104 lines
4.6 KiB
C++
104 lines
4.6 KiB
C++
/*
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* Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#include "precompiled.hpp"
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#include "memory/allocation.inline.hpp"
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#include "gc/g1/g1_globals.hpp"
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#include "gc/g1/g1EvacStats.hpp"
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#include "gc/shared/gcId.hpp"
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#include "logging/log.hpp"
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#include "trace/tracing.hpp"
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void G1EvacStats::log_plab_allocation() {
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PLABStats::log_plab_allocation();
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log_debug(gc, plab)("%s other allocation: "
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"region end waste: " SIZE_FORMAT "B, "
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"regions filled: %u, "
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"direct allocated: " SIZE_FORMAT "B, "
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"failure used: " SIZE_FORMAT "B, "
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"failure wasted: " SIZE_FORMAT "B",
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_description,
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_region_end_waste * HeapWordSize,
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_regions_filled,
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_direct_allocated * HeapWordSize,
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_failure_used * HeapWordSize,
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_failure_waste * HeapWordSize);
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}
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size_t G1EvacStats::compute_desired_plab_sz() {
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// The size of the PLAB caps the amount of space that can be wasted at the
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// end of the collection. In the worst case the last PLAB could be completely
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// empty.
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// This allows us to calculate the new PLAB size to achieve the
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// TargetPLABWastePct given the latest memory usage and that the last buffer
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// will be G1LastPLABAverageOccupancy full.
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//
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// E.g. assume that if in the current GC 100 words were allocated and a
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// TargetPLABWastePct of 10 had been set.
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//
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// So we could waste up to 10 words to meet that percentage. Given that we
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// also assume that that buffer is typically half-full, the new desired PLAB
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// size is set to 20 words.
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//
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// The amount of allocation performed should be independent of the number of
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// threads, so should the maximum waste we can spend in total. So if
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// we used n threads to allocate, each of them can spend maximum waste/n words in
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// a first rough approximation. The number of threads only comes into play later
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// when actually retrieving the actual desired PLAB size.
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//
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// After calculating this optimal PLAB size the algorithm applies the usual
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// exponential decaying average over this value to guess the next PLAB size.
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//
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// We account region end waste fully to PLAB allocation (in the calculation of
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// what we consider as "used_for_waste_calculation" below). This is not
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// completely fair, but is a conservative assumption because PLABs may be sized
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// flexibly while we cannot adjust inline allocations.
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// Allocation during GC will try to minimize region end waste so this impact
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// should be minimal.
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//
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// We need to cover overflow when calculating the amount of space actually used
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// by objects in PLABs when subtracting the region end waste.
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// Region end waste may be higher than actual allocation. This may occur if many
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// threads do not allocate anything but a few rather large objects. In this
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// degenerate case the PLAB size would simply quickly tend to minimum PLAB size,
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// which is an okay reaction.
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size_t const used_for_waste_calculation = used() > _region_end_waste ? used() - _region_end_waste : 0;
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size_t const total_waste_allowed = used_for_waste_calculation * TargetPLABWastePct;
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size_t const cur_plab_sz = (size_t)((double)total_waste_allowed / G1LastPLABAverageOccupancy);
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return cur_plab_sz;
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}
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G1EvacStats::G1EvacStats(const char* description, size_t desired_plab_sz_, unsigned wt) :
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PLABStats(description, desired_plab_sz_, wt),
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_region_end_waste(0),
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_regions_filled(0),
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_direct_allocated(0),
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_failure_used(0),
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_failure_waste(0) {
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}
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G1EvacStats::~G1EvacStats() { }
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