1 /*
2 * Copyright (c) 2018, 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "classfile/javaClasses.hpp"
26 #include "classfile/vmClasses.hpp"
27 #include "gc/shared/allocTracer.hpp"
28 #include "gc/shared/collectedHeap.hpp"
29 #include "gc/shared/memAllocator.hpp"
30 #include "gc/shared/threadLocalAllocBuffer.inline.hpp"
31 #include "gc/shared/tlab_globals.hpp"
32 #include "memory/universe.hpp"
33 #include "oops/arrayOop.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "prims/jvmtiExport.hpp"
36 #include "runtime/continuationJavaClasses.inline.hpp"
37 #include "runtime/handles.inline.hpp"
38 #include "runtime/sharedRuntime.hpp"
39 #include "runtime/javaThread.hpp"
40 #include "services/lowMemoryDetector.hpp"
41 #include "utilities/align.hpp"
42 #include "utilities/copy.hpp"
43 #include "utilities/globalDefinitions.hpp"
44
45 class MemAllocator::Allocation: StackObj {
46 friend class MemAllocator;
47
48 const MemAllocator& _allocator;
49 JavaThread* _thread;
50 oop* _obj_ptr;
51 bool _overhead_limit_exceeded;
52 bool _allocated_outside_tlab;
53 size_t _allocated_tlab_size;
54 bool _tlab_end_reset_for_sample;
55
56 bool check_out_of_memory();
57 void verify_before();
58 void verify_after();
59 void notify_allocation();
60 void notify_allocation_jvmti_sampler();
61 void notify_allocation_low_memory_detector();
62 void notify_allocation_jfr_sampler();
63 void notify_allocation_dtrace_sampler();
64 #ifdef ASSERT
65 void check_for_valid_allocation_state() const;
66 #endif
67
68 class PreserveObj;
69
70 public:
71 Allocation(const MemAllocator& allocator, oop* obj_ptr)
72 : _allocator(allocator),
73 _thread(JavaThread::cast(allocator._thread)), // Do not use Allocation in non-JavaThreads.
74 _obj_ptr(obj_ptr),
75 _overhead_limit_exceeded(false),
76 _allocated_outside_tlab(false),
77 _allocated_tlab_size(0),
78 _tlab_end_reset_for_sample(false)
79 {
80 assert(Thread::current() == allocator._thread, "do not pass MemAllocator across threads");
81 verify_before();
82 }
83
84 ~Allocation() {
85 if (!check_out_of_memory()) {
86 notify_allocation();
87 }
88 }
89
90 oop obj() const { return *_obj_ptr; }
91 };
92
93 class MemAllocator::Allocation::PreserveObj: StackObj {
94 HandleMark _handle_mark;
95 Handle _handle;
96 oop* const _obj_ptr;
97
98 public:
99 PreserveObj(JavaThread* thread, oop* obj_ptr)
100 : _handle_mark(thread),
101 _handle(thread, *obj_ptr),
102 _obj_ptr(obj_ptr)
103 {
104 *obj_ptr = nullptr;
105 }
106
107 ~PreserveObj() {
108 *_obj_ptr = _handle();
109 }
110
111 oop operator()() const {
112 return _handle();
113 }
114 };
115
116 bool MemAllocator::Allocation::check_out_of_memory() {
117 JavaThread* THREAD = _thread; // For exception macros.
118 assert(!HAS_PENDING_EXCEPTION, "Unexpected exception, will result in uninitialized storage");
119
120 if (obj() != nullptr) {
121 return false;
122 }
123
124 const char* message = _overhead_limit_exceeded ? "GC overhead limit exceeded" : "Java heap space";
125 if (!_thread->is_in_internal_oome_mark()) {
126 // -XX:+HeapDumpOnOutOfMemoryError and -XX:OnOutOfMemoryError support
127 report_java_out_of_memory(message);
128 if (JvmtiExport::should_post_resource_exhausted()) {
129 JvmtiExport::post_resource_exhausted(
130 JVMTI_RESOURCE_EXHAUSTED_OOM_ERROR | JVMTI_RESOURCE_EXHAUSTED_JAVA_HEAP,
131 message);
132 }
133
134 oop exception = _overhead_limit_exceeded ?
