1 /*
2 * Copyright (c) 2001, 2026, 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 "gc/parallel/mutableSpace.hpp"
26 #include "gc/shared/pretouchTask.hpp"
27 #include "gc/shared/spaceDecorator.hpp"
28 #include "memory/iterator.inline.hpp"
29 #include "memory/universe.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/javaThread.hpp"
32 #include "runtime/safepoint.hpp"
33 #include "utilities/align.hpp"
34 #include "utilities/macros.hpp"
35
36 MutableSpace::MutableSpace(size_t page_size) :
37 _last_setup_region(),
38 _page_size(page_size),
39 _bottom(nullptr),
40 _top(nullptr),
41 _end(nullptr) {}
42
43 void MutableSpace::numa_setup_pages(MemRegion mr, bool clear_space) {
44 assert(is_aligned(mr.start(), page_size()), "precondition");
45 assert(is_aligned(mr.end(), page_size()), "precondition");
46
47 if (mr.is_empty()) {
48 return;
49 }
50
51 if (clear_space) {
52 // Prefer page reallocation to migration.
53 os::disclaim_memory((char*) mr.start(), mr.byte_size());
54 }
55 os::numa_make_global((char*) mr.start(), mr.byte_size());
56 }
57
58 void MutableSpace::initialize(MemRegion mr,
59 bool clear_space,
60 bool mangle_space,
61 bool setup_pages,
62 WorkerThreads* pretouch_workers) {
63
64 assert(Universe::on_page_boundary(mr.start()) && Universe::on_page_boundary(mr.end()),
65 "invalid space boundaries");
66
67 if (setup_pages && (UseNUMA || AlwaysPreTouch)) {
68 // The space may move left and right or expand/shrink.
69 // We'd like to enforce the desired page placement.
70 MemRegion head, tail;
71 if (last_setup_region().is_empty()) {
72 // If it's the first initialization don't limit the amount of work.
73 head = mr;
74 tail = MemRegion(mr.end(), mr.end());
75 } else {
76 // Is there an intersection with the address space?
77 MemRegion intersection = last_setup_region().intersection(mr);
78 if (intersection.is_empty()) {
79 intersection = MemRegion(mr.end(), mr.end());
80 }
81 // All the sizes below are in words.
82 size_t head_size = 0, tail_size = 0;
83 if (mr.start() <= intersection.start()) {
84 head_size = pointer_delta(intersection.start(), mr.start());
85 }
86 if(intersection.end() <= mr.end()) {
87 tail_size = pointer_delta(mr.end(), intersection.end());
88 }
89 // Limit the amount of page manipulation if necessary.
90 if (NUMASpaceResizeRate > 0 && !AlwaysPreTouch) {
91 const size_t change_size = head_size + tail_size;
92 const float setup_rate_words = NUMASpaceResizeRate >> LogBytesPerWord;
93 head_size = MIN2((size_t)(setup_rate_words * head_size / change_size),
94 head_size);
95 tail_size = MIN2((size_t)(setup_rate_words * tail_size / change_size),
96 tail_size);
97 }
98 head = MemRegion(intersection.start() - head_size, intersection.start());
99 tail = MemRegion(intersection.end(), intersection.end() + tail_size);
100 }
101 assert(mr.contains(head) && mr.contains(tail), "Sanity");
102
103 if (UseNUMA) {
104 numa_setup_pages(head, clear_space);
105 numa_setup_pages(tail, clear_space);
106 }
107
108 if (AlwaysPreTouch) {
109 PretouchTask::pretouch("ParallelGC PreTouch head", (char*)head.start(), (char*)head.end(),
110 page_size(), pretouch_workers);
111
112 PretouchTask::pretouch("ParallelGC PreTouch tail", (char*)tail.start(), (char*)tail.end(),
113 page_size(), pretouch_workers);
114 }
115
116 // Remember where we stopped so that we can continue later.
117 set_last_setup_region(MemRegion(head.start(), tail.end()));
118 }
119
120 set_bottom(mr.start());
121 // When expanding concurrently with callers of cas_allocate, setting end
122 // makes the new space available for allocation by other threads. So this
123 // assignment must follow all other configuration and initialization that
124 // might be done for expansion.
