--- /dev/null 2016-02-17 13:41:52.116008013 +0100 +++ new/src/share/vm/gc/g1/g1HeapSizingPolicy.cpp 2016-03-17 13:51:34.272572025 +0100 @@ -0,0 +1,148 @@ +/* + * Copyright (c) 2016, 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/g1CollectedHeap.hpp" +#include "gc/g1/g1HeapSizingPolicy.hpp" +#include "gc/g1/g1Analytics.hpp" +#include "logging/log.hpp" +#include "runtime/globals.hpp" +#include "utilities/globalDefinitions.hpp" + +void G1HeapSizingPolicy::clear_ratio_check_data() { + _ratio_over_threshold_count = 0; + _ratio_over_threshold_sum = 0.0; + _pauses_since_start = 0; +} + +size_t G1HeapSizingPolicy::expansion_amount() { + double recent_gc_overhead = _analytics->recent_avg_pause_time_ratio() * 100.0; + double last_gc_overhead = _analytics->last_pause_time_ratio() * 100.0; + assert(GCTimeRatio > 0, + "we should have set it to a default value set_g1_gc_flags() " + "if a user set it to 0"); + const double gc_overhead_perc = 100.0 * (1.0 / (1.0 + GCTimeRatio)); + + double threshold = gc_overhead_perc; + size_t expand_bytes = 0; + + // If the heap is at less than half its maximum size, scale the threshold down, + // to a limit of 1. Thus the smaller the heap is, the more likely it is to expand, + // though the scaling code will likely keep the increase small. + if (_g1->capacity() <= _g1->max_capacity() / 2) { + threshold *= (double)_g1->capacity() / (double)(_g1->max_capacity() / 2); + threshold = MAX2(threshold, 1.0); + } + + // If the last GC time ratio is over the threshold, increment the count of + // times it has been exceeded, and add this ratio to the sum of exceeded + // ratios. + if (last_gc_overhead > threshold) { + _ratio_over_threshold_count++; + _ratio_over_threshold_sum += last_gc_overhead; + } + + // Check if we've had enough GC time ratio checks that were over the + // threshold to trigger an expansion. We'll also expand if we've + // reached the end of the history buffer and the average of all entries + // is still over the threshold. This indicates a smaller number of GCs were + // long enough to make the average exceed the threshold. + bool filled_history_buffer = _pauses_since_start == _num_prev_pauses_for_heuristics; + if ((_ratio_over_threshold_count == MinOverThresholdForGrowth) || + (filled_history_buffer && (recent_gc_overhead > threshold))) { + size_t min_expand_bytes = HeapRegion::GrainBytes; + size_t reserved_bytes = _g1->max_capacity(); + size_t committed_bytes = _g1->capacity(); + size_t uncommitted_bytes = reserved_bytes - committed_bytes; + size_t expand_bytes_via_pct = + uncommitted_bytes * G1ExpandByPercentOfAvailable / 100; + double scale_factor = 1.0; + + // If the current size is less than 1/4 of the Initial heap size, expand + // by half of the delta between the current and Initial sizes. IE, grow + // back quickly. + // + // Otherwise, take the current size, or G1ExpandByPercentOfAvailable % of + // the available expansion space, whichever is smaller, as the base + // expansion size. Then possibly scale this size according to how much the + // threshold has (on average) been exceeded by. If the delta is small + // (less than the StartScaleDownAt value), scale the size down linearly, but + // not by less than MinScaleDownFactor. If the delta is large (greater than + // the StartScaleUpAt value), scale up, but adding no more than MaxScaleUpFactor + // times the base size. The scaling will be linear in the range from + // StartScaleUpAt to (StartScaleUpAt + ScaleUpRange). In other words, + // ScaleUpRange sets the rate of scaling up. + if (committed_bytes < InitialHeapSize / 4) { + expand_bytes = (InitialHeapSize - committed_bytes) / 2; + } else { + double const MinScaleDownFactor = 0.2; + double const MaxScaleUpFactor = 2; + double const StartScaleDownAt = gc_overhead_perc; + double const StartScaleUpAt = gc_overhead_perc * 1.5; + double const ScaleUpRange = gc_overhead_perc * 2.0; + + double ratio_delta; + if (filled_history_buffer) { + ratio_delta = recent_gc_overhead - threshold; + } else { + ratio_delta = (_ratio_over_threshold_sum/_ratio_over_threshold_count) - threshold; + } + + expand_bytes = MIN2(expand_bytes_via_pct, committed_bytes); + if (ratio_delta < StartScaleDownAt) { + scale_factor = ratio_delta / StartScaleDownAt; + scale_factor = MAX2(scale_factor, MinScaleDownFactor); + } else if (ratio_delta > StartScaleUpAt) { + scale_factor = 1 + ((ratio_delta - StartScaleUpAt) / ScaleUpRange); + scale_factor = MIN2(scale_factor, MaxScaleUpFactor); + } + } + + log_debug(gc, ergo, heap)("Attempt heap expansion (recent GC overhead higher than threshold after GC) " + "recent GC overhead: %1.2f %% threshold: %1.2f %% uncommitted: " SIZE_FORMAT "B base expansion amount and scale: " SIZE_FORMAT "B (%1.2f%%)", + recent_gc_overhead, threshold, uncommitted_bytes, expand_bytes, scale_factor * 100); + + expand_bytes = static_cast(expand_bytes * scale_factor); + + // Ensure the expansion size is at least the minimum growth amount + // and at most the remaining uncommitted byte size. + expand_bytes = MAX2(expand_bytes, min_expand_bytes); + expand_bytes = MIN2(expand_bytes, uncommitted_bytes); + + clear_ratio_check_data(); + } else { + // An expansion was not triggered. If we've started counting, increment + // the number of checks we've made in the current window. If we've + // reached the end of the window without resizing, clear the counters to + // start again the next time we see a ratio above the threshold. + if (_ratio_over_threshold_count > 0) { + _pauses_since_start++; + if (_pauses_since_start > _num_prev_pauses_for_heuristics) { + clear_ratio_check_data(); + } + } + } + + return expand_bytes; +}