1 /*
2 * Copyright (c) 2000, 2018, 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 "precompiled.hpp"
26 #include "gc/shared/cardTableModRefBSCodeGen.hpp"
27 #include "gc/shared/cardTableModRefBS.inline.hpp"
28 #include "gc/shared/collectedHeap.hpp"
29 #include "gc/shared/genCollectedHeap.hpp"
30 #include "gc/shared/space.inline.hpp"
31 #include "logging/log.hpp"
32 #include "memory/virtualspace.hpp"
33 #include "oops/oop.inline.hpp"
34 #include "runtime/thread.hpp"
35 #include "services/memTracker.hpp"
36 #include "utilities/align.hpp"
37 #include "utilities/macros.hpp"
38
39 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and
40 // enumerate ref fields that have been modified (since the last
41 // enumeration.)
42
43 CardTableModRefBS::CardTableModRefBS(
44 CardTable* card_table,
45 const BarrierSet::FakeRtti& fake_rtti) :
46 ModRefBarrierSet(fake_rtti.add_tag(BarrierSet::CardTableModRef)),
47 _defer_initial_card_mark(false),
48 _card_table(card_table)
49 {}
50
51 CardTableModRefBS::CardTableModRefBS(CardTable* card_table) :
52 ModRefBarrierSet(BarrierSet::FakeRtti(BarrierSet::CardTableModRef)),
53 _defer_initial_card_mark(false),
54 _card_table(card_table)
55 {}
56
57 BarrierSetCodeGen* CardTableModRefBS::make_code_gen() {
58 return new CardTableModRefBSCodeGen();
59 }
60
61 void CardTableModRefBS::initialize() {
62 ModRefBarrierSet::initialize();
63 initialize_deferred_card_mark_barriers();
64 }
65
66 CardTableModRefBS::~CardTableModRefBS() {
67 delete _card_table;
68 }
69
70 void CardTableModRefBS::write_ref_array_work(MemRegion mr) {
71 _card_table->dirty_MemRegion(mr);
72 }
73
74 void CardTableModRefBS::invalidate(MemRegion mr) {
75 _card_table->invalidate(mr);
76 }
77
78 void CardTableModRefBS::print_on(outputStream* st) const {
79 _card_table->print_on(st);
80 }
81
82 // Helper for ReduceInitialCardMarks. For performance,
83 // compiled code may elide card-marks for initializing stores
84 // to a newly allocated object along the fast-path. We
85 // compensate for such elided card-marks as follows:
86 // (a) Generational, non-concurrent collectors, such as
87 // GenCollectedHeap(ParNew,DefNew,Tenured) and
88 // ParallelScavengeHeap(ParallelGC, ParallelOldGC)
89 // need the card-mark if and only if the region is
90 // in the old gen, and do not care if the card-mark
91 // succeeds or precedes the initializing stores themselves,
92 // so long as the card-mark is completed before the next
93 // scavenge. For all these cases, we can do a card mark
94 // at the point at which we do a slow path allocation
95 // in the old gen, i.e. in this call.
96 // (b) GenCollectedHeap(ConcurrentMarkSweepGeneration) requires
97 // in addition that the card-mark for an old gen allocated
98 // object strictly follow any associated initializing stores.
99 // In these cases, the memRegion remembered below is
100 // used to card-mark the entire region either just before the next
101 // slow-path allocation by this thread or just before the next scavenge or
102 // CMS-associated safepoint, whichever of these events happens first.
103 // (The implicit assumption is that the object has been fully
104 // initialized by this point, a fact that we assert when doing the
105 // card-mark.)
