1 /*
2 * Copyright (c) 2016, 2019, Red Hat, Inc. 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 "precompiled.hpp"
26
27 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
28 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
29 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
30 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
31 #include "gc/shenandoah/shenandoahUtils.hpp"
32 #include "runtime/atomic.hpp"
33 #include "services/memTracker.hpp"
34 #include "utilities/copy.hpp"
35
36 ShenandoahCollectionSet::ShenandoahCollectionSet(ShenandoahHeap* heap, ReservedSpace space, char* heap_base) :
37 _map_size(heap->num_regions()),
38 _region_size_bytes_shift(ShenandoahHeapRegion::region_size_bytes_shift()),
39 _map_space(space),
40 _cset_map(_map_space.base() + ((uintx)heap_base >> _region_size_bytes_shift)),
41 _biased_cset_map(_map_space.base()),
42 _heap(heap),
43 _has_old_regions(false),
44 _garbage(0),
45 _used(0),
46 _region_count(0),
47 _old_garbage(0),
48 _current_index(0) {
49
50 // The collection set map is reserved to cover the entire heap *and* zero addresses.
51 // This is needed to accept in-cset checks for both heap oops and NULLs, freeing
52 // high-performance code from checking for NULL first.
53 //
54 // Since heap_base can be far away, committing the entire map would waste memory.
55 // Therefore, we only commit the parts that are needed to operate: the heap view,
56 // and the zero page.
57 //
58 // Note: we could instead commit the entire map, and piggyback on OS virtual memory
59 // subsystem for mapping not-yet-written-to pages to a single physical backing page,
60 // but this is not guaranteed, and would confuse NMT and other memory accounting tools.
61
62 MemTracker::record_virtual_memory_type(_map_space.base(), mtGC);
63
64 size_t page_size = (size_t)os::vm_page_size();
65
66 if (!_map_space.special()) {
67 // Commit entire pages that cover the heap cset map.
68 char* bot_addr = align_down(_cset_map, page_size);
69 char* top_addr = align_up(_cset_map + _map_size, page_size);
70 os::commit_memory_or_exit(bot_addr, pointer_delta(top_addr, bot_addr, 1), false,
71 "Unable to commit collection set bitmap: heap");
72
73 // Commit the zero page, if not yet covered by heap cset map.
74 if (bot_addr != _biased_cset_map) {
75 os::commit_memory_or_exit(_biased_cset_map, page_size, false,
76 "Unable to commit collection set bitmap: zero page");
77 }
78 }
79
80 Copy::zero_to_bytes(_cset_map, _map_size);
81 Copy::zero_to_bytes(_biased_cset_map, page_size);
82 }
83
84 void ShenandoahCollectionSet::add_region(ShenandoahHeapRegion* r) {
85 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
86 assert(Thread::current()->is_VM_thread(), "Must be VMThread");
87 assert(!is_in(r), "Already in collection set");
88 assert(!r->is_humongous(), "Only add regular regions to the collection set");
89
90 _cset_map[r->index()] = 1;
91
92 if (r->affiliation() == YOUNG_GENERATION) {
93 _young_region_count++;
94 _young_bytes_to_evacuate += r->get_live_data_bytes();
95 if (r->age() >= InitialTenuringThreshold) {
96 _young_bytes_to_promote += r->get_live_data_bytes();
97 }
98 } else if (r->affiliation() == OLD_GENERATION) {
99 _old_region_count++;
100 _old_bytes_to_evacuate += r->get_live_data_bytes();
101 _old_garbage += r->garbage();
102 }
103
104 _region_count++;
105 _has_old_regions |= r->is_old();
106 _garbage += r->garbage();
107 _used += r->used();
108 // Update the region status too. State transition would be checked internally.
109 r->make_cset();
110 }
111
112 void ShenandoahCollectionSet::clear() {
113 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
114 Copy::zero_to_bytes(_cset_map, _map_size);
115
116 #ifdef ASSERT
117 for (size_t index = 0; index < _heap->num_regions(); index ++) {
118 assert (!_heap->get_region(index)->is_cset(), "should have been cleared before");
119 }
120 #endif
121
122 _garbage = 0;
123 _old_garbage = 0;
124 _used = 0;
125
126 _region_count = 0;
127 _current_index = 0;
128
129 _young_region_count = 0;
130 _young_bytes_to_evacuate = 0;
131 _young_bytes_to_promote = 0;
132
133 _old_region_count = 0;
134 _old_bytes_to_evacuate = 0;
135
136 _has_old_regions = false;
137 }
138
139 ShenandoahHeapRegion* ShenandoahCollectionSet::claim_next() {
140 // This code is optimized for the case when collection set contains only
141 // a few regions. In this case, it is more constructive to check for is_in
142 // before hitting the (potentially contended) atomic index.
143
144 size_t max = _heap->num_regions();
145 size_t old = Atomic::load(&_current_index);
146
147 for (size_t index = old; index < max; index++) {
148 if (is_in(index)) {
149 size_t cur = Atomic::cmpxchg(&_current_index, old, index + 1, memory_order_relaxed);
150 assert(cur >= old, "Always move forward");
151 if (cur == old) {
152 // Successfully moved the claim index, this is our region.
153 return _heap->get_region(index);
154 } else {
155 // Somebody else moved the claim index, restart from there.
156 index = cur - 1; // adjust for loop post-increment
157 old = cur;
158 }
159 }
160 }
161 return NULL;
162 }
163
164 ShenandoahHeapRegion* ShenandoahCollectionSet::next() {
165 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
166 assert(Thread::current()->is_VM_thread(), "Must be VMThread");
167
168 size_t max = _heap->num_regions();
169 for (size_t index = _current_index; index < max; index++) {
170 if (is_in(index)) {
171 _current_index = index + 1;
172 return _heap->get_region(index);
173 }
174 }
175
176 return NULL;
177 }
178
179 void ShenandoahCollectionSet::print_on(outputStream* out) const {
180 out->print_cr("Collection Set : " SIZE_FORMAT "", count());
181
182 debug_only(size_t regions = 0;)
183 for (size_t index = 0; index < _heap->num_regions(); index ++) {
184 if (is_in(index)) {
185 _heap->get_region(index)->print_on(out);
186 debug_only(regions ++;)
187 }
188 }
189 assert(regions == count(), "Must match");
190 }