1 /*
2 * Copyright (c) 2001, 2017, 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.
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23 */
24
25 #include "precompiled.hpp"
26 #include "gc/g1/collectionSetChooser.hpp"
27 #include "gc/g1/g1CollectedHeap.inline.hpp"
28 #include "gc/shared/space.inline.hpp"
29 #include "runtime/atomic.hpp"
30
31 // Even though we don't use the GC efficiency in our heuristics as
32 // much as we used to, we still order according to GC efficiency. This
33 // will cause regions with a lot of live objects and large RSets to
34 // end up at the end of the array. Given that we might skip collecting
35 // the last few old regions, if after a few mixed GCs the remaining
36 // have reclaimable bytes under a certain threshold, the hope is that
37 // the ones we'll skip are ones with both large RSets and a lot of
38 // live objects, not the ones with just a lot of live objects if we
39 // ordered according to the amount of reclaimable bytes per region.
40 static int order_regions(HeapRegion* hr1, HeapRegion* hr2) {
41 if (hr1 == NULL) {
42 if (hr2 == NULL) {
43 return 0;
44 } else {
45 return 1;
46 }
47 } else if (hr2 == NULL) {
48 return -1;
49 }
50
51 double gc_eff1 = hr1->gc_efficiency();
52 double gc_eff2 = hr2->gc_efficiency();
53 if (gc_eff1 > gc_eff2) {
54 return -1;
55 } if (gc_eff1 < gc_eff2) {
56 return 1;
57 } else {
58 return 0;
59 }
60 }
61
62 static int order_regions(HeapRegion** hr1p, HeapRegion** hr2p) {
63 return order_regions(*hr1p, *hr2p);
64 }
65
66 CollectionSetChooser::CollectionSetChooser() :
67 // The line below is the worst bit of C++ hackery I've ever written
68 // (Detlefs, 11/23). You should think of it as equivalent to
69 // "_regions(100, true)": initialize the growable array and inform it
70 // that it should allocate its elem array(s) on the C heap.
71 //
72 // The first argument, however, is actually a comma expression
73 // (set_allocation_type(this, C_HEAP), 100). The purpose of the
74 // set_allocation_type() call is to replace the default allocation
75 // type for embedded objects STACK_OR_EMBEDDED with C_HEAP. It will
76 // allow to pass the assert in GenericGrowableArray() which checks
77 // that a growable array object must be on C heap if elements are.
78 //
79 // Note: containing object is allocated on C heap since it is CHeapObj.
80 //
81 _regions((ResourceObj::set_allocation_type((address) &_regions,
82 ResourceObj::C_HEAP),
83 100), true /* C_Heap */),
84 _front(0), _end(0), _first_par_unreserved_idx(0),
85 _region_live_threshold_bytes(0), _remaining_reclaimable_bytes(0) {
86 _region_live_threshold_bytes =
87 HeapRegion::GrainBytes * (size_t) G1MixedGCLiveThresholdPercent / 100;
88 }
89
90 #ifndef PRODUCT
91 void CollectionSetChooser::verify() {
92 guarantee(_end <= regions_length(), "_end: %u regions length: %u", _end, regions_length());
93 guarantee(_front <= _end, "_front: %u _end: %u", _front, _end);
94 uint index = 0;
95 size_t sum_of_reclaimable_bytes = 0;
96 while (index < _front) {
97 guarantee(regions_at(index) == NULL,
98 "all entries before _front should be NULL");
99 index += 1;
100 }
101 HeapRegion *prev = NULL;
102 while (index < _end) {
103 HeapRegion *curr = regions_at(index++);
104 guarantee(curr != NULL, "Regions in _regions array cannot be NULL");
105 guarantee(!curr->is_young(), "should not be young!");
106 guarantee(!curr->is_pinned(),
107 "Pinned region should not be in collection set (index %u)", curr->hrm_index());
108 if (prev != NULL) {
109 guarantee(order_regions(prev, curr) != 1,
110 "GC eff prev: %1.4f GC eff curr: %1.4f",
111 prev->gc_efficiency(), curr->gc_efficiency());
112 }
113 sum_of_reclaimable_bytes += curr->reclaimable_bytes();
114 prev = curr;
115 }
116 guarantee(sum_of_reclaimable_bytes == _remaining_reclaimable_bytes,
117 "reclaimable bytes inconsistent, "
118 "remaining: " SIZE_FORMAT " sum: " SIZE_FORMAT,
119 _remaining_reclaimable_bytes, sum_of_reclaimable_bytes);
120 }
121 #endif // !PRODUCT
122
123 void CollectionSetChooser::sort_regions() {
124 // First trim any unused portion of the top in the parallel case.
