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