1 /* 2 * Copyright (c) 2001, 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/collectionSetChooser.hpp" 27 #include "gc/g1/g1CollectedHeap.inline.hpp" 28 #include "gc/g1/heapRegionRemSet.hpp" 29 #include "gc/shared/space.inline.hpp" 30 #include "runtime/atomic.hpp" 31 #include "utilities/quickSort.hpp" 32 33 // Order regions according to GC efficiency. This will cause regions with a lot 34 // of live objects and large remembered sets to end up at the end of the array. 35 // Given that we might skip collecting the last few old regions, if after a few 36 // mixed GCs the remaining have reclaimable bytes under a certain threshold, the 37 // hope is that the ones we'll skip are ones with both large remembered sets and 38 // a lot of 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 // Make sure that NULL entries are moved to the end. 42 if (hr1 == NULL) { 43 if (hr2 == NULL) { 44 return 0; 45 } else { 46 return 1; 47 } 48 } else if (hr2 == NULL) { 49 return -1; 50 } 51 52 double gc_eff1 = hr1->gc_efficiency(); 53 double gc_eff2 = hr2->gc_efficiency(); 54 55 if (gc_eff1 > gc_eff2) { 56 return -1; 57 } if (gc_eff1 < gc_eff2) { 58 return 1; 59 } else { 60 return 0; 61 } 62 } 63 64 // Determine collection set candidates: For all regions determine whether they 65 // should be a collection set candidates, calculate their efficiency, sort and 66 // return them as G1CollectionSetCandidates instance. 67 // Threads calculate the GC efficiency of the regions they get to process, and 68 // put them into some work area unsorted. At the end the array is sorted and 69 // copied into the G1CollectionSetCandidates instance; the caller will be the new 70 // owner of this object. 71 class G1BuildCandidateRegionsTask : public AbstractGangTask { 72 73 // Work area for building the set of collection set candidates. Contains references 74 // to heap regions with their GC efficiencies calculated. To reduce contention 75 // on claiming array elements, worker threads claim parts of this array in chunks; 76 // Array elements may be NULL as threads might not get enough regions to fill 77 // up their chunks completely. 78 // Final sorting will remove them. 79 class G1BuildCandidateArray : public StackObj { 80 81 uint const _max_size; 82 uint const _chunk_size; 83 84 HeapRegion** _data; 85 86 uint volatile _cur_claim_idx; 87 88 // Calculates the maximum array size that will be used. 89 static uint required_array_size(uint num_regions, uint num_workers, uint chunk_size) { 90 uint const max_waste = num_workers * chunk_size; 91 // The array should be aligned with respect to chunk_size. 92 uint const aligned_num_regions = ((num_regions + chunk_size - 1) / chunk_size) * chunk_size; 93 94 return aligned_num_regions + max_waste; 95 } 96 97 public: 98 G1BuildCandidateArray(uint max_num_regions, uint num_workers, uint chunk_size) : 99 _max_size(required_array_size(max_num_regions, num_workers, chunk_size)), 100 _chunk_size(chunk_size), 101 _data(NEW_C_HEAP_ARRAY(HeapRegion*, _max_size, mtGC)), 102 _cur_claim_idx(0) { 103 for (uint i = 0; i < _max_size; i++) { 104 _data[i] = NULL; 105 } 106 } 107 108 ~G1BuildCandidateArray() { 109 FREE_C_HEAP_ARRAY(HeapRegion*, _data); 110 } 111 112 // Claim a new chunk, returning its bounds [from, to[. 113 void claim_chunk(uint& from, uint& to) { 114 uint result = Atomic::add(_chunk_size, &_cur_claim_idx); 115 assert(_max_size > result - 1, 116 "Array too small, is %u should be %u with chunk size %u.", 117 _max_size, result, _chunk_size); 118 from = result - _chunk_size; 119 to = result; 120 } 121 122 // Set element in array. 123 void set(uint idx, HeapRegion* hr) { 124 assert(idx < _max_size, "Index %u out of bounds %u", idx, _max_size); 125 assert(_data[idx] == NULL, "Value must not have been set."); 126 _data[idx] = hr; 127 } 128 129 void sort_and_copy_into(HeapRegion** dest, uint num_regions) { 130 if (_cur_claim_idx == 0) { 131 return; 132 } 133 for (uint i = _cur_claim_idx; i < _max_size; i++) { 134 assert(_data[i] == NULL, "must be"); 135 } 136 QuickSort::sort(_data, _cur_claim_idx, order_regions, true); 137 for (uint i = num_regions; i < _max_size; i++) { 138 assert(_data[i] == NULL, "must be"); 139 } 140 for (uint i = 0; i < num_regions; i++) { 141 dest[i] = _data[i]; 142 } 143 } 144 }; 145 146 // Per-region closure. In addition to determining whether a region should be 147 // added to the candidates, and calculating those regions' gc efficiencies, also 148 // gather additional statistics. 