1 /*
2 * Copyright (c) 2018, 2019, 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/g1/g1CollectionSetChooser.hpp"
27 #include "gc/g1/g1RemSetTrackingPolicy.hpp"
28 #include "gc/g1/heapRegion.inline.hpp"
29 #include "gc/g1/heapRegionRemSet.hpp"
30 #include "runtime/safepoint.hpp"
31
32 bool G1RemSetTrackingPolicy::needs_scan_for_rebuild(HeapRegion* r) const {
33 // All non-free, non-young, non-closed archive regions need to be scanned for references;
34 // At every gc we gather references to other regions in young, and closed archive
35 // regions by definition do not have references going outside the closed archive.
36 // Free regions trivially do not need scanning because they do not contain live
37 // objects.
38 return !(r->is_young() || r->is_closed_archive() || r->is_free());
39 }
40
41 void G1RemSetTrackingPolicy::update_at_allocate(HeapRegion* r) {
42 if (r->is_young()) {
43 // Always collect remembered set for young regions.
44 r->rem_set()->set_state_complete();
45 } else if (r->is_humongous()) {
46 // Collect remembered sets for humongous regions by default to allow eager reclaim.
47 r->rem_set()->set_state_complete();
48 } else if (r->is_archive()) {
49 // Archive regions never move ever. So never build remembered sets for them.
50 r->rem_set()->set_state_empty();
51 } else if (r->is_old()) {
52 // By default, do not create remembered set for new old regions.
53 r->rem_set()->set_state_empty();
54 } else {
55 guarantee(false, "Unhandled region %u with heap region type %s", r->hrm_index(), r->get_type_str());
56 }
57 }
58
59 void G1RemSetTrackingPolicy::update_at_free(HeapRegion* r) {
60 /* nothing to do */
61 }
62
63 static void print_before_rebuild(HeapRegion* r, bool selected_for_rebuild, size_t total_live_bytes, size_t live_bytes) {
64 log_trace(gc, remset, tracking)("Before rebuild region %u "
65 "(ntams: " PTR_FORMAT ") "
66 "total_live_bytes " SIZE_FORMAT " "
67 "selected %s "
68 "(live_bytes " SIZE_FORMAT " "
69 "next_marked " SIZE_FORMAT " "
70 "marked " SIZE_FORMAT " "
71 "type %s)",
72 r->hrm_index(),
73 p2i(r->next_top_at_mark_start()),
74 total_live_bytes,
75 BOOL_TO_STR(selected_for_rebuild),
76 live_bytes,
77 r->next_marked_bytes(),
78 r->marked_bytes(),
79 r->get_type_str());
80 }
81
82 bool G1RemSetTrackingPolicy::update_humongous_before_rebuild(HeapRegion* r, bool is_live) {
83 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
84 assert(r->is_humongous(), "Region %u should be humongous", r->hrm_index());
85
86 if (r->is_archive()) {
87 return false;
88 }
89
90 assert(!r->rem_set()->is_updating(), "Remembered set of region %u is updating before rebuild", r->hrm_index());
91
92 bool selected_for_rebuild = false;
93 // For humongous regions, to be of interest for rebuilding the remembered set the following must apply:
94 // - We always try to update the remembered sets of humongous regions containing
95 // type arrays as they might have been reset after full gc.
96 if (is_live && oop(r->humongous_start_region()->bottom())->is_typeArray() && !r->rem_set()->is_tracked()) {
97 r->rem_set()->set_state_updating();
98 selected_for_rebuild = true;
99 }
100
101 size_t const live_bytes = is_live ? HeapRegion::GrainBytes : 0;
102 print_before_rebuild(r, selected_for_rebuild, live_bytes, live_bytes);
103
104 return selected_for_rebuild;
105 }
106
107 bool G1RemSetTrackingPolicy::update_before_rebuild(HeapRegion* r, size_t live_bytes) {
108 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
109 assert(!r->is_humongous(), "Region %u is humongous", r->hrm_index());
110
111 // Only consider updating the remembered set for old gen regions - excluding archive regions
112 // which never move (but are "Old" regions).
113 if (!r->is_old() || r->is_archive()) {
114 return false;
115 }
116
117 assert(!r->rem_set()->is_updating(), "Remembered set of region %u is updating before rebuild", r->hrm_index());
118
119 size_t between_ntams_and_top = (r->top() - r->next_top_at_mark_start()) * HeapWordSize;
120 size_t total_live_bytes = live_bytes + between_ntams_and_top;
121
122 bool selected_for_rebuild = false;
123 // For old regions, to be of interest for rebuilding the remembered set the following must apply:
124 // - They must contain some live data in them.
125 // - Only need to rebuild non-complete remembered sets.
126 // - Otherwise only add those old gen regions which occupancy is low enough that there
127 // is a chance that we will ever evacuate them in the mixed gcs.
128 if ((total_live_bytes > 0) &&
129 G1CollectionSetChooser::region_occupancy_low_enough_for_evac(total_live_bytes) &&
130 !r->rem_set()->is_tracked()) {
131
132 r->rem_set()->set_state_updating();
133 selected_for_rebuild = true;
134 }
135
136 print_before_rebuild(r, selected_for_rebuild, total_live_bytes, live_bytes);
137
138 return selected_for_rebuild;
139 }
140
141 void G1RemSetTrackingPolicy::update_after_rebuild(HeapRegion* r) {
142 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
143
144 if (r->is_old_or_humongous_or_archive()) {
145 if (r->rem_set()->is_updating()) {
146 assert(!r->is_archive(), "Archive region %u with remembered set", r->hrm_index());
147 r->rem_set()->set_state_complete();
148 }
149 G1CollectedHeap* g1h = G1CollectedHeap::heap();
150 // We can drop remembered sets of humongous regions that have a too large remembered set:
151 // We will never try to eagerly reclaim or move them anyway until the next concurrent
152 // cycle as e.g. remembered set entries will always be added.
153 if (r->is_starts_humongous() && !g1h->is_potential_eager_reclaim_candidate(r)) {
154 // Handle HC regions with the HS region.
155 uint const size_in_regions = (uint)g1h->humongous_obj_size_in_regions(oop(r->bottom())->size());
156 uint const region_idx = r->hrm_index();
157 for (uint j = region_idx; j < (region_idx + size_in_regions); j++) {
158 HeapRegion* const cur = g1h->region_at(j);
159 assert(!cur->is_continues_humongous() || cur->rem_set()->is_empty(),
160 "Continues humongous region %u remset should be empty", j);
161 cur->rem_set()->clear_locked(true /* only_cardset */);
162 }
163 }
164 G1ConcurrentMark* cm = G1CollectedHeap::heap()->concurrent_mark();
165 log_trace(gc, remset, tracking)("After rebuild region %u "
166 "(ntams " PTR_FORMAT " "
167 "liveness " SIZE_FORMAT " "
168 "next_marked_bytes " SIZE_FORMAT " "
169 "remset occ " SIZE_FORMAT " "
170 "size " SIZE_FORMAT ")",
171 r->hrm_index(),
172 p2i(r->next_top_at_mark_start()),
173 cm->liveness(r->hrm_index()) * HeapWordSize,
174 r->next_marked_bytes(),
175 r->rem_set()->occupied_locked(),
176 r->rem_set()->mem_size());
177 }
178 }