125 _end.release_store(mr.end());
126
127 if (clear_space) {
128 clear(mangle_space);
129 }
130 }
131
132 void MutableSpace::clear(bool mangle_space) {
133 set_top(bottom());
134 if (ZapUnusedHeapArea && mangle_space) {
135 mangle_unused_area();
136 }
137 }
138
139 #ifndef PRODUCT
140
141 void MutableSpace::mangle_unused_area() {
142 mangle_region(MemRegion(top(), end()));
143 }
144
145 void MutableSpace::mangle_region(MemRegion mr) {
146 SpaceMangler::mangle_region(mr);
147 }
148
149 #endif
150
151 HeapWord* MutableSpace::cas_allocate(size_t size) {
152 do {
153 // Read top before end, else the range check may pass when it shouldn't.
154 // If end is read first, other threads may advance end and top such that
155 // current top > old end and current top + size > current end. Then
156 // pointer_delta underflows, allowing installation of top > current end.
157 HeapWord* obj = _top.load_acquire();
158 if (pointer_delta(end(), obj) >= size) {
159 HeapWord* new_top = obj + size;
160 if (!_top.compare_set(obj, new_top)) {
161 continue; // another thread beat us to the allocation, try again
162 }
163 assert(is_object_aligned(obj) && is_object_aligned(new_top),
164 "checking alignment");
165 return obj;
166 } else {
167 return nullptr;
168 }
169 } while (true);
170 }
171
172 // Try to deallocate previous allocation. Returns true upon success.
173 bool MutableSpace::cas_deallocate(HeapWord *obj, size_t size) {
174 HeapWord* expected_top = obj + size;
175 return _top.compare_set(expected_top, obj);
176 }
177
178 void MutableSpace::oop_iterate(OopIterateClosure* cl) {
179 HeapWord* obj_addr = bottom();
180 HeapWord* t = top();
181 // Could call objects iterate, but this is easier.
182 while (obj_addr < t) {
183 obj_addr += cast_to_oop(obj_addr)->oop_iterate_size(cl);
184 }
185 }
186
187 void MutableSpace::object_iterate(ObjectClosure* cl) {
188 HeapWord* p = bottom();
189 while (p < top()) {
190 oop obj = cast_to_oop(p);
191 // When promotion-failure occurs during Young GC, eden/from space is not cleared,
192 // so we can encounter objects with "forwarded" markword.
193 // They are essentially dead, so skipping them
194 if (obj->is_forwarded()) {
195 assert(!obj->is_self_forwarded(), "must not be self-forwarded");
196 // It is safe to use the forwardee here. Parallel GC only uses
197 // header-based forwarding during promotion. Full GC doesn't
198 // use the object header for forwarding at all.
199 p += obj->forwardee()->size();
200 } else {
201 cl->do_object(obj);
202 p += obj->size();
203 }
204 }
205 }
206
207 void MutableSpace::print_short() const { print_short_on(tty); }
208 void MutableSpace::print_short_on( outputStream* st) const {
209 st->print("space %zuK, %d%% used", capacity_in_bytes() / K,
210 (int) ((double) used_in_bytes() * 100 / capacity_in_bytes()));
211 }
212
213 void MutableSpace::print() const { print_on(tty, ""); }
214 void MutableSpace::print_on(outputStream* st, const char* prefix) const {
215 st->print("%s", prefix);
216 MutableSpace::print_short_on(st);
217 st->print_cr(" [" PTR_FORMAT "," PTR_FORMAT "," PTR_FORMAT ")",
218 p2i(bottom()), p2i(top()), p2i(end()));
219 }
220
221 void MutableSpace::verify() {
222 HeapWord* p = bottom();
223 HeapWord* t = top();
224 while (p < t) {
225 oopDesc::verify(cast_to_oop(p));
226 p += cast_to_oop(p)->size();
227 }
228 guarantee(p == top(), "end of last object must match end of space");
229 }