149 class G1BuildCandidateRegionsClosure : public HeapRegionClosure { 150 G1BuildCandidateArray* _array; 151 152 uint _cur_chunk_idx; 153 uint _cur_chunk_end; 154 155 uint _regions_added; 156 size_t _reclaimable_bytes_added; 157 158 void add_region(HeapRegion* hr) { 159 if (_cur_chunk_idx == _cur_chunk_end) { 160 _array->claim_chunk(_cur_chunk_idx, _cur_chunk_end); 161 } 162 assert(_cur_chunk_idx < _cur_chunk_end, "Must be"); 163 164 hr->calc_gc_efficiency(); 165 _array->set(_cur_chunk_idx, hr); 166 167 _cur_chunk_idx++; 168 169 _regions_added++; 170 _reclaimable_bytes_added += hr->reclaimable_bytes(); 171 } 172 173 bool should_add(HeapRegion* hr) { return CollectionSetChooser::should_add(hr); } 174 175 public: 176 G1BuildCandidateRegionsClosure(G1BuildCandidateArray* array) : 177 _array(array), 178 _cur_chunk_idx(0), 179 _cur_chunk_end(0), 180 _regions_added(0), 181 _reclaimable_bytes_added(0) { } 182 183 bool do_heap_region(HeapRegion* r) { 184 // We will skip any region that's currently used as an old GC 185 // alloc region (we should not consider those for collection 186 // before we fill them up). 187 if (should_add(r) && !G1CollectedHeap::heap()->is_old_gc_alloc_region(r)) { 188 add_region(r); 189 } else if (r->is_old()) { 190 // Keep remembered sets for humongous regions, otherwise clean out remembered 191 // sets for old regions. 192 r->rem_set()->clear(true /* only_cardset */); 193 } else { 194 assert(r->is_archive() || !r->is_old() || !r->rem_set()->is_tracked(), 195 "Missed to clear unused remembered set of region %u (%s) that is %s", 196 r->hrm_index(), r->get_type_str(), r->rem_set()->get_state_str()); 197 } 198 return false; 199 } 200 201 uint regions_added() const { return _regions_added; } 202 size_t reclaimable_bytes_added() const { return _reclaimable_bytes_added; } 203 }; 204 205 G1CollectedHeap* _g1h; 206 HeapRegionClaimer _hrclaimer; 207 208 uint volatile _num_regions_added; 209 size_t volatile _reclaimable_bytes_added; 210 211 G1BuildCandidateArray _result; 212 213 void update_totals(uint num_regions, size_t reclaimable_bytes) { 214 if (num_regions > 0) { 215 assert(reclaimable_bytes > 0, "invariant"); 216 Atomic::add(num_regions, &_num_regions_added); 217 Atomic::add(reclaimable_bytes, &_reclaimable_bytes_added); 218 } else { 219 assert(reclaimable_bytes == 0, "invariant"); 220 } 221 } 222 223 public: 224 G1BuildCandidateRegionsTask(uint max_num_regions, uint chunk_size, uint num_workers) : 225 AbstractGangTask("G1 Build Candidate Regions"), 226 _g1h(G1CollectedHeap::heap()), 227 _hrclaimer(num_workers), 228 _num_regions_added(0), 229 _reclaimable_bytes_added(0), 230 _result(max_num_regions, chunk_size, num_workers) { } 231 232 void work(uint worker_id) { 233 G1BuildCandidateRegionsClosure cl(&_result); 234 _g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hrclaimer, worker_id); 235 update_totals(cl.regions_added(), cl.reclaimable_bytes_added()); 236 } 237 238 G1CollectionSetCandidates* get_sorted_candidates() { 239 HeapRegion** regions = NEW_C_HEAP_ARRAY(HeapRegion*, _num_regions_added, mtGC); 240 _result.sort_and_copy_into(regions, _num_regions_added); 241 return new G1CollectionSetCandidates(regions, 242 _num_regions_added, 243 _reclaimable_bytes_added); 244 } 245 }; 246 247 uint CollectionSetChooser::calculate_work_chunk_size(uint num_workers, uint num_regions) { 248 assert(num_workers > 0, "Active gc workers should be greater than 0"); 249 return MAX2(num_regions / num_workers, 1U); 250 } 251 252 bool CollectionSetChooser::should_add(HeapRegion* hr) { 253 return !hr->is_young() && 254 !hr->is_pinned() && 255 region_occupancy_low_enough_for_evac(hr->live_bytes()) && 256 hr->rem_set()->is_complete(); 257 } 258 259 G1CollectionSetCandidates* CollectionSetChooser::build(WorkGang* workers, uint max_num_regions) { 260 uint num_workers = workers->active_workers(); 261 uint chunk_size = calculate_work_chunk_size(num_workers, max_num_regions); 262 263 G1BuildCandidateRegionsTask cl(max_num_regions, chunk_size, num_workers); 264 workers->run_task(&cl, num_workers); 265 266 G1CollectionSetCandidates* result = cl.get_sorted_candidates(); 267 result->verify(); 268 return result; 269 }