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