| /* |
| * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| * |
| */ |
| |
| #include "precompiled.hpp" |
| #include "gc/g1/g1EvacStats.hpp" |
| #include "gc/shared/gcId.hpp" |
| #include "trace/tracing.hpp" |
| |
| void G1EvacStats::adjust_desired_plab_sz() { |
| if (PrintPLAB) { |
| gclog_or_tty->print(" (allocated = " SIZE_FORMAT " wasted = " SIZE_FORMAT " " |
| "unused = " SIZE_FORMAT " used = " SIZE_FORMAT " " |
| "undo_waste = " SIZE_FORMAT " region_end_waste = " SIZE_FORMAT " " |
| "regions filled = %u direct_allocated = " SIZE_FORMAT " " |
| "failure_used = " SIZE_FORMAT " failure_waste = " SIZE_FORMAT ") ", |
| _allocated, _wasted, _unused, used(), _undo_wasted, _region_end_waste, |
| _regions_filled, _direct_allocated, _failure_used, _failure_waste); |
| } |
| |
| if (ResizePLAB) { |
| |
| assert(is_object_aligned(max_size()) && min_size() <= max_size(), |
| "PLAB clipping computation may be incorrect"); |
| |
| if (_allocated == 0) { |
| assert((_unused == 0), |
| err_msg("Inconsistency in PLAB stats: " |
| "_allocated: " SIZE_FORMAT ", " |
| "_wasted: " SIZE_FORMAT ", " |
| "_region_end_waste: " SIZE_FORMAT ", " |
| "_unused: " SIZE_FORMAT ", " |
| "_used : " SIZE_FORMAT, |
| _allocated, _wasted, _region_end_waste, _unused, used())); |
| _allocated = 1; |
| } |
| // The size of the PLAB caps the amount of space that can be wasted at the |
| // end of the collection. In the worst case the last PLAB could be completely |
| // empty. |
| // This allows us to calculate the new PLAB size to achieve the |
| // TargetPLABWastePct given the latest memory usage and that the last buffer |
| // will be G1LastPLABAverageOccupancy full. |
| // |
| // E.g. assume that if in the current GC 100 words were allocated and a |
| // TargetPLABWastePct of 10 had been set. |
| // |
| // So we could waste up to 10 words to meet that percentage. Given that we |
| // also assume that that buffer is typically half-full, the new desired PLAB |
| // size is set to 20 words. |
| // |
| // The amount of allocation performed should be independent of the number of |
| // threads, so should the maximum waste we can spend in total. So if |
| // we used n threads to allocate, each of them can spend maximum waste/n words in |
| // a first rough approximation. The number of threads only comes into play later |
| // when actually retrieving the actual desired PLAB size. |
| // |
| // After calculating this optimal PLAB size the algorithm applies the usual |
| // exponential decaying average over this value to guess the next PLAB size. |
| // |
| // We account region end waste fully to PLAB allocation (in the calculation of |
| // what we consider as "used_for_waste_calculation" below). This is not |
| // completely fair, but is a conservative assumption because PLABs may be sized |
| // flexibly while we cannot adjust inline allocations. |
| // Allocation during GC will try to minimize region end waste so this impact |
| // should be minimal. |
| // |
| // We need to cover overflow when calculating the amount of space actually used |
| // by objects in PLABs when subtracting the region end waste. |
| // Region end waste may be higher than actual allocation. This may occur if many |
| // threads do not allocate anything but a few rather large objects. In this |
| // degenerate case the PLAB size would simply quickly tend to minimum PLAB size, |
| // which is an okay reaction. |
| size_t const used_for_waste_calculation = used() > _region_end_waste ? used() - _region_end_waste : 0; |
| |
| size_t const total_waste_allowed = used_for_waste_calculation * TargetPLABWastePct; |
| size_t const cur_plab_sz = (size_t)((double)total_waste_allowed / G1LastPLABAverageOccupancy); |
| // Take historical weighted average |
| _filter.sample(cur_plab_sz); |
| // Clip from above and below, and align to object boundary |
| size_t plab_sz; |
| plab_sz = MAX2(min_size(), (size_t)_filter.average()); |
| plab_sz = MIN2(max_size(), plab_sz); |
| plab_sz = align_object_size(plab_sz); |
| // Latch the result |
| _desired_net_plab_sz = plab_sz; |
| if (PrintPLAB) { |
| gclog_or_tty->print_cr(" (plab_sz = " SIZE_FORMAT " desired_plab_sz = " SIZE_FORMAT ") ", cur_plab_sz, plab_sz); |
| } |
| } |
| // Clear accumulators for next round. |
| reset(); |
| } |
| |