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/cardTableBarrierSet.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 CardTableBarrierSet::CardTableBarrierSet( 43 CardTable* card_table, 44 const BarrierSet::FakeRtti& fake_rtti) : 45 ModRefBarrierSet(fake_rtti.add_tag(BarrierSet::CardTableBarrierSet)), 46 _defer_initial_card_mark(false), 47 _card_table(card_table) 48 {} 49 50 CardTableBarrierSet::CardTableBarrierSet(CardTable* card_table) : 51 ModRefBarrierSet(BarrierSet::FakeRtti(BarrierSet::CardTableBarrierSet)), 52 _defer_initial_card_mark(false), 53 _card_table(card_table) 54 {} 55 56 void CardTableBarrierSet::initialize() { 57 initialize_deferred_card_mark_barriers(); 58 } 59 60 CardTableBarrierSet::~CardTableBarrierSet() { 61 delete _card_table; 62 } 63 64 void CardTableBarrierSet::write_ref_array_work(MemRegion mr) { 65 _card_table->dirty_MemRegion(mr); 66 } 67 68 void CardTableBarrierSet::invalidate(MemRegion mr) { 69 _card_table->invalidate(mr); 70 } 71 72 void CardTableBarrierSet::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 CardTableBarrierSet::on_slowpath_allocation_exit(JavaThread* thread, oop new_obj) { 119 #if defined(COMPILER2) || INCLUDE_JVMCI 120 if (!ReduceInitialCardMarks) { 121 return; 122 } 123 // If a previous card-mark was deferred, flush it now. 124 flush_deferred_card_mark_barrier(thread); 125 if (new_obj->is_typeArray() || _card_table->is_in_young(new_obj)) { 126 // Arrays of non-references don't need a post-barrier. 127 // The deferred_card_mark region should be empty 128 // following the flush above. 129 assert(thread->deferred_card_mark().is_empty(), "Error"); 130 } else { 131 MemRegion mr((HeapWord*)new_obj, new_obj->size()); 132 assert(!mr.is_empty(), "Error"); 133 if (_defer_initial_card_mark) { 134 // Defer the card mark 135 thread->set_deferred_card_mark(mr); 136 } else { 137 // Do the card mark 138 invalidate(mr); 139 } 140 } 141 #endif // COMPILER2 || JVMCI 142 } 143 144 void CardTableBarrierSet::initialize_deferred_card_mark_barriers() { 145 // Used for ReduceInitialCardMarks (when COMPILER2 or JVMCI is used); 146 // otherwise remains unused. 147 #if defined(COMPILER2) || INCLUDE_JVMCI 148 _defer_initial_card_mark = is_server_compilation_mode_vm() && ReduceInitialCardMarks && can_elide_tlab_store_barriers() 149 && (DeferInitialCardMark || card_mark_must_follow_store()); 150 #else 151 assert(_defer_initial_card_mark == false, "Who would set it?"); 152 #endif 153 } 154 155 void CardTableBarrierSet::flush_deferred_card_mark_barrier(JavaThread* thread) { 156 #if defined(COMPILER2) || INCLUDE_JVMCI 157 MemRegion deferred = thread->deferred_card_mark(); 158 if (!deferred.is_empty()) { 159 assert(_defer_initial_card_mark, "Otherwise should be empty"); 160 { 161 // Verify that the storage points to a parsable object in heap 162 DEBUG_ONLY(oop old_obj = oop(deferred.start());) 163 assert(!_card_table->is_in_young(old_obj), 164 "Else should have been filtered in on_slowpath_allocation_exit()"); 165 assert(oopDesc::is_oop(old_obj, true), "Not an oop"); 166 assert(deferred.word_size() == (size_t)(old_obj->size()), 167 "Mismatch: multiple objects?"); 168 } 169 write_region(deferred); 170 // "Clear" the deferred_card_mark field 171 thread->set_deferred_card_mark(MemRegion()); 172 } 173 assert(thread->deferred_card_mark().is_empty(), "invariant"); 174 #else 175 assert(!_defer_initial_card_mark, "Should be false"); 176 assert(thread->deferred_card_mark().is_empty(), "Should be empty"); 177 #endif 178 } 179 180 void CardTableBarrierSet::on_thread_detach(JavaThread* thread) { 181 // The deferred store barriers must all have been flushed to the 182 // card-table (or other remembered set structure) before GC starts 183 // processing the card-table (or other remembered set). 184 flush_deferred_card_mark_barrier(thread); 185 } 186 187 bool CardTableBarrierSet::card_mark_must_follow_store() const { 188 return _card_table->scanned_concurrently(); 189 }