1 /* 2 * Copyright (c) 2015, 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 "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 size_t G1EvacStats::compute_desired_plab_sz() { 50 // The size of the PLAB caps the amount of space that can be wasted at the 51 // end of the collection. In the worst case the last PLAB could be completely 52 // empty. 53 // This allows us to calculate the new PLAB size to achieve the 54 // TargetPLABWastePct given the latest memory usage and that the last buffer 55 // will be G1LastPLABAverageOccupancy full. 56 // 57 // E.g. assume that if in the current GC 100 words were allocated and a 58 // TargetPLABWastePct of 10 had been set. 59 // 60 // So we could waste up to 10 words to meet that percentage. Given that we 61 // also assume that that buffer is typically half-full, the new desired PLAB 62 // size is set to 20 words. 63 // 64 // The amount of allocation performed should be independent of the number of 65 // threads, so should the maximum waste we can spend in total. So if 66 // we used n threads to allocate, each of them can spend maximum waste/n words in 67 // a first rough approximation. The number of threads only comes into play later 68 // when actually retrieving the actual desired PLAB size. 69 // 70 // After calculating this optimal PLAB size the algorithm applies the usual 71 // exponential decaying average over this value to guess the next PLAB size. 72 // 73 // We account region end waste fully to PLAB allocation (in the calculation of 74 // what we consider as "used_for_waste_calculation" below). This is not 75 // completely fair, but is a conservative assumption because PLABs may be sized 76 // flexibly while we cannot adjust inline allocations. 77 // Allocation during GC will try to minimize region end waste so this impact 78 // should be minimal. 79 // 80 // We need to cover overflow when calculating the amount of space actually used 81 // by objects in PLABs when subtracting the region end waste. 82 // Region end waste may be higher than actual allocation. This may occur if many 83 // threads do not allocate anything but a few rather large objects. In this 84 // degenerate case the PLAB size would simply quickly tend to minimum PLAB size, 85 // which is an okay reaction. 86 size_t const used_for_waste_calculation = used() > _region_end_waste ? used() - _region_end_waste : 0; 87 88 size_t const total_waste_allowed = used_for_waste_calculation * TargetPLABWastePct; 89 size_t const cur_plab_sz = (size_t)((double)total_waste_allowed / G1LastPLABAverageOccupancy); 90 return cur_plab_sz; 91 } 92 93 G1EvacStats::G1EvacStats(const char* description, size_t desired_plab_sz_, unsigned wt) : 94 PLABStats(description, desired_plab_sz_, wt), 95 _region_end_waste(0), 96 _regions_filled(0), 97 _direct_allocated(0), 98 _failure_used(0), 99 _failure_waste(0) { 100 } 101 102 103 G1EvacStats::~G1EvacStats() { }