135 Universe::out_of_memory_error_gc_overhead_limit() :
136 Universe::out_of_memory_error_java_heap();
137 THROW_OOP_(exception, true);
138 } else {
139 THROW_OOP_(Universe::out_of_memory_error_java_heap_without_backtrace(), true);
140 }
141 }
142
143 void MemAllocator::Allocation::verify_before() {
144 // Clear unhandled oops for memory allocation. Memory allocation might
145 // not take out a lock if from tlab, so clear here.
146 JavaThread* THREAD = _thread; // For exception macros.
147 assert(!HAS_PENDING_EXCEPTION, "Should not allocate with exception pending");
148 debug_only(check_for_valid_allocation_state());
149 assert(!Universe::heap()->is_stw_gc_active(), "Allocation during GC pause not allowed");
150 }
151
152 #ifdef ASSERT
153 void MemAllocator::Allocation::check_for_valid_allocation_state() const {
154 // How to choose between a pending exception and a potential
155 // OutOfMemoryError? Don't allow pending exceptions.
156 // This is a VM policy failure, so how do we exhaustively test it?
157 assert(!_thread->has_pending_exception(),
158 "shouldn't be allocating with pending exception");
159 // Allocation of an oop can always invoke a safepoint.
160 _thread->check_for_valid_safepoint_state();
161 }
162 #endif
163
164 void MemAllocator::Allocation::notify_allocation_jvmti_sampler() {
165 // support for JVMTI VMObjectAlloc event (no-op if not enabled)
166 JvmtiExport::vm_object_alloc_event_collector(obj());
167
168 if (!JvmtiExport::should_post_sampled_object_alloc()) {
169 // Sampling disabled
170 return;
171 }
172
173 if (!_allocated_outside_tlab && _allocated_tlab_size == 0 && !_tlab_end_reset_for_sample) {
174 // Sample if it's a non-TLAB allocation, or a TLAB allocation that either refills the TLAB
175 // or expands it due to taking a sampler induced slow path.
176 return;
177 }
178
179 // If we want to be sampling, protect the allocated object with a Handle
180 // before doing the callback. The callback is done in the destructor of
181 // the JvmtiSampledObjectAllocEventCollector.
182 size_t bytes_since_last = 0;
183
184 {
185 PreserveObj obj_h(_thread, _obj_ptr);
186 JvmtiSampledObjectAllocEventCollector collector;
187 size_t size_in_bytes = _allocator._word_size * HeapWordSize;
188 ThreadLocalAllocBuffer& tlab = _thread->tlab();
189
190 if (!_allocated_outside_tlab) {
191 bytes_since_last = tlab.bytes_since_last_sample_point();
192 }
193
194 _thread->heap_sampler().check_for_sampling(obj_h(), size_in_bytes, bytes_since_last);
195 }
196
197 if (_tlab_end_reset_for_sample || _allocated_tlab_size != 0) {
198 // Tell tlab to forget bytes_since_last if we passed it to the heap sampler.
199 _thread->tlab().set_sample_end(bytes_since_last != 0);
200 }
201 }
202
203 void MemAllocator::Allocation::notify_allocation_low_memory_detector() {
204 // support low memory notifications (no-op if not enabled)
205 LowMemoryDetector::detect_low_memory_for_collected_pools();
206 }
207
208 void MemAllocator::Allocation::notify_allocation_jfr_sampler() {
209 HeapWord* mem = cast_from_oop<HeapWord*>(obj());
210 size_t size_in_bytes = _allocator._word_size * HeapWordSize;
211
212 if (_allocated_outside_tlab) {
213 AllocTracer::send_allocation_outside_tlab(obj()->klass(), mem, size_in_bytes, _thread);
214 } else if (_allocated_tlab_size != 0) {
215 // TLAB was refilled
216 AllocTracer::send_allocation_in_new_tlab(obj()->klass(), mem, _allocated_tlab_size * HeapWordSize,
217 size_in_bytes, _thread);
218 }
219 }
220
221 void MemAllocator::Allocation::notify_allocation_dtrace_sampler() {
222 if (DTraceAllocProbes) {
223 // support for Dtrace object alloc event (no-op most of the time)
224 Klass* klass = obj()->klass();
225 size_t word_size = _allocator._word_size;
226 if (klass != nullptr && klass->name() != nullptr) {
227 SharedRuntime::dtrace_object_alloc(_thread, obj(), word_size);
228 }
229 }
230 }
231
232 void MemAllocator::Allocation::notify_allocation() {
233 notify_allocation_low_memory_detector();
234 notify_allocation_jfr_sampler();
235 notify_allocation_dtrace_sampler();
236 notify_allocation_jvmti_sampler();
237 }
238
239 HeapWord* MemAllocator::mem_allocate_outside_tlab(Allocation& allocation) const {
240 allocation._allocated_outside_tlab = true;
241 HeapWord* mem = Universe::heap()->mem_allocate(_word_size, &allocation._overhead_limit_exceeded);
242 if (mem == nullptr) {
243 return mem;
244 }
245
246 size_t size_in_bytes = _word_size * HeapWordSize;
247 _thread->incr_allocated_bytes(size_in_bytes);
248
249 return mem;
250 }
251
252 HeapWord* MemAllocator::mem_allocate_inside_tlab_fast() const {
253 return _thread->tlab().allocate(_word_size);
254 }
255
256 HeapWord* MemAllocator::mem_allocate_inside_tlab_slow(Allocation& allocation) const {
257 HeapWord* mem = nullptr;
258 ThreadLocalAllocBuffer& tlab = _thread->tlab();
259
260 if (JvmtiExport::should_post_sampled_object_alloc()) {
261 tlab.set_back_allocation_end();
262 mem = tlab.allocate(_word_size);
263
264 // We set back the allocation sample point to try to allocate this, reset it
265 // when done.