125 if (_first_par_unreserved_idx > 0) {
126 assert(_first_par_unreserved_idx <= regions_length(),
127 "Or we didn't reserved enough length");
128 regions_trunc_to(_first_par_unreserved_idx);
129 }
130 _regions.sort(order_regions);
131 assert(_end <= regions_length(), "Requirement");
132 #ifdef ASSERT
133 for (uint i = 0; i < _end; i++) {
134 assert(regions_at(i) != NULL, "Should be true by sorting!");
135 }
136 #endif // ASSERT
137 if (log_is_enabled(Trace, gc, liveness)) {
138 G1PrintRegionLivenessInfoClosure cl("Post-Sorting");
139 for (uint i = 0; i < _end; ++i) {
140 HeapRegion* r = regions_at(i);
141 cl.doHeapRegion(r);
142 }
143 }
144 verify();
145 }
146
147 void CollectionSetChooser::add_region(HeapRegion* hr) {
148 assert(!hr->is_pinned(),
149 "Pinned region shouldn't be added to the collection set (index %u)", hr->hrm_index());
150 assert(!hr->is_young(), "should not be young!");
151 _regions.append(hr);
152 _end++;
153 _remaining_reclaimable_bytes += hr->reclaimable_bytes();
154 hr->calc_gc_efficiency();
155 }
156
157 void CollectionSetChooser::push(HeapRegion* hr) {
158 assert(hr != NULL, "Can't put back a NULL region");
159 assert(_front >= 1, "Too many regions have been put back");
160 _front--;
161 regions_at_put(_front, hr);
162 _remaining_reclaimable_bytes += hr->reclaimable_bytes();
163 }
164
165 void CollectionSetChooser::prepare_for_par_region_addition(uint n_threads,
166 uint n_regions,
167 uint chunk_size) {
168 _first_par_unreserved_idx = 0;
169 uint max_waste = n_threads * chunk_size;
170 // it should be aligned with respect to chunk_size
171 uint aligned_n_regions = (n_regions + chunk_size - 1) / chunk_size * chunk_size;
172 assert(aligned_n_regions % chunk_size == 0, "should be aligned");
173 regions_at_put_grow(aligned_n_regions + max_waste - 1, NULL);
174 }
175
176 uint CollectionSetChooser::claim_array_chunk(uint chunk_size) {
177 uint res = (uint) Atomic::add((jint) chunk_size,
178 (volatile jint*) &_first_par_unreserved_idx);
179 assert(regions_length() > res + chunk_size - 1,
180 "Should already have been expanded");
181 return res - chunk_size;
182 }
183
184 void CollectionSetChooser::set_region(uint index, HeapRegion* hr) {
185 assert(regions_at(index) == NULL, "precondition");
186 assert(!hr->is_young(), "should not be young!");
187 regions_at_put(index, hr);
188 hr->calc_gc_efficiency();
189 }
190
191 void CollectionSetChooser::update_totals(uint region_num,
192 size_t reclaimable_bytes) {
193 // Only take the lock if we actually need to update the totals.
194 if (region_num > 0) {
195 assert(reclaimable_bytes > 0, "invariant");
196 // We could have just used atomics instead of taking the
197 // lock. However, we currently don't have an atomic add for size_t.
198 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
199 _end += region_num;
200 _remaining_reclaimable_bytes += reclaimable_bytes;
201 } else {
202 assert(reclaimable_bytes == 0, "invariant");
203 }
204 }
205
206 void CollectionSetChooser::clear() {
207 _regions.clear();
208 _front = 0;
209 _end = 0;
210 _remaining_reclaimable_bytes = 0;
211 }
212
213 class ParKnownGarbageTask: public G1ParallelizeByRegionsTask {
214 class ParKnownGarbageHRClosure: public HeapRegionClosure {
215 G1CollectedHeap* _g1h;
216 CSetChooserParUpdater _cset_updater;
217
218 public:
219 ParKnownGarbageHRClosure(CollectionSetChooser* hrSorted,
220 uint chunk_size) :
221 _g1h(G1CollectedHeap::heap()),
222 _cset_updater(hrSorted, true /* parallel */, chunk_size) { }
223
224 bool doHeapRegion(HeapRegion* r) {
225 // Do we have any marking information for this region?
226 if (r->is_marked()) {
227 // We will skip any region that's currently used as an old GC
228 // alloc region (we should not consider those for collection
229 // before we fill them up).
230 if (_cset_updater.should_add(r) && !_g1h->is_old_gc_alloc_region(r)) {
231 _cset_updater.add_region(r);
232 }
233 }
234 return false;
235 }
236 };
237
238 CollectionSetChooser* _hrSorted;
239 uint _chunk_size;
240
241 public:
242 ParKnownGarbageTask(CollectionSetChooser* hrSorted, uint chunk_size, uint n_workers) :
243 G1ParallelizeByRegionsTask("ParKnownGarbageTask", n_workers),
244 _hrSorted(hrSorted), _chunk_size(chunk_size) {}
245
246 void work(uint worker_id) {
247 ParKnownGarbageHRClosure parKnownGarbageCl(_hrSorted, _chunk_size);
248 all_heap_regions_work(&parKnownGarbageCl, worker_id);
249 }
250 };
251
252 uint CollectionSetChooser::calculate_parallel_work_chunk_size(uint n_workers, uint n_regions) const {
253 assert(n_workers > 0, "Active gc workers should be greater than 0");
254 const uint overpartition_factor = 4;
255 const uint min_chunk_size = MAX2(n_regions / n_workers, 1U);
256 return MAX2(n_regions / (n_workers * overpartition_factor), min_chunk_size);
257 }
258
259 void CollectionSetChooser::rebuild(WorkGang* workers, uint n_regions) {
260 clear();
261
262 uint n_workers = workers->active_workers();
263
264 uint chunk_size = calculate_parallel_work_chunk_size(n_workers, n_regions);
265 prepare_for_par_region_addition(n_workers, n_regions, chunk_size);
266
267 ParKnownGarbageTask par_known_garbage_task(this, chunk_size, n_workers);
268 workers->run_task(&par_known_garbage_task);
269
270 sort_regions();
271 }