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. 22 * 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.do_heap_region(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 ParKnownGarbageHRClosure: public HeapRegionClosure { 214 G1CollectedHeap* _g1h; 215 CSetChooserParUpdater _cset_updater; 216 217 public: 218 ParKnownGarbageHRClosure(CollectionSetChooser* hrSorted, 219 uint chunk_size) : 220 _g1h(G1CollectedHeap::heap()), 221 _cset_updater(hrSorted, true /* parallel */, chunk_size) { } 222 223 bool do_heap_region(HeapRegion* r) { 224 // Do we have any marking information for this region? 225 if (r->is_marked()) { 226 // We will skip any region that's currently used as an old GC 227 // alloc region (we should not consider those for collection 228 // before we fill them up). 229 if (_cset_updater.should_add(r) && !_g1h->is_old_gc_alloc_region(r)) { 230 _cset_updater.add_region(r); 231 } 232 } 233 return false; 234 } 235 }; 236 237 class ParKnownGarbageTask: public AbstractGangTask { 238 CollectionSetChooser* _hrSorted; 239 uint _chunk_size; 240 G1CollectedHeap* _g1; 241 HeapRegionClaimer _hrclaimer; 242 243 public: 244 ParKnownGarbageTask(CollectionSetChooser* hrSorted, uint chunk_size, uint n_workers) : 245 AbstractGangTask("ParKnownGarbageTask"), 246 _hrSorted(hrSorted), _chunk_size(chunk_size), 247 _g1(G1CollectedHeap::heap()), _hrclaimer(n_workers) {} 248 249 void work(uint worker_id) { 250 ParKnownGarbageHRClosure par_known_garbage_cl(_hrSorted, _chunk_size); 251 _g1->heap_region_par_iterate_from_worker_offset(&par_known_garbage_cl, &_hrclaimer, worker_id); 252 } 253 }; 254 255 uint CollectionSetChooser::calculate_parallel_work_chunk_size(uint n_workers, uint n_regions) const { 256 assert(n_workers > 0, "Active gc workers should be greater than 0"); 257 const uint overpartition_factor = 4; 258 const uint min_chunk_size = MAX2(n_regions / n_workers, 1U); 259 return MAX2(n_regions / (n_workers * overpartition_factor), min_chunk_size); 260 } 261 262 void CollectionSetChooser::rebuild(WorkGang* workers, uint n_regions) { 263 clear(); 264 265 uint n_workers = workers->active_workers(); 266 267 uint chunk_size = calculate_parallel_work_chunk_size(n_workers, n_regions); 268 prepare_for_par_region_addition(n_workers, n_regions, chunk_size); 269 270 ParKnownGarbageTask par_known_garbage_task(this, chunk_size, n_workers); 271 workers->run_task(&par_known_garbage_task); 272 273 sort_regions(); 274 }