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/*
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* Copyright (c) 2018, 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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#ifndef SHARE_VM_GC_G1_G1REGIONMARKSTATSCACHE_HPP
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#define SHARE_VM_GC_G1_G1REGIONMARKSTATSCACHE_HPP
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#include "memory/allocation.hpp"
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#include "utilities/debug.hpp"
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#include "utilities/globalDefinitions.hpp"
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#include "utilities/pair.hpp"
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// Per-Region statistics gathered during marking.
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//
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// This includes
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// * the number of live words gathered during marking for the area from bottom
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// to ntams. This is an exact measure.
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// The code corrects later for the live data between ntams and top.
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struct G1RegionMarkStats {
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size_t _live_words;
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// Clear all members.
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void clear() {
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_live_words = 0;
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}
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// Clear all members after a marking overflow. Nothing to do as the live words
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// are updated by the atomic mark. We do not remark objects after overflow.
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void clear_during_overflow() {
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}
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bool is_clear() const { return _live_words == 0; }
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};
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// Per-marking thread cache for the region mark statistics.
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//
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// Each cache is a larg'ish map of region-idx -> G1RegionMarkStats entries that cache
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// currently gathered statistics; entries are evicted to the global statistics array
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// on every collision. This minimizes synchronization overhead which would be required
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// every time statistics change, as marking is very localized.
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// The map entry number is a power of two to allow simple and fast hashing using
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// logical and.
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class G1RegionMarkStatsCache {
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private:
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// The array of statistics entries to evict to; the global array.
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G1RegionMarkStats* _target;
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// Number of entries in the eviction target.
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uint _num_stats;
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// An entry of the statistics cache.
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struct G1RegionMarkStatsCacheEntry {
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uint _region_idx;
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G1RegionMarkStats _stats;
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void clear() {
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_region_idx = 0;
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_stats.clear();
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}
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bool is_clear() const {
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return _region_idx == 0 && _stats.is_clear();
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}
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};
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// The actual cache and its number of entries.
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G1RegionMarkStatsCacheEntry* _cache;
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uint _num_cache_entries;
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// Cache hits/miss counters.
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size_t _cache_hits;
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size_t _cache_misses;
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// Evict a given element of the statistics cache.
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void evict(uint idx);
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size_t _num_cache_entries_mask;
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uint hash(uint idx) {
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return idx & _num_cache_entries_mask;
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}
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G1RegionMarkStatsCacheEntry* find_for_add(uint region_idx);
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public:
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G1RegionMarkStatsCache(G1RegionMarkStats* target, uint max_regions, uint num_cache_entries);
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~G1RegionMarkStatsCache();
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void add_live_words(uint region_idx, size_t live_words) {
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G1RegionMarkStatsCacheEntry* const cur = find_for_add(region_idx);
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cur->_stats._live_words += live_words;
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}
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void reset(uint region_idx) {
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uint const cache_idx = hash(region_idx);
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G1RegionMarkStatsCacheEntry* cur = &_cache[cache_idx];
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if (cur->_region_idx == region_idx) {
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_cache[cache_idx].clear();
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}
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}
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// Evict all remaining statistics, returning cache hits and misses.
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Pair<size_t, size_t> evict_all();
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// Reset all cache entries to their default values.
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void reset();
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size_t hits() const { return _cache_hits; }
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size_t misses() const { return _cache_misses; }
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};
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#endif // SHARE_VM_GC_G1_G1REGIONMARKSTATSCACHE_HPP
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