266 allocation._tlab_end_reset_for_sample = true;
267
268 if (mem != nullptr) {
269 return mem;
270 }
271 }
272
273 // Retain tlab and allocate object in shared space if
274 // the amount free in the tlab is too large to discard.
275 if (tlab.free() > tlab.refill_waste_limit()) {
276 tlab.record_slow_allocation(_word_size);
277 return nullptr;
278 }
279
280 // Discard tlab and allocate a new one.
281 // To minimize fragmentation, the last TLAB may be smaller than the rest.
282 size_t new_tlab_size = tlab.compute_size(_word_size);
283
284 tlab.retire_before_allocation();
285
286 if (new_tlab_size == 0) {
287 return nullptr;
288 }
289
290 // Allocate a new TLAB requesting new_tlab_size. Any size
291 // between minimal and new_tlab_size is accepted.
292 size_t min_tlab_size = ThreadLocalAllocBuffer::compute_min_size(_word_size);
293 mem = Universe::heap()->allocate_new_tlab(min_tlab_size, new_tlab_size, &allocation._allocated_tlab_size);
294 if (mem == nullptr) {
295 assert(allocation._allocated_tlab_size == 0,
296 "Allocation failed, but actual size was updated. min: %zu"
297 ", desired: %zu, actual: %zu",
298 min_tlab_size, new_tlab_size, allocation._allocated_tlab_size);
299 return nullptr;
300 }
301 assert(allocation._allocated_tlab_size != 0, "Allocation succeeded but actual size not updated. mem at: "
302 PTR_FORMAT " min: %zu, desired: %zu",
303 p2i(mem), min_tlab_size, new_tlab_size);
304
305 // ...and clear or zap just allocated TLAB, if needed.
306 if (ZeroTLAB) {
307 Copy::zero_to_words(mem, allocation._allocated_tlab_size);
308 } else if (ZapTLAB) {
309 // Skip mangling the space corresponding to the object header to
310 // ensure that the returned space is not considered parsable by
311 // any concurrent GC thread.
312 size_t hdr_size = oopDesc::header_size();
313 Copy::fill_to_words(mem + hdr_size, allocation._allocated_tlab_size - hdr_size, badHeapWordVal);
314 }
315
316 tlab.fill(mem, mem + _word_size, allocation._allocated_tlab_size);
317 return mem;
318 }
319
320 HeapWord* MemAllocator::mem_allocate(Allocation& allocation) const {
321 if (UseTLAB) {
322 // Try allocating from an existing TLAB.
323 HeapWord* mem = mem_allocate_inside_tlab_fast();
324 if (mem != nullptr) {
325 return mem;
326 }
327 }
328
329 // Allocation of an oop can always invoke a safepoint.
330 debug_only(allocation._thread->check_for_valid_safepoint_state());
331
332 if (UseTLAB) {
333 // Try refilling the TLAB and allocating the object in it.
