages
527 _cache.flush(cl, &list);
528
529 const size_t overflushed = cl->overflushed();
530 if (overflushed > 0) {
531 // Overflushed, keep part of last page
532 ZPage* const page = list.last()->split(overflushed);
533 _cache.free_page(page);
534 }
535
536 // Destroy pages
537 size_t flushed = 0;
538 for (ZPage* page = list.remove_first(); page != NULL; page = list.remove_first()) {
539 flushed += page->size();
540 destroy_page(page);
541 }
542
543 return flushed;
544 }
545
546 class ZPageCacheFlushForAllocationClosure : public ZPageCacheFlushClosure {
547 public:
548 ZPageCacheFlushForAllocationClosure(size_t requested) :
549 ZPageCacheFlushClosure(requested) {}
550
551 virtual bool do_page(const ZPage* page) {
552 if (_flushed < _requested) {
553 // Flush page
554 _flushed += page->size();
555 return true;
556 }
557
558 // Don't flush page
559 return false;
560 }
561 };
562
563 void ZPageAllocator::flush_cache_for_allocation(size_t requested) {
564 assert(requested <= _cache.available(), "Invalid request");
565
566 // Flush pages
567 ZPageCacheFlushForAllocationClosure cl(requested);
568 const size_t flushed = flush_cache(&cl);
569
570 assert(requested == flushed, "Failed to flush");
571
572 const size_t cached_after = _cache.available();
573 const size_t cached_before = cached_after + flushed;
574
575 log_info(gc, heap)("Page Cache: " SIZE_FORMAT "M(%.0f%%)->" SIZE_FORMAT "M(%.0f%%), "
576 "Flushed: " SIZE_FORMAT "M",
577 cached_before / M, percent_of(cached_before, max_capacity()),
578 cached_after / M, percent_of(cached_after, max_capacity()),
579 flushed / M);
580
581 // Update statistics
582 ZStatInc(ZCounterPageCacheFlush, flushed);
583 }
584
585 class ZPageCacheFlushForUncommitClosure : public ZPageCacheFlushClosure {
586 private:
587 const uint64_t _now;
588 const uint64_t _delay;
589 uint64_t _timeout;
590
591 public:
592 ZPageCacheFlushForUncommitClosure(size_t requested, uint64_t delay) :
593 ZPageCacheFlushClosure(requested),
594 _now(os::elapsedTime()),
595 _delay(delay),
596 _timeout(_delay) {}
597
598 virtual bool do_page(const ZPage* page) {
599 const uint64_t expires = page->last_used() + _delay;
600 const uint64_t timeout = expires - MIN2(expires, _now);
601
602 if (_flushed < _requested && timeout == 0) {
603 // Flush page
604 _flushed += page->size();
605 return true;
606 }
607
608 // Record shortest non-expired timeout
609 _timeout = MIN2(_timeout, timeout);
610
611 // Don't flush page
612 return false;
613 }
614
615 uint64_t timeout() const {
616 return _timeout;
617 }
618 };
619
620 uint64_t ZPageAllocator::uncommit(uint64_t delay) {
621 // Set the default timeout, when no pages are found in the
622 // cache or when uncommit is disabled, equal to the delay.
623 uint64_t timeout = delay;
624
625 if (!_uncommit) {
626 // Disabled
627 return timeout;
628 }
629
630 size_t capacity_before;
631 size_t capacity_after;
632 size_t uncommitted;
633
634 {
635 SuspendibleThreadSetJoiner joiner;
636 ZLocker<ZLock> locker(&_lock);
637
638 // Don't flush more than we will uncommit. Never uncommit
639 // the reserve, and never uncommit below min capacity.
640 const size_t needed = MIN2(_used + _max_reserve, _current_max_capacity);
641 const size_t guarded = MAX2(needed, _min_capacity);
642 const size_t uncommittable = _capacity - guarded;
643 const size_t uncached_available = _capacity - _used - _cache.available();
644 size_t uncommit = MIN2(uncommittable, uncached_available);
645 const size_t flush = uncommittable - uncommit;
646
647 if (flush > 0) {
648 // Flush pages to uncommit
649 ZPageCacheFlushForUncommitClosure cl(flush, delay);
650 uncommit += flush_cache(&cl);
651 timeout = cl.timeout();
652 }
653
654 // Uncommit
655 uncommitted = _physical.uncommit(uncommit);
656 _capacity -= uncommitted;
657
658 capacity_after = _capacity;
659 capacity_before = capacity_after + uncommitted;
660 }
661
662 if (uncommitted > 0) {
663 log_info(gc, heap)("Capacity: " SIZE_FORMAT "M(%.0f%%)->" SIZE_FORMAT "M(%.0f%%), "
664 "Uncommitted: " SIZE_FORMAT "M",
665 capacity_before / M, percent_of(capacity_before, max_capacity()),
666 capacity_after / M, percent_of(capacity_after, max_capacity()),
667 uncommitted / M);
668
669 // Update statistics
670 ZStatInc(ZCounterUncommit, uncommitted);
671 }
672
673 return timeout;
674 }
675
676 void ZPageAllocator::enable_deferred_delete() const {
677 _safe_delete.enable_deferred_delete();
678 }
679
680 void ZPageAllocator::disable_deferred_delete() const {
681 _safe_delete.disable_deferred_delete();
682 }
683
684 void ZPageAllocator::debug_map_page(const ZPage* page) const {
685 assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
686 _physical.debug_map(page->physical_memory(), page->start());
687 }
688
689 class ZPageCacheDebugMapClosure : public StackObj {
690 private:
691 const ZPageAllocator* const _allocator;
692
693 public:
694 ZPageCacheDebugMapClosure(const ZPageAllocator* allocator) :
695 _allocator(allocator) {}
696
697 virtual void do_page(const ZPage* page) {
698 _allocator->debug_map_page(page);
699 }
700 };
701
702 void ZPageAllocator::debug_map_cached_pages() const {
703 assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
704 ZPageCacheDebugMapClosure cl(this);
705 _cache.pages_do(&cl);
706 }
707
708 void ZPageAllocator::debug_unmap_all_pages() const {
709 assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
710 _physical.debug_unmap(ZPhysicalMemorySegment(0 /* start */, ZAddressOffsetMax), 0 /* offset */);
711 }
712
713 bool ZPageAllocator::is_alloc_stalled() const {
714 assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
715 return !_queue.is_empty();
716 }
717
718 void ZPageAllocator::check_out_of_memory() {
719 ZLocker<ZLock> locker(&_lock);
720
721 // Fail allocation requests that were enqueued before the
722 // last GC cycle started, otherwise start a new GC cycle.
723 for (ZPageAllocRequest* request = _queue.first(); request != NULL; request = _queue.first()) {
724 if (request->total_collections() == ZCollectedHeap::heap()->total_collections()) {
725 // Start a new GC cycle, keep allocation requests enqueued
726 request->satisfy(gc_marker);
727 return;
728 }
729
730 // Out of memory, fail allocation request
731 _queue.remove_first();
732 request->satisfy(NULL);
733 }
734 }