1 /* 2 * Copyright (c) 2015, 2016, 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 "memory/allocation.inline.hpp" 27 #include "gc/g1/g1_globals.hpp" 28 #include "gc/g1/g1EvacStats.hpp" 29 #include "gc/shared/gcId.hpp" 30 #include "logging/log.hpp" 31 #include "trace/tracing.hpp" 32 33 void G1EvacStats::log_plab_allocation() { 34 PLABStats::log_plab_allocation(); 35 log_debug(gc, plab)("%s other allocation: " 36 "region end waste: " SIZE_FORMAT "B, " 37 "regions filled: %u, " 38 "direct allocated: " SIZE_FORMAT "B, " 39 "failure used: " SIZE_FORMAT "B, " 40 "failure wasted: " SIZE_FORMAT "B", 41 _description, 42 _region_end_waste * HeapWordSize, 43 _regions_filled, 44 _direct_allocated * HeapWordSize, 45 _failure_used * HeapWordSize, 46 _failure_waste * HeapWordSize); 47 } 48 49 void G1EvacStats::adjust_desired_plab_sz() { 50 log_plab_allocation(); 51 52 if (!ResizePLAB) { 53 // Clear accumulators for next round. 54 reset(); 55 return; 56 } 57 58 assert(is_object_aligned(max_size()) && min_size() <= max_size(), 59 "PLAB clipping computation may be incorrect"); 60 61 if (_allocated == 0) { 62 assert((_unused == 0), 63 "Inconsistency in PLAB stats: " 64 "_allocated: " SIZE_FORMAT ", " 65 "_wasted: " SIZE_FORMAT ", " 66 "_region_end_waste: " SIZE_FORMAT ", " 67 "_unused: " SIZE_FORMAT ", " 68 "_used : " SIZE_FORMAT, 69 _allocated, _wasted, _region_end_waste, _unused, used()); 70 _allocated = 1; 71 } 72 // The size of the PLAB caps the amount of space that can be wasted at the 73 // end of the collection. In the worst case the last PLAB could be completely 74 // empty. 75 // This allows us to calculate the new PLAB size to achieve the 76 // TargetPLABWastePct given the latest memory usage and that the last buffer 77 // will be G1LastPLABAverageOccupancy full. 78 // 79 // E.g. assume that if in the current GC 100 words were allocated and a 80 // TargetPLABWastePct of 10 had been set. 81 // 82 // So we could waste up to 10 words to meet that percentage. Given that we 83 // also assume that that buffer is typically half-full, the new desired PLAB 84 // size is set to 20 words. 85 // 86 // The amount of allocation performed should be independent of the number of 87 // threads, so should the maximum waste we can spend in total. So if 88 // we used n threads to allocate, each of them can spend maximum waste/n words in 89 // a first rough approximation. The number of threads only comes into play later 90 // when actually retrieving the actual desired PLAB size. 91 // 92 // After calculating this optimal PLAB size the algorithm applies the usual 93 // exponential decaying average over this value to guess the next PLAB size. 94 // 95 // We account region end waste fully to PLAB allocation (in the calculation of 96 // what we consider as "used_for_waste_calculation" below). This is not 97 // completely fair, but is a conservative assumption because PLABs may be sized 98 // flexibly while we cannot adjust inline allocations. 99 // Allocation during GC will try to minimize region end waste so this impact 100 // should be minimal. 101 // 102 // We need to cover overflow when calculating the amount of space actually used 103 // by objects in PLABs when subtracting the region end waste. 104 // Region end waste may be higher than actual allocation. This may occur if many 105 // threads do not allocate anything but a few rather large objects. In this 106 // degenerate case the PLAB size would simply quickly tend to minimum PLAB size, 107 // which is an okay reaction. 108 size_t const used_for_waste_calculation = used() > _region_end_waste ? used() - _region_end_waste : 0; 109 110 size_t const total_waste_allowed = used_for_waste_calculation * TargetPLABWastePct; 111 size_t const cur_plab_sz = (size_t)((double)total_waste_allowed / G1LastPLABAverageOccupancy); 112 // Take historical weighted average 113 _filter.sample(cur_plab_sz); 114 _desired_net_plab_sz = MAX2(min_size(), (size_t)_filter.average()); 115 116 log_sizing(cur_plab_sz, _desired_net_plab_sz); 117 // Clear accumulators for next round. 118 reset(); 119 } 120 121 G1EvacStats::G1EvacStats(const char* description, size_t desired_plab_sz_, unsigned wt) : 122 PLABStats(description, desired_plab_sz_, wt), 123 _region_end_waste(0), 124 _regions_filled(0), 125 _direct_allocated(0), 126 _failure_used(0), 127 _failure_waste(0) { 128 } 129 130 131 G1EvacStats::~G1EvacStats() { }