g1EvacStats.cpp revision 9056:dc9930a04ab0
12926Sphk/* 22926Sphk * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved. 32926Sphk * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 493150Sphk * 52926Sphk * This code is free software; you can redistribute it and/or modify it 62926Sphk * under the terms of the GNU General Public License version 2 only, as 72926Sphk * published by the Free Software Foundation. 82926Sphk * 950479Speter * This code is distributed in the hope that it will be useful, but WITHOUT 102926Sphk * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 112926Sphk * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 122926Sphk * version 2 for more details (a copy is included in the LICENSE file that 132886Sphk * accompanied this code). 142926Sphk * 152886Sphk * You should have received a copy of the GNU General Public License version 162886Sphk * 2 along with this work; if not, write to the Free Software Foundation, 174816Sphk * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 182886Sphk * 192886Sphk * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 202886Sphk * or visit www.oracle.com if you need additional information or have any 2115456Sphk * questions. 2215456Sphk * 2315456Sphk */ 2415456Sphk 2529526Scharnier#include "precompiled.hpp" 2615456Sphk#include "gc/g1/g1EvacStats.hpp" 2715456Sphk#include "gc/shared/gcId.hpp" 2815456Sphk#include "trace/tracing.hpp" 2915456Sphk 3015456Sphkvoid G1EvacStats::adjust_desired_plab_sz() { 3115456Sphk if (PrintPLAB) { 322886Sphk gclog_or_tty->print(" (allocated = " SIZE_FORMAT " wasted = " SIZE_FORMAT " " 332886Sphk "unused = " SIZE_FORMAT " used = " SIZE_FORMAT " " 342886Sphk "undo_waste = " SIZE_FORMAT " region_end_waste = " SIZE_FORMAT " " 352886Sphk "regions filled = %u direct_allocated = " SIZE_FORMAT " " 362886Sphk "failure_used = " SIZE_FORMAT " failure_waste = " SIZE_FORMAT ") ", 372886Sphk _allocated, _wasted, _unused, used(), _undo_wasted, _region_end_waste, 382886Sphk _regions_filled, _direct_allocated, _failure_used, _failure_waste); 392886Sphk } 402886Sphk 419491Sphk if (ResizePLAB) { 4217946Sphk 4315456Sphk assert(is_object_aligned(max_size()) && min_size() <= max_size(), 4417946Sphk "PLAB clipping computation may be incorrect"); 458857Srgrimes 462886Sphk if (_allocated == 0) { 472886Sphk assert((_unused == 0), 482886Sphk "Inconsistency in PLAB stats: " 492886Sphk "_allocated: " SIZE_FORMAT ", " 502886Sphk "_wasted: " SIZE_FORMAT ", " 512886Sphk "_region_end_waste: " SIZE_FORMAT ", " 522886Sphk "_unused: " SIZE_FORMAT ", " 532886Sphk "_used : " SIZE_FORMAT, 542886Sphk _allocated, _wasted, _region_end_waste, _unused, used()); 552886Sphk _allocated = 1; 5615456Sphk } 5715456Sphk // The size of the PLAB caps the amount of space that can be wasted at the 5815456Sphk // end of the collection. In the worst case the last PLAB could be completely 5915456Sphk // empty. 6015456Sphk // This allows us to calculate the new PLAB size to achieve the 6115456Sphk // TargetPLABWastePct given the latest memory usage and that the last buffer 6215456Sphk // will be G1LastPLABAverageOccupancy full. 6315456Sphk // 6415456Sphk // E.g. assume that if in the current GC 100 words were allocated and a 6515456Sphk // TargetPLABWastePct of 10 had been set. 6615456Sphk // 6715456Sphk // So we could waste up to 10 words to meet that percentage. Given that we 6815456Sphk // also assume that that buffer is typically half-full, the new desired PLAB 6915456Sphk // size is set to 20 words. 7015456Sphk // 7115456Sphk // The amount of allocation performed should be independent of the number of 7215456Sphk // threads, so should the maximum waste we can spend in total. So if 7315456Sphk // we used n threads to allocate, each of them can spend maximum waste/n words in 7415456Sphk // a first rough approximation. The number of threads only comes into play later 7515456Sphk // when actually retrieving the actual desired PLAB size. 7615456Sphk // 7715456Sphk // After calculating this optimal PLAB size the algorithm applies the usual 7815456Sphk // exponential decaying average over this value to guess the next PLAB size. 7915456Sphk // 8015456Sphk // We account region end waste fully to PLAB allocation (in the calculation of 8115456Sphk // what we consider as "used_for_waste_calculation" below). This is not 8215456Sphk // completely fair, but is a conservative assumption because PLABs may be sized 8315456Sphk // flexibly while we cannot adjust inline allocations. 8415456Sphk // Allocation during GC will try to minimize region end waste so this impact 8515456Sphk // should be minimal. 8615456Sphk // 8715456Sphk // We need to cover overflow when calculating the amount of space actually used 8815456Sphk // by objects in PLABs when subtracting the region end waste. 8915456Sphk // Region end waste may be higher than actual allocation. This may occur if many 9015456Sphk // threads do not allocate anything but a few rather large objects. In this 9115456Sphk // degenerate case the PLAB size would simply quickly tend to minimum PLAB size, 9215456Sphk // which is an okay reaction. 9315456Sphk size_t const used_for_waste_calculation = used() > _region_end_waste ? used() - _region_end_waste : 0; 9415456Sphk 9515456Sphk size_t const total_waste_allowed = used_for_waste_calculation * TargetPLABWastePct; 9615456Sphk size_t const cur_plab_sz = (size_t)((double)total_waste_allowed / G1LastPLABAverageOccupancy); 9715456Sphk // Take historical weighted average 9815456Sphk _filter.sample(cur_plab_sz); 9915456Sphk // Clip from above and below, and align to object boundary 10015456Sphk size_t plab_sz; 10115456Sphk plab_sz = MAX2(min_size(), (size_t)_filter.average()); 10215456Sphk plab_sz = MIN2(max_size(), plab_sz); 10315456Sphk plab_sz = align_object_size(plab_sz); 10415456Sphk // Latch the result 10515456Sphk _desired_net_plab_sz = plab_sz; 10615456Sphk if (PrintPLAB) { 10715456Sphk gclog_or_tty->print_cr(" (plab_sz = " SIZE_FORMAT " desired_plab_sz = " SIZE_FORMAT ") ", cur_plab_sz, plab_sz); 10815456Sphk } 1092886Sphk } 11013917Sphk // Clear accumulators for next round. 11113917Sphk reset(); 11213917Sphk} 11313917Sphk 11413917Sphk