106 // (c) G1CollectedHeap(G1) uses two kinds of write barriers. When a
107 // G1 concurrent marking is in progress an SATB (pre-write-)barrier
108 // is used to remember the pre-value of any store. Initializing
109 // stores will not need this barrier, so we need not worry about
110 // compensating for the missing pre-barrier here. Turning now
111 // to the post-barrier, we note that G1 needs a RS update barrier
112 // which simply enqueues a (sequence of) dirty cards which may
113 // optionally be refined by the concurrent update threads. Note
114 // that this barrier need only be applied to a non-young write,
115 // but, like in CMS, because of the presence of concurrent refinement
116 // (much like CMS' precleaning), must strictly follow the oop-store.
117 // Thus, using the same protocol for maintaining the intended
118 // invariants turns out, serendepitously, to be the same for both
119 // G1 and CMS.
120 //
121 // For any future collector, this code should be reexamined with
122 // that specific collector in mind, and the documentation above suitably
123 // extended and updated.
124 void CardTableModRefBS::on_slowpath_allocation_exit(JavaThread* thread, oop new_obj) {
125 if (!ReduceInitialCardMarks) {
126 return;
127 }
128 // If a previous card-mark was deferred, flush it now.
129 flush_deferred_card_mark_barrier(thread);
130 if (new_obj->is_typeArray() || _card_table->is_in_young(new_obj)) {
131 // Arrays of non-references don't need a post-barrier.
132 // The deferred_card_mark region should be empty
133 // following the flush above.
134 assert(thread->deferred_card_mark().is_empty(), "Error");
135 } else {
136 MemRegion mr((HeapWord*)new_obj, new_obj->size());
137 assert(!mr.is_empty(), "Error");
138 if (_defer_initial_card_mark) {
139 // Defer the card mark
140 thread->set_deferred_card_mark(mr);
141 } else {
142 // Do the card mark
143 invalidate(mr);
144 }
145 }
146 }
147
148 void CardTableModRefBS::initialize_deferred_card_mark_barriers() {
149 // Used for ReduceInitialCardMarks (when COMPILER2 or JVMCI is used);
150 // otherwise remains unused.
151 #if defined(COMPILER2) || INCLUDE_JVMCI
152 _defer_initial_card_mark = is_server_compilation_mode_vm() && ReduceInitialCardMarks && can_elide_tlab_store_barriers()
153 && (DeferInitialCardMark || card_mark_must_follow_store());
154 #else
155 assert(_defer_initial_card_mark == false, "Who would set it?");
156 #endif
157 }
158
159 void CardTableModRefBS::flush_deferred_card_mark_barrier(JavaThread* thread) {
160 #if defined(COMPILER2) || INCLUDE_JVMCI
161 MemRegion deferred = thread->deferred_card_mark();
162 if (!deferred.is_empty()) {
163 assert(_defer_initial_card_mark, "Otherwise should be empty");
164 {
165 // Verify that the storage points to a parsable object in heap
166 DEBUG_ONLY(oop old_obj = oop(deferred.start());)
167 assert(!_card_table->is_in_young(old_obj),
168 "Else should have been filtered in on_slowpath_allocation_exit()");
169 assert(oopDesc::is_oop(old_obj, true), "Not an oop");
170 assert(deferred.word_size() == (size_t)(old_obj->size()),
171 "Mismatch: multiple objects?");
172 }
173 write_region(deferred);
174 // "Clear" the deferred_card_mark field
175 thread->set_deferred_card_mark(MemRegion());
176 }
177 assert(thread->deferred_card_mark().is_empty(), "invariant");
178 #else
179 assert(!_defer_initial_card_mark, "Should be false");
180 assert(thread->deferred_card_mark().is_empty(), "Should be empty");
181 #endif
182 }
183
184 void CardTableModRefBS::on_thread_detach(JavaThread* thread) {
185 // The deferred store barriers must all have been flushed to the
186 // card-table (or other remembered set structure) before GC starts
187 // processing the card-table (or other remembered set).
188 flush_deferred_card_mark_barrier(thread);
189 }
190
191 bool CardTableModRefBS::card_mark_must_follow_store() const {
192 return _card_table->scanned_concurrently();
193 }