334 HeapWord* mem = mem_allocate_inside_tlab_slow(allocation);
335 if (mem != nullptr) {
336 return mem;
337 }
338 }
339
340 return mem_allocate_outside_tlab(allocation);
341 }
342
343 oop MemAllocator::allocate() const {
344 oop obj = nullptr;
345 {
346 Allocation allocation(*this, &obj);
347 HeapWord* mem = mem_allocate(allocation);
348 if (mem != nullptr) {
349 obj = initialize(mem);
350 } else {
351 // The unhandled oop detector will poison local variable obj,
352 // so reset it to null if mem is null.
353 obj = nullptr;
354 }
355 }
356 return obj;
357 }
358
359 void MemAllocator::mem_clear(HeapWord* mem) const {
360 assert(mem != nullptr, "cannot initialize null object");
361 const size_t hs = oopDesc::header_size();
362 assert(_word_size >= hs, "unexpected object size");
363 if (oopDesc::has_klass_gap()) {
364 oopDesc::set_klass_gap(mem, 0);
365 }
366 Copy::fill_to_aligned_words(mem + hs, _word_size - hs);
367 }
368
369 oop MemAllocator::finish(HeapWord* mem) const {
370 assert(mem != nullptr, "null object pointer");
371 // Need a release store to ensure array/class length, mark word, and
372 // object zeroing are visible before setting the klass non-null, for
373 // concurrent collectors.
374 if (UseCompactObjectHeaders) {
375 oopDesc::release_set_mark(mem, _klass->prototype_header());
376 } else {
377 oopDesc::set_mark(mem, markWord::prototype());
378 oopDesc::release_set_klass(mem, _klass);
379 }
380 return cast_to_oop(mem);
381 }
382
383 oop ObjAllocator::initialize(HeapWord* mem) const {
384 mem_clear(mem);
385 return finish(mem);
386 }
387
388 oop ObjArrayAllocator::initialize(HeapWord* mem) const {
389 // Set array length before setting the _klass field because a
390 // non-null klass field indicates that the object is parsable by
391 // concurrent GC.
392 assert(_length >= 0, "length should be non-negative");
393 if (_do_zero) {
394 mem_clear(mem);
395 mem_zap_start_padding(mem);
396 mem_zap_end_padding(mem);
397 }
398 arrayOopDesc::set_length(mem, _length);
399 return finish(mem);
400 }
401
402 #ifndef PRODUCT
403 void ObjArrayAllocator::mem_zap_start_padding(HeapWord* mem) const {
404 const BasicType element_type = ArrayKlass::cast(_klass)->element_type();
405 const size_t base_offset_in_bytes = arrayOopDesc::base_offset_in_bytes(element_type);
406 const size_t header_size_in_bytes = arrayOopDesc::header_size_in_bytes();
407
408 const address base = reinterpret_cast<address>(mem) + base_offset_in_bytes;
409 const address header_end = reinterpret_cast<address>(mem) + header_size_in_bytes;
410
411 if (header_end < base) {
412 const size_t padding_in_bytes = base - header_end;
413 Copy::fill_to_bytes(header_end, padding_in_bytes, heapPaddingByteVal);
414 }
415 }
416
417 void ObjArrayAllocator::mem_zap_end_padding(HeapWord* mem) const {
418 const size_t length_in_bytes = static_cast<size_t>(_length) << ArrayKlass::cast(_klass)->log2_element_size();
419 const BasicType element_type = ArrayKlass::cast(_klass)->element_type();
420 const size_t base_offset_in_bytes = arrayOopDesc::base_offset_in_bytes(element_type);
421 const size_t size_in_bytes = _word_size * BytesPerWord;
422
423 const address obj_end = reinterpret_cast<address>(mem) + size_in_bytes;
424 const address base = reinterpret_cast<address>(mem) + base_offset_in_bytes;
425 const address elements_end = base + length_in_bytes;
426 assert(elements_end <= obj_end, "payload must fit in object");
427 if (elements_end < obj_end) {
428 const size_t padding_in_bytes = obj_end - elements_end;
429 Copy::fill_to_bytes(elements_end, padding_in_bytes, heapPaddingByteVal);
430 }
431 }
432 #endif
433
434 oop ClassAllocator::initialize(HeapWord* mem) const {
435 // Set oop_size field before setting the _klass field because a
436 // non-null _klass field indicates that the object is parsable by
437 // concurrent GC.
438 assert(_base_size > 0, "oop_size must be positive.");
439 mem_clear(mem);
440 java_lang_Class::set_oop_size(mem, _base_size);
441 return finish(mem);
442 }